Synthesis of phthalic and maleic anhydrides from n-pentane: reactivity of possible intermediates and co-feeding experiments

The mechanism of synthesis of phthalic and maleic anhydrides from n-pentane on vanadyl pyrophosphate is analyzed. The research involved studying the reactivity of some of the possible intermediates or of useful probe mols. (C5 linear and cyclic olefins, 2-Me furan, n-amyl alc., 1-bromopentane, 4 Me tetrahydrophthalic anhydride and hexahydrophthalic anhydride), co-feeding expts. (pentane or 1-pentene and butadiene, 2 Me furan or n-butane), and anal. of the catalytic behavior of C1-C10 alkanes. The results indicate the specificity of (VO)2P2O7 for the formation of phthalic anhydride from n-pentane which forms by a parallel reaction with respect to maleic anhydride. The reaction of phthalic anhydride synthesis does not involve gas phase Diels-Alder like reactions, but rather (i) a surface reaction between an adsorbed diene and on adsorbed O-contg. intermediate or (ii) a surface template reaction between two adsorbed, possibly cyclic, activated hydrocarbons. The possible mechanisms of formation of phthalic and maleic anhydrides are discussed taking into account the strong inhibition and adsorption effects obsd. by feeding C5 dienic mols. [on SciFinder(R)]