Synthesis, DFT and kinetic studies of chromic S-methyldithizone

Abstract

Dithizone is one of the most well-known trace-metal analysis reagents, however, its S-alkylated derivatives received very little attention up to date. Synthesis, kinetic studies of its photo- and chronochromic reactions, as well as DFT and TDDFT results are presented here. For comparitive purposes the corresponding phenylmercury complex was also synthesized and included in this study. Blue-shifts in λmax of the S-methylated compounds are in excess of 60 nm as compared to the metal complex. Relative geometry optimized energies, atomic charge distribution in conjunction with 1H NMR, as well as TDDFTs all point to the pink syn geometry of S-methyldithizone as the prevalent isomer, with the yellow anti geometry only of slightly higher (3.8 kJ/mol) energy. B3LYP provides significantly better UV–visible spectrum approximation than LC-BLYP, OLYP and PW91. At 20 °C the rate of the chronochromic reaction is 0.0073 s−1 in chloroform, and that of the photochromic return reaction is 0.0023 s−1 in ethanol.