Electrochemical and spectroscopic study of the addition of several nucleophiles to 1,2,5-thiadiazole 1,1-dioxide derivatives

The nucleophilic addition reactions of several alcohols and 1-propanethiol to a C=N double bond of 3,4-disubstituted derivatives of 1,2,5-thiadiazole 1,1-dioxide were studied in acetonitrile solution. The substrates used were 3.4-diphenyl (1a), 3-methyl-4-phenyl (1b), phenanthro[9,10-c] (1c) and ace naphtho[1,2-c]-1,2,5-thiadiazole I,l-dioxide (Id), 3,3-diphenyl-1,2,5-thiad iazoline 1,1-dioxide (2a) and 4-ethoxy-5-methyl-3.4-diphenyl-1,2,5-thiadiaz oline 1,1-dioxide (2b). Spectroscopically (UV-VIS) and electrochemically (c yclic voltammetry) measured equilibrium constants at 25.0 degrees C are pre sented and discussed for the reaction of la and Ib with alcohols (methanol, n-propanol. n-butanol, isobutanol, 7-propanol, sec-butanol, tert-butanol, ethylene glycol, allyl alcohol and 2-phenylethanol). A reaction of 1-propan ethiol with ic was observed, but the alcohols did not react with Ic, Id or the thiadiazolines (2a, 2b). The effect of the solvent on the equilibrium c onstant of the la-ethanol system was measured using, besides acetonitrile, propylene carbonate, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide and tert-butanol. The results were correlated with an empirical H-bond acceptor solvent parameter. Previously unreported spectroscopic (UV- VIS, IRI H-1 and C-13 NMR) data for some of the compounds studied are also provided. Copyright (C) 2000 John Wiley & Sons. Ltd.