ChemInform Abstract: Reaction of Tertiary Aliphatic Amines with Halogens. Kinetics and Products of the Reaction of Tribenzylamine with Molecular Bromine and Tribromide Ion.

Abstract

A reinvestigation of the reaction of tribenzylamine with bromine has proved that the crystalline product previously reported to be an amine·Br2 1 : 1 adduct of type (C6H5CH2)3NBr+Br– is actually a mixture of tribenzylammonium and NN-dibenzylbenzylidenaminium tribromides. A kinetic study carried out in 1,2-dichloroethane with the stopped-flow technique has shown the transient formation of a 1 : 1 tribenzylamine·Br2 charge-transfer complex having a formation constant Kf of 9.7(1.0) I mol–1 at 25 °C. This is followed by a fast oxidation-reduction reaction leading to NN-dibenzylbenylidenaminium bromide and HBr, which is captured by the amine to give tribenzylammonium bromide. Both bromide salts are instantaneously transformed, by association with the remaining Br2, into the corresponding tribromides, which are then consumed at a much slower rate by the oxidative cleavage of the amine. Tetrabutylammonium tribromide has been independently shown to react slowly with tribenzylamine through two processes, with respective rate constants at 25 °C k2Br3–== 3.1(0.4)× 10–4 and k2Br2≥ 8.9 × 102 l mol–1 s–1, the former interpretable as a bromide-assisted and the latter as an unassisted elimination of HBr from the 1 : 1 amine·Br2 charge-transfer complex.