GB734622A - Continuous process for the preparation of hydroxy aromatic carboxylates - Google Patents

Abstract

A continuous process for the preparation of aromatic hydroxy carboxylates comprises continuously absorbing carbon dioxide under superatmospheric pressure in an anhydrous solution or suspension of an alkali metal phenoxide in a neutral or basic liquid which is a hydrocarbon, ketone, ether, amine or heterocyclic compound and continuously passing the resulting mixture through a reaction vessel maintained under carboxylation reaction conditions, the time of passage of said mixture through said reaction vessel being at least sufficient to effect reaction between the alkali metal phenoxide and the carbon dioxide to produce an alkali metal aromatic hydroxy carboxylate. Specified phenols of which the alkali metal salts may be used may be mono or poly-nuclear aromatic or heterocyclic compounds which contain at least one hydroxyl group substituted in the aromatic nucleus and may contain other nuclear substituents such as hydrocarbon radicals, halogen atoms, amino groups, nitro groups, ether groups and carboxylic or sulphonic acid groups, e.g. phenol, alkyl phenols such as cresols, alkyl phenols obtained by reacting a phenol with one or more alcohols, alkyl halides, ethers or olefines, particularly mono- or di-alkyl phenols obtained by alkylating a phenol with olefines containing from 8 to 18 carbon atoms obtained by cracking petroleum fractions, halogen - substituted phenols, nitrophenols, aminophenols, 1- or 2-naphthol, 5 : 6 : 7 : 8 - tetrahydro - 2 - naphthol, halogen-substituted naphthols, nitronaphthols, aminonaphthols, 2- or 4-hydroxydiphenyl, p-benzylphenol, 1- or 2-anthrol, 1 : 2- and 1 : 4-dihydroxybenzene, and 1 : 2- and 1 : 5-dihydroxynaphthalene. As neutral or basic organic liquids there are mentioned aromatic hydrocarbons such as benzene, toluene, xylenes, ethyl benzene, cumene, aliphatic hydrocarbons such as heptane, octane, decane, kerosine, gas oil, white oils, cyclohexane, methylcyclohexane and the tetra- and deca-hydronaphthalenes, ketones such as methyl ethyl ketone, methyl isobutyl ketone, ethyl n-butyl ketone, diethyl ketone, di-isopropyl ketone, di-isobutyl ketone, di-sec.-butyl ketone, 2-octanone, di-n-butyl ketone, butyl n-hexyl ketone, pinacoline, cyclopentanone and acetophenone, ethers such as di-isobutyl ether, ethyl amyl ether, ethyl n-butyl ether, ethyl n-hexyl ether, ethyl n-heptyl ether, 1 : 3- and 1 : 4-dioxanes, 1 : 4-dioxene, 2-methyl-1 : 3-dioxane, anisole and phenetole, and basic liquids such as aliphatic primary, secondary and tertiary amines such as n-amylamine, n-heptylamine, 2-amino-n-heptane, dipropylamine, triethylamine, tripropylamine, carbocyclic amines such as aniline and heterocyclic compounds such as pyridine, piperidine, picolines, lutidines, collidines, and quinoline and its homologues. The phenoxide solution or suspension can be prepared by reacting the alkali metal or alkali metal hydroxide with the solution of the phenol, or preferably by the process of Specification 734,605. In the first stage of the reaction dry carbon dioxide is continuously absorbed in the anhydrous solution of the alkali metal phenoxide, preferably at a temperature equal to or above (e.g. 20 DEG higher than) that to be employed in the second stage, and suitably at pressures up to 2000 pounds per square inch. The solution should contain at least one molecular equivalent of carbon dioxide per molecule of phenoxide, and is preferably saturated. Carbon dioxide in gaseous, liquid or solid form can be used. In the second stage the solution or suspension passes to the reaction vessel which may be operated at temperatures of 100 DEG to 300 DEG C. and pressures up to 2000 (e.g. 75 to 600) lbs. per square inch. Preferably there is no gas space in the reaction mixture and the latter flows without turbulence. The products may be converted to the free acids or to the alkaline earth metal salts. The reaction product may be further treated, batchwise or continuously, according to the process of Specification 634,598. In an example the process is applied to the carboxylation of a xylene solution of a mixture of alkylphenols obtained by alkylating phenol with a mixture of olefins containing 14 to 18 carbon atoms obtained by cracking a petroleum fraction. Methyl isobutyl ketone, pyridine or dioxane can be used instead of xylene.