Sulfinic-carboxylic acid anhydride

Oxidation of (3-thiolactone 308 with m-chloroperbenzoic acid gives a low yield of the mixed sulfinic-carboxylic acid anhydride 331. ... 

Thietanone 1,1-dioxides are unknown, although the tetraphenyl compound may be an intermediate in the oxidation of the 2-thietanone 308 with m-chloro-perbenzoic acid to the sulfinic-carboxylic acid anhydride 331. The methods discussed below apply to 3-thietanone 1,1-dioxides and derivatives. 

Thionyl chloride is another activating agent employed for reactions between aromatic carboxylic acids and phenols in pyridine solution. The mechanism suggested does not involve the formation of an acid chloride but assumes the existence of an intermediary mixed sulfinic anhydride which undergoes reaction with phenolic endgroups (Scheme 2.32).311... 

Among the oxyacids of sulfur the predilection to form an anhydride with a sulfur-sulfur bond, rather than one with an oxygen bridge between the two sulfurs, is not restricted to sulfenic acids. We will see in a subsequent section that sulfinic acids also do this. Their anhydrides have the sulfinyl sulfone structure. RS(0)S02R, rather than RS(0)0S(0)R. What is unique about the sulfenic acid-thiolsulfinate system, however, is the fact that the anhydride (thiolsulfinate) is strongly preferred thermodynamically over the acid at equilibrium. With any other type of common acid the reverse is true, of course. The uniqueness of the sulfenic acid-thiolsulfinate situation can perhaps best be appreciated by realizing that, if the same stability relationship between acid and anhydride were to exist for carboxylic acids, acetic acid would spontaneously dehydrate to acetic anhydride ... 

The carbonyl group of an acid chloride is also a sufficiently electropositive center that acylation of a sulfinate ion occurs at oxygen (123) rather than sulfur (Schank, 1967 Kobayashi, 1966b). The mixed sulfinic-carboxylic anhydrides... 

A variant that eliminates the production of water and that has proved effective for esterification of hydroxy and aromatic amino acids involves the use of thionyl chloride instead of acid. At a low temperature, the alcohol reacts with the chloride, generating methyl sulfinyl chloride, which produces the ester, probably through the mixed carboxylic acid-sulfinic acid anhydride (Figure 3.18, B). p-Toluenesulfonyl chloride added to the acid and benzyl alcohol serves the same purpose in the preparation of benzyl esters. 

Kohn et developed a one-step preparation of a stable carboxylic-sulfinic acid anhydride by oxidizing 3,3,4,4-tetraphenyl-) -propionothiolac-tone with a peracid (Eq. 50). 

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