My (very unreliable) school textbook tells me:

Lower alcohols form a solid derivative with certain metal salts.


It is for this reason that ethanol cannot be dried/concentrated using anhydrous calcium chloride.

Nowhere else in the book, is there any reference to this supposed reaction between a lower alcohol (ethanol) and a metal salt (calcium chloride). So I couldn't read more about this from there...

Googling wasn't much help; though I did find this paper that seems to concur with my textbook (albeit, with more detail) ... the paper is dated all the way back to 1923, so I suspect the modern Chemist's view of the matter would be different (the paper makes use of the term "alcoholate", which no longer carries the same meaning).


Does ethanol really react with calcium chloride to form some "solid derivative"?


Do lower alcohols (methanol and ethanol to name a few) really react with "metal salts" (textbook didn't specify, so i would use the following examples: copper sulfate and magnesium chloride)?


2 Answers 2


The apparent answer is yes, to quote from a source (composed from extracts of old chemistry journal):

Calcium chloride forms addition compounds with the alcohols. On evaporating a solution in ethyl alcohol at a low temperature rectangular plates of $\ce{2CaCl2.7C2H5OH}$ are deposited. The compounds $\ce{CaCl2.3C2H5OH}$ and $\ce{CaCl2.CH3OH}$ have also been separated, as well as a mono- and a di-acetone compound, and compounds with isobutyl and amyl alcohols.

So, if you are working with a cold solution of $\ce{C2H5OH}$ with $\ce{CaCl2}$ exposed to air undergoing evaporation, it is possible to form an addition compound (taking the form of rectangular plates) with the formula, $\ce{2CaCl2.7C2H5OH}$ or $\ce{CaCl2.3C2H5OH}$.


Yes, I think that lower alcohols cannot be dried using $\ce{CaCl2}$ as they form stable complexes with it but higher alcohols can be dried using $\ce{CaCl2}$ as they form unstable complexes while water forms stable complex. On the other hand, aromatic alcohols like phenols can't be dried using $\ce{CaCl2}$ as they are somewhat acidic in nature.

At the same time, I assume that all salts wouldn't do the same thing with lower alcohols as each salt-alcohol complex has its own degree of stability and the salt-water complex may be more stable than the former. So, I don't recommend $\ce{CuSO4}$ as a drying agent.


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