GB671077A - A process for the manufacture of methyl methacrylate starting from the lactide and/or linear polycondensation products of alpha-hydroxy isobutyric acid - Google Patents

Abstract

Methyl methacrylate is produced by effecting transesterification between the lactide and/or linear polycondensation product of a -hydroxy isobutyric acid and 5-15 molar equivalents of methyl acetate, and pyrolysing the product to convert the methyl a -acetoxy isobutyrate to methyl methacrylate and acetic acid. The transesterification is preferably effected with an acid catalyst, suitably phosphoric, boric or sulphuric acid or an acid phosphate or sulphate. With boric acid or ammonium bisulphate, temperature is 110-210 DEG C. The pyrolysis may be effected at 400-600 DEG C. at a contact time of 5-60 seconds, using a tube having a length to diameter of 4-10 : 1 with an acidic packing comprising a polymerization inhibitor such as copper. The methyl methacrylate may be isolated by fractionation, washed with water or brine, and the water frozen out. The acetic acid may be esterified with methanol for re-use. The lactide and 5-100 per cent by weight of ammonium bisulphate may be kept at 180 DEG C. while 9 molar equivalents of methyl acetate are passed through at such a rate that, with the vapours passing to a 10 theoretical plate column operating at a reflux ratio of 5-10 : 1, a product fraction temperature of 80-85 DEG C. is maintained. The product is pyrolysed in a tube packed with, e.g. quartz coated with phosphoric acid and copper powder, and the vapours condensed. Distillation up to 80 DEG C. removes methyl acetate. The residue is treated with 96 per cent H2SO4 at 40-90 DEG C., and methanol then added while removing a methyl acetatemethanol azeotrope. Steam distillation of the residue isolates the methyl methacrylate.