Effect of solvent on the reactions of coordination complexes. Part 10. kinetics of solvolysis of cis(chloro)(1-amino-propan-2-ol)bis-(ethylenediamine)cobalt(III) in methanol + water, propan-2-ol + water, and t-butanol + water media

✍ Scribed by Anadi C. Dash; Prafulla K. Das

• Publisher: John Wiley and Sons
• Year: 1990
• Tongue: English
• Weight: 574 KB
• Volume: 22
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550220309

✦ Synopsis

Abstract

The solvolysis of cis(chloro)(1‐amino‐propan‐2‐ol)bis(ethylenediamine)cobalt(III) in aqueous alcoholic media using methanol, propan‐2‐ol, t‐butanol as cosolvents, resulted in the formation of the (N,O) chelated product__cis__[Co(en)~2~(NH~2~CH~2~CHOHCH~3~)]^3+^. The pseudo first order rate constant decreased with increasing molfraction (X~org~) of alcohols, the decrease being less marked as the bulkiness of hydrophobic moiety of alcohol increased. The plots of log 𝓀~obs~ vs. reciprocal of the bulk dielectric constant of the solvents, log 𝓀~obs~ vs. Grunwald‐Winstein solvent parameter and log 𝓀~obs~, vs. X~obs~ under isodielectric condition (D~s~ = 50, at 50°C) for CH~3~OH/H~2~O, C~2~H~5~OH/H~2~O, (CH~3~)~2~CHOH/H~2~O, (CH~3~)~3~COH/H~2~O, (CH~2~)~2~(OH)~2~/H~2~O, and (CH~3~)~2~ C  O/H~2~O in water rich media indicated that both solvent structural effects and presumably the hydrophobic interaction appreciably mediate the reaction. The calculated values of the relative transfer free energy at 25°C[ΔG~t~(C^3−^)‐ΔG~t~(i.s)~(s←w)~] where C^3+^ and i.s. denote the dissociative transition state {cis[Co(en)~2~(NH~2~CH~2~CHOHCH~3~)]^3+^}* and the initial state, respectively, indicated that the tripositive transition state is more effectively solvated by the mixed solvent media, than the dipositive initial state, the effect appeared to be more significant with increasing X~org~. The plots of activation enthalpy and entropy against X~org~ exhibited maxima and minima indicating that enthalpy and entropy changes associated with the solvent shell reorganization of the reactant contribute to the overall activation parameters.