Kinetics and mechanism of the addition of triphenylphosphoniocyclopentadienide to tetrahalo-p-benzoquinones. Part III. The disubstitution of chloranil and bromanil

Chloranil and bromanil react with an excess of triphenylphosphoniocyclopentadienide to yield the 2,5- and 2,6-disubstituted quinone derivatives through two parallel, second-order reactions. Kinetic data suggest that the reaction proceeds in two steps, involving addition to form a polar betaine intermediate followed by elimination of hydrogen halide. The activation parameters strongly suggest that the loss of halide is of the E(1) type. The empirical rate law has been established carrying but a multi-response non-linear least-squares analysis followed by a Gaussian de-convolution of the visible spectra of the reaction mixtures.