Propylene carbonate (CAS NO. ) is manufactured by reaction of 1,2-propylene oxide with CO₂ in the presence of a catalyst (quaternary ammonium halide). Contaminants include propylene oxide, carbon dioxide, 1,2- and 1,3-propanediols, allyl alcohol and ethylene carbonate. Propylene carbonate can be purified by percolation through molecular sieves (Linde 5A, dried at 350 °C for 14h under a stream of argon), followed by distn under vac.  It can be stored over molecular sieves under an inert gas atmosphere. When purified in this way it contains less than 2ppm water. Activated alumina and dried CaO have been also used as drying agents prior to fractional distn under reduced pressure. It has been dried with 3A molecular sieves and distd under nitrogen in the presence of p-toluenesulfonic acid. Then redistilled and the middle fraction collected.