Catalytic aspects in the transformation of pinenes to p-cymene

The reaction investigated in this work is the dehydrogenation of alpha -pin ene to p-cymene over carriers impregnated with Pd. An optimal acid strength is required to cleave selectively the C-C bond in the cyclobutane ring of oc-pinene. Too strong acid sites such as in zeolites favor side reactions l ike oligomerization and cracking. Too weak acid sites fail to cleave the af orementioned C-C bond and rapid hydrogenation of the alpha -pinene is a con sequence. Hydrogenolysis is also a major side reaction leading to tetrameth ylcyclohexanes. A reaction mechanism is proposed in which first isomerizati on is involved followed by hydrogenation/dehydrogenation to stabilize the c omponents. The catalyst has a dual-functionality with the acid sites in cha rge of isomerization and the metallic sites responsible of hydrogenation/de hydrogenation. The use of crude sulfate turpentine (CST) as raw material sh ows that beta -pinene has a similar reactivity as alpha -pinene and high yi elds of p-cymene can be obtained from this cheap starting material. The sul fur remains however a major drawback. (C) 2001 Elsevier Science B.V. All ri ghts reserved.