Acrylic Acid: Ethylene Cyanohydrin Heated with Sulphuric Acid and Water

Acrylic acid is the starting point here for ethyl acrylate and the acrylic paint medium. Hill's ICI process (US 2,026,894, 1936) heats ethylene cyanohydrin with strong sulphuric acid and a little water: the nitrile becomes the acid, water is split off, and ammonium bisulphate crystallises out. Copper foil and hydroquinone stop the acid from polymerising. The example made 51 parts of acrylic acid, boiling chiefly at 140 °C, from 71 parts of cyanohydrin. The picture: our diagram.