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

Abstract

3-Methyl-4-phenyl-l,2,5-thiadiazole 1,l-dioxide (TMP), as well as 3,4-dimethyl-1,2,5-thiadiazole 1,l-dioxide (TMM), react with ethanol (EtOH), which adds to one of their C=N double bonds. The equilibrium constants for the addition reaction are measured in mixed acetonitrile (ACN) -EtOH solvents by means of UV spectroscopy in the case of TMP, and by I3c NMR spectroscopy in the case of TMM, since TMM presents only terminal UV absorption. Both equilibrium constants are also estimated through cyclic voltammetry (CV) experiments. In the case of TMP, the ethanol molecule adds to the C=N bond located on the methyl-substituted side of the substrate, according to 13c NMR spectroscopy and CV results. 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 that corresponding to T M P undergoes a relatively slow homogeneous second-order reaction with the substrate (k = 3 x lo2 M-' S-I). The equilibrium constant for EtOH addition and the voltammetric properties of the substrates are compared with those of the previously studied 3,4-diphenyl derivative (TPP).Key words: electrochemistry, thiadiazoles, structure-reactivity relations, kinetics.

Crystallographic study and molecular orbital calculations of 1,2,5-thiadiazole 1,1-dioxide derivatives

“…In Figure 7. HF/6±31G** electrostatic potential of 3-methyl-4-phenyl-1,2,5-thiadiazole 1,1-dioxide (II) on the molecular plane our studies on the nucleophilic addition of alcohols to the C=N double bond of 1,2,5-thiadiazole 1,1-dioxide derivatives, we have found that the addition reaction takes place at a measurable rate for I, II 36 and III. 5 The addition occurs preferentially on C(2) for II.…”

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

“…As a part of our electrochemical work on thiadiazoles, we have recently reported [16][17][18] that ethanol (EtOH) adds reversibly to 3,4-diphenyl-(1a; Scheme 1) or to 3methyl-4-phenyl-1,2,5-thiadiazole 1,1-dioxide (1b) in a 1:1 molar ratio to give the corresponding 1,2,5-thiadiazoline 1,1-dioxides [4-ethoxy-3,4-diphenyl (2a.EtOH) and 4-ethoxy-4-methyl-3-phenyl (2b.EtOH)].…”

Additions of water, hydroxide ions, alcohols and alkoxide ions to carbonyl and azomethine bonds

“…Thus 3-and 4-alkyl or aryl substituted 1,2,5-thiadiazole-1,1-dioxides have the ability to bind covalently water and alcohols. Spectroscopic 130,131 and electrochemical [131][132][133][134] studies proved additions of numerous alcohols to the thiaziazole ring either in a acetonitrile solution or using the same alcohol both as a reagent and as a solvent. The equilibria in acetonitrile solutions are rather slowly established.…”