Propylene carbonate

Propylene carbonate is an organic compound with the formula C₄H₆O₃. It is a cyclic 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 as the racemic mixture in most contexts.
The name carbonate indicates a carbonate ester, an organic compound containing the carbonate group, not a salt of carbonic acid,,characterized by the presence of the carbonate ion, a polyatomic ion with the formula.

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 corresponding reaction of 1,2-propanediol with phosgene is complex, yielding not only propylene carbonate but also oligomeric products.
Propylene carbonate can also be synthesized from urea and propylene glycol over zinc acetate.

Applications

As a solvent

Propylene carbonate is used as a polar, aprotic solvent. It has a high molecular dipole moment, considerably higher than those of acetone and ethyl acetate. 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.

Electrolyte

Due to its high relative permittivity of 64, it is frequently used as a high-permittivity component of electrolytes in lithium batteries, usually together with a low-viscosity solvent. Its high polarity allows it to create an effective solvation shell around lithium ions, thereby creating a conductive electrolyte. However, it is not used in lithium-ion batteries due to its destructive effect on graphite.

Other

Propylene carbonate can also be found in some adhesives, paint strippers, and in cosmetics. It is also used as plasticizer. Propylene carbonate is also used as a solvent for removal of CO₂ from natural gas and synthesis gas where H₂S is not also present. This use was developed by El Paso Natural Gas Company and Fluor Corporation in the 1950s for use at the Terrell County Gas Plant in West Texas, now owned by Occidental Petroleum.
Propylene carbonate product may be converted to other carbonate esters by transesterification as well.
In electrospray ionization mass spectrometry, propylene carbonate is doped into low surface tension solutions to increase analyte charging.
In Grignard reaction propylene carbonate might be used to create tertiary alcohols.

Safety

Clinical studies indicate that propylene carbonate does not cause skin irritation or sensitization when used in cosmetic preparations, whereas moderate skin irritation is observed when used undiluted. No significant toxic effects were observed in rats fed propylene carbonate, exposed to the vapor, or exposed to the undiluted liquid. In the US, propylene carbonate is not regulated as a volatile organic compound because it does not contribute significantly to the formation of smog and because its vapor is not known or suspected to cause cancer or other toxic effects.