# Why can't I dry/concentrate ethanol using calcium chloride ... or can I?

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"?

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)?

• You understand what happens with water when CaCl2 absorbs it? Why wouldn't ethanol do the same? Oct 28 '17 at 18:33
• sciencedirect.com/science/article/pii/0040603181801475 Oct 28 '17 at 20:22
• @Curt That confirms the ethanol- $CaCl_2$ "solid derivative". Know anything about ethanol/methanol reacting with other metal salts? Thanks again for the link! O:) Oct 29 '17 at 2:54
• Strongly related: chemistry.stackexchange.com/questions/54878/… Oct 29 '17 at 3:19
• @Nilay Yep, very strongly related :D Oct 29 '17 at 3:53

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.