ARENEDIAZONIUM SALTS - NEW PROBES OF THE INTERFACIAL COMPOSITIONS OF ASSOCIATION COLLOIDS .1. BASIC APPROACH, METHODS, AND ILLUSTRATIVE APPLICATIONS

Product yields from the reactions of two different arenediazonium salt s, z-ArN2+BF4-, bound to cetyltrimethylammonium halide ((CTA)X; X = Cl , Br) micelles and to aqueous three-component (CTA)X microemulsions co ntaining an alcohol (R'OH), either 1-butanol (BuOH)or 1-hexanol (HexOH ), are ''snap shots'' of the relative quantities of halide ion, water, and alcohol nucleophiles at the aggregates' interfaces. Yields of ary l ether, aryl halide, and phenol products measured simultaneously by H PLC are consistent with high concentrations of these nucleophiles in t he immediate vicinity of the aggregates' interfaces. The interfacial c oncentration of each nucleophile is estimated from the yield of its re spective product over wide ranges of (CTA)X and R'OH concentrations by assuming that the selectivities of the long-chain (hexadecyl), water- insoluble, aggregate-bound arenediazonium ions, 16-ArN2+, toward anion ic or neutral nucleophiles compared to water are the same as the selec tivities of the short-chain (methyl), water-soluble analogues, 1-ArN2, toward the same nucleophiles in aqueous solutions. The suitability o f dediazoniation reactions as interfacial probes and the basic assumpt ions used in our approach are described. The observed rate constants f or dediazoniation of the arenediazonium salts are almost completely in dependent of the salt, (CTA)X, and R'OH concentrations, consistent wit h rate-determining loss of N2 to give an aryl cation which reacts at d iffusion-controlled rates with available nucleophiles. Salt-induced sp ectral shifts indicate formation of ion pairs in the ground state, and all our data are consistent with a heterolytic dediazoniation mechani sm in which product distributions are determined by the equilibrium di stribution of the ensemble of ground-state arenediazonium cation.anion and arenediazonium cation-molecule intimate pairs. Comparisons with p revious results and potential applications are briefly discussed. The companion paper shows that ether product yields can also be used to es timate R'OH binding constants over a wide range of alcohol and surfact ant concentrations.