Patent GB-757658-A (GB)
Title: A process for separating tertiary-alkyl substituted benzoic acids from mixtures containing said acids
IPC: C07C51/48
Filed: 1954-07-20
Abstract: Tertiary-alkyl-substituted benzoic acids having no appreciable water solubility are extracted from crude mixtures containing the acids in admixture with other compounds including one or more hydrocarbons and one or more oxygen-containing organic compounds by extracting the crude mixture in the liquid phase at a temperature above about 50 DEG C. with a solvent comprising a solution in an aqueous medium of a water-soluble ammonium or alkali-metal or alkaline-earth metal salt of a carboxylic acid, which carboxylic acid is itself substantially water-insoluble, and then cooling the resultant extract phase to separate the desired tertiaryalkyl-substituted benzoic acid.  The salt in the aqueous solvent may be a salt of the tertiaryalkyl benzoic acid to be recovered from the crude mixture or of any tertiary-alkyl-substituted benzoic acid, which may also be further substituted with alkyl or cycloalkyl groups such as methyl or ethyl, or of benzoic acid or of a benzoic acid substituted by one or more aliphatic or cycloaliphatic radicals such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl or pentyl groups. Specified metal salts are those of sodium, potassium, lithium and strontium.  The aqueous medium may be water or mixtures of water with organic solvents such as methanol, ethanol, propanol, isopropanol, sec-butanol, acetone or dioxane.  The crude mixture containing the acid may be subjected to a pretreatment comprising filtration or centrifugation and/or washing or scrubbing with water at above 50 DEG  C. prior to the extraction. The extraction may be conducted as a continuous or batch process at atmospheric or increased pressure by contacting the crude mixture with the aqueous salt solution as described above, and cooling the aqueous extract.  Separate recovery of two isomers, such as meta- and para-tertiary butyl benzoic acids from a mixture containing them, may be effected by controlled step-wise cooling and filtration. The crude mixture may be a crude oxidation product obtained by oxidizing one or more aromatic hydrocarbons including a tertiary-alkyl-substituted benzene hydrocarbon having at least one tertiary-alkyl radical which may contain from 4 to 21 carbon atoms and at least one non-tertiary-alkyl radical which may contain from 1 to 4 carbon atoms, such as ortho-, meta- and para-tertiary-butyl toluene, ortho-, meta- and para-tertiary-amyl toluene, the tertiary-butyl xylenes, 2-propyl-4-tertiary-butyl ethyl benzene, and the ortho-, meta- and para-isomers of the tertiary nonyl-, dodecyl-, tetradecyl-, pentadecyl-, hexadecyl, octadecyl-, eicosyl and heneicosyl-toluenes, to form the corresponding tertiary-alkyl-substituted benzoic acids. The oxidation may be effected by an oxygen-containing gas and catalysts specified are oxides, hydroxides, and organic salts of cobalt, manganese, lead, iron, nickel, copper, vanadium, chromium, mercury and combinations thereof.  In a continuous process, tertiary-butyl toluene is oxidized with an oxygen-containing gas under pressure in the presence of cobalt octoate, the oxidation mixture is filtered to remove aromatic dicarboxylic acids such as terephthalic acid, washed with hot water and subjected to counter-current extraction with an aqueous solution of sodium tertiary-butyl benzoate at above 50 DEG  C. and at atmospheric pressure.  The raffinate phase may be washed with hot water prior to recycling to the oxidation stage.  The extract phase is cooled and the tertiary-butyl benzoic acid removed by filtration and washed with fresh solvent and hot water or a hydrocarbon such as benzene, toluene, tertiary-butyl toluene or hexane.  The filtrate is recycled as solvent to the extraction stage, a portion being bled from the process to prevent a build-up of impurities.  In an example, the extraction of an oxidation mixture containing meta- and para-tertiary-butyl benzoic acid with sodium tertiary-butyl benzoate to give para-tertiary-butyl benzoic acid is described.