GB773436A - Improvements in or relating to the preparation of polyhydric alcohols - Google Patents

Abstract

Polyhydric alcohols are prepared by passing aqueous halohydrins and inorganic basic hydrolysing agents through a plurality of reaction stages maintained at hydrolysing temperatures above 25 DEG C., the mixture introduced into the first stage containing only a substantial part of the total stoichiometric requirement of basic agents for the hydrolysis, and additional amounts of basic agent being introduced at one or more subsequent reaction stages in such a manner that the pH value of the reaction mixture is maintained at between 8 and 10 throughout the reaction. Temperatures between 75 DEG C. and 250 DEG C. are generally suitable for carrying out the process. In operations at temperatures in the range of about 75 DEG C. to about 110 DEG C. the reaction may be carried out at atmospheric pressure, but at higher temperatures it is preferred to carry out the reaction under super-atmospheric pressure, provided preferably by carbon dioxide under pressure. The reaction is preferably carried out with a total amount of base which is at least equivalent to the halogen in the starting halohydrin. Generally about 2 to 15 per cent excess of basic agent is used. The basic agent is divided among the different reaction stages in the proportions required to maintain the reaction mixture therein at the required pH value. Suitable inorganic bases are, for example, alkali metal hydroxides, carbonates, phosphates, polyphosphates or borates. The halohydrins used as starting materials may be substituted by aromatic or cycloaliphatic groups. In the examples: (a) epichlorhydrin containing about 25 per cent by weight of dichlorhydrins is hydrolysed in a vessel divided into five compartments by injecting the epichlorhydrin mixed with sodium carbonate solution into the first compartment and adding sodium hydroxide to subsequent compartments so that the pH is maintained at the value 9.6; glycerin is separated from the reaction mixture; (b) similarly 1-chloro-2.3-epoxy butane yields 1.2.3-trihydroxybutane, p-methyl epichlorhydrin yields b -methyl glycerin, ethylene and propylene chlorohydrin yield ethylene and propylene glycol respectively, 1-chloro-2.3-dihydroxybutane and 2-chloro - 1.3 - dihydroxybutane yield a - methyl glycerine, 1 - chloro - 2 - methyl - 2.3 - dihydroxybutane yields b -methyl glycerine, 1-bromo-3.4-dihydroxypetane yields 1.3.4-trihydroxy-pentane and 1.4-dihydroxy-5-chlorodecane yields 3.4.5-trihydroxydecane. Specification 569,717, [Group IV], is referred to.