Kinetics of the formation of the mandelatoiron(III) complex

Abstract

The kinetics of formation of the monomadelatoiron(III) complex have been studied over the range 0–25°C with a stopped-flow technique. Variation of acidity has enabled the derivation of reaction rates for reaction of both the Fe³⁺ and FeOH²⁺ ions. At 25°, the rate constant for the Fe³⁺– mandelic acid reaction is 4·0 l. mole^–1 sec.^–1 and that of FeOH²⁺–mandelic acid is 2·56 × 10³ l. mole^–1 sec.^–1. Thermodynamic data for the reaction of the hydroxo-complex are ΔH‡= 6 ± 2 kcal. mole^–1 and ΔS‡=–25 ± 5 e.u. The mechanism proposed is consistent with an S_N1 reaction involving loss of a water molecule in the rate-determining step.