Kinetics and intermediates in the several forward and reverse reactions of nitro-substituted arenediazonium ions with hydroxide ion

Abstract

Stopped- and quenched-flow kinetics and rapid-scanning u.v. spectrophotometry have been applied to the kinetics of the forward and reverse reactions of ArN₂⁺ with OH^–, where Ar bears one or more strongly electronegative substituents (Cl, NO₂), in which case the syn-diazotate (formed rapidly from the initially produced diazohydroxide) functions as a reactive intermediate leading to the thermodynamically favoured anti-diazotate. Measurements of forward and reverse rates in some cases have enabled the determination of equilibrium constants for both acid–base and isomerisation reactions. It has thus been possible to extend the number of compounds for which these data are available, and hence derive more complete linear free energy relationships for both kinetic and equilibrium constants. (These include determinations of σ and σ⁺ parameters for the 2-nitro- and 2-chloro-groups.) A complete description of the quenched-flow apparatus is provided. Time-resolved u.v.–visible spectra of the transient syn-diazotate have been obtained for the 4-nitro-, 2-chloro-4-nitro-, 2-chloro-4-nitro-, and 2,4-dinitro-substituted materials.