The catalytic isomerization reaction of α-pinene to camphene over a clinoptilolite catalyst was investigated in a batch reactor open to the atmosphere between 130 and 155°C. The catalyst was selective to the isomerization of α-pinene to camphene. The effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene and selectivity to camphene were determined. The reaction fits a first-order parallel reaction with rate constants of k 1 = 3.020·10 −2 e −33381.6/RT for the production of camphene and of k 2 = 1.576·10 −2 e −31096.53/RT for the production of limonene. JAOCS 74, 1145JAOCS 74, -1151JAOCS 74, (1997.
KEY WORDS:Camphene, isomerization, kinetics of isomerization of α-pinene, selective catalyst.The purpose of this study was to investigate the effects of several variables, such as reaction temperature, amount of catalyst, stirring speed and catalyst particle size, on the conversion of α-pinene to camphene (X c ), and on the overall selectivity for camphene over an activated clinoptilolite zeolite catalyst, which was found as the most selective after a selectivity screening test. We also wanted to develop a suitable rate equation for the isomerization of α-pinene to camphene.Camphene is an important industrial chemical from which many products of commerce, such as toxaphene, isobornyl acetate, isoborneol, and camphor are made. Comparatively small amounts are used to produce fragrance chemicals by reaction with phenols.Camphene is produced commercially by treatment of α-pinene over acidic catalysts in the absence of water (Scheme 1). It can be produced similarly from β-pinene and from pinene-containing materials, such as gum turpentine, wood turpentine and sulfate turpentine, which are obtained in the manufacture of paper from delignification of wood. Isomerization of α-pinene is generally carried out at reflux temperature in the presence of titania, minerals that contain a specific group of silicates (halloysite, zeolites), or activated clays. Preparation of the catalyst has a great influence on product yields and composition. The chief by-products of the isomerization are tricyclene, which is always obtained with camphene as an equilibrium product, and p-menthadienes.Many one-step methods with catalysts have been suggested in the literature (1) for the preparation of camphene. Various types of catalysts, both organic and inorganic, as well as mineral, have been reported to promote the isomerization of pinene directly to camphene. The catalysts must be treated with an acid to activate the surface. The time for complete conversion of the terpene being isomerized varies with the nature and amount of the catalyst used and the temperature employed. Carson (2) used chlorites, and Kirkpatrick (3) tried halloysite as catalyst for the isomerization of pinene to camphene and obtained a yield of 60% by weight. Korotov et al.(4) prepared camphene by isomerization of pinene in the presence of TiO 2 . Afanas'eva and coworkers (5,6) st...