Micellar Catalysis of Organic Reactions. XXVI. S_NAr Reactions of Azide Ions

Abstract

The azidodehalogenation of a number of aromatic compounds has been studied in the presence of micelles of cetyltrimethylammonium bromide (ctab). The variation of the observed rate of reaction with ctab concentration has been treated by using the model of Rodenas and Vera to determine the rate constant for reaction in the micellar pseudo-phase, k₂^m, the binding constant of the substrate to the micelle, K_s, and the nucleophile-micellar counter ion exchange constant K^Az_Br :. The ratio of the rate constants in the micellar pseudo-phase and in water varied between 0.9 and 52. For reactions involving the production of a dianionic intermediate the largest catalysis was found for compounds containing two nitro groups to stabilize the double negative charge. In addition significant differences in the catalysis were found between compounds having the reaction centre at the micelle-water interface and those for which the reaction centre was more buried inside the micelle. As previously reported the resulting aryl azides undergo cyclization to form a benzofuroxan if a nitro group is located ortho to the azide group. Furthermore, a reversible photochemical reaction was detected for two compounds having a carboxylate group ortho to the azide group.