Location: Bio-oils ResearchTitle: Production of industrially useful and renewable p-cymene by catalytic dehydration and isomerization of perillyl alcohol
Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2020
Publication Date: 2/19/2021
Citation: Moser, B.R., Jackson, M.A., Doll, K.M. 2021. Production of industrially useful and renewable p-cymene by catalytic dehydration and isomerization of perillyl alcohol. Journal of the American Oil Chemists' Society. 98(3):305–316. https://doi.org/10.1002/aocs.12468.
Interpretive Summary: This research describes a renewable and sustainable route to a chemical that is normally produced by petrochemical means. Cymene is industrially important as a precursor for other important industrial chemicals and as a component or precursor for pesticides, fungicides, herbicides, and pharmaceuticals. It is found naturally in cumin and thyme but petrochemical routes have been devised to augment its supply due to its limited natural availability. This research discovered a renewable method to produce cymene from a common limonene metabolite (perillyl alcohol) that avoids petrochemical building blocks. Limonene is widely available due to its abundance in citrus rinds from orange, lemon, mandarin, grapefruit, and lime. This research may ultimately expand markets for bio-based chemicals, thus reducing the environmental impact of and demand for petroleum-derived products while simultaneously enhancing rural economies by increasing the use of agricultural materials.
Technical Abstract: We report the dehydration and isomerization of renewable perillyl alcohol to industrially useful p-cymene in 91.1% yield utilizing 2.0 mol % para-toluenesulfonic acid (pTsOH) catalyst at 110 ºC as a 3.0 M solution in toluene. Lower reaction temperatures, catalyst loadings and/or starting concentrations resulted in lower yields of p-cymene as well as longer reaction times. Conversion of perillyl alcohol to p-cymene yielded atom and carbon economies of 88.1% and 100% as well as an E-factor of 2.7, thereby indicating that the process was both green and sustainable. A lower yield of 86.0% was observed when the reaction was performed neat, but a lower E-factor of 0.4 indicated that neat conditions were more desirable from an environmental perspective. Application of the optimized parameters to 3.0 M solutions of dl-limonene led predominantly to oligomerization (91.6%) as opposed to dehydroisomerization (4.9%), which was attributed to the strong Brønsted acidity of pTsOH. Additionally, camphene (43.5%), terpinene isomers (15.3%) and limonene (13.9%) were obtained when dehydroisomerization was attempted on 3.0 M solutions of alpha- and beta-pinene, which was once again attributed to the acidity of the catalyst. Oligomerization was strongly favored when dehydroisomerization of dl-limonene, alpha- and beta-pinene was attempted neat. In summary, synthesis of renewable p-cymene was readily achieved from perillyl alcohol with catalytic pTsOH but competing side reactions suppressed yield when dehydroisomerization of dl-limonene, alpha- and beta-pinene was attempted due to the strong Brønsted acidity of the catalyst.