GB678468A - Improvements in or relating to the production of 2:3-dihydrofurans - Google Patents

Abstract

A process for the production of a 2 : 3-dihydrofuran of the general formula: <FORM:0678468/IV (b)/1> wherein R, R1 and R2 are the same or different and each is a hydrogen atom or an alkyl group, which comprises heating a 2 : 5 dihydrofuran of the general formula: <FORM:0678468/IV (b)/2> in the presence of an alkali metal aliphatic alcoholate or alternatively an alkali metal hydroxide and an aliphatic alcohol. Suitable alcoholates are the ethoxides, isopropylates and tertiarybutylates of sodium and potassium. The reaction is preferably effected in an alcohol solution. The 2 : 3-dihydrofuran produced in the reaction may be hydrolysed to obtain the corresponding g -hydroxyl carbonyl derivative which may be converted to another derivative, e.g. the oxime. 2 : 5-Dihydrofuran may be obtained by the dehydration of 2-butene-1 : 4-diol. A mixture of 2 : 3-dihydro- and 2 : 5-dihydrofurans obtained by the elimination of 1 mol. of halo-acid from 4-halogenotetrahydrofurans may be converted substantially completely to 2 : 3-dihydrofuran by the process. 2 : 5-Dihydrofuran is converted to 2 : 3-dihydrofuran by heating in closed vessels with in examples (I) potassium hydroxide and tertiary butyl alcohol, (II) sodium dissolved in ethyl alcohol, (III) sodium dissolved in tertiarybutyl alcohol, (IV) potassium dissolved in tertiarybutyl alcohol. In example II the product is isolated as the oxime. In examples (V) and (VI) the proportion of 2 : 3 isomers in mixtures of methyl and diethyl-dihydrofurans obtained by the action of caustic potash on 2-methyl - 4 - bromotetrahydrofuran and 2 : 2-diethyl - 4 - bromotetrahydrofuran respectively is increased by heating the mixtures in closed vessels with potassium in tertiary butyl alcohol. Oximes are formed from the hydrolysis products of the 2 : 3-isomers by treatment with hydroxylamine hydrochloride.