2-Sulfobenzoic anhydride

White to beige crystals or crystalline powder

Polymerization inhibitor.

2-sulfobenzoic acid anhydride was prepared as follows: under the protection of N2, in a 50mL three-necked flask, add 9.0g of saccharin solid and 13mL of concentrated sulfuric acid (concentration of 98%), stirring reaction at 140 for 2h, cooled to room temperature, a large number of solids precipitated in the reaction mixture, filtration, filtering of the resulting solids were washed with iced water, drying, to obtain the white solid of 2-sulfobenzoic acid anhydride 7.3g. The yield was 81%.

The anhydride is purified by distillation in a vacuum and readily solidifies to a crystalline mass on cooling. [Heitman J Am Chem Soc 34 1594 1912.] Alternatively purify it by dissolving it in the minimum volume of toluene and refluxing for 2hours using a Dean-Stark trap. Evaporate under reduced pressure and distil the anhydride at 18mm. It is then recrystallised three times from its own weight of dry *C6H6. It is sensitive to moisture and should be stored in the dark in a dry atmosphere. The O-methyloxime has m 110-112o [Levy Tetrahedron Lett 3289 1972]. If the sample has hydrolysed extensively (presence of OH band in the IR) then treat with an equal bulk of SOCl2, reflux it for 3hours (CaCl2 tube), evaporate and distil the residue in a vacuum, then recrystallise it from *C6H6, Et2O/*C6H6 or CHCl3 (EtOH free by passing through Al2O3, or standing over CaCl2). [Clarke & Dreger Org Synth Coll Vol I 495 1941.] It is used for modifying -amino functions of lysyl residues in proteins [Bagree et al. FEBS Lett 120 275 1980]. [Beilstein 19 I 659, 19 II 137, 19 III/IV 1641, 19/4 V 215.]