GB878268A - Improvements in the production of dialkyl esters of iso- and/or terephthalic acid - Google Patents

Abstract

In a process for the production of iso- and terephthalic acid dialkyl esters of lower alkanols with 1 to 4 carbon atoms at least one dialkyl benzene with two oxidisable side chains in the same positions as the carboxylic ester groups in the desired diester and with 1 to 4 carbon atoms in each side chain or at least one chlorine-substituted dialkyl benzene of the same alkyl chain length in which up to two hydrogen atoms attached to at least one carbon atom of at least one alkyl group are substituted by chlorine, is treated in an alkanolic solution which contains at least 60 to about 98% by weight of an alkanol with 1 to 4 carbon atoms with reference to the weight of the whole solution, with a gas containing molecular oxygen at a temperature between 120 DEG and 220 DEG C. and a pressure of at least 8 atmospheres up to about 500 atmospheres in the liquid phase. Starting materials specified include 1,3- and 1,4-cymenes, diisopropyl benzene, m- and p-xylyl chloride, xylylene dichloride, xylidene dichloride, m-and p-chlormethylcumenes, 1,3- and 1,4-chlorethylcumenes and 1,4-bis-(chlorethyl)-benzene. Catalysts specified include salts of manganese, cobalt or vanadium with acetic, butyric, ethyl-hexanoic, crotonic, oleic or naphthenic acids. As reaction promoters bromides of alkali metals e.g. potassium, of ammonium, and of heavy metals such as manganese, cobalt or nickel may be employed. The pressure employed should be sufficient to ensure the presence of the alcohol in the liquid phase. The process may be carried out batchwise or continuously. Initial materials recovered and such oxidation intermediates as toluic acid alkyl esters, diacetylbenzene, acetylbenzoic acid alkyl esters, p or m-bis(2)hydroxy-isopropylbenzene, aldehydic benzoic acid esters and toluic aldehyde are preferably recycled or further oxidised by themselves. The iso- and terephthalic acid esters may be converted to polyesters after recrystallisation and/or vacuum distillation. In examples: Dimethyl terephthalate is obtained by oxidising p-diisopropylbenzene in the presence of cobalt naphthenate, manganese oleate and methanol, part of the product being drawn off during the reaction and fresh methanolic diisopropylbenzene containing cobalt naphthenate and manganous stearate being supplied (1); dimethyl isophthalate is obtained by oxidation of m-diisopropylbenzene in the presence of manganese acetate (2); dimethylterephthalate is obtained by oxidation of p-diisopropyl benzene in the presence of cobalt bromide and methanol (3); dimethyl terephthalate and various intermediate oxidation products are obtained from p-xylene with a catalyst comprising manganese acetate and cobalt bromide (4); dimethyl isophthalate together with intermediate oxidation products are obtained by oxidation of m-xylene in the presence of manganese acetate, cobalt bromide vanadic acid and methanol, the intermediate products being recycled (5); a mixture of dimethyl o-, iso- and terephthalates and methyl benzoate is obtained similarly using a starting material containing o-, m- and p-xylenes and ethyl benzene (6); a mixture of dimethyl o-, iso- and terephthalates is obtained by oxidation of a corresponding mixture of diethyl benzenes (7); dimethyl terephthalate is obtained by oxidation of p-cymene under conditions similar to those employed in (4) (8); dimethyl terephthalate is obtained by oxidising p-isopropylbenzyl chloride in the presence of methanol, manganese acetate, cobalt bromide and sodium hydroxide, the intermediate products also obtained being recycled (9); dimethyl terephthalate is obtained by oxidising p-xylylene dichloride under similar conditions (10); dimethyl terephthalate is obtained by oxidation of p-diiso-propyl benzene in the presence of manganese and cobalt bromides, intermediate products being recycled and the distillation of the reaction mixture being assisted by leading in superheated methanol vapour (11); a process similar to (6) is carried out using cobalt bromide and manganese acetate as catalysts (12). Among the intermediate products mentioned in the examples are monomethyl terephthalate, methyl toluates, toluic acid and esters thereof, p-acetylbenzoic acid and its methyl ester, p-hydroxymethyl acetophenone, p-acetyl benzaldehyde and benzoic acid ester. Specification 825,998 is referred to.