Effects of Monovalent and Divalent Anionic Dodecyl Sulfate Surfactants on the Dediazoniation of 2-, 3-, and 4-Methylbenzenediazonium Tetrafluoroborate

Abstract

We have examined the kinetics and mechanism of dediazoniation of 2-, 3- and 4-methylbenzenediazonium tetrafluoroborate (OMBD, MMBD, and PMBD) in aqueous micellar solutions of sodium dodecyl sulfate and copper dodecyl sulfate at two different NaCl concentrations by combining spectrophotometric and high-performance liquid chromatography (HPLC) measurements. The method allows simultaneous determination of product yields and rates of formation for all dediazoniation products and, indirectly, the rate of decomposition of the diazonium salt. The preferential location of OMBD, MMBD, and PMBD is in the Stern layer, a very anisotropic region. A substantial fraction of diazonium ions are bonded to the micellar aggregates, and formation of strong ion pairs between OMBD, MMBD, and PMBD diazonium salts with the sulfate headgroup of the surfactants is not significant. HPLC analysis of dediazoniation products indicates that, within experimental error, quantitative conversion to products is achieved, with cresol as the major product. Observed rate constants for the dediazoniation reaction in the presence of both monovalent and divalent surfactants are constant for OMBD but decrease slightly for MMBD and PMBD with increasing surfactant concentration. The data are interpreted in terms of the polarity of the environment of diazonium salts in the micellar aggregate. All evidence is consistent with an Dn + An mechanism, i.e., rate-determining formation of an aryl cation that reacts immediately with any available nucleophile.