A new method for the determination of the rate constants for the disproportionation of semiquinone radicals from nonstationary kinetics of Chain reactions between quinoneimines and hydroquinones

A new method is suggested for the determination of the rate constants for the disproportionation of semiquinone radicals k ₆ from the kinetics of chain reactions between quinoneimines and hydroquinones under nonstationary conditions. The k ₆ values were determined in solvents of various natures, including comparatively low-polarity solvents in which hydroquinones are poorly soluble. The k ₆ values were found from the dependence of the degree of quinoneimine concentration lowering during a certain time (∼20 s) after reaction beginning (when the reaction occurred under nonstationary conditions) on the rate of initiation. Techniques for overcoming difficulties caused by the absence of the limiting chain propagation stage in reactions between quinoneimines and hydroquinones were suggested. The developed method of the nonstationary kinetics of chain reactions was applied to selectively determine the rate constant for the disproportionation of 2,5-dichloroseniquinone radicals, which is one of parallel chain termination stages in the chain reaction between N,N’-diphenyl-1,4-benzoquinonediimine and 2,5-dichlorohydroquinone, k ₆ = (5.8−7.1) × 10⁶ l/(mol s) in chlorobenzene at 298 K.