Highly selective solvent-free hydrogenation of pinenes to added-value cis-pinane

Abstract

Heterogeneous catalysts based on different active metals (Pd, Pt, Ru, and Rh) and supports (carbon and alumina) were systematically tested for hydrogenation of pinenes under various reaction conditions including heating and/or sonication. Among all, Ru provided some of the best results. After sonication, Ru/C was found highly active and selective for the reduction of a-pinene alone into cis-pinane (99% selectivity at 100% conversion).However, in the absence of sonication the same catalyst was completely inactive. Alumina appeared to be a support with a beneficial chemical effect on the activity of the Ru. Indeed, Ru/Al 2 O 3 was found very active and selective for hydrogenation of both aand b-pinene into cis-pinane (99e100% selectivity at 100% conversion) under mild reaction conditions (room temperature, 400 Psi H 2 ). The selectivity toward cis-pinane decreased in the following order: Ru > Rh > Pt > Pd. An extremely low leaching rate of Ru and other metals determined by inductively coupled plasma mass spectrometry confirmed the heterogeneous nature of this catalytic solvent-free hydrogenation. Ru/C was successfully recycled seven times with no decline in activity and selectivity, whereas Ru/Al 2 O 3 could be used only once to convert pinenes to cis-pinane. Solubilization prediction tests of some natural products have revealed that pinane compares very well with n-hexane and may be an alternative to this fossil-based solvent. When compared experimentally with n-hexane, cis-pinane solubilized 42, two, and three times more of b-carotene, vanillin, and rosmarinic acid, respectively.

Green Hydrogenation: Solvent-Free Hydrogenation of Pinenes for An Undergraduate Organic Chemistry Laboratory

“…We have recently successfully performed a solvent-free hydrogenation of pinenes over various catalysts. Extensive tests under various experimental conditions allowed us to perform a stereoselective hydrogenation in favor of the cis -pinane isomer. ,, Pinane has proven to be a good solvent for the extraction of various natural products and could be an interesting solvent to replace a fossil-based solvent such as n -hexane …”

“…Extensive tests under various experimental conditions allowed us to perform a stereoselective hydrogenation in favor of the cis-pinane isomer. 9,17,18 Pinane has proven to be a good solvent for the extraction of various natural products and could be an interesting solvent to replace a fossil-based solvent such as nhexane. 17 Experiments that introduce principles of green chemistry 6 as well as development of renewable products will allow students to see beyond the basic chemistry concepts.…”