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

The 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 degrees C and 55 degrees C; the reaction is described by log k = 11.2 - 7.5/2.3 RT [kcal/mol] the rate constant for rearrangement at 20 degrees C is 4.0X10(5) 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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)