Maleic anhydride with hexamethylbenzene

Maleic anhydride and hexamethylbenzene form a 1 1 charge-transfer complex in methylcyclohexane solvent with a UV maximum at 340 tx. Ultraviolet irradiation of these solutions brings about the formation of carbon dioxide, pentamethylbenzylsuccinic anhydride, and resinous products (see Chapter 6). Analytical data suggest the polymeric material has a decarboxylated MA building block. Charge-transfer complexes were not detected in solid-state mixtures of MA and pentamethyl-benzene. Ultraviolet irradiation of these solid mixtures gives cyclic dimer, 1,2,3,4-cyclobutanetetracarboxylic anhydride 2, and resinous products. Pentamethylbenzylsuccinic anhydride, due to the possible absence of charge-transfer complexes, was not isolated from the solid-state photoreaction. 

In a related example, the [D, A] complex of hexamethylbenzene and maleic anhydride reaches a photostationary state with no productive reaction (Scheme 17). However, if the photoirradiation is carried out in the presence of an acid, the anion radical in the resulting contact ion pair14 is readily protonated, and the redox equilibrium is driven toward the coupling (in competition with the back electron transfer) to yield the photoadduct.81... 

Bryce-Smith and Gilbert have shown that toluene, t-butylbenzene, chlorobenzene, o- andp-xylene, and biphenyl all undergo photoaddition to maleic anhydride, yielding 1 2 adducts [33], All the substituents decrease the rate of formation of adducts. Benzonitrile, nitrobenzene, phenol, methyl benzoate, durene, hexamethylbenzene, naphthalene, and biphenylene fail to undergo the addition of these, benzonitrile, nitrobenzene, methyl benzoate, and biphenylene do not form charge-transfer complexes. Bradshaw [34] found that various alkylben-zenes give 1 2 adducts with maleic anhydride upon photosensitization with acetophenone. 

In the related photochemical context, the EDA complex of hexamethylbenzene and maleic anhydride merely reaches a photostationary state (equation 15 Scheme 4) with no productive photochemist, except when acid is present to trap the acceptor anion on its way to the photoadduct in equation (16). ... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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