Kinetics and mechanism of the chain reaction of N,N'-diphenyl-1,4-benzoquinone diimine with thiophenol in chlorobenzene

The regularities of the reaction of N,N'-diphenyl-1,4-benzoquinone diimine with thiophenol in chlorobenzene at 343 K were studied by kinetic spectrophotometry. The reaction orders were determined for the components under the conditions when the concentration of thiophenol considerably exceeded that of quinone diimine: n (QDI) = 1.5 for quinone diimine and n (PhSH) = 1.0 for thiophenol. The initiators (azo-bis-isobutyronitrile and tetraphenylhydrazine) were found to considerably accelerate the reaction, which suggests that the reaction proceeded by the chain mechanism. The reaction chain length changed from one dozen to several dozens of units depending on the experimental conditions. The chain mechanism (kinetic scheme) of the reaction was suggested; it agrees with the experimental data, according to which the chains are initiated simultaneously by the second and third order reactions between quinone diimine and thiophenol. The rate constants of these stages at 343 K were determined: k (bi) = 0.014 +/- 0.002 L mol(-1)s(-1); k (tri) = 22.8 +/- 1.8 L-2 mol(-2)s(-1). The limiting stage of chain propagation was concluded to be the reaction of the thiyl radical with quinone diimine; the rate constant of this stage was evaluated: k (pr) similar to 1.3 x 10(6) L mol(-1) s(-1) at 343 K.