Reactivities of free ions and crown ether-complexes ion pairs in the protonation of fluorenylsodium by 9-methylfluorene

Abstract

The mechanism of the proton abstraction reaction between 9-methylfluorene and fluorenylsodium or its complex with dimethyldibenzo-18-crown-6 was studied spectrophotometrically in tetrahydropyran (THP), 1,2-dimethoxyethane (DME), and tetrahydrofuran (THF). Ion pairs as well as free carbanions participate in the reaction. Their rate constants and the equilibrium constant of the reaction were determined. The rate constant of the free ions increases from 85 in THF to 1 300 I mol^–1 s^–1 in THP. These values are much higher than the rate constants for the tight ion pairs or those for DME- or crown-complexed loose ion pairs, all of which are equal or less than 2 I mol^–1 s^–1. The equilibrium constant varies between 1 and 2.4 depending on the solvent and structure of the ion pair.