Propylene carbonate
Propylene carbonate (often abbreviated PC) is an organic compound with the formula CH3C2H3O2CO. It is a carbonate ester derived from propylene glycol. This colorless and odorless liquid is useful as a polar, aprotic solvent. Propylene carbonate is chiral but is used exclusively as the racemic mixture.
Preparation
Although many organic carbonates are produced using phosgene, propylene and ethylene carbonates are exceptions. They are mainly prepared by the carbonation of the epoxides:
The process is particularly attractive since the production of these epoxides consumes carbon dioxide. Thus this reaction is a good example of a green process. The corresponding reaction of 1,2-propanediol with phosgene is complex, yielding not only propylene carbonate but also oligomeric products.
Applications
As a solvent
Propylene carbonate is used as a polar, aprotic solvent. It has a high molecular dipole moment (4.9 D), considerably higher than those of acetone (2.91 D) and ethyl acetate (1.78 D). It is possible, for example, to obtain potassium, sodium, and other alkali metals by electrolysis of their chlorides and other salts dissolved in propylene carbonate.
Trimethylene carbonate
Trimethylene carbonate or 1,3-propylene carbonate is a 6-membered cyclic carbonate ester. It is a colourless solid that upon heating converts to the polytrimethyl carbonate. Such polymers are of interest for biomedical applications. An isomeric derivative is propylene carbonate, a colourless liquid that does not spontaneously polymerize.
Preparation
This compound may be prepared from 1,3-propanediol and ethyl chloroformate (a phosgene substitute), or from oxetane and carbon dioxide with an appropriate catalyst:
This cyclic carbonate undergoes ring-opening polymerization to give poly(trimethylene carbonate), abbreviated PTC. The polymer PTC is of commercial interest as a biodegradable polymer with biomedical applications.
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