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

Abstract

The kinetics of the reaction of nicotinic acid (H2L+) with hydroxopentaaquarhodium(III) has been studied over the range 2.58 less than or equal to 10(3)[H2L+] less than or equal to 12.9, 3.50 less than or equal to pH less than or equal to 4.30, 45degrees less than or equal to t less than or equal to 65degrees at I = 0.1 mol dm(-3) (NaClO4). The reaction takes place via an outer sphere association between RhOH2+ 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 25degrees and I = 0.1 mol dm(-3) (NaClO4) is estimated to be 3.78 x 10(-5) s(-1). Delta(#) and DeltaS(#) for k(an) path are found to be 33.3 +/- 4 kJ mol(-1) and -218 12 JK(-1) mol(-1) respectively. Anation reaction of RhOH2+ follows an I-a path.