Ammoxidation of α-methylstyrene to atroponitrile over U-Sb-oxide catalysts

Abstract

Atroponitrile (α-phenylacrylonitrile) can be synthesized by the direct catalytic ammoxidation of α-methylstyrene. Conversions to atroponitrile of 57% per pass with a selectivity of 85% are attained using a Nb-promoted USb 4.6O 13.2 catalyst. Several other USboxide catalysts give similar results. A detailed study of reaction variables shows that an optimal yield of atroponitrile is formed under conditions of short contact times (0.5 sec), low surface area (7 m 2/g), low feed: air + diluent ratio ( 1 120 ), and N 2 dilution. The structure of the major product of α-methylstyrene ammoxidation has been unambiguously determined as α-phenylacrylonitrile by ir, NMR, and low-voltage mass spectrometry. Atroponitrile dimerizes to 1,4-dicyano-1-phenyl-1,2,3,4-tetrahydronaphthalene (DPT) in benzene solution with second-order kinetics and an E a of 14.8 kcal/mole, typical of other Diels-Alder reactions. The dimer exists in both crystalline and amorphous forms. The rate of cinnamonitrile formation from ammoxidation of allylbenzene is 2.9 times faster than from β-methylstyrene, suggesting that the ammoxidation of aromatic olefins proceeds through a common allylic intermediate.