Patent GB-409733-A (GB)
Title: Manufacture of unsaturated esters and of intermediates
IPC: C07C67/327
Filed: 1932-10-03
Abstract: Sulphates of alkyl a -hydroxyisobutyrates, of the formula <FORM:0409733/IV/1> are manufactured by treating an alkyl a -hydroxyisobutyrate with an agent capable of converting it into its sulphuric ester, e.g. chlorosulphonic acid, oleum, sulphur trioxide or the addition product thereof with a tertiary base, or a pyrosulphate, in the presence or absence of a solvent or other reagent, e.g. a tertiary base.  Alkyl methacrylates are manufactured by subjecting a sulphate of an alkyl a -hydroxyisobutyrate, with or without isolation from the reaction mixture in which it has been formed, to a heat treatment, in the presence or absence of a suspending medium or of a diluent which is advantageously a dehydrating solid or a substance which combines with free sulphuric acid, e.g. anhydrous sodium sulphate.  When using chlorosulphonic acid in the first stage, the a -hydroxyisobutyric ester is added slowly with stirring to 1--1\ba1/2\be molecular proportions of chlorosulphonic acid at a moderate temperature, e.g. 50--80 DEG  C., and either the viscous solution is poured into cold water and the oily layer is separated, washed and distilled, or a tertiary base, e.g. diethylaniline, is added and the mixture is fractionally distilled.  In examples: (1) ethyl a -hydroxyisobutyrate is added to 1.25 molecular proportions of chlorosulphonic acid at 50 DEG  C., the product is poured into ice water, the upper layer is separated, washed with sodium carbonate solution and with water, dried over anhydrous sodium sulphate and distilled, producing ethyl methacrylate; alternatively diethylaniline is added to the reaction product which is then distilled, the distillate being shaken with potassium carbonate and redistilled; (2) n-butyl a -hydroxyisobutyrate is added to chlorosulphonic acid at 45--50 DEG C., the product is poured into ice water and the upper layer is separated, washed and distilled with the addition of hydroquinone, to yield n-butyl methacrylate; (3) methyl a -hydroxyisobutyrate is added to an equimolecular proportion of chlorosulphonic acid below 10 DEG C., producing a solid mass of the sulphuric ester, from which hydrogen chloride is removed by putting it under vacuum; the product, with or without admixture with anhydrous sodium sulphate, is heated under reduced pressure, when methyl methacrylate distils over and is worked up by adding soda ash and anhydrous sodium sulphate and redistilling; alternatively after adding anhydrous sodium sulphate the mixture is heated to 100 DEG  C. and then stirred into ice, methyl methacrylate separating as an upper oily layer which is separated and distilled; (4) methyl a -hydroxyisobutyrate is added to oleum and the resulting solution of the sulphuric ester in sulphuric acid is distilled under reduced pressure with or without the addition of anhydrous sodium sulphate, the product being worked up as in (3); (5) methyl a -hydroxyisobutyrate is boiled under reflux with two molecular proportions of sodium pyrosulphate, the mixture is distilled and the methyl methacrylate is washed, dried and, if desired, redistilled; (6) ethyl a -hydroxyisobutyrate similarly yields ethyl methacrylate; (7) methyl a -hydroxyisobutyrate is refluxed with pyridinesulphur trioxide and the mixture is distilled, the distillate being washed with dilute hydrochloric acid, dried over anhydrous potassium carbonate and sodium sulphate, and fractionated.