GB757455A - A process for the separation of tertiary-alkyl-substituted benzoic acids from mixtures containing said acids - Google Patents

Abstract

Tertiary-alkyl-substituted benzoic acids are separated from a crude oxidation product obtained by the oxidation of one or more aromatic hydrocarbons including a tertiary-alkyl-substituted benzene hydrocarbon having at least one tertiary-alkyl radical and at least one non-tertiary-alkyl radical as substituents in its benzene ring, by treating said crude oxidation product at a temperature above about 50 DEG C. with sufficient aqueous alkali-metal or ammonium base to form a mixture having a pH between 7 and 8, separating an aqueous phase therefrom, adding to said aqueous phase at a temperature above about 50 DEG C. sufficient concentrated strong mineral acid to form a mixture having a pH between 6 and 7 and separating therefrom a solid phase consisting of said tertiary-alkyl-substituted benzoic acid. The tertiary-alkyl-substituted benzene hydrocarbon may contain a tertiary-alkyl radical of 4 to 21 carbon atoms and a non-tertiary-alkyl radical of 1 to 4 carbon atoms and the following hydrocarbons are mentioned: o-, m- and p-tertiary-butyl toluene, o-, m- and p-tertiary-amyl toluene, the o-, m- and p-isomers of tertiary-nonyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, octadecyl, eicosyl and heneicosyl toluenes, 3 : 5-di-tertiary-butyl toluene, the tertiary - butyl xylenes, the tertiary - heptyl xylenes and 2-propyl-4-tertiary-butyl ethyl benzene. These form the corresponding tertiary alkyl benzoic acids such as tertiary-butyl and tertiary-amyl benzoic acid, and 3 : 5-di-tertiary butyl benzoic acid. The alkali-metal or ammonium bases specified are hydroxides and carbonates such as sodium, potassium, lithium or ammonium hydroxides and sodium carbonate or bicarbonate. Strong mineral acids specified are sulphuric, hydrochloric and phosphoric acids. The process may be a batch, semicontinuous or continuous operation conducted at atmospheric or superatmospheric pressure. Separation between isomers of tertiary-alkyl benzoic acids may be effected by controlled stepwise acidification of the aqueous phase. With a mixture of m- and p-tertiary-butyl benzoic acids, acidification of the hot aqueous phase to a pH between 6 and 7 results in the separation of the p-isomer, further acidification to pH between 5.3 and 6 causes separation of the m-isomer. Phthalic acids such as terephthalic acid, separate on acidification of the aqueous phase to a pH below 5.3. In examples: (1) p-tertiary-butyl toluene is oxidized in the presence of a cobalt catalyst and the product treated with aqueous sodium hydroxide to bring the pH to 7.5, the aqueous phase is treated with concentrated sulphuric acid to a pH of 6.5 when p-tertiary-butyl benzoic acid separates; the colour of this acid on heating is compared with that of crude tertiary-butyl benzoic acid; (2) a mixture of m- and p-tertiary butyl toluene is oxidized as in (1) and treated with aqueous sodium hydroxide to a pH of 7.8, the aqueous phase acidified with sulphuric acid to pH 6.5 to give p-tertiary-butyl benzoic acid, further acidification of the mother-liquors gives a mixture of m-and p-tertiary butyl benzoic acid.