In phthalimide synthesis by direct o-xylene ammoxidn. on V-Ti-O catalysts a suitable distribution of surface V species on the TiO2 surface makes possible the simultaneous insertion of two different types of heteroatoms in the alkylarom. mol. The mechanism of reaction involves intermediate formation of o-tolunitrile and the selectivity is detd. by (a) the competition between the oxidn. of the mononitrile to phthalimide and ammoxidn. to phthalonitrile and (b) the competition between ammoxidn. of o-xylene to o-tolunitrile and total oxidn. to carbon oxides. High yields of phthalimide may be obtained on a suitable V-Ti-O catalyst. Maleimide synthesis is studied on vanadyl pyrophosphate catalyst, active phase in butane conversion to maleic anhydride. Lower yields of maleimide are formed on this catalyst both from n-butane and 1-butene. It is suggested that in this case the formation of the maleimide occurs by reaction of maleic anhydride with the ammonia. [on SciFinder(R)]