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Veterans at Risk: The Health Effects of Mustard Gas and Lewisite
competition factors for sulfur mustard was compiled during World War II. It should be emphasized, however, that despite the large differences in affinities of some nucleophiles, the overall rates of reaction of sulfur mustard are approximately equal. This is consistent with the proposed reaction mechanism, in which the rate-limiting step in the reaction of sulfur mustard in aqueous media is the formation of the cyclic sulfonium intermediate.
In addition to the potential contribution of sulfonium salts to the biologic activity of sulfur mustard, the oxidized forms of sulfur mustard may also be of importance. The reactions of the sulfoxide [OS(CH2CH2Cl)2] are much slower than those of the sulfone [O2S(CH2 CH2Cl)2], leading to a detoxification mechanism (oxidation of sulfur mustard to its sulfoxide). The sulfone, on the other hand, is quite reactive via the elimination of HCl to form the divinylsulfone to which nucleophiles add (5-9):
The sulfone is particularly important, since conjugates of it have been identified in the urine of rats dosed intravenously with sulfur mustard.
Reaction of Sulfur Mustard with Various Nucleophiles
Sulfur mustard reacts with sodium salts of alcohols (R; ethanol, methanol, etc.) to give ethers, but the yields are only fair (5-10):
With the corresponding sulfur compounds, almost quantitative yields are obtained (5-11):
The formation of the dimethyl derivative, which is harmless and can be distilled, has been used to characterize sulfur mustard.
With salts of organic acids, esters of thiodiglycol are produced (5-12):
Sulfur mustard reacts readily with secondary amines, but one amine group of the product may be eliminated (5-13):