GB727074A - Manufacture of monochloroacetic acid - Google Patents

Abstract

Monochloracetic acid of low dichloracetic acid content is obtained by passing chlorine into a mixture of glacial acetic acid with either acetyl chloride or acetic anhydride and sulphuric and/or phosphoric acid or the sulphate, phosphate, nitrate, acetate or chloride or manganese, chromium, calcium, cobalt, nickel, sodium, zinc, barium, potassium, lithium, caesium, magnesium, vanadium, copper, silver, cadmium or tin. These acids and salts ionize in glacial acetic acid and inhibit the formation of dichloracetic acid by decomposing the peroxides simultaneously produced during the reaction. Chlorination should not be carried beyond 85 per cent and excess acetic acid, by-product ahydrides and the acetyl chloride in the reaction mixture are removed by distillation at ordinary pressure, preferably passing hydrogen chloride in countercurrent through the products in a packed tower at a temperature above the boiling-point of acetyl chloride before fractionation of the monochloracetic acid at reduced pressure. In examples, chlorine is passed into a reactor equipped with a reflux condenser, an agitator and gas distributer, containing glacial acetic acid, acetic anhydride and the compound which decomposes peroxides. Acetic anhydride is added periodically and acetyl chloride finally removed from the products by passing in recovered hydrogen chloride. The remaining mixture is then distilled to free it from the compound which decomposes peroxides and the distillate again distilled under reduced pressure. In a modification, the acetyl chloride and excess acetic acid are removed as a first fraction and the mono- and di-chloracetic acids as a second fraction from the crude product by fractional distillation under vacuum in a column packed with glass helices. A flow sheet is given in which the excess acetic acid, by-products and recovered materials are recycled.