GB638763A - A process for the preparation of esters - Google Patents

Abstract

1 : 3-Diacyloxy-1-alkenes of the formula <FORM:0638763/IV (b)/1> where R1 and R2 are hydrocarbon or heterocyclic which may be substituted by groups not interfering with the reaction, and R3, R4 and R5 are hydrogen or as R1 and R2, are prepared from a 1 : 1-diacyloxy-2-alkene by heating in presence of an acidic catalyst. The groups R may be, for example, alkyl, e.g. methyl to heptyl, aromatic, e.g. phenyl, tolyl, and benzyl, cycloaliphatic, e.g. cyclohexenyl and cyclohexyl, alkenyl, e.g. vinyl and allyl, aralkenyl, e.g. 2-phenylallyl, alkynyl and heterocyclic such as furfuryl, thienyl and sulpholanyl. R1 and R2 are preferably lower alkyl, up to 7 carbon atoms. Specified acidic catalysts are hydrochloric, phosphoric, p-toluenesulphonic and dichloroacetic acids, and zinc and magnesium chlorides and sodium dihydrogen phosphate. Preferred reaction temperatures are between 70 DEG and 150 DEG C., and the reaction may be carried out in vapour or liquid phase; in the latter case an inert solvent, e.g. ether, may be employed. Preferably, there is present a small amount of the anhydride of the acid from which the acyloxy groups of the di-ester are derived. The double bond of the diacyloxy alkene may be saturated by hydrogenation in the usual way and then the compound hydrolysed to give the 1 : 3-diol, e.g. trimethylene glycol. The hydrogenation catalyst, e.g. Raney nickel, should be free from alkali. In the examples: (1-3) 1 : 1-diacetoxy-2-propene is heated with sulphuric acid in ether, optionally in the presence of acetic anhydride, to give 1 : 3-diacetoxypropene-1, which (5) is hydrogenated to give the p diacetate of trimethylene glycol; (4) 1 : 1-diacetoxy-2-methyl-2-propene is treated with sulphuric acid to give 1 : 3-diacetoxy-2-methylpropene-1, which (6) is hydrogenated to the diacetate of 2-methyl-1 : 3-propanediol.