Formation and Reaction of Br₂•- Radicals in the Ionic Liquid Methyltributylammonium Bis(trifluoromethylsulfonyl)imide and in Other Solvents

Reaction of solvated electrons with BrCH 2 CH 2 Br produces Br - and • CH 2 CH 2 Br, which decomposes rapidly into CH 2 CH 2 and Br • . Reaction of Br • with Br - forms Br 2 •- . The stability of Br 2 •- is much greater in the ionic liquid and in acetonitrile than in water or alcohols. The rate constant for oxidation of chlorpromazine by Br 2 •- radicals decreases upon changing the solvent from water (≈6 × 10 9 L mol -1 s -1 ) to methanol (2.8 × 10 9 L mol -1 s -1 ), ethanol (1.2 × 10 9 L mol -1 s -1 ), isopropyl alcohol (1.2 × 10 9 L mol -1 s -1 ), 1-propanol (7.5 × 10 8 L mol -1 s -1 ), tert -butyl alcohol (3.0 × 10 8 L mol -1 s -1 ), acetonitrile (2.0 × 10 7 L mol -1 s -1 ), N, N -dimethylformamide (5.3 × 10 6 L mol -1 s -1 ), the ionic liquid methyltributylammonium bis(trifluoromethylsulfonyl)imide (1.1 × 10 6 L mol -1 s -1 ), and hexamethylphosphoramide (≤8 × 10 4 L mol -1 s -1 ). The rate constants show poor correlation with typical solvent polarity parameters, but reasonable correlations with hydrogen bond donor acidity and with anion-solvation tendency parameters. From the good correlation with the free energy of transfer of Br - ions from water to the various solvents, it is suggested that the change in the energy of solvation of Br - in the different solvents is the main factor that affects the rate constant of the reaction through its effect on the reduction potential of Br 2 •- and the driving force of the reaction.