Bisphenol A: Phenol and Acetone in 70 % Sulfuric Acid, Greenhalgh 1934

Phenol and acetone stirred for a day in about 70 % sulfuric acid at 45–60 °C join, two phenols to one acetone, into bisphenol A, which comes out as a solid to be filtered and washed (Greenhalgh, ICI, US 1,977,627, 1934: 65–70 % yield). Acid of this strength can be handled in lead. Bisphenol A is the other half of epoxy resin. The picture: our diagram of the four stages.