Kinetics and mechanism of the reaction of hydroxopentaaquarhodium(III) ion with L-aspartic acid in aqueous media

Abstract

The kinetics of the reaction of L-aspartic acid (H₃L⁺) with hydroxopentaaquarhodium (III) has been studied over the range 2.58≤10³[H₃L⁺] ≤ 12.90, 3.49 ≤<i>p</i>H≤ 4.3, 50°≤ <i>t </i>≤65 °C and <i>I=</i>0.1mol dm^-3(NaClO₄).The reaction takes place via an outer sphere association between RhOH²⁺ and (H₃L⁺) followed by transformation of the outer into an inner-sphere complex (chelate is formed) by slow interchange. The anation rate constant RhOH³⁺ at 25°C and <i>I= </i>0.1mol dm^- (NaClO₄) is found to be 2.2×10^-6s^-l. Δ<i>H^#</i> and Δ<i>S^#</i> for <i>k</i>_an path are found to be 62.0±1.2 kJ mol^-1 and -120.8 ±3.4 JK^-1mol^-1 respectively. Anation reaction of RhOH²⁺ follows an Ia path.