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

The kinetics of the reaction of picolinic acid (HL+) with hydroxopentaaquarhodium(III) have been studied over the range 2.58 less than or equal to 10(3) [HL+] less than or equal to 12.90, 3.68 less than or equal to pH less than or equal to 4.3, 45degrees less than or equal to t less than or equal to 65degrees and I = 0.1 mol dm(-3) (NaClO4). The reaction takes place via an outer-sphere association between RhOH2+ and HL (conjugate base of HL+) 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 2.34 x 10(-5) s(-1). DeltaH(not equal) and DeltaS(not equal) for k(an) path are evaluated. Anation reaction of RhOH2+ follows an I-a path.