GB815198A - Improvements in or relating to the production of aromatic acid esters - Google Patents

Abstract

Aromatic acid esters are produced by treating an alkyl benzene simultaneously with an oxygen-containing gas and a lower alkanol containing 1-3 carbon atoms in a reaction zone which is maintained at an elevated temperature, and the water formed during the esterification is continuously removed from the reaction zone. The reaction may be carried out in the temperature range 250-750 DEG F., preferably 300-600 DEG F., and the pressure may be in the range 10-1000 atmospheres, preferably 250-1500 p.s.i.g. Suitable alkanols are methanol, ethanol, n-propanol and isopropanol and the alkanol is fed into the reaction mixture at such a rate that its concentration is approximately 0.5 per cent by weight. Mono- and poly-substituted alkyl benzenes and their partially oxidized and esterified derivatives are suitable for the oxidation and the following aromatic compounds are specified: monoalkyl substituted benzenes, e.g. toluene, ethylbenzene and cumene; polysubstituted benzenes, e.g. o-, m-, p-xylene and durene; partially oxidized compounds, e.g. methyl p-toluate; mixtures of these compounds, e.g. p-xylene and methyl p-toluate; propylbenzene, cymene, hemimellitine, pseudocumene mesitylene, p-methyl benzyl alcohol, tolualdehyde, toluic acid, toluic anhydride, durylic acid, 2 : 5-dimethylterephthalic acid, 4 : 6-dimethylisophthalic acid, methyl trimellitic acid, methyl durylate, the dimethyl esters of 2 : 5-dimethylterephthalic acid and 4 : 6-dimethyl isophthalic acid, and trimethyl methyltrimellitate. It is advantageous to have an oxidation catalyst present in the reaction zone and oxides, hydroxides and organic and inorganic salts of cobalt, manganese, cerium, vanadium, lead, chromium and iron may be used, the metal toluates, naphthenates and stearates being preferred. The process may be worked continuously or batchwise. In the examples in which cobalt naphthenate is used as catalyst and air is used as the oxygen-containing gas, p-xylene is treated with (1) (2) methanol where the products include dimethyl terephthalate, methyl p-toluate, terephthalic acid, methyl hydrogen terephthalate and p-toluic acid; (3) methanol to give dimethyl terephthalate; (4) ethanol to give ethyl p-toluate and diethyl terephthalate; (5) isopropanol to give isopropyl p-toluate and di-isopropyl terephthalate; (6) n-propanol to give n-propyl p-toluate and di-n-propyl terephthalate; durene is reacted with (7 (8) (9) (10) (11) methanol under various conditions to give methyl durylate, the dimethyl esters of 2 : 5-dimethylterephthalic acid and 4 : 6 - dimethylisophthalic acid, trimethyl methyltrimellitate, tetramethyl pyromellitate and a small amount of dicarboxylic acids; (12) toluene, ethylbenzene, o-xylene, m-xylene and cumene are treated with methanol and the esters recovered; (13) methyl p-toluate is treated with methanol and dimethyl terephthalate recovered; (14) a mixture of p-xylene and methanol is treated with a mixture of methyl p-toluate and methanol, dimethyl terephthalate is recovered; (15) p-xylene is treated with a mixture of p-xylene and methanol and dimethyl terephthalate and methyl p-toluate are recovered; (16) (17) methyl p-toluate is treated with a mixture of methanol and methyl p-toluate to give dimethyl terephthalate. Examples 14-17 illustrate the continuous process. A further example is given to show how, in the reaction of p-xylene with methanol, the loss as carbon dioxide decreases as the methanol feed rate increases.