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My (very unreliable) school textbook tells me:

Lower alcohols form a solid derivative with certain metal salts.

and,

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).


Question:

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

Additionally,

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)?

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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 $\ce{CaCl2.3C2H5OH}$.

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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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