GB1002083A - Production of hydroxybenzenes - Google Patents

Abstract

A cyclohexane of the formula C6H(12-n)(R)n, in which n is 0-3, R is an alkyl group of 1-10 carbon atoms and, when n is 2 or 3, the groups R are attached to different nuclear carbon atoms, is treated in the liquid phase with air or other gas containing molecular oxygen in the presence of a boron compound capable of reacting with the cyclohexanol or alkylcyclohexanol formed in the reaction to form an ester, and the cyclohexanol or alkylcyclohexanol, preferably after removal of unreacted cyclohexane compound and after decomposition of the ester by hydrolysis, is then converted into the corresponding phenol, at least in part, by dehydrogenation. Alternatively, the decomposition of the ester may precede the removal of unreacted cyclohexane compound. The reaction of the cyclohexane or alkylcyclohexane with the boron compound is preferably effected under conditions which permit the escape of water, e.g. as a cyclohexane-water azeotrope which is condensed, the separated cyclohexane being returned to the reaction mixture. The reaction may be effected at 75-300 DEG C., preferably 140-180 DEG C., and an initiator of the reaction, e.g. cyclohexanone or a mixture of cobalt naphthenate and acetaldehyde, may be present. Suitable boron compounds are boric, metaboric or tetraboric acid, boron oxide, or boric esters, e.g. methyl or ethyl borate or methyl, ethyl or propyl, meta- or tri-borate. The molecular proportion of boron compound (calculated as boric acid) should preferably exceed the molecular proportion of cyclohexanol or alkylcyclohexanol formed. In addition to cyclohexanol or alkylcyclohexanol, the reaction products include minor proportions of other compounds, e.g. cyclohexanone, cyclohexyl hydroperoxide, tertiary alcohols, e.g. 1 - methylcyclohexanol, acyclic ketones, e.g. 2-heptanone, and glycols, e.g. 1,2-methylcyclohexanediol. The separation of the reaction product from the boron compound is preferably effected by hydrolysis at 50-150 DEG C., whereafter the boron compound is filtered off and the filtrate decanted to separate the organic product. The cyclohexanol or alkylcyclohexanol, after separation from the boron compound, may be further refined before it is dehydrogenated to yield a phenol, or it may first be treated to convert its tertiary alcohol content into other products useful in the process. Thus, the crude product may be distilled to separate (when methylcyclohexane is the starting material) 1-methylcyclohexanol, which may then be dehydrated, e.g. by passage over alumina at 200-400 DEG C., to yield methylcyclohexene, which may be hydrogenated to yield the starting material, or simultaneous dehydration and dehydrogenation may be effected. The dehydrogenation of the cyclohexanol or alkylcyclohexanol to a phenol may be effected at 250-475 DEG C. at a pressure between 100 mm. and 3 atm., preferably at 325-400 DEG C., and atmospheric pressure, in the presence of a dehydrogenation catalyst, e.g. nickel, palladium, cobalt, copper or zinc but preferably platinum on carbon. Examples are given of the manufacture of phenol and cresols from cyclohexane and methylcyclohexane, respectively, and reference is made also to the treatment of t-butylcyclohexane, diethyl-cyclohexane. trimethylcyclohexane, methyl-ethylcyclohexane and methylisopropylcyclo-hexane. Specification 929,680 is referred to.