GB647971A - Improvements in preparation of isopentenyl propyl ketone - Google Patents

Abstract

Isopentenyl propyl ketone is prepared by heating n-butyraldehyde with isoprene in proportions ranging from 1 to 20 mols. of butyraldehyde per mol. of isoprene in the presence of dibenzoyl peroxide at a temperature of from 65 DEG to 100 DEG C. until the isopentenyl propyl ketone is formed and then isolating the same. Generally, a large excess of aldehyde is used; as an alternative to using an excess, the isoprene may be added incremently to the reaction mixture, thus in effect maintaining a considerable excess of aldehyde throughout the major portion of the reaction. The reaction time generally varies from 1 to 50 or more hours depending on temperature, pressure and acceptable yield of ketone produced. Pressures greater than atmospheric are used if necessary to keep the reactants in the liquid phase. A suitable amount of catalyst is from 0.5 to 15 mol. per cent of the isoprene. The ketone may be recovered by removal of unreacted material and fractionation of the residue. In the example, 68 parts by weight isoprene are added dropwise over 20 hours to 720 parts n-butyraldehyde in presence of dibenzoyl peroxide at 80-85 DEG C. and the mixture heated a further 11 hours-6.8 parts of the desired ketone are recovered. The Specification as open to inspection under Sect. 91 relates to the production of ketones by reacting a conjugated diene with an n-alkanal, sec.-alkanal, cycloalkanal or an aralkanal under free radical conditions. The products are stated to have the general formula R-CO-(X)n-H where R is the radical derived from the aldehyde, X is the bivalent radical derived from the diene and n is an integer from 1 to 9. Reactants mentioned are acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, heptaldehyde, octaldehyde, cyclopentanal, cyclohexanal, phenylacetaldehyde, and butadiene hydrocarbons such as butadiene-1 : 3, 2-methyl-butadiene-1 : 3, 2 : 3-dimethyl-butadiene-1 : 3 and piperylene. The source of free radicals may be ultra-violet light or a compound which decomposes to give free radicals such as organic peroxides, e.g. acyl peroxides such as diacetyl peroxide, dibenzoyl peroxide, acetyl benzoyl peroxide, alkyl peroxides such as t-butyl hydroperoxide; hydrogen peroxide; per-salts, e.g. alkali persulphates, percarbonates and perborates; hydrazine derivatives such as hydrazine sulphate, hydrazine hydrochloride and dibenzoyl hydrazine; organo metallic compounds such as tetraethyl lead. The reaction may be carried out in the presence of inert diluents such as n-hexane, benzene or cyclohexane; temperatures of 25 DEG to 150 DEG C. may be employed while pressures up to 2000 lbs. per square inch may be used when the diene is normally gaseous. This subject-matter does not appear in the Specification as accepted.