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Reaction of sulphoxides with (dichloroiodo)benzene or with bromine in the presence of pyridine affords the corresponding α-halogeno-sulphoxides. Some reactions of α-halogeno-sulphoxides are here described.

α-Chlorination of dialkyl and aryl alkyl sulphoxides by iodobenzene dichloride is highly stereospecific, and in benzyl methyl sulphoxide involves the proton diastereotopic to that which is preferentially exchanged by deuterium in NaOD–D2O.

Sulphides react with the stoicheiometric quantity of iodobenzene dichloride in aqueous pyridine between –40 and 20° to give high yields of the corresponding sulphoxides. The reaction applies to aliphatic, aromatic, and heterocyclic sulphides. The influence of electronic and steric effects is small. In vinylic sulphides containing electron-withdrawing groups β to the sulphur atom, oxidation is followed by heterolytic cleavage of the S–C(ethylenic) bond. An excess of reagent may lead to the formation of sulphones or chlorosulphoxides. Both reactions are much slower than mono-oxidation, so that, under the conditions indicated, oxidation of sulphides with one molar proportion of reagent leads exclusively to sulphoxides. Use of 18O-enriched water readily gives 18O-labelled sulphoxides.

5,6-Bisphenylsulphinylnorborn-2-enes are converted into iodohydrins by reactions involving intramolecular nucleophilic attack by sulphinyl-oxygen at an electrophilic carbon, and concomitant nucleophilic attack at sulphur by a water molecule, with inversion of chirality of the sulphinyl group. The reaction is strictly conditioned by steric factors. Under the conditions in which a sulphinyl group with appropriate configuration reacts, a second sulphinyl group in an unfavourable position in the same molecule remains unaltered. Conversion of 5,6-endo-anti,exo-syn-bisphenylsulphinylnorborn-2-ene into the endo-syn,exo-syn-isomer, and vice-versa, via iodohydrins, constitutes a Walden cycle at the sulphur atom.

Conversion of syn- and anti-3-endo-phenylsulphinylbicyclo[2,2,1]hept-5-ene-2-endo-carboxylic acids and esters into anti- and syn-iodohydrins, respectively, with inversion of configuration of the sulphinyl-group, and then conversion of the iodohydrins into the anti- and syn-bicycloheptene sulphoxides constitutes a Walden cycle at the sulphur atom. The inversion which accompanies the formation of iodohydrins is caused by intramolecular nucleophilic attack by sulphinyl-oxygen on the norbornene double bond, and hydrolysis of the intermediate O-alkylsulphoxonium salts. A new, selective method of converting iodohydrins into alkenes is described.

Conversion of (+)-methyl p-tolyl sulphoxide into the corresponding (–)- or (+)-α-halogenomethyl derivatives in the presence or in the absence of silver nitrate, respectively, involves inversion of configuration at sulphur in one of the two reactions; the inversion was proved to occur without any breaking of bonds at the chiral centre or any diastereomeric interaction in the transition state.