3- Sulfopropionic anhydride

In 2000, Mitsui Chemicals found that anhydrides of the sulfonic and carboxylic acids, such as 3-sulfopropionic anhydride (51) and 2-sulfobenzoic anhydride (52), can be used as additives in small quantities [79]. 

Optically active diaryl(acylamino)(acyloxy)spiro-A-4-sulfanes are key intermediates for the interconversion of a sulfoxide stereocenter (see Section 4.05.3.6). As an example, sulfoxide (i )-211 was transformed into spirosulfane (A)-212 using sulfopropionic anhydride. A selective S-O cleavage occurs with tetrafluoroborate affording (i )-213, which is then transformed into sulfoxide (A)-214 with inverted configuration at sulfur <2001TA745>. 

Aliphatic carboxylic acids may be sulfonated directly to sulfocar-boxylic acids in which the sulfonic acid group is on the a-carbon atom. Better results are sometimes obtained by sulfonation of the corresponding alkylmalonic acid followed by decarboxylation. Sulfonation of propionic anhydride with pyrosulfuric acid gives a-sulfopropionic acid (75%). Several simple olefinic acids containing a sulfonic acid group in the a-position have been made by direct sulfonation of a.,/3-olefinic acids or /3-halo acids. In the latter case, dehydrohalogenation accompanies sulfonation. 

Sulfosuccinic and sulfopropionic acids are economically attractive when synthesized in situ or offsite from maleic anhydride or acrylic acid. Both are subject to oxidation, but should give nonvolatile degradation products. Synthesis of sulfopropionic acid can give undesirable polyacrylic acid impurities. 

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