Nucleophilic reactivity of the azide ion in various solvents

The kinetics of the reactions of the azide ion with benzhydrylium ions were investigated photometrically in different alcohol/acetonitrile mixtures and in DMSO at 20 degrees C. Since the competing reactions of the benzhydrylium ions with the solvents are generally slower, the second-order rate constants of the reactions of the benzhydrylium ions with the azide ion can unambiguously be determined to yield nucleophilicity parameters N and s for the azide ion in different alcohols. Several reactions of the benzhydrylium, ions with the azide ion are reversible, which allowed the determination of the equilibrium constants and the rate constants of the reverse reactions. It is found that benzhydrylium ions with annelated six-membered rings are better electrophiles and better electrofuges than the five-membered ring analogs due to the lower intrinsic barriers of the former reactions. Copyright (c) 2007 John Wiley & Sons, Ltd.