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

Abstract

2LSChloranil and bromanil react with an excess of triphenylphosphoniocyclopentadienide to yield the 2 5and 2,6-disubstituted quinone derivatives through t w o parallel, second-order reactions. Kinetic data suggest that the reaction proceeds in t w o steps, involving addition to form a polar betaine intermediate followed b y elimination of hydrogen halide. The activation parameters strongly suggest that the loss of halide is of the E, type. The empirical rate law has been established carrying out a multi-response non-linear least-squares analysis followed b y a Gaussian de-convolution of the visible spectra of the reaction mixtures.The reaction of triarylphosphoniocyclopentadienides 1 with tetrahalo-p-benzoquinones 2 proceeds to give monosubstituted products 3 in virtually quantitative yield which have been characterized by UV spectroscropy (A = 700 nm), multinuclear NMR and X-ray ~rystallography.~-~ @+Ar,

Time-Resolved Resonance Raman and Density Functional Studies on the Ground State and Short-Lived Intermediates of Tetrabromo-p-benzoquinone

“…Quinones are involved in a wide range of phenomenon from naturally occurring biological processes to chemical reactions. , Some of the most interesting reactions of quinones proceed via their photochemically created transient states. Several photoinduced reactions are known, e.g., addition to unsaturated compounds such as olefins, styrenes, acetylenes, and heteroatomic systems. − Further, because of their extensive use as electron acceptors in charge-transfer salts, they are subjects of several studies for their unique conduction properties . Although the four haloanils and the parent benzoquinone show very different properties, experimental efforts have largely concentrated on the parent quinone − and its fluorinated and chlorinated analogues. − Since their electron affinities vary from 1.86 eV for p -benzoquinone to 2.95 eV for fluoranil, the effect of different substitutions on the reactivities of these quinones is expected to be significant.…”

“…Several photoinduced reactions are known, e.g., addition to unsaturated compounds such as olefins, styrenes, acetylenes, and heteroatomic systems. [3][4][5] Further, because of their extensive use as electron acceptors in charge-transfer salts, they are subjects of several studies for their unique conduction properties. 6 Although the four haloanils and the parent benzoquinone show very different properties, experimental efforts have largely concentrated on the parent quinone [7][8][9][10][11][12][13][14][15][16][17][18][19] and its fluorinated and chlorinated analogues.…”