GB863511A - Process for the manufacture of benzene-1-3-disulphonic acid - Google Patents

Abstract

<FORM:0863511/IV (b)/1> Benzene-1, 3-disulphonic acid is produced by reacting benzene with sulphur trioxide in a single-stage process by carrying out the reaction at a temperature above 100 DEG C. in a mixture containing benzene-1, 3-disulphonic acid and sulphuric acid or sulphur trioxide. In order to produce as pure a product as possible, it is advantageous to carry out the reaction in the presence of a sodium salt such as sodium sulphate or the sodium salt of benzene-1, 3-disulphonic acid. In an example, a sulphonation mixture containing 35% by weight of benzene-1, 3-disulphonic acid, 65% by weight of sulphuric acid and a quantity of sodium benzene-1, 3-disulphonate amounting to about 5% by weight p (calculated on the whole reaction-mixture) is circulated, at 135 DEG -140 DEG C., through the apparatus shown by means of pump 5 at the rate of 17 litres per hour. Liquid sulphur dioxide is introduced, at the rate of 400 grams per hour, below the surface of the mixture in vessel 1; and benzene is introduced into vessel 2 at the rate of 177 grams per hour. A final product containing 92% of benzene-1, 3-disulphonic acid is withdrawn through valve 6. Specification 747,659 is referred to.