Revisiting the reactions of nucleophiles with arenediazonium ions: dediazoniation of arenediazonium salts in aqueous and micellar solutions containing alkyl sulfates and alkanesulfonates and an ab initio analysis of the reaction pathway

Abstract

Dediazoniation of 2,4,6-trimethylbenzenediazonium tetrafluoroborate, 1-ArN₂BF₄ (for the z-Ar compounds described in this paper, z refers to the length of the carbon chain of the substituent at C4 of the benzene ring), in aqueous solutions containing sodium methyl sulfate, NaMeSO₄, or sodium methanesulfonate, NaMeSO₃, yields 2,4,6-trimethylphenol, 1-ArOH, 2,4,6-trimethylphenyl methyl sulfate, 1-ArOSO₃Me and 2,4,6-trimethylphenyl methanesulfonate, 1-ArO₃SMe, respectively. The relative yields of 1-ArO₃SMe or 1-ArOSO₃Me and 1-ArOH depend on the NaMeSO₄ or NaMeSO₃ concentrations. 4-n-Hexadecyl-2,6-dimethylbenzenediazonium tetrafluoroborate, 16-ArN₂BF₄, was used to determine the local head group concentration in sodium dodecyl sulfate and sodium dodecanesulfonate micelles by chemical trapping comparing the relative product yields with those obtained in water using the short chain analogs.

Ab initio calculations of the spontaneous dediazoniation of phenyldiazonium ion in the gas phase, as well as in aqueous solution with, or without, added MeSO₃⁻, yield potential energy surfaces for the reaction. For this model the calculated and experimental values of the spontaneous dediazoniation rate constants in aqueous solution, as well as the product composition, were similar to those obtained with 1-ArN₂⁺. These results suggest that in aqueous solution nucleophiles can only compete with water if a diazonium ion·nucleophile complex is formed prior to N₂ loss. Calculations show that the addition of nucleophiles to the arenediazonium ion occurs without a saddle point in the potential energy surface, suggesting that the free phenyl cation is not an obligatory intermediate in aqueous solutions.

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