Kinetics and mechanism of the reaction of hydroxopentaaquarhodium(III) ion with L-proline in aqueous solution

Abstract

The kinetics of the reaction of L-proline (H2L+) with hydroxopentaaquarhodium(III) has been studied over the range 2.48 <= 10(3) [H2L+] <= 7.44, 3.5 <= pH <= 4.5, 50 degrees <= t <= 70 degrees at I = 0.1 mol dm(-3), (NaClO4). The reaction proceeds through an outersphere association beween [Rh(OH)](2+) and HL (conjugate base of H2L+) followed by transformation of the outer into an inner sphere complex (chelate is formed) by slow interchange. The anation rate constant k(an) of RhOH2+ at 25 degrees C and I = 0.1 mol dm(-3) (NaClO4) is estimated to be 1.56 x 10(-4) s(-1). Delta H-not equal and Delta S-not equal for k(an) path are found to be 54.5 +/- 3.5 kJ mol(-1) and -135.7 +/- 10.5 JK(-1) mol(-1) respectively. The. product of the reaction has been isolated and characterised. The substitution reaction follows an Ia path.