Maleic anhydride–hexamethylbenzene mixtures in methylcyclohexane solution and in the solid state. Part I. Physical properties

Abstract

KC (M-l) CL 2-04 f . 0.28 2.76 f 0.09 2.22 f 0.09 2-06 & 0-14 1.90 f 0-16 1.78 f 0.16 1-64 f 0.15 590 &-130 620 5 80 900 f 110 1140 f 120 1420 + 140 1690 -f 160 2130 f 180 2 1.56 f 0.15 2320 * 200 0 1.52 f 0.15 2420 f 210 $4 1.50 & 0-15 2420 & 220 e a 1.44 f 0.15 2420 f 240 2 1-35 f 0.18 2400 f 260 a 1.26 f 0.16 2300 f 300 bl, 1-45 f 0.16 1830 f 230 ' 1.49 f 0.16

Synthetic Aspects of Photochemical Electron Transfer Reactions

“…Accordingly, capture of the benzylic radical formed in this way by triplet oxygen would yield the hydroperoxide 262, a precursor by methanolysis and dehydration of the respective ether 258 and aldehyde 263. The higher oxidation products, 259 and 260, were shown to arise by secondary reaction of 258 and 263, respectively. In retrospect, a more reasonable route for production of 261 appears to be by sequential electron-proton transfers.…”

“…In an early study, Wasserman and his co-workers (197) uncovered unusual benzylic oxidation reactions of hexamethylbenzene 257 and suggested mechanisms involving direct arene-sensitizer interaction in a primary event following excitation. A hydrogen atom abstraction mechanism was proposed to rationalize the Methylene Blue sensitized transformation of 257 to the mono 258 and bis 259 ethers and the phthalide 260. Accordingly, capture of the benzylic radical formed in this way by triplet oxygen would yield the hydroperoxide 262, a precursor by methanolysis and dehydration of the respective ether 258 and aldehyde 263.…”

“…This sequential electron-proton transfer process, formally corresponding to hydrogen atom transfer, is responsible for several interesting carbon-carbon bond forming reactions of aromatic hydrocarbons. An early example of a photobenzylation reaction through this route is present in investigations of Paciszewski (259,260) (271) A detailed analysis of this system(272) has uncovered strong evidence in support of a sequential electron-proton transfer mechanism for this process. TF A triplet quenching by toluene does not display a primary deuterium isotope effect, consistent with a pathway for excited-state deactivation which involves reversible electron transfer rather than hydrogen atom abstraction.…”