Sodium Bichromate synthesis questions

[sYnThOmAtIc]

If one were to follow the synthesis of potassium dichromate to the point of forming the sodium bichromate only what else could be used as a starting chromium salt? Could a quantity of chromic acid containing 104g of chromium metal be used instead? Like say 550g of CrO3? Or would the oxygen cause problems? And how much chromium chloride would you need to jsut jump in and start at the alkali addition at the start of the formation of sodium chromate?

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.


EDIT: Woooops the mole calculator I used didn't recognize Cr and gave me a mass for C being 20% of the 60g per mole weight. I found the proper weight using a different calculator.... So would 210g CrO3 be a suitable replacement..?

[terbium]

So would 210g CrO3 be a suitable replacement..?
A suitable replacement for what? Chromium metal, chromium hydroxide, sodium dichromate? CrO3 is already hexavalent chromium, you should be able to add just the NaOH to a solution of CrO3 and procede to isolating the sodium dichromate.

[sYnThOmAtIc]

Sorry about not being specific as to the replacement product. Just for the record, dicrhomate and bichromate are one in the same right? Thanks terbium...  

[terbium]

Yes, dichromate and bichromate are the same.

[sYnThOmAtIc]

What happens to the bichromate chemically during the oxidation of say anethole or isoeugenol? Like what chemical does it turn into, or mixture?

Seeing as such a ridiculous ammount of bichromate is used, it would need to be reused a couple times. Is there any way around using such a high ammount of bichromate for oxidation of anethole/isoeugenol? If not, does this method scale well?

Or maybe another way to make anisaldehyde or vanillin that isn't on the 5gram level, but rather 100g?
I've seen only ozone, vanadium pentoxide, and bichromate for making anisaldehyde, but their all on the 5gram level. And the V2O5 doesn't seem very economical at it's low batch size and requirment for h202 and t-butylalcohol the latter being the hardest part to get.  And info on bichromate seems to be limited to meth and the h2so4 methods.

Is there not a better way to make an aldehyde on the 100gram level?

[Nicodem]

What happens to the bichromate chemically during the oxidation of say anethole or isoeugenol? Like what chemical does it turn into, or mixture?

The dichromate anion gets reduced to chromium (III) salts which usualy decompose with water (unles if very acidic medium) to chromium (III) oxide.

[gsus]

a more dilute HCl is ok to form the CrCl3. there will be a lot of H2 and HCl fumes for a while, hood is a must. neutralization can b done w/carb or bicarb instead of OH. if the Cr was  free of Fe, adding OH to the Cr(OH)3 will give soluble chromite. all reactions to now have been at RT
but now it is heated and H2O2 is added as soon as it boils.
rapid stirring and slow addn of course. the 3% H2O2 will work. experimenters might try percarb. any recipe calling for chromic acid, chromate, or dichromate can use the chromate produced above. add 1:1 mole H2SO4 for dichromate.
and 2mol acid to get equivalent in chromic acid. this assumes that your chromate is pure. that is y i recommend using KOH to neuter your Cr(OH)3. Na and K chromate are v.sol. in cold and hot H2O. K dichro is also vsol in hot H2O but but at 0C satd soln 4.3% and crystallizes very nicely. due to this low sol ion exchange between Na dichro and KCl should b feasible. merck says so! you can also melt a CrO3/sulfate/chloride cake and separate the Cr03 layer. industrially, chromite is roasted w/carbonate in air and the chromate leached out. if you got your chrome by HCl/18-0 stainless, the Fe will also form a trichloride and trihydroxide. but no chromite will dissolve in the water, it is bound to the Fe. this hurts nothing, as it doesn't react w/H2O2-just pour off the yellow sol. chromate
and repeat your boiling sludge/OH-/H2O2 till no more yellow comes out. if from 18-8(nickel) then b sure the soln at the chromate stage is always very basic, then drop this into conc acid to prevent double salt of Ni and Cr that forms in neutral soln. im grasping at straws on that last one and so are you if you're using 18-8 stainless. the air roasting process may work, maybe only chromate and excess carbonate are leached out.

[sYnThOmAtIc]

The dichromate anion gets reduced to chromium (III) salts which usualy decompose with water (unles if very acidic medium) to chromium (III) oxide

So the solution can be rotovaped and crystalized to obtain CrO3? And I guess if that is found to be insufficient the solution can be run through an electrochemical cell to plate the chrome onto a carbon rod which can be electrostripped in hcl to give the ?chromium(III)chloride? and jump into that synth at that point....

[gsus]

trivalent Cr oxide is Cr203. it is green, insolH2O, slowly sol HCl, giving CrCl3. should have mentioned earlier that Cr+HCl=CrCl3 only with air contact of the sol., or else CrCl2 happens in a predominately HCl atm. dilute H2SO4 works the same way. HNO3 or conc H2SO4 wont dissolve Cr.
  roasting the Cr2O3 in air with carbonate will give chromate but this can suck as fused Cr203 is very hard and resistant to acids. should be spread v thin for roasting, the chromate is leached out w/H2O. this oxidation does not happen very fast and  nitrate or chlorate will help, just like in the making of KMnO4 from MnO2.
 if you add a base to a +3 salt, you get the hydroxide. adding more base will dissolve it, giving the chromite. you can add the H202/OH to this, but thats a lot of OH to expose to the air to (and clean up), so its usually oxidized as the precipitate.
  you can also fuse a +3 salt with nitrate(turns into nitrite) and alkali carbonate to get the chromate.
 Cr203 that hasnt been fused (or CrCl3) can be converted to chromyl Cl by heating in a current of Cl2. look up the Etard reaction for typical use. the usual way to make it is by heating (di)chromate with H2SO4 and NaCl or other H2SO4 transposable chloride.
  the CrO2Cl2 sublimes. this is very useful stuff, but like most everything very useful Very! Nasty! stuff. it fumes (very low mp) and the fumes, well, of course you have a fume hood. because otherwise you could die. there is more in TFSE.
 
  Cr+6 can also be made by adding Cr+3 and an oxidizer such as ClO3- to alkaline alkali peroxide soln such as NaO2.
  for Cr03, pure dry dichromate is slowly heated w/H2SO4. the 93% is ok. the hydrated bisulfate will melt round 160C. at 200C the CrO3 is molten and all on the bottom. remove heat very fast because the dec. point and mp are the same. tap the CrO3 molten or skim off the bisulfate then cool the CrO3 container in ice water fast.

no warranty expressed or implied

[sYnThOmAtIc]

I neglected to do some homework before posting that. I forgot that CrO3 was a (VI) species. I just jumped to the conclusion (III) oxide as a trioxide forgetting that the (III) has nothing to do with the ammount of O molecules.

Well shit, Cr2O3 is about fucking useless.

chromium from chromite by taking the chromite and treating it with molten alkali and oxygen, converting the chromium to alkali chromate and the latter is dissolved in water and precipitated as sodium dichromate which is then reduced with carbon to chromium oxide and the oxide is then reduced with aluminum to make chromium metal

If chrome oxide won't dissolve in water how can you precipitate the metal? Do you know of something that chrome oxide is soluable in? I've never had much luck precipitating metals with aluminum before. They were always formed around chunks of Al. I never took the time to figure out how to separate them and just tossed the mess.

[gsus]

remember the thermite demo? if youve never seen this, it is awesome. Cr can be produced the same way, substituting Cr203 for Fe203. it is mixed w/ Al powder and ignited with a "fuse" of Mg. this provides the necessary heat to start the Very! Fast! Exothermic! reaction.
  the fuse also gives you time to get the hell away. this fast sort of reaction is best because the Cr will turn back in to Cr203 in air at only 200-250C.
  as long as Cr2O3 wasnt heated above 500C it'll dissolve in acids but not fast and best in HCl.
  of course you can reduce the oxide w/C to Cr. it has also been done by fusing CrCl3 with Zn or Mg in NaCl or KCl flux. the excess metals are removed with Cr insol HNO3. have a feeling no one will b doing these things for the obvious reasons. industrial preps at best.
 some helpful dichromate hints that didnt get on my (un)original post: the +6 Ca cpds are made like the others. the cool thing about it is that the chromate crystallizes nicely. the dichro is more sol tho.
  as said elsewhere, cryst of the K and Na chromates can go wrong as the sulfates interfere w/ purity. the dichromates are a little easier-they tend to cryst last. best to just convert Na to the K dichro and not fuck around with the others. boil the Na dichro and whatever crap is in it with KCl. the NaCl will come out first(no, really) and the K dichro on cooling, if you get the conc. right.

[sYnThOmAtIc]

Huh? The Cr2O3 can be reduced with carbon as well? So your saying Cr2O3 that has never been subjected to high temps will dossolve in HCL? So how does the carbon reduction work? In solution or fusing? Dissolve Cr2O3 in HCl and add graphite powder and heat? I think I may try that or electrolytic reduction if it will dissolve in HCl.

Edit:

Alright, I found some info on that.. "Isolate the metal by the heating of chromium oxide (Cr2O3) and charcoal. In 1893, Moissan reduced the chromium oxide with charcoal in an electrical furnace and in 1898, Goldschmidt prepared chromium without traces of carbon by reduction of Cr2O3 with aluminum"

It seems like carbon would be easier to remove than aluminum. Once the metal is obtained it can be dissolved in HCl and the carbon filtered off.

It still looks impratical becasue I'm assuming "heating with charcoal" involves extremely high temperatures and a fine powder mixture of both. I hope this carbon reduction works on solutions if one can be made?

[gsus]

if you heat to 900-1100C any Cr cpd that is finely ground with the (bi)carbonate of K or Na +an oxidizer(nitrate, nitrite, chlorate...) you get the chromate.
  i would rather put the HCl/Cr203 out on the back porch and wait patiently. once you precipitate the hydroxide its all downhill.
  just beware Cr dusts and all +2 and +6 cpds.

..but we're all fucking peasants, as far as i can see...

[sYnThOmAtIc]

That high temp crazy shit is out of my comfort zone. I think I'd rather wait for it dissolve like you say.

When the Cr2O3 finally dissolves in the HCl it turns into Chromium(III)chloride right? I'm not sure what you meant by precipitating the hydroxide. I'm assuming from the newly made CrCl3 like in the dichromate synth?

Thanks for the patience man  

[foxy2]

just beware Cr dusts and all +2 and +6 cpds.

You mean that using Cr+6 as an instant tanning solution is a bad idea?

[gsus]

yes, it is. you will turn green, people will stare. your skin will have good resistance to the elements, tho.

.. a working class hero is something to be...

[Polverone]

Once upon a time, I took Cr2O3 from a ceramics supplier, mixed it with the appropriate amounts of sodium carbonate and nitrate (as learned from a 19th century industrial chemistry encyclopedia) and heated it in a test tube in a gas flame. I had to heat the tube until it softened and deformed, but I finally formed a little plug of impure sodium chromate, canary yellow and still containing many little speckles of green Cr2O3.

Much more recently, I tried doing something similar, but using no carbonate and an excess of KNO3 or NaNO3. To my surprise, the Cr2O3 (same stuff as in the earlier experiment) easily and completely dissolved in the molten nitrate in only a few minutes, with considerable evolution of NO2 (beware this gas!). And this was only with an alcohol lamp flame, well below the softening point of the test tube.

Even more interesting to me, I got the red/orange color of dichromate, not the yellow of chromate, so I didn't even need a separate acidification/crystallization stage to transform chromate to dichromate.

I guess that old industrial practice was to use as little nitrate as possible, since this was more economical, but it seems that using extra nitrate can save considerable time and effort. For many oxidations, I don't even think having some nitrate present will be deleterious, as long as you have enough dichromate (i.e. separation of dichromate from leftover nitrate may not be necessary).

[sYnThOmAtIc]

all reactions to now have been at RT
but now it is heated and H2O2 is added as soon as it boils.
rapid stirring and slow addn of course. the 3% H2O2 will work. experimenters might try percarb. any recipe calling for chromic acid, chromate, or dichromate can use the chromate produced above. add 1:1 mole H2SO4 for dichromate.

This sounds interesting. Rather not use expensive H2O2 on this if 3% works just fine. 

Ok, took a milliliter of chromium chlroide solution(104g Cr, 500ml HCl) and precipitated it with ammonium hydroxide{much cheaper and easier to separate than residual salts, just let evaporate). Scraped some of the chromium hydroxide off the filter paper and tossed it into some water and threw in a pellet of NaOH. Poured in about ten milliliters of 3% H2O2 and it instantly turned yellow. This was done to make sure tings were good up to now and that the chromium was pure as advertised. Never got any insoluables except for carbon at the HCL digestion. Noticed some slow bubbling of the now yellow solution for some time?

So this is my question. You mention boiling the mixture the doc says nothing of this and my small scale reaction turned completely yellow instantly, but it bubbled for a while. Was the bubbling the reaction continuing or the excess H2O2 breaking down? How long does one need to let this react to form yellow chromate completely assuming they did this at the scale written about an dwith 30%? What kind of changes should be amde when using 3% H2O2? Like increased volume, reaction time, temp, etc. Does one just use ten times the original ammount of 30%(10x320ml) or same volume with other modifications? Okay, so it's more than A question.

[ning]

Exactly what is it that chromates can do that can't bee done by TCCA, NaOCl, H2O2, oxone, and KMnO4?

In particular, it seems KMnO4 is almost universally interchangeable with K2Cr2O7

Sorry, but ning has an extreme dislike of nasty metals used as disposeable reagents.

[gsus]

ha! i've been concentrating 3% for a couple days now for exactly this purpose! first of all, let me say, IMHO this sucks. i've got plenty of nitrate and Cr2O3 and Cr(OH)3, a blowtorch and various gases, and the hot way is superior of course as long as the fumes are vented, but i am doing this H202 method again anyways. penance for my sins.

  i would not put much stock in the yellow color. takes very little chromate to give a lot of color. i say boil because with the 3%, i got nothing but this yellow color if i didn't. the solution is brought to a boil before and peroxide is added. feel free to experiment and do the opposite of everything i say though. i'm a grammar god, or so i've been led to believe, not a chemistry god.

 on a side note, Na peroxide hydrate may be of good use here, i've never made it before though. this might change soon. would not have thought of this today without your questions! 

  no matter what concentration you use, you will need strong  bottom stirring, and an addition funnel sort of device.

  when the H2O2 is added, things get a little! foamy. thus the addition funnel is dropping slowly, so this does take a while. in any case, the yield with the 3% was not great, despite some variation and several tries. this may not be entirely due to the strength of the peroxide however. there is good reason why this is not a lab or industrial method. i just kept dripping H2O2 until 10-20X excess was added. i also used excess NaOH. and of course i followed no specific recipe, i resisted the internet and those library building thingies and their Cr+6 recipes with all of my Luddian strength until just a couple days before i signed up here. shows how smart/hip/wise/informed/trustworthy i am.

  now the sucky part. if your solution contains ions other than K and Cr04, you have excess base, you skip crystallization because you just get yellow crap not nice pure crystalline chromate no matter how many times you recrystallize, you use too much crap-grade H2SO4, tap water, and then you concentrate and add to sat'd KCl and get? crap! crap in-crap out! how best to separate at this point? add lotsa H2SO4 or reduce back to +3! so do it right because although addition compounds of Cr+6 aren't mentioned in many books, they sure do exist! very old test for +6: a tiny bit of very diluted not-warm acid sol'n added to H202 gives a nice blue perchromic acid. very sensitive (1:40000) thus the dilution.

  what i'm trying to say is that chromate/dichromate/chloride/sulfate/chromic acid doesn't always crystallize well under less than careful conditions, and even when they do, they don't do it completely. following explicit recipes from the old days or doing enough experimentation to write your own is the way to go.

  i haven't been poisoned yet. the powdering and transfers of it etc. are the worst part, i think. though the dichromate can have a darkish artificial-orange-juice look to it, i never drank any. how long do you think it would last as +6 if you flushed it down the toilet? seriously. if you have a septic tank this would be a bad idea as your microbes would die, but otherwise i think not so bad in small quantity. i believe that where +6 is found in the wild, it is associated with releases into rivers or high mineral/Mn02-low organic soils. it is definitely easy to reduce in the lab. it is also easy to recycle, well, as easy as this is. in the end, it is cheaper to just buy dichromate. but this isn't about what can be bought for how much. but thanks everyone for being so freaked out over reactive chemicals. drives down the price!