The Grignard Reagent Formation Reaction of 2‐Chloro‐1,1,1‐triphenylethane Revisited

Abstract

AbstractThe reaction of 2‐chloro‐1,1,1‐triphenylethane (1) with magnesium in THF has been reinvestigated. The reaction produced a dark‐red solution and after deuterolysis with D2O, 1,1,1‐triphenylethane (2; 16 %), 2‐D‐1,1,1‐triphenylethane (3; 52 %) and 1,1,2‐triphenylethene (4; 26 %) were isolated. Rate constants for phenyl migration in the 2,2,2‐triphenylethyl radical were measured directly between 23 °C and 55 °C; the reaction is described by log k = 11.2 – 7.5/2.3 RT [kcal/mol] and the rate constant for rearrangement at 20 °C is 4.0 × 105 s–1. The combined results support the intermediate formation of radicals in the reaction of chloride 1 with magnesium. The red colour of the reaction mixture, however, indicates the formation of a carbanionic species, which has not yet been identified. The diffusion model for Grignard formation reactions of Garst et al. is in line with the product distribution. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)