Cation Radicals as Intermediates in Aromatic Halogenation with Iodine Monochloride: Solvent and Salt Effects on the Competition between Chlorination and Iodination
摘要:
Three distinct classes of substitutional reactivity can be discerned in the halogenation of a series of methyl-substituted methoxybenzenes (ArH) with iodine monochloride (ICl), namely, exclusive iodination, exclusive chlorination, and mixed iodination/chlorination. Spectral studies establish the prior formation of the charge-transfer complex [ArH,ICl] which suffers electron transfer to afford the reactive triad [ArH.+, I-., Cl-] according to Scheme 1. Separate reactivity studies show that chlorination and iodination can result from the quenching of the aromatic cation radical by chloride and iodine (atom), respectively. Iodination versus chlorination thus represents the competition between radical-pair and ion-pair collapse from the reactive triad, and it is predictably modulated by solvent polarity and added salt.
Unexpected dimeric products from the amidomethylation of pentasubstituted benzenes
作者:David Wiedenfeld、Mark A. Minton、Vladimir N. Nesterov、David R. Glass、Crystal L. Montoya
DOI:10.1016/j.tetlet.2004.03.175
日期:2004.5
An isomeric series of unexpected diarylmethane products with flexible substituents, isolated from amidomethylation reactions of p-dimethoxybenzene derivatives, was analyzed by X-ray crystallography to reveal novel solid-state structures, two of which have identical elemental cell parameters.
Radical cation mechanism of aromatic halogenation by halogens or iodine chloride in 1,1,1,3,3,3-hexafluoropropan-2-ol
作者:Lennart Eberson、Michael P. Hartshorn、Finn Radner、Ola Persson
DOI:10.1039/a705393b
日期:——
The reaction between aromatic compounds ArH and halogenating agents, viz. iodine chloride, chlorine, bromine, iodine, N-bromosuccinimide and N-chlorosuccinimide, in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) has been investigated. EPR spectroscopy established that these reagents produced persistent radical cations ArH˙+ from ArH with Erev(ArH˙+/ArH) up to 1.6, 1.3, 1.4, 1.1, 1.5 and 1.2 V vs. Ag/AgCl