GB640260A - A process for the preparation of unsaturated hydrocarbons from unsaturated aldehydes or ketones - Google Patents

Abstract

Unsaturated hydrocarbons, more particularly dienes, are obtained by reacting a non-tertiary non-aromatic saturated alcohol with an alpha, beta - olefinically unsaturated non - aromatic aldehyde or ketone containing a linear group of at least four contiguous carbon atoms serially joined by aliphatic carbon-to-carbon bonds, including the carbonyl carbon atom, and which may form an alicyclic ring or a part thereof, in the vapour phase, at a temperature of at least 200 DEG C., but below that at which substantial decomposition reactions occur, and in the presence of a polyvalent metal of the second or third group of the Periodic Table at a correlated rate of flow of reactants over catalyst at which hydrogen transfer-dehydration occurs but which is below that at which substantial formation of unsaturated alcohols as final product occurs in the presence of the same catalyst. Aldehydes and ketones employed preferably contain six carbon atoms, aldehydes may be mono-olefinic many being specified such as alpha-ethyl-beta-methyl-acrolein, alpha, beta-dipropylacrolein and alpha-propyl-beta-ethylacrolein or may contain more than one olefinic linkage as in alpha - ethyl - beta - isopropenylacrolein, many alicyclic aldehydes are also specified including alpha - cyclopentyl - acrolein, beta - cyclohexylacrolein, alpha-propyl-beta-(methylcyclohexyl)-acrolein, 1 - cyclopentene - carboxaldehyde and 4 - methyl - 1 - cyclopentene - carboxaldehyde, similarly ketones may be mono-olefinic or contain more than one olefinic linkage and those specified include methyl vinyl ketone, mesityl oxide, butyl isopropenyl ketone, isophorone, 1-acetyl-1-cyclohexene, diisopropenyl ketone and 4-isopropenyl-2-cyclohexen-1-one. The aldehydes and ketones may contain more than one carbonyl group. The use of ketones is preferred particularly acyclic or alicyclic monoolefinic ketones containing one carbonyl group. Alcohols specified include ethyl and isopropyl alcohol and cyclohexanol and are preferably monohydric alcohols with not more than four carbon atoms in the molecule, isopropyl alcohol being of especial use. Oxides may be used singly or mixed and those specified are alumina, preferably in an active form, and magnesium oxide and mixtures of alumina with chromium, iron, zinc or copper oxides or boron trioxide, calcium and zinc oxide, and beryllium and zinc oxide. The catalyst may be supported on conventional supports. Temperatures of 200-400 DEG C., especially 230-350 DEG C. are preferred, although temperatures employed vary to some degree depending on the catalyst and reactants used. The reaction would appear to proceed via the unsaturated alcohol from which one molecule of water is removed and it is for this reason that the catalysts are referred to as hydrogen transfer - dehydration catalysts. Usually an excess of alcohol is employed, e.g. ratios of alcohol to carbonyl compound of from 2 : 1 to 12 : 1, particularly 4 : 1 to 11 : 1 being instanced. Flow rates vary with reactants, but are generally low, e.g. 0.02-0.10 total gm.-mols. of reactants per 100 c.c.s. of catalyst per minute preferably 0.035-0.08, particularly 0.04-0.06 gm.-mols. per 100 c.c.s. per minute at 230-350 DEG C. with a catalyst comprising chromium oxide and alumina or zinc oxide-alumina. Water or hydrogen should be absent. Catalysts may be regenerated by burning with air or a gas containing free oxygen and maintain their efficiency. The product may be isolated by fractional distillation and usually consists of p a mixture of isomeric dienes. In examples, isopropyl alcohol and mesityl oxide are reacted in molar proportions of 6 : 1 with flow rates of 0.049 over (1) alumina and chromium oxide at 271 DEG C., (2) aluminium and zinc oxide at 240 DEG C., and (3) magnesium oxide at 460 DEG C. in (5) in proportions of 6 : 1, with a flow rate of 0.073 over alumina and zinc and calcium oxides at 270 DEG C., (6) proportions of 10.2 : 1, with a flow rate of 0.051 over alumina and chromium oxide at 270 DEG C., (8) proportions of 10.4 : 1, flow rate of 0.049, catalyst as (6) but at 253 DEG C., and (9) proportions of 6.2 : 1, flow rate of 0.049 over alumina and cobalt oxide at 250 DEG C. in each of the above cases methylpentadienes are obtained in (4) ethyl alcohol and isophorone in proportions of 4 : 1, flow rate of 0.05 are passed over the catalyst of (1) at 300 DEG C. and in (7) isopropyl alcohol and isophorone are reacted with the conditions of (4) to yield trimethylcyclohexadienes, in (10) isopropyl alcohol and methyl isopropenyl ketone are reacted with the conditions of (4) to give isoprene and in (11) and (12) alpha-ethyl, beta-propyl-acrolein and isopropyl alcohol and homomesityl oxide and sec.-butyl alcohol are reacted as in (4) to yield respectively ethyl-hexadienes and octadienes. Specification 619,014 is referred to. In the Specification as open to inspection under Sect. 91 the carbonyl compounds may be acetylenic and may contain aromatic groups, e.g. alpha-phenyl, b -ethylacrolein and phenethyl vinyl ketone and may contain inert substituents such as halogen, nitro, amino, cyano and ether groups. Alcohols may also be unsaturated and aromatic, e.g. allyl and benzyl alcohol and diphenyl carbinol. This subject-matter does not appear in the Specification as accepted.