Mechanism of octahedral substitutions in non-aqueous media. Part IV. Rates of replacement reactions in trans-chloroammine- and cis-chloroaquo-bis(ethylenediamine)cobalt(III) ions in alcoholic solutions

Abstract

In methanolic solution (as in aqueous solution) the chloride of trans-chloroamminebis(ethylenediamine)cobalt(III) ion can be easily replaced by a nucleophilic reagent. The specific rate of this replacement is independent of the thiocyanate concentration but shows a nearly linear dependence on the reciprocal perchloric acid concentration. At elevated temperatures (95°) the NH₃ group can be also replaced by thiocyanate, giving the di-isothiocyanatocomplex ion. The replacement reactions in the cis-chloroaquo-complex ion in alcoholic solutions do not give the same reaction products as in aqueous solutions. In aqueous solution the diaquo-complex is formed whilst in methanol or ethanol the cis-chloroaquo-complex ion reacts spontaneously with its anion, giving quantitatively trans-[Co en₂ClX]X with the rates independent of the anion concentration. The mechanism of these reactions is discussed.