| Summary: | The kinetics and mechanisms of the reactions of arenediazonium cations, ArN2+, with a selection of suitably activated naphthalene-based coupling compounds, including some of particular industrial significance, have been investigated over a wider pH range than before. The dependence of the coupling rate constant on both ring substituents on the arenediazonium cations and the steric and electronic effects of substituent groups on the coupler have been rationalised. It has been shown that the σ+-constants give a better correlation than the Hammett σ-constants for the rate coefficients for the reaction of ArN2+ with the commercially important sodium 2,3-dihydroxynaphthalene-6-sulphonate. When used as a buffer, borax drastically modifies the rate constant -pH profile of certain coupling reactions as a result of the production of a cyclic complex between the coupler and borate ions. The crystal structure of an aryldiazotate, namely disodium syn-benzenedlazotate-4-sulphonate, has been determined for the first time, and the diazotate group shown to exhibit a 'cis' configuration in contrast to the conclusion reached on kinetic grounds by Sterba. The kinetics and mechanisms of the highly complex equilibria between ArN2+ and the corresponding aryldiazotates have been studied and some rate and equilibrium constants measured; these results, together with those from the literature, have been plotted against substituent constants to obtain ρ-values. Compounds having 2- substituents were included after determination of their σ-constants, although the data points from the 2,6-dichloro-4-nitro compound was found to deviate substantially from certain linear free energy relationships. The large rate constant of the N-O bond splitting of syn-aryldiazohydroxides containing strongly electron-withdrawing substituents were measured with a purpose-built 'quenched stopped flow' apparatus. These values enabled extension of those already available to give a good Hammett plot.
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