Author Topic: Drying agents and their compatibilities  (Read 3168 times)

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Drying agents and their compatibilities
« on: February 03, 2003, 02:29:00 AM »
I don't know how many of you are interested in the compatibilities of different drying agents as I would guess most of you already have your favorite drying agent that you use with the reactions that you've gotten down pat and therefore don't need to look any further...if it works, don't fix it :-)  However there may be a few bees that aren't happy with the one they are using or just want to try a different for them here is a brief compatibility chart for reference use.  Hope it helps, if you've got any questions feel free to ask and I'll try to answer them correctly when I stop back...


Alumina-->Mainly as a drying agent in a desiccator or as a column through which liquid is percolated.
Aluminium Amalgam-->Mainly used for removing traces of water from alcohols, which are distilled from it after refluxing.
Barium Oxide-->Suitable for drying organic bases.
Barium Perchlorate-->Expensive. Used in desiccators (covered with a metal guard). Unsuitable for drying solvents or organic material where contact is necessary, because of the danger of EXPLOSION.
Calcium Chloride-->Large capacity for absorption of water, giving the hexahydrate below 30°, but is fairly slow in action and not very efficient. Its main use is for preliminary drying of alkyl and aryl halides, most esters, saturated and aromatic hydrocarbons and ethers. Unsuitable for drying alcohols and amines, fatty acids, amides, amino acids, ketones, phenols, or some aldehydes and esters. Calcium chloride is suitable for drying the following gases: hydrogen, hydrogen chloride, carbon monoxide, carbon dioxide, sulfur dioxide, nitrogen, methane, oxygen, also paraffins, ethers, olefines and alkyl chlorides.
Calcium Oxide-->Suitable for alcohols and amines (but does not dry them completely). Unsuitable for acidic compounds and esters. Suitable for drying gaseous amines and ammonia.
Calcium Sulfate-->Available commercially as Drierite. It forms the hemihydrate, 2CaSO4.H2O, so that its capacity is fairly low (6.6% of its weight of water), and hence is best used on partially dried substances. It is very efficient (being comparable with phosphorus pentoxide and concentrated sulfuric acid). Suitable for most organic compounds. Solvents boiling below 100° can be dried by direct distillation from calcium sulfate.
Copper (II) Sulfate-->Suitable for esters and alcohols. Preferable to sodium sulfate in cases where solvents are sparingly soluble in water (for example, benzene or toluene).
Magnesium Amalgam-->Mainly used for removing traces of water from alcohols, which are distilled from it after refluxing.
Magnesium Perchlorate-->Expensive (Available commercially as Dehydrite).Used in desiccators. Unsuitable for drying solvents or any organic material where contact is necessary, because of the danger of EXPLOSION.
Magnesium Sulfate -->More rapid and effective than sodium sulfate. It has a large capacity, forming MgSO4.7H2O below 48°. Suitable for the preliminary drying of most organic compounds.
Phosphorus Pentoxide-->Very rapid and efficient, but difficult to handle and should only be used after the organic material has been partially dried, for example with magnesium sulfate. Suitable for acid anhydrides, alkyl and aryl halides, ethers, esters, hydrocarbons and nitriles, and for use in desiccators. Not suitable with acids, alcohols, amines or ketones, or with organic molecules from which a molecule of water can be fairly readily abstracted by an elimination reaction. Suitable for drying the following gases: hydrogen, oxygen, carbon dioxide, carbon monoxide, sulfur dioxide, nitrogen, methane, ethylene and paraffins. It is available with an indicator (cobalt salt, blue when dry and pink when wet) under the name Sicapent (from Merck).
Potassium (metal)-->Properties and applications are similar to those for sodium, and it is a correspondingly hazardous substance.
Potassium Carbonate-->Has a moderate efficiency and capacity, forming the dihydrate. Suitable for an initial drying of alcohols, bases, esters, ketones and nitriles by shaking with them, then filtering off. Also suitable for salting out water-soluble alcohols, amines and ketones. Unsuitable for acids, phenols and other acidic substances.
Potassium Hydroxide-->Solid potassium hydroxide is very rapid and efficient. Its use is limited almost entirely to the initial drying of organic bases. Alternatively, sometimes the base is shaken first with a concentrated solution of potassium hydroxide to remove most of the water present. Unsuitable for acids, aldehydes, ketones, phenols, amides and esters. Also used for drying gaseous amines and ammonia.
Silica Gel-->Granulated silica gel is a commercially available drying agent for use with gases, in desiccators, and (because of its chemical inertness) in physical instruments (pH meters, spectrometers, balances). Its drying action depends on physical adsorption, so that silica gel must be used at room temperature or below. By incorporating cobalt chloride into the material it can be made self indicating, re-drying in an oven at 110° being necessary when the color changes from blue to pink.
Sodium (metal)--> Used as a fine wire or as chips, for more completely drying ethers, saturated hydrocarbons and aromatic hydrocarbons which have been partially dried (for example with calcium chloride or magnesium sulfate). Unsuitable for acids, alcohols, alkyl halides, aldehydes, ketones, amines and esters. Reacts violently if much water is present and can cause a fire with highly flammable liquids.
Sodium Hydroxide(Red Devil Lye)-->Properties and applications are similar to those for potassium hydroxide. Sodium-potassium alloy. Used as lumps. Lower melting than sodium, so that its surface is readily renewed by shaking. Properties and applications are similar to those for sodium.
Sodium Sulfate-->Has a large capacity for absorption of water, forming the decahydrate below 33°, but drying is slow and inefficient, especially for solvents that are sparingly soluble in water. It is suitable for the preliminary drying of most types of organic compounds.
Sulfuric Acid-->Widely used in desiccators. Suitable for drying bromine, saturated hydrocarbons, alkyl and aryl halides. Also suitable for drying the following gases: hydrogen, hydrogen chloride, nitrogen, carbon dioxide, carbon monoxide, chlorine, methane and paraffins. Unsuitable for alcohols, bases, ketones or phenols. Also available with an indicator (a cobalt salt, blue when dry and pink when wet) under the name Sicacide  for desiccators.


  • Guest
A big thanks
« Reply #1 on: February 03, 2003, 03:11:00 AM »
Thanks for the post mr_pyrex this is a excellent post   8)   for all  .


  • Guest
good one, and timely too
« Reply #2 on: February 10, 2003, 09:45:00 AM »
TY for the list, it does indeed help.
BTW on the couch there is a post that is full of boo-hoos and bees wondering where all the 'old skool' posters went... I think you were mentioned;)


  • Guest
Good show old man
« Reply #3 on: February 10, 2003, 08:41:00 PM »
mr_pyrex comes back swinging, Good to see ya again and excellent post indeed..


  • Guest
« Reply #4 on: April 18, 2004, 01:45:00 AM »
I thought the addition this would be useful because this thread is a part of an FAQ and it helped me a lot back when I had questions on drying. 

Posted by RatHead on December 22, 1997 at 09:38:36:

The removal of admixed or dissolved water from starting materials and finished products is an important feature of organic chemistry and lab work. As a rule, water must be considered as an objectional impurity and must be removed since it may bring on undesired reactions (hydrolytic) or exert an undesired catalytic effect.

Sometimes the slight presence of water can preclude a reaction such as Grignard formation. On the other hand it would be foolish to remove all traces of water from substances that will later be placed in an aqueous medium. With that in mind, the selection of drying agents is important both for speed of drying and also the potential for reaction with the substance to be dried.

Organic liquids should always be separated from any aqueous layers before and possibly after interaction with drying agents. Now, the selection of an appropiate drying agent involves consideration of the chemical properties of the agent and of the substances involved. Typical drying agents include: Anhydrous calcium Chloride or Sulfate, Potassium Carbonate, Sodium or Potassium Hydroxide, Quick Lime (Calcium Oxide), Magnesium or Sodium Sulfates, Alkali metals (typically Sodium, but almost any can be used including Magnesium metal, and last but not least Phosphorus Pentoxide an extremely effective drying agent.

Cost and availability are generally the driving forces in small labs. Anhydrous calcium chloride is widely used because of its high capacity and cheapness. It is moderately efficient but not very rapid in action, consequently it should remain in contact with the liquid for an ample amount of time. Fused and crushed it is more effective than the porous form since the latter tends to occlude organic liquid. Calcium chloride can form a series of hydrates: a dihydrate, a tetra hydrate, and a hexahydrate (mp 30). Despite its effectiveness it is limited. Calcium Chloride should not be used to dry alcohols or amines since they react with it to form molecular compounds similiar to hydrates ( read loss of product!) Certain aldehydes, ketones,acids amides, and esters also can form loose complexes.

It is also inadvisable to use for acidic substances such as acids or phenols since the technical product containssmall amounts of basic materials. Anhydrous magnesium sulfate has alarge drying capacity and is both rapid and efficient. It is insoluble and chemically inert absorbing up to 105% by weight. Therefore, it can be used for almost all compounds. Anhydrous sodium sulfate is also inert but it acts slowly and not very effective. Anhydrous calcium sulfate "Drierite" is extremely rapid and efficent. It is also inert and insoluble but it can absorb only 6.6% of its own weight so a preliminary drying with another agent is often needed. Anhydrous potassium carbonate may be used for drying neutral and basic substances (alcohols,amines,ketones,esters,nitriles etc.) but not any substance with an acidic presence e.g. phenols or acids.

Potassium carbonate is primarily used to salt out water soluble alcohols, amines, and ketones from aqueous solutions and as a preliminary drier it forms a trihydrate and a dihydrate. Sodium and potassium hydroxide are rapid and effective drying agents for organic bases (amines). Their use is quite limited however since they can react with many compounds in the presence of water and they also are soluble in many organic liquids making them difficult to remove.
Calcium oxide (quicklime) is a slow but efficent drying agent that reacts by chemical combination rather than hydration the oxide and resulting hydroxide are stable to heat and are practically nonvolatile, consequently the spent agent is easily removed. It is frequently used to dry low molecular weight alcohols and amines but cannot be used on acidic or alkali sensitive substances. Sodium metal is most effective but can only be used on the most inert types of compounds e.g. saturated aromatic hydrocarbons and ethers preliminary drying is required.

Phosphorus pentoxide is exceedingly efficient and rapid but it can only be used on previously dried material and only on hydrocarbons,low-boiling ethers,alkyl and aryl halides,simple esters, and nitriles. It will react with almost all other compounds due to its expense and difficulty in handling (severe burns possible), it should only be used when extreme dryness is required.

Note: I assume everyone knows safe handling procedures for sodium. Recommendations: Hydrocarbons (and some ethers)- Calcium chloride or sulfate, sodium (metal) phosphorus pentoxide. Alcohols - potassium carbonate, anhydrous sulfates, (NO CALCIUM CHLORIDE), quicklime. Amines - sodium or potassium hydroxide or quicklime (prefered). Alkyl or aryl halides - calcium chloride, anhydrous sulfates, phosphorous pentoxide. Aldehydes - Magnesium sulfate, calcium sulfate, or sodium sulfate. Ketones - potassium carbonate, anhydrous sulfates. NOTE WHEN ADDING A DRYING AGENT IT SHOULD ALWAYS BE RECENTLY PREPARED SOME COMMERCIAL SAMPLES CAN CONTAIN AS MUCH AS 20% WATER!! the addition og magnesium sulfate should always be as afluffy powder which will become damp and sink to the bottom contine to add and stir or shake untill the powder no longer dampens in the liquid. GOOD LUCK and I hope this helps.


  • Guest
Drying of ACETONE
« Reply #5 on: June 27, 2004, 11:39:00 PM »
Since this post I have had several bees ask me if it was alright to dry acetone by way of either calcium chloride, silica gel or magnesium sulfate....And in a word the answer is--> NO!  
  The recommended drying agent for ACETONE is CALCIUM SULFATE(Drierite) and no this isn't my opinion this is a fact that is stated in the text-->Purification of Laboratory Chemicals.
  It states ...Silica gel and alumina, or mildy acidic or basic desiccants cause acetone to undergo the aldol condensation, so that its water content is INCREASED by passage through these reagents.  This also occurs to some extent when phosphrous pentoxide or sodium amalgam is used.  Anhydrous magnesium sulfate is an inefficent drying agent and calcium chloride forms an additional compound.  Drierite offers the minimum acid and base catalysis of aldol formation and is the recommended drying agent for this solvent[Coetzee and Siao Inorg Chem 14V 2 1987; Riddick and Bunger Organic Solvents Wiley-Interscience, N.Y., 3rd edn, 1970].
  So there is your answer with regards to ACETONE....Use Calcium Sulfate and leave it in direct contact for several hours before decanting.  Pyrex out of recommendations ;-)


  • Guest
Plaster Of Paris
« Reply #6 on: June 28, 2004, 08:00:00 AM »
Calcium Sulfate Hemihydrate is also know as plaster of paris.
Hemihydrate means the molecular ratio of water molecules to anhydrous compound is 1:2
Does anyone know if an oven bake would dry this out enough.


  • Guest
dry it out?
« Reply #7 on: June 28, 2004, 08:19:00 AM »
If it's what I think it is, an oven bake is just the thing to dry it out... leaving you with hardened plaster.


  • Guest
what about
« Reply #8 on: June 29, 2004, 09:40:00 AM »
Done some pretty good drying of acetone w/calcium carbonate as well as baked epsoms.... ::)