ABSOLUTE KINETICS OF AMINIUM RADICAL REACTIONS WITH OLEFINS IN ACETONITRILE SOLUTION

Photolysis of N-nitrosamines in acidic acetonitrile produces aminium r adical cations via protonation of the initially-formed aminyl radicals . The kinetics of these species can be monitored by transient UV spect roscopy via their absorption band which is found at ca. 300 nm in the case of the piperidinium radical, for example. By measuring the aminiu m radicals' lifetimes as a function of the concentration of added olef in, absolute values for the bimolecular rate constants for the additio n reactions were obtained. In the case of the piperidinium radical, th ese rate constants varied from <1 x 10(6) M(-1) s(-1) for acrylonitril e to 1.1 +/- 0.1 x 10(9) M(-1) s(-1) for 1,1-diphenylethylene and gene rally increased with decreasing ionization potential of the olefin, th us confirming the electrophilic nature of the piperidinium radical. Th e rate constants for analogous reactions of diethylaminium radicals we re 1.5-25 times smaller indicating the importance of steric factors in aminium radical additions to olefins. The rate constant for the intra molecular 1,5-addition of the secondary aminium radical cation to an u nactivated double bond is estimated to be ca. 1 x 10(6) s(-1), but the intramolecular addition rate constant increases to >1 x 10(8) s(-1) u pon the phenyl substitution at the olefinic terminus.