Determination of the nucleophilic reactivity constants for a series of N-(n-propyl)-N′-(para-R-benzoyl)thioureas towards trans-[Pt(pyridine)2Cl2]

The relative nucleophilic reaction constants npt, for a series of N-(n-propyl)-N′-(para-R-benzoyl)thioureas (R=H, CH3O, (CH3)3C, Br, Cl, C7H15O, I, NO2) have been determined for the substrate trans-[PtCl2(pyridine)2] in methanol–water (75:25 v/v at 30 °C and μ=0.03), and are compared with that of unsubstituted thiourea. The bimolecular substitution reaction constants k2 were found to vary from 12.1±1.3 to 6.0±0.4 (for thiourea), corresponding to relative nucleophilicity constants of 4.08–3.78. A small but detectable influence of the substituent has been found on these constants, the npt values decreasing in the order H∼CH3O>Cl>C7H15O∼t-but∼I>Br>NO2>thiourea. Essentially however, the nucleophilicity of the series of N-(n-propyl)-N′-(para-R-benzoyl)-thioureas resembles that of thiourea.