3,4-DISUBSTITUTED-DERIVATIVES OF 1,2,5-THIADIAZOLE 1,1-DIOXIDE - ETHANOL ADDITION-REACTIONS AND ELECTROREDUCTION OF 3-METHYL-4-PHENYL AND 3,4-DIMETHYL DERIVATIVES IN ACETONITRILE AND ETHANOL SOLVENTS

3-Methyl-4-phenyl-1,2,5-thiadiazole 1,1-dioxide (TMP), as well as 3,4- dimethyl-1,2,5-thiadiazole 1,1-dioxide (TMM), react with ethanol (EtOH ), which adds to one of their C=N double bonds. The equilibrium consta nts for the addition reaction are measured in mixed acetonitrile (ACN) - EtOH solvents by means of UV spectroscopy in the case of TRIP, and by C-13 NMR spectroscopy in the case of TMM, since TMM presents only t erminal UV absorption. Both equilibrium constants are also estimated t hrough cyclic voltammetry (CV) experiments. In the case of TRIP, the e thanol molecule adds to the C=N bond located on the methyl-substituted side of the substrate, according to C-13 NMR spectroscopy and CV resu lts. The electroreduction characteristics of the substrates and their ethanol addition products are studied using CV techniques in ACN, EtOH , and ACN-EtOH solvent mixtures. The radical anion formed by the first electron transfer to TMM is unstable and decomposes rapidly while tha t corresponding to TRIP undergoes a relatively slow homogeneous second -order reaction with the substrate (k = 3 x 10(2) M(-1) s(-1)). The eq uilibrium constant for EtOH addition and the voltammetric properties o f the substrates are compared with those of the previously studied 3,4 -diphenyl derivative (TPP).