Quaternary ammonium bromide catalyzd chloride for bromide redistributions between carbon of alkyl halides and tin of tri-n-butyltin halides

Abstract Quaternary ammonium bromides have been found to strongly catalyze reversible chloride for bromide substitution reactions by tri-n-butyltin chloride on benzyl bromide and n-octyl bromide. However, they have only a small effect upon the rate of the corresponding reaction with benzhydryl bromide. It is suggested that the catalytic effect involves initial coordination of bromide ion with tri-n-butyltin chloride to form a nucleophilic anionic complex containing pentavalent tin which is reactive for backside displacements at carbon of sterically unhindered alkyl halides. No catalytic effects could be demonstrated, however, for ligands such as pyridine or N , N -dimethylformamide which could potentially form zwitterionic complexes with tri-n-butyltin chloride.