SYNTHESIS AND KINETICS OF THE ACID-HYDROLYSIS OF THE OTHLOOXALATO-S,O-BIS(ETHYLENEDIAMINE)CHROMIUM(III) COMPLEX

Cis-[Cr(en)(2)(SC2O3)]Cl . H2O has been synthesized by a new method in volving the reaction of cis-[Cr(en)(2)Cl-2]Cl with K2SC2O3 at 60 degre es C and the kinetics of the acidic aquation of this complex have been studied. The complex has been characterized by IR and electronic spec troscopic techniques. The aquation of the purified product was carried out at 30, 40 and 50 degrees C in acidic media at constant ionic stre ngth. The experimental result indicates a pH-dependent aquation of the compound in HCl solutions to yield H2S and ethylenediamine. The plot of the rate of the reaction versus the square of the proton concentrat ion, [H+](2), produces a straight line giving the pseudo-first-order r ate constant, k(obs). Activation energies were found to be proportiona l with the entropies in various acidic solutions. The ''isokinetic tem perature'' of 285 K and the free energy of activation, Delta G double dagger = 94.7 kJ mol(-1), were determined from the linear relationship . The results of experiments for the aquation of this compound suggest a mechanism through formation of a conjugate acid of an asymmetric at om, and the Cr-S bond cleavage is considered as the rate determining s tep.