GB1025141A - Improvements in or relating to a process for the oxidation of olefins - Google Patents

Abstract

Saturated ketones are made by oxidizing olefines of the formula R1(R2)C=C(H)R3 wherein R1 is hydrogen or a C1- 6 and R2 and R3 are C1- 6 alkyl groups, separating the reaction mixture into a fraction consisting of unreacted olefin which is recycled to oxidation stage and a fraction containing oxycompounds, hydrogenating the oxycompounds, treating the hydrogenation products under acid conditions to give a fraction consisting of olefines which is recycled and a fraction comprising oxycompounds which is dehydrogenated to give a product which is essentially saturated ketones. Suitable starting materials are 2-methylbutene - 2,2 - methylpentene - 2,2 - methylhexene - 2,2,3 - dimethylpentene - 2 or mixtures thereof. The oxidation may be carried out with or without a catalyst in the liquid or vapour phase. The unreacted olefin is conveniently separated from the crude oxidate, which contains unsaturated peroxides, ketones, aldehydes, alcohols and epoxides, by distillation under reduced pressure in the presence of an inert diluent or, alternatively, by subjecting the oxidate to selective hydrogenation to reduce unsaturated peroxides to unsaturated alcohols and distilling the mixture. Before being returned to the oxidation stage the unreacted olefin may be treated under acid conditions in order to isomerize the mixture to one containing mainly olefins of the above formula rather than 1-olefins. This isomerization may be carried out in the reaction zone in which the hydrogenation products, which are obtained from the oxycompounds by conventional means, are treated with a solid acid catalyst, e.g. alumina, or an aqueous acid, e.g. sulphuric, in order to convert epoxides to ketones, alcohols to olefins and olefins to predominantly olefins of the type used in the headstock. Preferably the acid conditions are such that only tertiary alcohols are dehydrated to olefins. The resulting products are separated into an olefin fraction for recycling and an oxycompound fraction containing mostly secondary alcohols and ketones which is subjected to known dehydration conditions to obtain a product containing a high proportion of ketones which can be isolated by distillation. Any small amounts of close-boiling aldehydes present can be removed by oxidation or acetal formation followed by distillation. The process is illustrated by reference to schematic flow drawings in which the feed is (1) 52% 4 - methylpentene - 2, 13% 2 - methylpentene-2, 30% 2-methylpentene-1 and 5% 4-methylpentene-1 and (2) 64.4% 4-methylpentene-2, 14.0% 2-methylpentene-2 and smaller amounts of other olefins and the product in both cases is a mixture of ethylisopropyl ketone and methylisobutyl ketone.