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

Transformations of α-pinene, limonene, terpinolene, and α-terpinene were studied in liquid phase on sulfated zirconia having 15% H₂SO₄, with the aim of identifing the pathway of α-pinene isomerization. The principal products obtained in α-pinene isomerization were camphene, tricyclene, limonene, and terpinolene; the concentration maxima observed at 120°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, α-terpinene, and γ-terpinene; then the concentration of these products decreased. The terpinolene reaction yielded principally m-cymenene, whereas the α-terpinene transformation produced p-cymene. Studies of the initial rates of transformation of terpenes indicate a very high rate for α-pinene, intermediate for limonene and α-terpinene, and very low for terpinolene. The scheme proposed to interpret the results of the α-pinene isomerization reaction on sulfated zirconia is in agreement with reaction schemes proposed by A. Allahverdiev, S. Irandoust, and D. Y. Murzin (Isomerization of α-Pinene over Clinoptilolite.