Patent GB-807650-A (GB)
Title: Process for the preparation of benzene dicarboxylic acids
IPC: C07C51/487
Filed: 1955-05-09
Abstract: Benzene dicarboxylic acids are made by reacting benzene or toluene with an olefine of from 2 to 4 carbon atoms in a molar ratio of 1.6 to 2.5 mols. of olefine per mol. of benzene when benzene is reacted and in a mol. ratio of 0.8 to 1.5 mols. of olefine per mol. of toluene when toluene is reacted, in the presence of an aluminium chloride catalyst either in a concentration of up to 1 per cent by weight based on the benzenoid compound to produce a reaction mixture containing a dialkylbenzene fraction containing a major proportion of the para isomer or in a concentration of above 1 per cent to produce a reaction mixture containing a dialkylbenzene fraction containing a major proportion of the meta isomer, separating the dialkylbenzene fraction from the reaction mixture, oxidizing it to the corresponding dicarboxylic acid mixture, and separating individual dicarboxylic acids therefrom.  The alkylation may be effected at 50-110 DEG  C. The benzene and toluene may contain some paraffins.  Isopropyl chloride may be used as a catalyst promoter.  The dialkylbenzene fraction may be separated by fractional distillation of the reaction mixture.  The mono- and tri- or higher alkyl benzenes also obtained may be recycled to the alkylation; the mol. ratio of olefine used is then reduced to allow for the alkyl groups introduced into the reaction by the recycling, one mol. of alkyl group being regarded as being equivalent to one mol. of olefine.  The oxidation of the dialkylbenzene fraction may be effected with air or other oxygen-containing gas in the presence of an oxidation catalyst comprising an oxide, hydroxide, halide or organic salt of lead, manganese, iron, nickel, cobalt, chromium, vanadium, copper or mercury or mixtures thereof.  An inert reaction medium may be used such as benzene, a halogenated aromatic compound liquid at 25 DEG  C. and having a boiling point of 273-430 DEG  C. such as chlorinated polyor biphenyls, an aliphatic carboxylic acid of 2-8 carbon atoms such as acetic, propionic, butyric, isobutyric, pentanoic, or ethoxy acetic acids, or an araliphatic acid of up to 8 carbon atoms such as phenylacetic acid.  Inorganic or organic peroxides such as benzoyl peroxide or perbenzoic or peracetic acid or substances which readily form a peroxide in the presence of gaseous oxygen such as acetaldehyde and aliphatic aldehydes of 3 to 5 carbon atoms, acetone and aliphatic ketones of 4 to 6 carbon atoms, diethyl ether and aliphatic ethers of 5 to 10 carbon atoms, hexene, cyclohexene and olefines of 7 to 12 carbon atoms may also be present.  The oxidation may be conducted under pressure and at a temperature of 160-250 DEG C. and gives a mixture of crude dicarboxylic acids of approximately the same isomer constitution as the dialkylbenzene fraction.  The phthalic acid may be removed by heating to form and volatilize phthalic anhydride which may be recovered.  The mixture of isophthalic and terephthalic acids may be separated by conversion to the corresponding alkyl esters containing 1-4 carbon atoms in the alkyl groups and fractional distillation, followed by hydrolysis of the esters if desired.  In examples, propylene is reacted with benzene and toluene and the dialkylbenzene fractions obtained are oxidized.