Formation and reaction of Br2•- radicals in the ionic liquid methyltributylammonium bis(trifluoromethylsulfonyl)imide and in other solvents

Reaction of solvated electrons with BrCH2CH2Br produces Br- and .CH2CH2Br, which decomposes rapidly into CH2=CH2 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 (approximate to6 x 10(9) L mol(-1) s(-1)) to methanol (2.8 x 10(9) L mol(-1) s(-1)), ethanol (1.2 x 10(9) L mol(-1) s(-1)), isopropyl alcohol (1.2 x 10(9) L mol(-1) s(-1)), 1-propanol (7.5 x 10(8) L mol(-1) s(-1)), tert-butyl alcohol (3.0 x 10(8) L mol(-1) s(-1)), acetonitrile (2.0 x 10(7) L mol(-1) s(-1)), N,N-dimethylformamide (5.3 X 10(6) L mol(-1) s(-1)), the ionic liquid methyltributylammonium. bis(trifluoromethylsulfonyl)imide (1.1 x 10(6) L mol(-1) s(-1)), and hexamethylphosphoramide (less than or equal to8 X 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 anioji-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.