GB785100A - Production of unsaturated aliphatic esters - Google Patents

Abstract

A catalyst containing manganese oxides supported on activated silica gel, suitable for condensations of formaldehyde with compounds containing hydrogen atoms activated by electron attracting groups, e.g. esters of aliphatic acids, is prepared by mixing silica gel particles (of size 80-200 mesh) with just enough of an aqueous solution of manganous acetate to wet the silica gel completely, allowing the mixture to stand for 1 hour, drying it overnight in an oven at 85-100 DEG C. and afterwards heating the dry particles in the fluidized state in a stream of air at 350 DEG C. for 1 hour. A catalyst comprising lead oxide on activated silica gel is prepared in a similar manner from lead acetate.ALSO:Esters of unsubstituted a ,b -unsaturated aliphatic monocarboxylic acids are made by the reaction in the vapour phase and at elevated temperature of formaldehyde and an ester of an unsubstituted saturated aliphatic monocarboxylic acid having at least two hydrogen atoms attached to the same carbon atom as the carboxyl group. It is preferred to react formaldehyde with a lower alkyl ester of a saturated lower carboxylic acid (i.e. an ester of a saturated aliphatic acid with an alcohol, neither of which contains more than four carbon atoms in the molecule) to give the corresponding lower alkyl ester of acrylic acid or of an alkyl-substituted acrylic acid. Preferably, the reaction is effected in the presence of a solid material which is a catalyst for condensation reactions involving formaldehyde and a compound containing hydrogen atoms activated by the proximity of an electron-attracting group, the catalyst being maintained at an elevated temperature. The preferred catalysts are basic metal compounds such as basic salts or oxides, e.g. manganese oxides, sodium phosphate, sodium pyrophosphate, zinc oxide, lead oxide, sodium hydroxide, manganese acetate and lead acetate. The catalyst may be deposited on a carrier such as activated alumina or silica, and is preferably in a finely divided fluidized form although a fixed bed may also be used. Suitable ester reactants are methyl acetate, methyl propionate and esters of other alcohols and fatty acids having at least two carbon atoms in the molecule, such as ethyl, propyl and butyl acetates, propionates and butyrates. The reactants preferably should not contain more than 10 per cent of water based on the formaldehyde and preferably the formaldehyde is anhydrous or of low water content only. The formaldehyde may be obtained from a solution of paraformaldehyde containing 5-10 per cent of water in methanol or another lower aliphatic alcohol, e.g. butanol, or from trioxane or methylol. The molar ratio of formaldehyde to ester in the reaction mixture is preferably between 0.3 and 3. The reaction is preferably effected at 250-400 DEG C., the optimum range being 340-370 DEG C. The pressure may be atmospheric, subatmospheric or superatmospheric. The esters may be obtained by condensing the hot vaporous reaction products by cooling and fractionally distilling the condensate. In examples: (1) a mixture of methyl acetate and a solution of paraformaldehyde in methanol is vaporized in a heated flasher, the vapours are passed continuously through a fluidized bed of manganese oxide catalyst supported on activated silica gel at 300-400 DEG C., and the vapours leaving the fluidized bed are condensed and methyl acrylate is recovered by distillation; (2) methyl propionate is similarly treated to yield methyl methacrylate; (3) Example (1) is repeated using methyl propionate and trioxane, the catalyst being maintained at 350-360 DEG C. and methyl acrylate and a -methacrolein are recovered; (4) in a process similar to (3), lead acetate is used as the catalyst.