Micellar effects on the rates of formation and decomposition of the hydroxy Meisenheimer complex of 1,3,6,8-tetranitronaphthalene

Abstract

The surface-active cation hexadecyltrimethylammonium bromide (CTAB) increases, the anion sodium dodecyl sulphate (NaLS) decreases, and the uncharged polyoxyethylene (15) nonylphenol (lgepal CO-730) does not alter the equilibrium constant for the formation of a complex (II) between 1,3,6,8-tetranitronaphthalene (I) and hydroxide ions in aqueous solutions. These effects have been dissected into those influencing the second-order rate constant for the formation, k₁, and the first-order rate constant for the decomposition, k_–1, of complex (II). Micellar effects are primarily on k₁[k₁(CTAB)/k₁⁰= 36, k₁⁰/k₁(NaLS)= 43, k⁰_–1/k_–1(CTAB)= 2·8, and k⁰_–1/k_–1(NaLS)ca. 1]. Kinetic data on the effects of surfactant concentration on k₁ gave the binding constants between (I) and CTAB (1·9 × 10⁵| mol^–1), between (I) and NaLS (3·6 × 10³| mol^–1), and between (II) and CTAB (3·9 × 10⁵ l mol^–1). The nature of these micellar effects are discussed in terms of electrostatic interactions and are related to analogous micellar effects on nucleophilic aromatic substitutions.