Organotin halide equilibria. Part III. Comparison of the stability constants of 2,2′-bipyridyl adducts of diorganotin di-isothiocyanates and dichlorides in benzene and toluene solutions

Abstract

Stability constants have been obtained for dialkyltin di-isothiocyanate–2,2′-bipyridyl adducts, R2Sn(NCS)2,bipy (R = Bu, octyl), and dioctyltin dichloride–2,2′-bipyridyl adducts, octyl2SnCl2,bipy, in benzene solution at 30, 35, and 40 °C. Some values in toluene solution are also reported. Comparisons of these stability constants show that the di-isothiocyanates are considerably better acceptors than the dichloride (by factors of ca. 500). The enthalpy (–ΔH/kcal mol–1) and entropy of formation (–ΔS/cal mol–1 K–1) of the adducts were for Bu2Sn(NCS)2, bipy, octyl2Sn(NCS)2,bipy, and octyl2SnCl2,bipy in benzene solution 16·8, 38·2; 17·2, 38·4; and 12·7 and 34·8, respectively. The values for octyl2SnCl2 in toluene were 12·6 and 35·1. Spectral indications of [R2Sn(NCS)2]2,bipy adducts in solution were obtained.