Catalysis of gas and liquid phase ionic and radical rearrangements of α- and β-pinene by metal(IV) phosphate polymers

Abstract

Gas-phase rearrangements of α- and β-pinene catalysed by metal(IV) phosphate polymers have been studied. The phosphates catalyse carbocation rearrangements in both substrates as expected, but catalysis of a modified radical rearrangement of α-pinene to yield α-pyronene has also been observed. Reduction in the acidity of the catalysts by exchange of protons with copper or ammonium ions, or by heating them to convert phosphates into pyrophosphates suppresses the carbocation reaction whilst having little effect on the rate of the radical reaction. Reasons for the alteration in the mode of the radical reaction, which normally yields ocimene and alloocimene, are discussed.