Isomerization of α-Pinene, limonene, α-terpinene, and terpinolene on sulfated zirconia

Transformations of a-pinene, limonene, terpinolene, and (x-terpinene were studied in liquid phase on sulfated zirconia having 15% H2SO4. with the aim of identifing the pathway of a-pinene isomerization. The principal products obtained in a-pinene isomerization were camphene, tricyclene, limonene, and terpinolene; the concentration maxima observed at 120 degrees C and 180 min were 53, 6.1, 7.7, and 3.0%, respectively. The principal products formed in the limonene transformation after a 20-min reaction time were terpinolene, alpha-terpinene, and gamma-terpinene; then the concentration of these products decreased. The terpinolene reaction yielded principally m-cymenene, whereas the alpha-terpinene transformation produced p-cymene. Studies of the initial rates of transformation of terpenes indicate a very high rate for a-pinene, intermediate for limonene and (x-terpinene, and very low for terpinolene. The scheme proposed to interpret the results of the a-pinene isomerization reaction on sulfated zirconia is in agreement with reaction schemes proposed by A. Allahverdiev, S. Irandoust, and D.Y. Murzin (Isomerization of alpha-Pinene over Clinoptilolite, J. Catal. 185:352-362, 1999).