Patent GB-760679-A (GB)
Title: Production of esters
IPC: C07C69/78
Filed: 1952-11-03
Abstract: A process for the production of an ester of an aromatic carboxylic acid comprises oxidizing an alkyl aromatic hydrocarbon or partially oxidized alkyl aromatic hydrocarbon with ammonium sulphate, sulphur or an inorganic watersoluble sulphur compound having at least part of its sulphur at a valence below +6, and water at a temperature above approximately 500 DEG  F. and under a superatmospheric pressure sufficient to maintain a part of the water in the liquid phase heating the oxidation product with an alcohol, and recovering the ester of a benzene carboxylic acid. By "partially oxidized alkyl aromatic hydrocarbon" is meant an alkyl aromatic hydrocarbon, alcohol or ketone.  The water-soluble sulphur compound is preferably a sulphide.  Other suitable sulphur compounds are elemental sulphur, sulphur dioxide, sulphide ion and thiosulphate ion.  The esterification process may be applied to the crude oxidation reaction mixture or to a separated oxidation product containing acids and amides, and may be effected at normal or superatmospheric pressures, with or without a catalyst such as sulphuric acid.  Temperatures of 200 DEG  to 500 DEG  F. are suitable in the absence of catalyst. Advantageously at least one mol. of sulphuric acid per mol. of phthalic acid derivative is employed.  Alcohols from methyl to octyl are suitable.  Ammonia, recovered as its sulphate in the esterification is returned to the oxidation process.  In examples: (1) p-xylene, hydrogen sulphide, ammonium sulphate and water are heated at 620 DEG  F., the pressure rising to 3000 p.s.i..  After removal of sulphur the product (terephthalic acid amides and ammonium terephthalates) is evaporated to dryness and heated with methanol and sulphuric acid to give dimethyl terephthalate; (2) a similar process is carried out using ammonium sulphide in place of hydrogen sulphide; (3) isophthalic acid amides and ammonium salts, prepared from m-xylene similarly to Example (1) are heated under pressure at 450 DEG  F. with methanol to give dimethyl isophthalate; (4) the oxidation product (mixed phthalic and terephthalic acid amides), prepared from mixed xylenes similarly to Example (1) is heated with 2-ethylhexanol to give the esters of isophthalic and terephthalic acids; (5) an oxidation product is obtained in the first part of Example (1) is heated with butanol and sulphuric acid to give di-butyl isophthalate; (6) a -methyl-naphthalene is oxidized similarly to Example (1) and the dried reaction product (a -naphthoic acid amide) is refluxed with methanol and sulphuric acid to give methyl a -naphthoate; (7) methyl benzoate is prepared similarly to Example (1) from toluene; (8) a mixture containing trimethylbenzene methyl ethyl benzene and some non-aromatic hydrocarbons (reformed naphtha) is oxidized as in Example (1) and the product refluxed with methanol and sulphuric acid to give trimesic acid, trimethyl ester, dimethyl terephthalate, dimethyl isophthalate and methyl benzoate; (9) Example (3) is repeated using m-toluic acid in place of m-xylene. Reference has been directed by the Comptroller to Specification 706,042.