Oxidation of thioamides

The oxidation of thioamides 63 with a wide variety of oxidizing agents is a well-employed method for the synthesis of 3,5-disubstituted-l,2,4-thiadiazoles 64 <1982AHC285>. However, this method is limited mainly to arylthioamides. The most common oxidizing agents tend to be halogens, hydrogen peroxide, dimethyl sulfoxide (DMSO), and nitrous acid. Yields from these reactions are variable and depend on the thioamide, oxidant, and conditions used (Equation 19). By-products such as nitriles and isothiocyanates are usually formed. 

Formation of the Nitrogen-Sulfur Bond 3.6.1 Oxidation of Thioamides... 

Oxidation of thioamides with I2, Br2 or H202 to diimino disulfides, followed by acid-catalyzed cyclization with elimination of amine, is an important route to symmetrically substituted 1,2,4-dithiazolylium salts (43) (79NKK389), and structures (47) (79CHE1187). The preparation of the 3-phenyl-l,2,4-thiazolines (35), and thus (36), is a related reaction. 

Thiadiazoles carrying identical groups at the 3- and 5-positions are obtained by the oxidation of thioamides 5-chloro-l,2,4-thiadiazoles resnlt from the reaction of amidines with perchloromethyl... 

Hofmann s classical synthesis of 3,5-disubstituted 1,2,4-thiadiazoles by the oxidation of thioamides (1869)3 continues to be further exemplified. The oxidants employed include iodine,9-11 bromine,12 chlorine,13 and nitrous acid,14 as well as /V-chlorobenzamidine (which is recovered as benzamidine)15 and IV-sulfinyl-p-toluenesulfonamide (which evolves sulfur dioxide in the process).16 Irradiation with UV light in the presence of oxygen effects the same reaction, but has not been used on a preparative scale.17... 

Evidence for the intermediate formation of an aminosulphene during the oxidative elimination of sulphur from thioamides is provided by the production of imidates on oxidation of thioamide 5-oxides in the presence of alcohols. (See Section 2, p. 138.) Oxidation of thiohydrazides gave the disulphides (111 X = S2, Ar = Ar = = R = Ph), which on further oxidation with... 

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