benzene-1,3-disulphonic acid

Definition

ChEBI: A member of the class of benzenesulfonic acids consisting of benzene carrying two sulfo groups at positions 1 and 3 respectively.

Production Methods

Benzene-1,3-disulphonic acid is formed as the main product in the sulfonation of benzene or benzenesulfonic acid with excess oleum at temperatures of 80 – 250 ℃. In proportion to the oleum concentration and reaction temperature 1 – 29% of diphenyl sulfone disulfonic acid is formed as an undesired byproduct.

Preparation

Benzene is introduced into a cast-steel agitator vessel containing 100% sulfuric acid. The contents of the reactor are heated to 100 ℃ and kept at this temperature for one hour. The products of the reaction (monosulfonation) are transferred to an agitator vessel containing 65% oleum. The temperature rises from 30 to 80 ℃ and is maintained at this level for another 1 – 2 h. The sulfonation mass is freed from sulfate ions in the normal way by adding calcium hydroxide or calcium carbonate and then removing the gypsum. It is then converted with sodium carbonate into the disodium salt, which is dried on a drum dryer. The yield is 93% and the product has a purity of 96%.
Particularly pure 1,3-benzenedisulfonic acid is obtained according to the process of Hooker Chemical Corp. Benzene is sulfonated with 96% sulfuric acid at a molar ratio of the reactants of 1:3.4. The temperature is initially 65 ℃, but is then raised to 80 ℃. The water of the reaction is then removed by evaporation at 33 mbar and 200 ℃. Finally, during disulfona- tion at 1.3 mbar and 210 – 235 ℃, sulfuric acid and reaction water are distilled. The reaction product has a purity of 98.7% and a solidification point of 136 ℃. The process also can be operated continuously.

Purification Methods

Free it from H2SO4 by conversion to the calcium or barium salts (using Ca(OH)2 or Ba(OH)2, and filtering). The calcium salt is then converted to the potassium salt, using K2CO3. Both the potassium and the barium salts are recrystallised from H2O, and the acid is regenerated by passing through the H+ form of a strong cation exchange resin. The acid is recrystallised twice from conductivity water and dried over CaCl2 at 25o. [Atkinson et al. J Am Chem Soc 83 1570 1961.] It has also been crystallised from Et2O and dried in a vacuum oven. The S-benzylisothiuronium salt has m 214.3o (from EtOH/H2O). [Beilstein 11 IV 553.] It is best kept as the disodium salt [831-59-4] which decomposes on heating [Beilstein 11 H 199, 11 I 48, 11 II 213, 11 III 453.]