Dibutyl Phthalate: Phthalic Anhydride and Butyl Alcohol, Water Drawn Off under Vacuum

Dibutyl phthalate is an ester used to make PVC and other plastics soft. Crowell and Ebe's process (US 1,864,893, 1932) warms phthalic anhydride and butyl alcohol with a little sulphuric acid at 82–87 °C, then draws the water off under a gentle vacuum as it forms, carried over with butyl alcohol. What stays behind is nearly pure ester, about 97 % yield, with no need to distil the ester itself (it boils at 340 °C). The picture: our diagram.