Some Photochemistry of Maleic Anhydride: the Addition to Benzene and the Dimerization

Citation

Hardham, William Morgan (1965) Some Photochemistry of Maleic Anhydride: the Addition to Benzene and the Dimerization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/g5sc-av21. https://resolver.caltech.edu/CaltechETD:etd-02182003-110831

Abstract

The detailed mechanism of the sensitized and unsensitized addition of maleic anhydride (MA) to benzene has been determined. By suitable quenching studies on both additions and use of a variety of sensitizers a triplet mechanism has been established. Studies of the variation of initial quantum yield with concentration of reactants showed the benzene and MA effects to be independent. This information, together with the fact that the benzene-MA charge transfer complex is a better quencher of benzophenone triplets than free MA by a factor of 13 led by elimination to the following mechanism. Energy transfer or direct absorption leads to the triplet state of the complex which can decay to a cyclohexadiene-like intermediate or dissociate to triplet MA and benzene. The major energy loss in the sequence comes from decay of MA triplets before they recombine with benzene. Competition between Diels-Alder addition of MA and dissociation of the intermediate provides the other energy loss and the MA concentration effect.

By comparison of the rates of energy transfer from three ketones to MA or the complex determined by photo reduction or flash photolytic techniques and from the phosphorescence spectrum of MA we calculate that the triplet state of the complex is ~2 kcal./mole lower than that of MA.

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