Sulfoxides oxygen exchange

The behavior of chiral phenyl /-butyl sulfoxide 219 and a-phenyl-ethyl phenyl sulfoxide 220 is completely different in strongly acidic media and in the presence of halide ions. Two reactions were found (266) to occur in parallel. One results in the loss of optical activity, and the second leads to the decomposition of the sulfoxide. It was observed that the racemization process is not accompanied by [ 0] oxygen exchange. In the case of sulfoxide 220 the complete loss of optical activity at chiral sulfur is accompanied by partial racemization at the chiral carbon center. These results are consistent with a sulfenic acid-ion-pair mechanism formulated by Modena and co-workers (266) as follows (it is obvious that the formation of achiral sulfenic acid is responsible for racemization). 

Racemization of diaryl and alkyl aryl sulfoxides accompanied by oxygen exchange was also observed in a-halogenoacetic acids (270, 271) and phosphoric acid (272). 

Reaction of water with organosulfur cation radicals and dications also plays a role in the exchange of sulfoxide oxygen with the oxygen atom of water in acid solutions (Oae, 1970 Oae et al., 1974). 

The sulfoxidation of normal Cl4-CI7 paraffins with sulfur dioxide, oxygen, and water is performed under UV radiation in parallel reactors (1 in Fig. 3). The reaction enthalpy is dissipated by cooling of the paraffin in heat exchangers. The 30- to 60-kW UV lamps are cooled by a temperature-controlled water cycle. The reaction mixture leaving the reactors separates spontaneously into two phases in 2. The lighter paraffin phase is recirculated to the reactors. The composition of the heavy raw acid phase is shown in Table 5. 

If for some special reason the entering and leaving groups are forced into a situation where one must occupy a radial position and the other an apical one, the reaction will proceed with retention of configuration at the sulfinyl group. The exchange of oxygen-18 between dimethyl sulfoxide and l80-labeled, optically active methyl p-tolyl sulfoxide (153) (Oae et al., 1968) would appear... 

Oae and co-workers (288) were the first to show that nucleophilic displacement at sulfur is accompanied by retention of configuration. They found that chiral 0-labeled alkyl aryl sulfoxides exchange oxygen with dimethylsulfoxide at about 150°C, almost without racemization. To explain the steric course (retention) of this reaction, the formation of a trigonal-bipyramidal intermediate 246 was postulated in which the entering and departing oxygen atoms occupy apical and equatorial positions, respectively. 

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