Chain mechanism of the reactions of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol and 1-decanethiol

Abstract

The kinetics of the reactions of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol and 1-decanethiol in chlorobenzene at 343 K has been investigated spectrophotometrically in an argon atmosphere with monitoring of the disappearance of quinone diimine as its absorbance in the visible range. The acceleration of the reactions in the presence of initiators—tetraphenylhydrazine and azobisisobutyronitrile—indicates that the reactions proceed via a chain mechanism under the chosen experimental conditions. The chain length of the reactions in the absence of an initiator is estimated: ν ≈ 10 units in the reaction of quinone diimine with thiophenol and ν ≈ 100 units in the reaction with 1-decanethiol at a quinone diimine concentration of about 10−4 mol/L and thiol concentrations of about 10−3 mol/L. The dependence of the kinetic parameters of the initiated reaction on the thiophenol concentration suggests that the reaction of the thiyl radical with quinone diimine is the rate-determining step of chain propagation. The rate constant of this reaction is estimated at k pr = 3.2 × 105 L mol−1 s−1. The rates of chain initiation due to the direct interaction of the initial reactants are estimated. In these reactions, the homolytic cleavage of the S-H bond occurs in the thiol, due to which, other conditions being equal, the radical formation rate in the quinone diiminethiophenol system is at least two orders of magnitude higher than that in the quinone diimine-1-decanethiol, in which the strength of S-H bond is higher. A radical chain mechanism is proposed for the reaction of quinone diimine with the thiols on the basis of the data obtained.