deltaH - 9-11-2015 at 23:23
It is well known that unstabilised chloroform degrades in air and sunlight to form phosgene gas.
The reaction between phosgene gas and an alcohol is fast and the basis of both the stabilisation of chloroform (by adding 1% ethanol) as well as a
method of synthesizing ethylene carbonate by its reaction with ethylene glycol.
Combining these facts, would it not be possible to prepare ethylene carbonate from chloroform and ethylene glycol by exposing such a mixture to both
air and sunlight while minimising evaporative losses?
The nice thing about the reaction is that it's water free and only form HCl as its co-product, simplifying the purification of the resulting
carbonate.
gdflp - 10-11-2015 at 09:25
One issue I believe with directly using ethylene glycol to absorb the phosgene is it's tendency to polymerize due to the presence of diol and
dicarboxylic acid. Typically, ethylene carbonate is prepared by the transesterification of methyl or ethyl carbonate to minimize polymer formation.
I don't have much experience on this topic, but I have a feeling that this method would produce a significantly more polymerized product. You may be
better off using ethanol or methanol initially to react with the phosgene, then transesterifying the resultant carbonate with ethylene glycol to form
the desired ethylene carbonate.
deltaH - 10-11-2015 at 10:53
I read somewhere (?wikipedia?) that the reverse is commercially practiced, i.e. that they make dimethyl carbonate by transesterification of ethylene
carbonate and methanol.
As for the polymerization issue, while I am also no expert in this, I only know that they usually use large diols, like bisphenols, for making
polycarbonate plastics. With ethylene glycol, I think cyclisation might be strongly favoured because of the close proximity of the hydroxyl groups.
The problem though with this reaction is that I'm not sure how it can be practically carried out in the amateur context. Maybe one could fill a glass
soda bottle with 1/20th its volume with a stoichiometric amount of compressed oxygen through a tire valve, careful to be well under the safe pressure
for the bottle.
One could add an amine to scavenge the HCl, but it makes it less amateur friendly doing so, plus you have added contaminants to deal with.
The beauty of using just chloroform, glycol and oxygen is that when it's done, you need only heat open to drive off the HCl and chloroform and you
will left with a solution of ethylene carbonate contaminated only with residual ethylene glycol.
EDITED glycol to carbonate, DUH!
[Edited on 11-11-2015 by deltaH]