Electrophilic substitution of five-membered heterocyclic compounds : electrophilic substitution of the phenyl-1,2,4-triazoles : synthetic studies of some [beta]-triketones

The action of most common oxidising agents on 1,2,4- triazoline -3 -thione leads to ready cleavage of the C-S bond to yield 1,2,4-triazole. Prior to this work no 1,2,4-triazole - 3 -sulphonic acids had been reported. Several oxidative methods have been developed which yield 1,2,4-triazole -3 -sulphonic acid; of these chlorine oxidation is the most convenient. A literature survey of the oxidation of heterocyclic thiols and thiones has been made. Syntheses of substituted 1,2,4- triazoline -3 -thiones have been reviewed. Thirty monosubstituted 1,2,4-triazoline -3 -thiones as well as several disubstituted 1 1 2,4-triazoline-3-thiones, 1,2 1 4- triazolidine -3,5 -dithiones, di -(1,2,4-triazoline -3-thiones), and fused ring 1,2,4-triazoline -3 -thiones have been prepared. Chlorine oxidation of all these compounds has been investigated. In most cases the corresponding sulphonyl chlorides were formed initially, and these were then hydrolysed to the sulphonic acid or converted to the sulphonamide. Approximately thirty acids and fifteen amides were prepared in this way. With certain 2-substituted 1,2,4-triazoline -3 -thiones no sulphonyl chlorides nor sulphonic acids could be isolated, while with certain substituents in the 4-position the intermediate sulphonyl chlorides were formed but could not be converted into the corresponding sulphonic acids. Bromine oxidation of several monosubstituted 1,2,4- triazoline -3 -thiones also yielded the corresponding sulphonic acids though yields were very poor for the parent thione.