A review of chromium compound synthesis

[megalomania]

While doing some digging for my website I have compiled this little primer for the improvised synthesis of many different chromium compounds. Since they all seem to be interrelated synthesis wise (one is used to make another) I thought I would combine them all on one page. Since the information is rather hard to come by, anyone that wishes to expand on what I have, or add corrections if I made a mistake, please do so.

I know there are many different chromium containing compounds, but these are the common ones. I have also expounded on where one can obtain OTC sources of chromium.

Synthesis of chromium compounds

The primary source of the element chromium is the naturally occurring ore chromite, or iron chromate, a mixture of ferrous oxide and chromium oxide, FeO•Cr2O3. The most abundant OTC sources are from ceramic and pottery suppliers that sell chromium compounds as pigments and glazes. Another major OTC source is suppliers of metalworking chemicals that sell chromates as patinas (chemicals that make metal look aged).
Depending on what kind of chromium compound you get, and where you get it, the price is rather reasonable. Iron chromate sells for as little as $0.80 per pound from ceramics suppliers, and chromium oxide goes for $6-$7 per pound. Potassium and sodium dichromate goes for $5-$10 per pound from ceramic and patina suppliers.
Many other kinds of chromium compounds exist, but are not so easily found. Chromium compounds tend to be rather toxic, so this limits their usefulness in consumer products. Dichromate salts may be more difficult to obtain because they are watched chemicals by the DEA.
Chromium compounds are quite interchangeable. The inexpensive and readily obtainable chromium oxides are quite easily converted into the more useful dichromate salts.

Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. Potassium chromate can also be formed by adding a solution of potassium hydroxide to a solution of potassium dichromate.

Sodium chromate: Can be prepared exactly as potassium chromate except sodium compounds are used in place of potassium.

Lead chromate: Lead chromate can be precipitated from a solution of either sodium or potassium chromate by adding a soluble lead salt such as lead nitrate or acetate.

Potassium dichromate: Acetic acid (vinegar) added to crystals of potassium chromate will form a solution of potassium dichromate that crystallizes as ruby red prisms. It may also be prepared by thoroughly mixing a finely powdered mixture of iron chromate with potassium carbonate and calcium oxide. The mixture is heated to 150 C to dry it, and then to bright redness with frequent stirring. The mass is allowed to cool, and then digested in a small quantity of boiling water. A small amount of potassium carbonate is added to the solution to decompose and calcium chromate that may have formed, thus precipitating calcium carbonate which is filtered off. The solution is then acidified with any aqueous acid to form potassium dichromate. The solution is evaporated to dryness leaving behind crystals of potassium dichromate. The crystals can be purified by recrystallizing from water.

Sodium dichromate: Can be prepared as potassium dichromate except sodium compounds are used in place of potassium.

Lead dichromate: Strongly heat potassium nitrate until it is liquefied. Slowly add lead chromate to the liquid salt and stir. Allow the mixture to cool and add to water to dissolve the potassium dichromate and unreacted potassium nitrate. The insoluble red powder of lead dichromate will remain. Lead dichromate can also be made by boiling 2 moles of lead chromate with 1 mole of calcium hydroxide.

Chromium oxide Cr2O3: May be prepared by heating sodium or potassium dichromate, or chromium trioxide, to red heat and washing the product with water. It may also be prepared by strongly heating chromium oxide heptahydrate to drive off the water. Chromium oxide heptahydrate can be prepared by boiling a solution of potassium or sodium dichromate with hydrochloric acid. Ethyl alcohol is added turning the solution green. Ammonium hydroxide is then added to precipitate crystals of chromic hydroxide heptahydrate. Chromium oxide green, or chromium oxide dihydrate can be prepared by heating the heptahydrate to 200-220 C in an inert oxygen free environment. It may also be prepared by heating a mixture of 10 g of potassium dichromate and 18 g of boric acid to low redness. The cooled mass is digested with water forming the dihydrate. These compounds may also be referred to as chromium hydroxides.

Chromium (IV) oxide CrO2: May be prepared by bubbling nitric oxide gas (NO) into a warm dilute solution of potassium dichromate. Chromium (IV) oxide is slowly precipitated. The precipitate is washed with water, then with ethyl alcohol, and dried at 250 C for several hours until a constant weight is obtained.

Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed by adding chromium trioxide to water.

Chromium trioxide: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Cool the solution in an ice bath to precipitate crystals of chromium trioxide. Decant off the acid solution and place the crystals on filter paper to absorb the remaining acid and moisture. The drying should be done in a desiccator to protect the crystals from moisture. Chromium trioxide can also be obtained by evaporating a solution of chromic acid to dryness. For high purity chromium trioxide see the procedure for chromium fluoride below.

Chromic chloride: May be prepared by dissolving hydrated chromium oxide in hydrochloric acid and evaporating off the liquid. It may also be prepared by adding, by weight, 1 part of either sodium or potassium dichromate to 6 parts of hydrochloric acid and gently heating for a few seconds to initiate the reaction. Chlorine gas will be evolved, so do this reaction is a well ventilated area.

Chromous chloride: May be prepared by passing dry hydrogen gas through a strongly heated tube containing chromic chloride.

Chromium oxychloride: Dissolve potassium dichromate and an excess of sodium chloride in a minimum of water. Evaporate this solution to dryness obtain a co-crystallized mixture of the two salts. Place the crystals in a distillation apparatus and add a small volume of concentrated sulfuric acid (95%). Gently heat the mixture to distill over the red-brown gas of chromium oxychloride.

Chromium fluoride: May be prepared by distilling a mixture of lead chromate and fluorspar (calcium fluoride) in concentrated sulfuric acid. The distillation receiver must be cooled to -100 C to condense the chromium fluoride and the entire apparatus must be protected from moisture. Glass will decompose chromium fluoride, and is attacked by the subsequent hydrogen fluoride gas, so some other material such as lead or stainless steel must be used in the distillation apparatus. Upon exposure to moist air chromium fluoride decomposes to hydrofluoric acid and chromium trioxide. The chromium trioxide thus obtained is of high purity. When the ultimate desired product is either chromium trioxide or hydrofluoric acid super cooling is not necessary and the distillate can be passed directly into water.

Ammonium chromate: Add chromium oxychloride to ammonium hydroxide. A yellow colored liquid will form containing ammonium chromate.

Ammonium dichromate: If acid (hydrochloric or sulfuric) is added to the ammonium chromate solution prepared above the color will change to a red-yellow indicating the presence of ammonium dichromate.

Chromium nitrate: Strongly heat a crucible of chromium oxide with a Bunsen burner. Add the heated chromium oxide to a beaker of boiling concentrated (>95%) nitric acid. Upon cooling the acid in an ice bath, brown crystals of chromium nitrate 15 hydrate precipitate. After decanting off the acid and washing the dried crystals become the gray colored 9 hydrate when left in the open air.

[megalomania]

While doing some digging for my website I have compiled this little primer for the improvised synthesis of many different chromium compounds. Since they all seem to be interrelated synthesis wise (one is used to make another) I thought I would combine them all on one page. Since the information is rather hard to come by, anyone that wishes to expand on what I have, or add corrections if I made a mistake, please do so.

I know there are many different chromium containing compounds, but these are the common ones. I have also expounded on where one can obtain OTC sources of chromium.

Synthesis of chromium compounds

The primary source of the element chromium is the naturally occurring ore chromite, or iron chromate, a mixture of ferrous oxide and chromium oxide, FeO•Cr2O3. The most abundant OTC sources are from ceramic and pottery suppliers that sell chromium compounds as pigments and glazes. Another major OTC source is suppliers of metalworking chemicals that sell chromates as patinas (chemicals that make metal look aged).
Depending on what kind of chromium compound you get, and where you get it, the price is rather reasonable. Iron chromate sells for as little as $0.80 per pound from ceramics suppliers, and chromium oxide goes for $6-$7 per pound. Potassium and sodium dichromate goes for $5-$10 per pound from ceramic and patina suppliers.
Many other kinds of chromium compounds exist, but are not so easily found. Chromium compounds tend to be rather toxic, so this limits their usefulness in consumer products. Dichromate salts may be more difficult to obtain because they are watched chemicals by the DEA.
Chromium compounds are quite interchangeable. The inexpensive and readily obtainable chromium oxides are quite easily converted into the more useful dichromate salts.

Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. Potassium chromate can also be formed by adding a solution of potassium hydroxide to a solution of potassium dichromate.

Sodium chromate: Can be prepared exactly as potassium chromate except sodium compounds are used in place of potassium.

Lead chromate: Lead chromate can be precipitated from a solution of either sodium or potassium chromate by adding a soluble lead salt such as lead nitrate or acetate.

Potassium dichromate: Acetic acid (vinegar) added to crystals of potassium chromate will form a solution of potassium dichromate that crystallizes as ruby red prisms. It may also be prepared by thoroughly mixing a finely powdered mixture of iron chromate with potassium carbonate and calcium oxide. The mixture is heated to 150 C to dry it, and then to bright redness with frequent stirring. The mass is allowed to cool, and then digested in a small quantity of boiling water. A small amount of potassium carbonate is added to the solution to decompose and calcium chromate that may have formed, thus precipitating calcium carbonate which is filtered off. The solution is then acidified with any aqueous acid to form potassium dichromate. The solution is evaporated to dryness leaving behind crystals of potassium dichromate. The crystals can be purified by recrystallizing from water.

Sodium dichromate: Can be prepared as potassium dichromate except sodium compounds are used in place of potassium.

Lead dichromate: Strongly heat potassium nitrate until it is liquefied. Slowly add lead chromate to the liquid salt and stir. Allow the mixture to cool and add to water to dissolve the potassium dichromate and unreacted potassium nitrate. The insoluble red powder of lead dichromate will remain. Lead dichromate can also be made by boiling 2 moles of lead chromate with 1 mole of calcium hydroxide.

Chromium oxide Cr2O3: May be prepared by heating sodium or potassium dichromate, or chromium trioxide, to red heat and washing the product with water. It may also be prepared by strongly heating chromium oxide heptahydrate to drive off the water. Chromium oxide heptahydrate can be prepared by boiling a solution of potassium or sodium dichromate with hydrochloric acid. Ethyl alcohol is added turning the solution green. Ammonium hydroxide is then added to precipitate crystals of chromic hydroxide heptahydrate. Chromium oxide green, or chromium oxide dihydrate can be prepared by heating the heptahydrate to 200-220 C in an inert oxygen free environment. It may also be prepared by heating a mixture of 10 g of potassium dichromate and 18 g of boric acid to low redness. The cooled mass is digested with water forming the dihydrate. These compounds may also be referred to as chromium hydroxides.

Chromium (IV) oxide CrO2: May be prepared by bubbling nitric oxide gas (NO) into a warm dilute solution of potassium dichromate. Chromium (IV) oxide is slowly precipitated. The precipitate is washed with water, then with ethyl alcohol, and dried at 250 C for several hours until a constant weight is obtained.

Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed by adding chromium trioxide to water.

Chromium trioxide: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Cool the solution in an ice bath to precipitate crystals of chromium trioxide. Decant off the acid solution and place the crystals on filter paper to absorb the remaining acid and moisture. The drying should be done in a desiccator to protect the crystals from moisture. Chromium trioxide can also be obtained by evaporating a solution of chromic acid to dryness. For high purity chromium trioxide see the procedure for chromium fluoride below.

Chromic chloride: May be prepared by dissolving hydrated chromium oxide in hydrochloric acid and evaporating off the liquid. It may also be prepared by adding, by weight, 1 part of either sodium or potassium dichromate to 6 parts of hydrochloric acid and gently heating for a few seconds to initiate the reaction. Chlorine gas will be evolved, so do this reaction is a well ventilated area.

Chromous chloride: May be prepared by passing dry hydrogen gas through a strongly heated tube containing chromic chloride.

Chromium oxychloride: Dissolve potassium dichromate and an excess of sodium chloride in a minimum of water. Evaporate this solution to dryness obtain a co-crystallized mixture of the two salts. Place the crystals in a distillation apparatus and add a small volume of concentrated sulfuric acid (95%). Gently heat the mixture to distill over the red-brown gas of chromium oxychloride.

Chromium fluoride: May be prepared by distilling a mixture of lead chromate and fluorspar (calcium fluoride) in concentrated sulfuric acid. The distillation receiver must be cooled to -100 C to condense the chromium fluoride and the entire apparatus must be protected from moisture. Glass will decompose chromium fluoride, and is attacked by the subsequent hydrogen fluoride gas, so some other material such as lead or stainless steel must be used in the distillation apparatus. Upon exposure to moist air chromium fluoride decomposes to hydrofluoric acid and chromium trioxide. The chromium trioxide thus obtained is of high purity. When the ultimate desired product is either chromium trioxide or hydrofluoric acid super cooling is not necessary and the distillate can be passed directly into water.

Ammonium chromate: Add chromium oxychloride to ammonium hydroxide. A yellow colored liquid will form containing ammonium chromate.

Ammonium dichromate: If acid (hydrochloric or sulfuric) is added to the ammonium chromate solution prepared above the color will change to a red-yellow indicating the presence of ammonium dichromate.

Chromium nitrate: Strongly heat a crucible of chromium oxide with a Bunsen burner. Add the heated chromium oxide to a beaker of boiling concentrated (>95%) nitric acid. Upon cooling the acid in an ice bath, brown crystals of chromium nitrate 15 hydrate precipitate. After decanting off the acid and washing the dried crystals become the gray colored 9 hydrate when left in the open air.

[megalomania]

While doing some digging for my website I have compiled this little primer for the improvised synthesis of many different chromium compounds. Since they all seem to be interrelated synthesis wise (one is used to make another) I thought I would combine them all on one page. Since the information is rather hard to come by, anyone that wishes to expand on what I have, or add corrections if I made a mistake, please do so.

I know there are many different chromium containing compounds, but these are the common ones. I have also expounded on where one can obtain OTC sources of chromium.

Synthesis of chromium compounds

The primary source of the element chromium is the naturally occurring ore chromite, or iron chromate, a mixture of ferrous oxide and chromium oxide, FeO•Cr2O3. The most abundant OTC sources are from ceramic and pottery suppliers that sell chromium compounds as pigments and glazes. Another major OTC source is suppliers of metalworking chemicals that sell chromates as patinas (chemicals that make metal look aged).
Depending on what kind of chromium compound you get, and where you get it, the price is rather reasonable. Iron chromate sells for as little as $0.80 per pound from ceramics suppliers, and chromium oxide goes for $6-$7 per pound. Potassium and sodium dichromate goes for $5-$10 per pound from ceramic and patina suppliers.
Many other kinds of chromium compounds exist, but are not so easily found. Chromium compounds tend to be rather toxic, so this limits their usefulness in consumer products. Dichromate salts may be more difficult to obtain because they are watched chemicals by the DEA.
Chromium compounds are quite interchangeable. The inexpensive and readily obtainable chromium oxides are quite easily converted into the more useful dichromate salts.

Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. Potassium chromate can also be formed by adding a solution of potassium hydroxide to a solution of potassium dichromate.

Sodium chromate: Can be prepared exactly as potassium chromate except sodium compounds are used in place of potassium.

Lead chromate: Lead chromate can be precipitated from a solution of either sodium or potassium chromate by adding a soluble lead salt such as lead nitrate or acetate.

Potassium dichromate: Acetic acid (vinegar) added to crystals of potassium chromate will form a solution of potassium dichromate that crystallizes as ruby red prisms. It may also be prepared by thoroughly mixing a finely powdered mixture of iron chromate with potassium carbonate and calcium oxide. The mixture is heated to 150 C to dry it, and then to bright redness with frequent stirring. The mass is allowed to cool, and then digested in a small quantity of boiling water. A small amount of potassium carbonate is added to the solution to decompose and calcium chromate that may have formed, thus precipitating calcium carbonate which is filtered off. The solution is then acidified with any aqueous acid to form potassium dichromate. The solution is evaporated to dryness leaving behind crystals of potassium dichromate. The crystals can be purified by recrystallizing from water.

Sodium dichromate: Can be prepared as potassium dichromate except sodium compounds are used in place of potassium.

Lead dichromate: Strongly heat potassium nitrate until it is liquefied. Slowly add lead chromate to the liquid salt and stir. Allow the mixture to cool and add to water to dissolve the potassium dichromate and unreacted potassium nitrate. The insoluble red powder of lead dichromate will remain. Lead dichromate can also be made by boiling 2 moles of lead chromate with 1 mole of calcium hydroxide.

Chromium oxide Cr2O3: May be prepared by heating sodium or potassium dichromate, or chromium trioxide, to red heat and washing the product with water. It may also be prepared by strongly heating chromium oxide heptahydrate to drive off the water. Chromium oxide heptahydrate can be prepared by boiling a solution of potassium or sodium dichromate with hydrochloric acid. Ethyl alcohol is added turning the solution green. Ammonium hydroxide is then added to precipitate crystals of chromic hydroxide heptahydrate. Chromium oxide green, or chromium oxide dihydrate can be prepared by heating the heptahydrate to 200-220 C in an inert oxygen free environment. It may also be prepared by heating a mixture of 10 g of potassium dichromate and 18 g of boric acid to low redness. The cooled mass is digested with water forming the dihydrate. These compounds may also be referred to as chromium hydroxides.

Chromium (IV) oxide CrO2: May be prepared by bubbling nitric oxide gas (NO) into a warm dilute solution of potassium dichromate. Chromium (IV) oxide is slowly precipitated. The precipitate is washed with water, then with ethyl alcohol, and dried at 250 C for several hours until a constant weight is obtained.

Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed by adding chromium trioxide to water.

Chromium trioxide: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Cool the solution in an ice bath to precipitate crystals of chromium trioxide. Decant off the acid solution and place the crystals on filter paper to absorb the remaining acid and moisture. The drying should be done in a desiccator to protect the crystals from moisture. Chromium trioxide can also be obtained by evaporating a solution of chromic acid to dryness. For high purity chromium trioxide see the procedure for chromium fluoride below.

Chromic chloride: May be prepared by dissolving hydrated chromium oxide in hydrochloric acid and evaporating off the liquid. It may also be prepared by adding, by weight, 1 part of either sodium or potassium dichromate to 6 parts of hydrochloric acid and gently heating for a few seconds to initiate the reaction. Chlorine gas will be evolved, so do this reaction is a well ventilated area.

Chromous chloride: May be prepared by passing dry hydrogen gas through a strongly heated tube containing chromic chloride.

Chromium oxychloride: Dissolve potassium dichromate and an excess of sodium chloride in a minimum of water. Evaporate this solution to dryness obtain a co-crystallized mixture of the two salts. Place the crystals in a distillation apparatus and add a small volume of concentrated sulfuric acid (95%). Gently heat the mixture to distill over the red-brown gas of chromium oxychloride.

Chromium fluoride: May be prepared by distilling a mixture of lead chromate and fluorspar (calcium fluoride) in concentrated sulfuric acid. The distillation receiver must be cooled to -100 C to condense the chromium fluoride and the entire apparatus must be protected from moisture. Glass will decompose chromium fluoride, and is attacked by the subsequent hydrogen fluoride gas, so some other material such as lead or stainless steel must be used in the distillation apparatus. Upon exposure to moist air chromium fluoride decomposes to hydrofluoric acid and chromium trioxide. The chromium trioxide thus obtained is of high purity. When the ultimate desired product is either chromium trioxide or hydrofluoric acid super cooling is not necessary and the distillate can be passed directly into water.

Ammonium chromate: Add chromium oxychloride to ammonium hydroxide. A yellow colored liquid will form containing ammonium chromate.

Ammonium dichromate: If acid (hydrochloric or sulfuric) is added to the ammonium chromate solution prepared above the color will change to a red-yellow indicating the presence of ammonium dichromate.

Chromium nitrate: Strongly heat a crucible of chromium oxide with a Bunsen burner. Add the heated chromium oxide to a beaker of boiling concentrated (>95%) nitric acid. Upon cooling the acid in an ice bath, brown crystals of chromium nitrate 15 hydrate precipitate. After decanting off the acid and washing the dried crystals become the gray colored 9 hydrate when left in the open air.

[Marvin]

Its a fair overview, but its like watching a professional chemist from another building with binoculars. Almost all the details that should be present in a synthesis are missing. For example,

"Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. "

How is this actually supposed to be done by the reader? How much iron chromate, how much pot carbonate, how much pot nitrate? If strongly heated, how strong? Until red hot? White hot? Until fumes stop? will this evolve nitric oxides? Do we need a fume hood, a gas mask? After we've done this, how do we extract the product, leaching, recrystalisation? Which products can be filtered, what will crystalise first?

Under dichromate, you have a different synthesis for the chromate starting material with no reason for the change using calcium oxide and no oxidising agent. Why the difference? What's the oxidising agent, air? Again how much of anything do we use? When we acidify, how much acetic acid will we need? What pH should the resulting solution be at and how is this best measured? Can we use the yellow/orange colour change of the chromate/dichromate itself?

"Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed ..."

Huh? Thats it? How is this even supposed to work? Am I supposed to take the still mostly sulphuric acid solution and just put it in a bottled marked 'Chromic acid' or was this a very badly butchered chromic oxide method and adding that to water?

So far, nothing leads me to suspect these methods have actually been tried in this form. That bothers me because there are a fair few reliable inorganic prep books and individual methods floating around that give detailed instructions for this sort of thing. The only use I can see of a compiled file would be to offer tried and tested modifications to these in order to use other starting materials or improvised equipment.

[Marvin]

Its a fair overview, but its like watching a professional chemist from another building with binoculars. Almost all the details that should be present in a synthesis are missing. For example,

"Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. "

How is this actually supposed to be done by the reader? How much iron chromate, how much pot carbonate, how much pot nitrate? If strongly heated, how strong? Until red hot? White hot? Until fumes stop? will this evolve nitric oxides? Do we need a fume hood, a gas mask? After we've done this, how do we extract the product, leaching, recrystalisation? Which products can be filtered, what will crystalise first?

Under dichromate, you have a different synthesis for the chromate starting material with no reason for the change using calcium oxide and no oxidising agent. Why the difference? What's the oxidising agent, air? Again how much of anything do we use? When we acidify, how much acetic acid will we need? What pH should the resulting solution be at and how is this best measured? Can we use the yellow/orange colour change of the chromate/dichromate itself?

"Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed ..."

Huh? Thats it? How is this even supposed to work? Am I supposed to take the still mostly sulphuric acid solution and just put it in a bottled marked 'Chromic acid' or was this a very badly butchered chromic oxide method and adding that to water?

So far, nothing leads me to suspect these methods have actually been tried in this form. That bothers me because there are a fair few reliable inorganic prep books and individual methods floating around that give detailed instructions for this sort of thing. The only use I can see of a compiled file would be to offer tried and tested modifications to these in order to use other starting materials or improvised equipment.

[Marvin]

Its a fair overview, but its like watching a professional chemist from another building with binoculars. Almost all the details that should be present in a synthesis are missing. For example,

"Potassium chromate: A finely powdered mixture of iron chromate, potassium carbonate and potassium nitrate are strongly heated in a furnace with frequent stirring. The nitrate ignites the mixture and the chromium oxide is oxidized to chromium trioxide, which then combines with the carbonate forming potassium chromate. "

How is this actually supposed to be done by the reader? How much iron chromate, how much pot carbonate, how much pot nitrate? If strongly heated, how strong? Until red hot? White hot? Until fumes stop? will this evolve nitric oxides? Do we need a fume hood, a gas mask? After we've done this, how do we extract the product, leaching, recrystalisation? Which products can be filtered, what will crystalise first?

Under dichromate, you have a different synthesis for the chromate starting material with no reason for the change using calcium oxide and no oxidising agent. Why the difference? What's the oxidising agent, air? Again how much of anything do we use? When we acidify, how much acetic acid will we need? What pH should the resulting solution be at and how is this best measured? Can we use the yellow/orange colour change of the chromate/dichromate itself?

"Chromic acid: Add 1 part of a saturated solution of potassium dichromate to 1.5 parts of concentrated sulfuric acid (about 95%). Chromic acid is also formed ..."

Huh? Thats it? How is this even supposed to work? Am I supposed to take the still mostly sulphuric acid solution and just put it in a bottled marked 'Chromic acid' or was this a very badly butchered chromic oxide method and adding that to water?

So far, nothing leads me to suspect these methods have actually been tried in this form. That bothers me because there are a fair few reliable inorganic prep books and individual methods floating around that give detailed instructions for this sort of thing. The only use I can see of a compiled file would be to offer tried and tested modifications to these in order to use other starting materials or improvised equipment.

[nbk2000]

How is this actually supposed to be done by the reader?


This is where the 'skilled in the arts' clause comes into play. :p

[nbk2000]

How is this actually supposed to be done by the reader?


This is where the 'skilled in the arts' clause comes into play. :p

[nbk2000]

How is this actually supposed to be done by the reader?


This is where the 'skilled in the arts' clause comes into play. :p

[megalomania]

Well as for some details being missing, that is due to the rarity of information. If you say there is better out there I believe you, but I have not seen any. Good details for the really old chemicals are rather hard to come by.

[megalomania]

Well as for some details being missing, that is due to the rarity of information. If you say there is better out there I believe you, but I have not seen any. Good details for the really old chemicals are rather hard to come by.

[megalomania]

Well as for some details being missing, that is due to the rarity of information. If you say there is better out there I believe you, but I have not seen any. Good details for the really old chemicals are rather hard to come by.

[Marvin]

This is what Ive been able to scrape together in a few days. Ive been caught a little off guard by the use of 'chromic', its not consistant as an oxidation state. Chromic oxide is Cr2O3, ie Cr (+3), chromic chloride is CrCl3 also Cr (+3) but chromic acid is H2CrO4 (or perhaps more apropriatly CrO3.H2O with CrO3 being called chromic anhydride) ie, Cr (+6)

Details for chromite + alkali + lime. Amount of alkali carbonate should be stoichiometric for formation of chromate. Lime is added for several reasons, one important one seems to be that it keeps the mass from fusing, which would vastly reduce the surface area oxygen can get to. The lime process doubles yeilds according to one text and should be added to the extent of 80% of the weight of the ore if the Cr2O3 contents are 30 to 40% and 120-130% if in excess of 50% Cr2O3. Oxidation is typically 95% complete at 1160C after 30mins and decomposition sets in around 1260C. At 700C oxidation is 'slow' but no details are given.

According to Polverone in a sciencemadness thread, Cr2O3 can be fused with alkali nitrates to yeild dichromate directly (no acidification step). This is unexpected but not impossible.

The better information I was thinking of turned out to be a permanganate method, not dichromate. Whoops, but a fair amount of stuff is present. It should also be noted that Cr 3+ salts are much less toxic than Cr 6+ salts.

Chromic trichloride classic method is to heat chromic oxide (Cr2O3) in a stream of sulphur chloride or carbon tet vapour in a tube furnace. Not very convenient. Dissolving Cr2O3 in concentrated hydrochloric acid and then evaporating to dryness produces a hydrate, if this is heated strongly it loses virtually all of the water but some decomposition to C2O3 occurs colouring the mass green. If the residue is heated to a high temperature, 700C seems in the right range, the chromic chloride sublimes leaving the chromic oxide behind.

From Inorganic preperations by walton (scan by S.C. Wack). The extraction by precipitation of the strontium salt is a must to avoid but the oxidation step is clearly sound.


Potassium Dichromate from Chromite.

Chromite, FeCr2O4, is the principal ore of chromium. Chromates and dichromates are obtained from it by fusion with sodium or potassium carbonate with access of air; the iron is oxidized from the ferrous to the ferric condition and the chromium from oxidation state +3 to +6. The melt is taken up with water, sulfuric acid is added, and the dichromate is separated by a rather complicated frational crystallization process which is a good example of the use of phase diagrams (34).

The procedure which follows is adapted to the small scale of the laboratory. Potassium nitrate is added in the fusion to hasten oxidation, and the chromate is separated from the solution of the melt by precipitation instead of by fractional crystallization.

In an iron dish place 20 grams of potassium carbonate, 20 grams of potassium hydroxide, and 10 grams of potassium nitrate. Support the dish on a piece of asbestos board with a hole cut to fit it, and heat with a Meker burner until the mixture is melted. Then add 20 grams of finely powdered chromite, a little at a time, stirring with a stiff iron wire or the end of an old file. Heat as much as is necessary to keep the mass fluid. Effervescence occurs as the mineral is added. When all the chromite has been added, heat as strongly as possible for 20 minutes, stirring occasionally, and then cool. While the dish and contents are still hot but not so hot that undue spattering is caused, place the dish in a large evaporating dish containing enough water to cover it, and boil until all the material in the dish has been loosened. After a few minutes boiling the solution should be bright yellow. If it is still green after 10 minutes' boiling, add a little hydrogen peroxide. Then filter, washing the residue on the filter paper with hot water. What is this residue?

Evaporate the combined filtrate and washings, which contain the chromate, to 100 to 150 ml. Add 1:1 hydrochloric acid or nitric acid carefully, with stirring, to the hot solution to neutralize excess alkali and decompose carbonate. A precipitate of silica will probably appear. After a point the mixture will start getting brownish. Stop adding acid, and filter. Add to the hot filtrate about 25 grams of strontium chloride hydrate and enough concentrated ammonia (about 4 ml) to cause the formation of a large yellow precipitate of strontium chromate. Cool to room temperature and filter off this precipitate. It may be possible to recover more strontium chromate from the filtrate by adding ammonia. Wash the precipitate with dilute ammonia water, dry it, and weigh. To prepare potassium dichromate from this strontium chromate, add the calculated amount of potassium acid sulfate dissolved in aboat 50 ml of water, and digest on the steam bath until the solid appears pure white. This process should take about half an hour. Then filter and evaporate the filtrate until crystals start to form. Cool to near 0C, filter off the crystals, dry, and weigh. Calculate the percentage yield, assuming that the chromite contained 30 per cent of chromium.

34, See H. A. Doerner, Chem. and Met. Eng., 47 (1940), 688.



From Rhodium's collection (still down last I checked), untested but supported by the walton procidure which uses hydrogen peroxide to correct any unoxidised chromium.


Potassium Dichromate from Chromium Metal or Cr(III)
by Nitro

--------------------------------------------------------------------------------

Hey chemists out there! This is a new synthesis of POTASSIUM DICHROMATE, a potent oxidizer which can be used to make GOOD things. I cannot give you refs cause I have discovered this myself. The idea came from a german chemistry lexikon, Römpp's, which said that Cr(OH)3 reacts with NaOH/H2O2 to form chromate.

WARNING
This file was written for informational purposes only. You should not attempt to make it and to use this controlled (in Europe it is) stuff to make illegal drugs or to poison someone. :) :) Potassium dichromate is toxic. A dose of 4-10 g of it can and will cause the death of a man if ingested.

Starting material can be:

Chromium metal
Chrome-nickel wire
Any Chromium(III) salt
Synthesis
Weigh out 104 g Chromium metal and dissolve it in 500 ml of fuming (37%) HCl (or equimolar amount of dilute H2SO4) in a preferably large beaker. Add the metal to the acid in small portions and warm if the rxn goes too slowly. When it's all dissolved, filter the solution to remove insoluble material the chrome was contained with. In another beaker, dissolve 245 g pure NaOH in enough water and let the solution cool to 20-40°C. Add this alkali solution slowly to the filtered chromium(III)-chloride solution. A greenish or grayish precipitate of Cr(OH)3 will form. Filter this, squeeze it out and wash it 3 times with distilled water. You don't need to dry it, just put it into a clean beaker and add: 1) a solution of 160 g NaOH in just sufficient water and 2) approx. 350 ml of 30% hydrogen peroxide. Add the reagents carefully for that they don't splash. The green Cr(OH)3 will dissolve and the soln will turn a very beautiful yellow of sodium chromate. If you boil the solution for some time and then crystallizate it, you can get Na2CrO4, but we want to proceed to potassium dichromate now.

Add 164 ml of concentrated HCl. The color will immediately change to orange. This is the color of the Cr2O72- anion. Now boil the solution down to approx. 50% its original volume. After cooling white crystals of NaCl can be removed and discarded.

Now weigh out 149 g of Potassium chloride (or equimolar amount of either K2CO3, KOH, or KNO3). Dissolve it in 80°C hot water to prepare a hot saturated solution. Pour this solution into the orange solution of sodium bichromate. Orange crystals of the crude product will form. Filter them after cooling to 10°C.

Recrystalizate the product twice from distilled water. Store in well-stoppered bottle.

If you started from chrome-nickle, then some insoluble nickle(II)-hydroxide will remain undissolved after adding NaOH/H2O2. This can be filtered. If you had Cr(III)-salts, then just dissolve them in water and add NaOH soln.

The solubility of K2Cr2O7 is only 7 g/100 g water, but that of Na2Cr2O7 is more than 100 g/100 g. Therefore, if you add a potassium salt solution to Na2Cr2O7 soln, K2Cr2O7 will crystallizate readily.

The yield of this synth is almost quantitative, around 280-290 g if you did it right (>95%). There is only loss of material which remains on the filter etc.


Some more useful stuff from walton (same scan, S.C. Wack) for chromic anhydride,


Chromium Trioxide.

Chromic acid is a rather weak acid and is also unstable, losing water easily to form its anhydride, CrO3. This oxide is extremely soluble in water, but the solubility is greatly reduced by adding sulfuric acid, as will be seen in the phase diagram in Fig. 21. It is therefore an easy matter to precipitate chromium trioxide by adding an excess of sulfuric acid to a solution of a chromate or dichromate. The difficulty comes in drying and handling the product, which is extremely hygroscopic and powerfully oxidizing.

Dissolve 30 grams (0.10 mole) of sodium dichromate, Na2Cr2O7.2H2O, in 25 ml of water. Stir into the cold solution 40 grams of concentrated sulfuric acid (22 ml), adding the acid slowly as soon as the precipitate begins to appear. Let the hot solution cool to about 25C and filter the crystals on a glass or asbestos filter under suction. Use the apparatus shown in Fig. 22, which is designed to permit dry air to be sucked over the crystals to remove excess solvent. The filter is a cylindrical tube A in the bottom of which is fused a coarse sintered glass plate B, or, less desirably, a perforated porcelain or glass plate on which is laid a circle of glass filter cloth or a mat of asbestos fiber or glass wool. The tube A should first be weighed dry, with the filter in place and the upper end closed by a solid rubber stopper. During the filtration and drying, the tube is kept closed at the upper end by a rubber stopper which carries a tube connected to a phosphorus pentoxide drying tube D and a calcium chloride tower C, as shown in Fig. 22. First suck the crystals as free as possible from adhering mother liquor. Then turn off the suction, pour over the crystals about 10 ml of concentrated nitric acid, and suck the acid through slowly. Repeat with two more 20-ml portions of concentrated nitric acid and then suck dry air through the crystals for two hours or more until the crystals are perfectly .dry and loose. Quickly replace the stopper at the top of A with the solid stopper, and weigh the tube and contents. The difference in weight between this weighing and the weight of the empty tube gives the weight of the product.



A phase diagram is given, but its small and seems illustrative only, the text says,
"Fig. 21. The system CrO3 - H2O - SO3. The compositions are in moles. The curves for 25C and 40C are practically the same. (Data of Gilbert, Buckley, and Masson, J. Chem. Soc., 1922, page 1934.)"

Fig 22 is what is described, two towers one to dessicate the air with P2O5 (!) and the other to run this air over the CrO3. Why it isn't simply dried using a dessicator is not clear, an analysis method is also provided.

[Marvin]

This is what Ive been able to scrape together in a few days. Ive been caught a little off guard by the use of 'chromic', its not consistant as an oxidation state. Chromic oxide is Cr2O3, ie Cr (+3), chromic chloride is CrCl3 also Cr (+3) but chromic acid is H2CrO4 (or perhaps more apropriatly CrO3.H2O with CrO3 being called chromic anhydride) ie, Cr (+6)

Details for chromite + alkali + lime. Amount of alkali carbonate should be stoichiometric for formation of chromate. Lime is added for several reasons, one important one seems to be that it keeps the mass from fusing, which would vastly reduce the surface area oxygen can get to. The lime process doubles yeilds according to one text and should be added to the extent of 80% of the weight of the ore if the Cr2O3 contents are 30 to 40% and 120-130% if in excess of 50% Cr2O3. Oxidation is typically 95% complete at 1160C after 30mins and decomposition sets in around 1260C. At 700C oxidation is 'slow' but no details are given.

According to Polverone in a sciencemadness thread, Cr2O3 can be fused with alkali nitrates to yeild dichromate directly (no acidification step). This is unexpected but not impossible.

The better information I was thinking of turned out to be a permanganate method, not dichromate. Whoops, but a fair amount of stuff is present. It should also be noted that Cr 3+ salts are much less toxic than Cr 6+ salts.

Chromic trichloride classic method is to heat chromic oxide (Cr2O3) in a stream of sulphur chloride or carbon tet vapour in a tube furnace. Not very convenient. Dissolving Cr2O3 in concentrated hydrochloric acid and then evaporating to dryness produces a hydrate, if this is heated strongly it loses virtually all of the water but some decomposition to C2O3 occurs colouring the mass green. If the residue is heated to a high temperature, 700C seems in the right range, the chromic chloride sublimes leaving the chromic oxide behind.

From Inorganic preperations by walton (scan by S.C. Wack). The extraction by precipitation of the strontium salt is a must to avoid but the oxidation step is clearly sound.


Potassium Dichromate from Chromite.

Chromite, FeCr2O4, is the principal ore of chromium. Chromates and dichromates are obtained from it by fusion with sodium or potassium carbonate with access of air; the iron is oxidized from the ferrous to the ferric condition and the chromium from oxidation state +3 to +6. The melt is taken up with water, sulfuric acid is added, and the dichromate is separated by a rather complicated frational crystallization process which is a good example of the use of phase diagrams (34).

The procedure which follows is adapted to the small scale of the laboratory. Potassium nitrate is added in the fusion to hasten oxidation, and the chromate is separated from the solution of the melt by precipitation instead of by fractional crystallization.

In an iron dish place 20 grams of potassium carbonate, 20 grams of potassium hydroxide, and 10 grams of potassium nitrate. Support the dish on a piece of asbestos board with a hole cut to fit it, and heat with a Meker burner until the mixture is melted. Then add 20 grams of finely powdered chromite, a little at a time, stirring with a stiff iron wire or the end of an old file. Heat as much as is necessary to keep the mass fluid. Effervescence occurs as the mineral is added. When all the chromite has been added, heat as strongly as possible for 20 minutes, stirring occasionally, and then cool. While the dish and contents are still hot but not so hot that undue spattering is caused, place the dish in a large evaporating dish containing enough water to cover it, and boil until all the material in the dish has been loosened. After a few minutes boiling the solution should be bright yellow. If it is still green after 10 minutes' boiling, add a little hydrogen peroxide. Then filter, washing the residue on the filter paper with hot water. What is this residue?

Evaporate the combined filtrate and washings, which contain the chromate, to 100 to 150 ml. Add 1:1 hydrochloric acid or nitric acid carefully, with stirring, to the hot solution to neutralize excess alkali and decompose carbonate. A precipitate of silica will probably appear. After a point the mixture will start getting brownish. Stop adding acid, and filter. Add to the hot filtrate about 25 grams of strontium chloride hydrate and enough concentrated ammonia (about 4 ml) to cause the formation of a large yellow precipitate of strontium chromate. Cool to room temperature and filter off this precipitate. It may be possible to recover more strontium chromate from the filtrate by adding ammonia. Wash the precipitate with dilute ammonia water, dry it, and weigh. To prepare potassium dichromate from this strontium chromate, add the calculated amount of potassium acid sulfate dissolved in aboat 50 ml of water, and digest on the steam bath until the solid appears pure white. This process should take about half an hour. Then filter and evaporate the filtrate until crystals start to form. Cool to near 0C, filter off the crystals, dry, and weigh. Calculate the percentage yield, assuming that the chromite contained 30 per cent of chromium.

34, See H. A. Doerner, Chem. and Met. Eng., 47 (1940), 688.



From Rhodium's collection (still down last I checked), untested but supported by the walton procidure which uses hydrogen peroxide to correct any unoxidised chromium.


Potassium Dichromate from Chromium Metal or Cr(III)
by Nitro

--------------------------------------------------------------------------------

Hey chemists out there! This is a new synthesis of POTASSIUM DICHROMATE, a potent oxidizer which can be used to make GOOD things. I cannot give you refs cause I have discovered this myself. The idea came from a german chemistry lexikon, Römpp's, which said that Cr(OH)3 reacts with NaOH/H2O2 to form chromate.

WARNING
This file was written for informational purposes only. You should not attempt to make it and to use this controlled (in Europe it is) stuff to make illegal drugs or to poison someone. :) :) Potassium dichromate is toxic. A dose of 4-10 g of it can and will cause the death of a man if ingested.

Starting material can be:

Chromium metal
Chrome-nickel wire
Any Chromium(III) salt
Synthesis
Weigh out 104 g Chromium metal and dissolve it in 500 ml of fuming (37%) HCl (or equimolar amount of dilute H2SO4) in a preferably large beaker. Add the metal to the acid in small portions and warm if the rxn goes too slowly. When it's all dissolved, filter the solution to remove insoluble material the chrome was contained with. In another beaker, dissolve 245 g pure NaOH in enough water and let the solution cool to 20-40°C. Add this alkali solution slowly to the filtered chromium(III)-chloride solution. A greenish or grayish precipitate of Cr(OH)3 will form. Filter this, squeeze it out and wash it 3 times with distilled water. You don't need to dry it, just put it into a clean beaker and add: 1) a solution of 160 g NaOH in just sufficient water and 2) approx. 350 ml of 30% hydrogen peroxide. Add the reagents carefully for that they don't splash. The green Cr(OH)3 will dissolve and the soln will turn a very beautiful yellow of sodium chromate. If you boil the solution for some time and then crystallizate it, you can get Na2CrO4, but we want to proceed to potassium dichromate now.

Add 164 ml of concentrated HCl. The color will immediately change to orange. This is the color of the Cr2O72- anion. Now boil the solution down to approx. 50% its original volume. After cooling white crystals of NaCl can be removed and discarded.

Now weigh out 149 g of Potassium chloride (or equimolar amount of either K2CO3, KOH, or KNO3). Dissolve it in 80°C hot water to prepare a hot saturated solution. Pour this solution into the orange solution of sodium bichromate. Orange crystals of the crude product will form. Filter them after cooling to 10°C.

Recrystalizate the product twice from distilled water. Store in well-stoppered bottle.

If you started from chrome-nickle, then some insoluble nickle(II)-hydroxide will remain undissolved after adding NaOH/H2O2. This can be filtered. If you had Cr(III)-salts, then just dissolve them in water and add NaOH soln.

The solubility of K2Cr2O7 is only 7 g/100 g water, but that of Na2Cr2O7 is more than 100 g/100 g. Therefore, if you add a potassium salt solution to Na2Cr2O7 soln, K2Cr2O7 will crystallizate readily.

The yield of this synth is almost quantitative, around 280-290 g if you did it right (>95%). There is only loss of material which remains on the filter etc.


Some more useful stuff from walton (same scan, S.C. Wack) for chromic anhydride,


Chromium Trioxide.

Chromic acid is a rather weak acid and is also unstable, losing water easily to form its anhydride, CrO3. This oxide is extremely soluble in water, but the solubility is greatly reduced by adding sulfuric acid, as will be seen in the phase diagram in Fig. 21. It is therefore an easy matter to precipitate chromium trioxide by adding an excess of sulfuric acid to a solution of a chromate or dichromate. The difficulty comes in drying and handling the product, which is extremely hygroscopic and powerfully oxidizing.

Dissolve 30 grams (0.10 mole) of sodium dichromate, Na2Cr2O7.2H2O, in 25 ml of water. Stir into the cold solution 40 grams of concentrated sulfuric acid (22 ml), adding the acid slowly as soon as the precipitate begins to appear. Let the hot solution cool to about 25C and filter the crystals on a glass or asbestos filter under suction. Use the apparatus shown in Fig. 22, which is designed to permit dry air to be sucked over the crystals to remove excess solvent. The filter is a cylindrical tube A in the bottom of which is fused a coarse sintered glass plate B, or, less desirably, a perforated porcelain or glass plate on which is laid a circle of glass filter cloth or a mat of asbestos fiber or glass wool. The tube A should first be weighed dry, with the filter in place and the upper end closed by a solid rubber stopper. During the filtration and drying, the tube is kept closed at the upper end by a rubber stopper which carries a tube connected to a phosphorus pentoxide drying tube D and a calcium chloride tower C, as shown in Fig. 22. First suck the crystals as free as possible from adhering mother liquor. Then turn off the suction, pour over the crystals about 10 ml of concentrated nitric acid, and suck the acid through slowly. Repeat with two more 20-ml portions of concentrated nitric acid and then suck dry air through the crystals for two hours or more until the crystals are perfectly .dry and loose. Quickly replace the stopper at the top of A with the solid stopper, and weigh the tube and contents. The difference in weight between this weighing and the weight of the empty tube gives the weight of the product.



A phase diagram is given, but its small and seems illustrative only, the text says,
"Fig. 21. The system CrO3 - H2O - SO3. The compositions are in moles. The curves for 25C and 40C are practically the same. (Data of Gilbert, Buckley, and Masson, J. Chem. Soc., 1922, page 1934.)"

Fig 22 is what is described, two towers one to dessicate the air with P2O5 (!) and the other to run this air over the CrO3. Why it isn't simply dried using a dessicator is not clear, an analysis method is also provided.

[Marvin]

This is what Ive been able to scrape together in a few days. Ive been caught a little off guard by the use of 'chromic', its not consistant as an oxidation state. Chromic oxide is Cr2O3, ie Cr (+3), chromic chloride is CrCl3 also Cr (+3) but chromic acid is H2CrO4 (or perhaps more apropriatly CrO3.H2O with CrO3 being called chromic anhydride) ie, Cr (+6)

Details for chromite + alkali + lime. Amount of alkali carbonate should be stoichiometric for formation of chromate. Lime is added for several reasons, one important one seems to be that it keeps the mass from fusing, which would vastly reduce the surface area oxygen can get to. The lime process doubles yeilds according to one text and should be added to the extent of 80% of the weight of the ore if the Cr2O3 contents are 30 to 40% and 120-130% if in excess of 50% Cr2O3. Oxidation is typically 95% complete at 1160C after 30mins and decomposition sets in around 1260C. At 700C oxidation is 'slow' but no details are given.

According to Polverone in a sciencemadness thread, Cr2O3 can be fused with alkali nitrates to yeild dichromate directly (no acidification step). This is unexpected but not impossible.

The better information I was thinking of turned out to be a permanganate method, not dichromate. Whoops, but a fair amount of stuff is present. It should also be noted that Cr 3+ salts are much less toxic than Cr 6+ salts.

Chromic trichloride classic method is to heat chromic oxide (Cr2O3) in a stream of sulphur chloride or carbon tet vapour in a tube furnace. Not very convenient. Dissolving Cr2O3 in concentrated hydrochloric acid and then evaporating to dryness produces a hydrate, if this is heated strongly it loses virtually all of the water but some decomposition to C2O3 occurs colouring the mass green. If the residue is heated to a high temperature, 700C seems in the right range, the chromic chloride sublimes leaving the chromic oxide behind.

From Inorganic preperations by walton (scan by S.C. Wack). The extraction by precipitation of the strontium salt is a must to avoid but the oxidation step is clearly sound.


Potassium Dichromate from Chromite.

Chromite, FeCr2O4, is the principal ore of chromium. Chromates and dichromates are obtained from it by fusion with sodium or potassium carbonate with access of air; the iron is oxidized from the ferrous to the ferric condition and the chromium from oxidation state +3 to +6. The melt is taken up with water, sulfuric acid is added, and the dichromate is separated by a rather complicated frational crystallization process which is a good example of the use of phase diagrams (34).

The procedure which follows is adapted to the small scale of the laboratory. Potassium nitrate is added in the fusion to hasten oxidation, and the chromate is separated from the solution of the melt by precipitation instead of by fractional crystallization.

In an iron dish place 20 grams of potassium carbonate, 20 grams of potassium hydroxide, and 10 grams of potassium nitrate. Support the dish on a piece of asbestos board with a hole cut to fit it, and heat with a Meker burner until the mixture is melted. Then add 20 grams of finely powdered chromite, a little at a time, stirring with a stiff iron wire or the end of an old file. Heat as much as is necessary to keep the mass fluid. Effervescence occurs as the mineral is added. When all the chromite has been added, heat as strongly as possible for 20 minutes, stirring occasionally, and then cool. While the dish and contents are still hot but not so hot that undue spattering is caused, place the dish in a large evaporating dish containing enough water to cover it, and boil until all the material in the dish has been loosened. After a few minutes boiling the solution should be bright yellow. If it is still green after 10 minutes' boiling, add a little hydrogen peroxide. Then filter, washing the residue on the filter paper with hot water. What is this residue?

Evaporate the combined filtrate and washings, which contain the chromate, to 100 to 150 ml. Add 1:1 hydrochloric acid or nitric acid carefully, with stirring, to the hot solution to neutralize excess alkali and decompose carbonate. A precipitate of silica will probably appear. After a point the mixture will start getting brownish. Stop adding acid, and filter. Add to the hot filtrate about 25 grams of strontium chloride hydrate and enough concentrated ammonia (about 4 ml) to cause the formation of a large yellow precipitate of strontium chromate. Cool to room temperature and filter off this precipitate. It may be possible to recover more strontium chromate from the filtrate by adding ammonia. Wash the precipitate with dilute ammonia water, dry it, and weigh. To prepare potassium dichromate from this strontium chromate, add the calculated amount of potassium acid sulfate dissolved in aboat 50 ml of water, and digest on the steam bath until the solid appears pure white. This process should take about half an hour. Then filter and evaporate the filtrate until crystals start to form. Cool to near 0C, filter off the crystals, dry, and weigh. Calculate the percentage yield, assuming that the chromite contained 30 per cent of chromium.

34, See H. A. Doerner, Chem. and Met. Eng., 47 (1940), 688.



From Rhodium's collection (still down last I checked), untested but supported by the walton procidure which uses hydrogen peroxide to correct any unoxidised chromium.


Potassium Dichromate from Chromium Metal or Cr(III)
by Nitro

--------------------------------------------------------------------------------

Hey chemists out there! This is a new synthesis of POTASSIUM DICHROMATE, a potent oxidizer which can be used to make GOOD things. I cannot give you refs cause I have discovered this myself. The idea came from a german chemistry lexikon, Römpp's, which said that Cr(OH)3 reacts with NaOH/H2O2 to form chromate.

WARNING
This file was written for informational purposes only. You should not attempt to make it and to use this controlled (in Europe it is) stuff to make illegal drugs or to poison someone. :) :) Potassium dichromate is toxic. A dose of 4-10 g of it can and will cause the death of a man if ingested.

Starting material can be:

Chromium metal
Chrome-nickel wire
Any Chromium(III) salt
Synthesis
Weigh out 104 g Chromium metal and dissolve it in 500 ml of fuming (37%) HCl (or equimolar amount of dilute H2SO4) in a preferably large beaker. Add the metal to the acid in small portions and warm if the rxn goes too slowly. When it's all dissolved, filter the solution to remove insoluble material the chrome was contained with. In another beaker, dissolve 245 g pure NaOH in enough water and let the solution cool to 20-40°C. Add this alkali solution slowly to the filtered chromium(III)-chloride solution. A greenish or grayish precipitate of Cr(OH)3 will form. Filter this, squeeze it out and wash it 3 times with distilled water. You don't need to dry it, just put it into a clean beaker and add: 1) a solution of 160 g NaOH in just sufficient water and 2) approx. 350 ml of 30% hydrogen peroxide. Add the reagents carefully for that they don't splash. The green Cr(OH)3 will dissolve and the soln will turn a very beautiful yellow of sodium chromate. If you boil the solution for some time and then crystallizate it, you can get Na2CrO4, but we want to proceed to potassium dichromate now.

Add 164 ml of concentrated HCl. The color will immediately change to orange. This is the color of the Cr2O72- anion. Now boil the solution down to approx. 50% its original volume. After cooling white crystals of NaCl can be removed and discarded.

Now weigh out 149 g of Potassium chloride (or equimolar amount of either K2CO3, KOH, or KNO3). Dissolve it in 80°C hot water to prepare a hot saturated solution. Pour this solution into the orange solution of sodium bichromate. Orange crystals of the crude product will form. Filter them after cooling to 10°C.

Recrystalizate the product twice from distilled water. Store in well-stoppered bottle.

If you started from chrome-nickle, then some insoluble nickle(II)-hydroxide will remain undissolved after adding NaOH/H2O2. This can be filtered. If you had Cr(III)-salts, then just dissolve them in water and add NaOH soln.

The solubility of K2Cr2O7 is only 7 g/100 g water, but that of Na2Cr2O7 is more than 100 g/100 g. Therefore, if you add a potassium salt solution to Na2Cr2O7 soln, K2Cr2O7 will crystallizate readily.

The yield of this synth is almost quantitative, around 280-290 g if you did it right (>95%). There is only loss of material which remains on the filter etc.


Some more useful stuff from walton (same scan, S.C. Wack) for chromic anhydride,


Chromium Trioxide.

Chromic acid is a rather weak acid and is also unstable, losing water easily to form its anhydride, CrO3. This oxide is extremely soluble in water, but the solubility is greatly reduced by adding sulfuric acid, as will be seen in the phase diagram in Fig. 21. It is therefore an easy matter to precipitate chromium trioxide by adding an excess of sulfuric acid to a solution of a chromate or dichromate. The difficulty comes in drying and handling the product, which is extremely hygroscopic and powerfully oxidizing.

Dissolve 30 grams (0.10 mole) of sodium dichromate, Na2Cr2O7.2H2O, in 25 ml of water. Stir into the cold solution 40 grams of concentrated sulfuric acid (22 ml), adding the acid slowly as soon as the precipitate begins to appear. Let the hot solution cool to about 25C and filter the crystals on a glass or asbestos filter under suction. Use the apparatus shown in Fig. 22, which is designed to permit dry air to be sucked over the crystals to remove excess solvent. The filter is a cylindrical tube A in the bottom of which is fused a coarse sintered glass plate B, or, less desirably, a perforated porcelain or glass plate on which is laid a circle of glass filter cloth or a mat of asbestos fiber or glass wool. The tube A should first be weighed dry, with the filter in place and the upper end closed by a solid rubber stopper. During the filtration and drying, the tube is kept closed at the upper end by a rubber stopper which carries a tube connected to a phosphorus pentoxide drying tube D and a calcium chloride tower C, as shown in Fig. 22. First suck the crystals as free as possible from adhering mother liquor. Then turn off the suction, pour over the crystals about 10 ml of concentrated nitric acid, and suck the acid through slowly. Repeat with two more 20-ml portions of concentrated nitric acid and then suck dry air through the crystals for two hours or more until the crystals are perfectly .dry and loose. Quickly replace the stopper at the top of A with the solid stopper, and weigh the tube and contents. The difference in weight between this weighing and the weight of the empty tube gives the weight of the product.



A phase diagram is given, but its small and seems illustrative only, the text says,
"Fig. 21. The system CrO3 - H2O - SO3. The compositions are in moles. The curves for 25C and 40C are practically the same. (Data of Gilbert, Buckley, and Masson, J. Chem. Soc., 1922, page 1934.)"

Fig 22 is what is described, two towers one to dessicate the air with P2O5 (!) and the other to run this air over the CrO3. Why it isn't simply dried using a dessicator is not clear, an analysis method is also provided.

[tmp]

Mega, and others, thanks for the info. I've often found that intensive
searches of chemistry forums usually yield what I'm looking for.
Sometimes, a university professor will put a synthesis on the net so the
students have an easier access. As for starting materials, Mega, you
hit the nail on the head. I found both chromium oxide and iron chromate
at my local pottery supplier. BTW, chromium oxide mixed with magnesium
powder makes for a spectacular thermite ! :D :D :D

[tmp]

Mega, and others, thanks for the info. I've often found that intensive
searches of chemistry forums usually yield what I'm looking for.
Sometimes, a university professor will put a synthesis on the net so the
students have an easier access. As for starting materials, Mega, you
hit the nail on the head. I found both chromium oxide and iron chromate
at my local pottery supplier. BTW, chromium oxide mixed with magnesium
powder makes for a spectacular thermite ! :D :D :D

[tmp]

Mega, and others, thanks for the info. I've often found that intensive
searches of chemistry forums usually yield what I'm looking for.
Sometimes, a university professor will put a synthesis on the net so the
students have an easier access. As for starting materials, Mega, you
hit the nail on the head. I found both chromium oxide and iron chromate
at my local pottery supplier. BTW, chromium oxide mixed with magnesium
powder makes for a spectacular thermite ! :D :D :D

[Jacks Complete]

Just a note, but Chromium is a cancer-causing agent, as well as toxic. Don't eat the stuff or breathe it.

[Jacks Complete]

Just a note, but Chromium is a cancer-causing agent, as well as toxic. Don't eat the stuff or breathe it.

[Jacks Complete]

Just a note, but Chromium is a cancer-causing agent, as well as toxic. Don't eat the stuff or breathe it.

[Marvin]

Chromium (+6) is carcinogenic, chromium (+3) is a human dietary requirement. Doesn't make it safe, but t its not worth going overboard safety wise. To dispose of a chromium compound reduction to Cr 3+ and running down the drain with water should be fine.

Now then, here is a very useful one, its not in any of my books as a synth, and I havnt been able to find it nosing through any of the scanned iorganic prep books. Its in the Society of Amateur Scientists electronic newsletter in an article by Norm Stanley.


It is not a difficult matter to prepare small quantities of this reactive liquid in the home laboratory. The chromyl chloride (b.p. 117 C) is recovered by distillation from the reaction mixture. Since the vapor and liquid attack organic materials (including rubber stoppers) it is preferable to work with all glass apparatus. If you're fortunate enough to own or have access to a good selection of standard taper ground joint ware, or that venerable symbol of the chemist, a glass retort, then you'r e all set. Otherwise, don't despair; I used the apparatus shown in Figure 2 with satisfactory results. Rubber stoppers were used; these may have to be replaced after one or two uses in the corrosive environment. Applying a thin coating of silicone stopcock grease may retard attack The air condenser was bent from a length of glass tubing. I recommend neon sign tubing, which is easily worked in a gas flame. If you have some glass working expertise, you can blow a bulb in the riser to serve as a trap for any liquid that may spurt over. The condensed CrO2Cl2 is collected in a U-tube cooled by immersion in a jar of cold water.

The distillation should be carried out in an efficient fume hood or in a well-ventilated area, preferably open air, as CrO2Cl2 vapor is toxic and extremely irritating(1).

Thoroughly mix 20 g potassium dichromate and 8 g sodium chloride (don' t use iodized table salt) and place in a 500 mL Erlenmeyer flask. Add 100 mL conc. sulfuric acid and attach the condenser and receiver. Heat cautiously with a Bunsen flame, taking care that the mixture doesn't froth and spurt over into the condenser. Continue distillation until no more material distills over. Theoretically, the yield should be about 20 g (10 mL) of CrO2Cl2. Store in a glass-stoppered amber glass bottle.


The full article is currently here,
http://www.sas.org/E-Bulletin/2002-04-19/chem/body.html

The Etard reaction mentioned in the article is a high yeild general reaction for turning methyl groups on an aromatic ring into aldehyde groups. For the simple case of benzaldehyde there are easier and safer methods of course.

[Marvin]

Chromium (+6) is carcinogenic, chromium (+3) is a human dietary requirement. Doesn't make it safe, but t its not worth going overboard safety wise. To dispose of a chromium compound reduction to Cr 3+ and running down the drain with water should be fine.

Now then, here is a very useful one, its not in any of my books as a synth, and I havnt been able to find it nosing through any of the scanned iorganic prep books. Its in the Society of Amateur Scientists electronic newsletter in an article by Norm Stanley.


It is not a difficult matter to prepare small quantities of this reactive liquid in the home laboratory. The chromyl chloride (b.p. 117 C) is recovered by distillation from the reaction mixture. Since the vapor and liquid attack organic materials (including rubber stoppers) it is preferable to work with all glass apparatus. If you're fortunate enough to own or have access to a good selection of standard taper ground joint ware, or that venerable symbol of the chemist, a glass retort, then you'r e all set. Otherwise, don't despair; I used the apparatus shown in Figure 2 with satisfactory results. Rubber stoppers were used; these may have to be replaced after one or two uses in the corrosive environment. Applying a thin coating of silicone stopcock grease may retard attack The air condenser was bent from a length of glass tubing. I recommend neon sign tubing, which is easily worked in a gas flame. If you have some glass working expertise, you can blow a bulb in the riser to serve as a trap for any liquid that may spurt over. The condensed CrO2Cl2 is collected in a U-tube cooled by immersion in a jar of cold water.

The distillation should be carried out in an efficient fume hood or in a well-ventilated area, preferably open air, as CrO2Cl2 vapor is toxic and extremely irritating(1).

Thoroughly mix 20 g potassium dichromate and 8 g sodium chloride (don' t use iodized table salt) and place in a 500 mL Erlenmeyer flask. Add 100 mL conc. sulfuric acid and attach the condenser and receiver. Heat cautiously with a Bunsen flame, taking care that the mixture doesn't froth and spurt over into the condenser. Continue distillation until no more material distills over. Theoretically, the yield should be about 20 g (10 mL) of CrO2Cl2. Store in a glass-stoppered amber glass bottle.


The full article is currently here,
http://www.sas.org/E-Bulletin/2002-04-19/chem/body.html

The Etard reaction mentioned in the article is a high yeild general reaction for turning methyl groups on an aromatic ring into aldehyde groups. For the simple case of benzaldehyde there are easier and safer methods of course.

[Marvin]

Chromium (+6) is carcinogenic, chromium (+3) is a human dietary requirement. Doesn't make it safe, but t its not worth going overboard safety wise. To dispose of a chromium compound reduction to Cr 3+ and running down the drain with water should be fine.

Now then, here is a very useful one, its not in any of my books as a synth, and I havnt been able to find it nosing through any of the scanned iorganic prep books. Its in the Society of Amateur Scientists electronic newsletter in an article by Norm Stanley.


It is not a difficult matter to prepare small quantities of this reactive liquid in the home laboratory. The chromyl chloride (b.p. 117 C) is recovered by distillation from the reaction mixture. Since the vapor and liquid attack organic materials (including rubber stoppers) it is preferable to work with all glass apparatus. If you're fortunate enough to own or have access to a good selection of standard taper ground joint ware, or that venerable symbol of the chemist, a glass retort, then you'r e all set. Otherwise, don't despair; I used the apparatus shown in Figure 2 with satisfactory results. Rubber stoppers were used; these may have to be replaced after one or two uses in the corrosive environment. Applying a thin coating of silicone stopcock grease may retard attack The air condenser was bent from a length of glass tubing. I recommend neon sign tubing, which is easily worked in a gas flame. If you have some glass working expertise, you can blow a bulb in the riser to serve as a trap for any liquid that may spurt over. The condensed CrO2Cl2 is collected in a U-tube cooled by immersion in a jar of cold water.

The distillation should be carried out in an efficient fume hood or in a well-ventilated area, preferably open air, as CrO2Cl2 vapor is toxic and extremely irritating(1).

Thoroughly mix 20 g potassium dichromate and 8 g sodium chloride (don' t use iodized table salt) and place in a 500 mL Erlenmeyer flask. Add 100 mL conc. sulfuric acid and attach the condenser and receiver. Heat cautiously with a Bunsen flame, taking care that the mixture doesn't froth and spurt over into the condenser. Continue distillation until no more material distills over. Theoretically, the yield should be about 20 g (10 mL) of CrO2Cl2. Store in a glass-stoppered amber glass bottle.


The full article is currently here,
http://www.sas.org/E-Bulletin/2002-04-19/chem/body.html

The Etard reaction mentioned in the article is a high yeild general reaction for turning methyl groups on an aromatic ring into aldehyde groups. For the simple case of benzaldehyde there are easier and safer methods of course.

[Jome skanish]

I've had Cr2O3 sitting in a test tube with 30% hydrocloric acid for over 24 hours now, there seem to be nothing happening at all, the acid is still without any sign of turning Cr+3 - green. Is something wrong with the procedure Marvin mentioned or does it need high temperature or something? The difference between 30 and 37% cant be that great, can it?

It would be great to have access to chromates and dicromates from Cr2O3 without having to melt things in crucibles.

[Jome skanish]

I've had Cr2O3 sitting in a test tube with 30% hydrocloric acid for over 24 hours now, there seem to be nothing happening at all, the acid is still without any sign of turning Cr+3 - green. Is something wrong with the procedure Marvin mentioned or does it need high temperature or something? The difference between 30 and 37% cant be that great, can it?

It would be great to have access to chromates and dicromates from Cr2O3 without having to melt things in crucibles.

[Jome skanish]

I've had Cr2O3 sitting in a test tube with 30% hydrocloric acid for over 24 hours now, there seem to be nothing happening at all, the acid is still without any sign of turning Cr+3 - green. Is something wrong with the procedure Marvin mentioned or does it need high temperature or something? The difference between 30 and 37% cant be that great, can it?

It would be great to have access to chromates and dicromates from Cr2O3 without having to melt things in crucibles.

[Marvin]

I can't personally vouch for any of these methods, I will say they look sound though.

I also can't see where anything Ive quoted talks about adding Cr2O3 to hydrochloric acid. Nitro's method talks about chromium metal which I had previously thought not active enough to liberate hydrogen but I'm prepaired to suspend my disbelief on that count.

Pottery grade Cr2O3 is much much less reactive than the freshly precipitated hydrated oxide. Again I can't vouch for this, the closest experience Ive had is with lapidary ceric oxide in my somewhat successful attempts to produce ceric sulphate, another potent oxidiser. I would be inclined to try sulphuric acid of different concentrations, starting with concentrated, and pounding the oxide into a very very find powder first. Reducing to chromium with aluminium is one possibility or its back to a furnace until you get enough in salt form to recycle.

[Marvin]

I can't personally vouch for any of these methods, I will say they look sound though.

I also can't see where anything Ive quoted talks about adding Cr2O3 to hydrochloric acid. Nitro's method talks about chromium metal which I had previously thought not active enough to liberate hydrogen but I'm prepaired to suspend my disbelief on that count.

Pottery grade Cr2O3 is much much less reactive than the freshly precipitated hydrated oxide. Again I can't vouch for this, the closest experience Ive had is with lapidary ceric oxide in my somewhat successful attempts to produce ceric sulphate, another potent oxidiser. I would be inclined to try sulphuric acid of different concentrations, starting with concentrated, and pounding the oxide into a very very find powder first. Reducing to chromium with aluminium is one possibility or its back to a furnace until you get enough in salt form to recycle.

[Marvin]

I can't personally vouch for any of these methods, I will say they look sound though.

I also can't see where anything Ive quoted talks about adding Cr2O3 to hydrochloric acid. Nitro's method talks about chromium metal which I had previously thought not active enough to liberate hydrogen but I'm prepaired to suspend my disbelief on that count.

Pottery grade Cr2O3 is much much less reactive than the freshly precipitated hydrated oxide. Again I can't vouch for this, the closest experience Ive had is with lapidary ceric oxide in my somewhat successful attempts to produce ceric sulphate, another potent oxidiser. I would be inclined to try sulphuric acid of different concentrations, starting with concentrated, and pounding the oxide into a very very find powder first. Reducing to chromium with aluminium is one possibility or its back to a furnace until you get enough in salt form to recycle.

[Jome skanish]

Guess I misunderstood what you wrote. The hydroxide behaves completely different than the oxide, simply by adding more KOH I got it to dissolve very fast, and I'd think the same thing would happen if hydrochloric acid was added. The oxide does not react at all, even for weeks it seems. The dehydration seems to be quite irreversible.

Cr-metal from Cr2O3/Al thermite dissolves fast in 30% HCl. I had to bring it outside because the heat made lots of HCl vapor to fly around, but that might be due to a small ammount of Al and Al2O3 in the Chromium.

[Jome skanish]

Guess I misunderstood what you wrote. The hydroxide behaves completely different than the oxide, simply by adding more KOH I got it to dissolve very fast, and I'd think the same thing would happen if hydrochloric acid was added. The oxide does not react at all, even for weeks it seems. The dehydration seems to be quite irreversible.

Cr-metal from Cr2O3/Al thermite dissolves fast in 30% HCl. I had to bring it outside because the heat made lots of HCl vapor to fly around, but that might be due to a small ammount of Al and Al2O3 in the Chromium.

[Jome skanish]

Guess I misunderstood what you wrote. The hydroxide behaves completely different than the oxide, simply by adding more KOH I got it to dissolve very fast, and I'd think the same thing would happen if hydrochloric acid was added. The oxide does not react at all, even for weeks it seems. The dehydration seems to be quite irreversible.

Cr-metal from Cr2O3/Al thermite dissolves fast in 30% HCl. I had to bring it outside because the heat made lots of HCl vapor to fly around, but that might be due to a small ammount of Al and Al2O3 in the Chromium.

[kurtz]

Chromium
A Comprehensive Treatise on Inorganic and Theoretical Chemistry
Volume 11, Chapter 60
J.W. Mellor
1931
362 pp.

can be found at:
http://rapidshare.de/files/1988880/mellor_actitc_11_60_cr.rar.html

[kurtz]

Chromium
A Comprehensive Treatise on Inorganic and Theoretical Chemistry
Volume 11, Chapter 60
J.W. Mellor
1931
362 pp.

can be found at:
http://rapidshare.de/files/1988880/mellor_actitc_11_60_cr.rar.html

[kurtz]

Chromium
A Comprehensive Treatise on Inorganic and Theoretical Chemistry
Volume 11, Chapter 60
J.W. Mellor
1931
362 pp.

can be found at:
http://rapidshare.de/files/1988880/mellor_actitc_11_60_cr.rar.html

[Moltar]

I have a detail to the potassium dichromate and the chloric method. 1 mol of
finely powdered sodium dichromate and 3 mol of potassium chloride is heated and stirred in a beaker. The will form potassium dichromate and sodium chloride.

Na2Cr2O7 + 2 KCl -> K2Cr2O7 + 2 NaCl

In what solution is the sodium dichromate soluble that it can removed and filtered from the remainder of the sodium chloride ?

The potassium dichromate is heated above 500 degree centigrade, it will decompose into potassium chromate, chromium(III)oxide and oxygen.

2 K2Cr2O7 -> Cr2O3 + 2 K2CrO4 + 1,5 O2

[Thermiteisfun]

I have a grout that contains iron oxide as well as chromium oxide, but for the life of me I can't find the proportions.

I'm wondering if I can possibly use this in a pyro comp or somehow separate the silica. The product is called "Polyblend sanded grout" labeled "3 grout. The instructions state to mix 1 pint water with 7lbs powder.
Would it be possible to use this in any kind of comp with the silica in it?

Edit: I didn't want to make a new thread so I found one that had the chromium oxide because that is what I want, the mix also has Fe2O3 which I also want.

http://www.skcinternational.com/nioshdbs/npg/npgd0521.htm
http://www.chemexper.com/chemicals/supplier/cas/2425-85-6.html

[nbk2000]

I don't suppose the thought of using a MAGNET ever occurred, did it?

The only thing in those lists that is magnetic is the iron. :p

As for the chromium...