Self-metathesis and the subsequent dehydrogenation of EPA resulting in benzene, 5-decenedioic acid and 5-octenoic acid in the absence of hydrogen. In the presence of even 1 atmosphere hydrogen, benzene and the saturated compound are formed. Credit: Pingen et al. Click image to enlarge.

Green Car Congress reports that researchers at the University of Konstanz in Germany have now developed a two-step, one-pot process for the synthesis of benzene from the five-fold unsaturated fatty acid eicosapentaenoic acid (EPA), a component of microalgae oils. Their paper is published in the RSC journal Green Chemistry.

Benzene, an aromatic hydrocarbon, is a natural component of crude oil and one of the elementary petrochemicals. It is used as a precursor to the manufacture of more complex chemicals, and, with a high octane number, is an important component of gasoline.

The two step-process — olefin metathesis and the catalytic dehydrogenation of the resulting 1,4-cyclohexadiene — produces two equivalents of benzene per EPA substrate molecule. The only major by-products are 5-octenoic acid and 5-decenedioic acid.

Further, performing the dehydrogenation step under hydrogen pressure results in the formation of their saturated analogues — sebacic acid and octanoic acid, both desirable products — while the simultaneous dehydrogenation step to benzene is not hampered.

Olefin metathesis was carried out in the presence of a solvent. Without any further purification, a solid dehydrogenation catalyst was added and the reaction mixture was heated to optimum dehydrogenation conditions.

The team investigated whether both reactions could be combined into a single step; however, the metathesis step was hampered under that condition, and did not reach full conversion.

The researchers noted that while the production of benzene from fatty acids is not economically viable yet, their scheme does provide a perspective to access this important building block from non-fossil sources efficiently.

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