Micellar-promoted homolytic dediazoniation of p-nitrobenzenediazonium tetrafluoroborate

We have examined the kinetics and mechanism of dediazoniation of p-nitrobenzenediazonium tetrafluoroborate (PNBD) in aqueous micellar solutions of sodium dodecyl sulfate (SDS) and copper dodecyl sulfate (Cu(SD)(2)) at different H3O+ and NaCl concentrations by combining spectrophotometric and highperformance 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. H-1 NMR data indicate that the -N-2(+) group of PNBD is preferentially located 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 PNBD and the sulfate headgroup of the surfactants is not significant. HPLC analysis of dediazoniation products indicates that, in the absence of micelles, only the heterolytic products p-nitrophenol, ArOH, and p-nitrochlorobenzene, ArCl, are detected in important amounts. In the presence of micelles, significant quantities of the reduction product p-nitrobenzene, ArH, are formed, its yield being dependent on both [H3O+] and [SDS], suggesting that in micellar systems a new dediazoniation mechanism, homolytic, operates simultaneously with the heterolytic one. Analysis of the kinetic data indicates that both mechanisms are competitive, being the heterolytic one predominant under all experimental conditions employed.