SURFACTANT EFFECTS UPON NUCLEOPHILIC AROMATIC-SUBSTITUTION - OBSERVATION OF DOUBLE RATE MAXIMA

First order rate constants of the reaction of 2,4-dinitrochloronaphthalene (DNCN) with excess OH- go through double maxima with increasing concentrations of cetyltrialkylammonium chloride or bromide (C16H33NR3X; CTAX, R = Me; CTEAX, R = Et; CTPAX, R = n-Pr; CTBAX, R = n-Bu; X = Cl, Br). The relative heights of the two maxima depend upon [DNCN] and there is only a single maximum with very dilute DNCN (4 × 10-6M) and with added NaBr. There are also double rate maxima in reactions of DNCN with N3- and with morpholine. The first rate maxima are ascribed to reactions mediated by submicellar assemblies and the second to reaction in micelles. Tri-n-octylalkylammonium mesylates (alkyl = Me, Et) do not micellize but they speed reactions of DNCN with OH- and N3-. Rates of reaction of OH- with p-nitrophenyl diphenyl phosphate go through a single maximum in micellized CTBABr. These observations suggest that interaction of submicellar assemblies activates the substrate toward nucleophiles but that micelles assist reaction by concentrating both reactants in the small interfacial volume. © 1992.