GB823233A - Production of sorbic acid - Google Patents

Abstract

Sorbic acid is produced by eliminating the elements of an alkanol from a 3,5-dialkoxyhexanoic acid, each molecule of the compound undergoing this dealcoholation forming two molecules of alkanol and a molecule of sorbic acid. The dealcoholation is preferably effected by heating the said dialkoxy acid in the presence of a strong base, such as sodium, potassium, lithium, calcium or barium hydroxides, the alcohol produced being distilled off during or after the reaction. The 3,5-dialkoxyhexanoic acid may be obtained by hydrolysing 1,1,3,5-tetra-alkoxyhexane to produce a 3,5-dialkoxyhexanal, for example by reacting the tetraalkoxyhexane batchwise or continuously with water in the presence of an acid, followed by oxidation of the 3,5-dialkoxyhexanal, for example using air or other oxygen-containing gas in the presence of a multivalent metal, e.g. cobalt or manganese, or a compound of such a metal, and preferably in the presence of an oxidation resistant solvent, such as acetic or formic acid. Alternatively, the 1,1,3,5-tetraalkoxyhexane may be hydrolysed and oxidized simultaneously to produce the 3,5-dialkoxyhexanoic acid by passing an oxygen-containing gas through a solution of the tetra-alkoxyhexane in an oxidation-resistant solvent, e.g. acetic acid, containing a minor amount of water and an oxidation catalyst, such as a manganese or cobalt compound. If desired, an oxidation promoter, such as acetaldehyde, may be added to the reaction mixture.