Introduction Terephthalic acid (PTA) is essential for the preparation of a variety of polyester fibers and is largely produced via the catalytic oxidation of petroleum-derived p-xylene. To reduce our dependence on fossil fuels, alternative, sustainable routes to produce terephthalic acid from biomass derivatives are highly desirable. Diels-Alder cycloaddition with ethylene has been used to synthesize PTA precursors from biomass-derived molecules, but this process is limited by the low yields of either the starting chemicals or the product. Ru-catalyzed olefin metathesis, and in particular cross-metathesis, has become an important tool for the formation of new carbon–carbon bonds and, as shown here, it can be used for the preparation of valuable PTA precursors. Results and discussion We have investigated the ruthenium-catalyzed cross metathesis of renewable and inexpensive chemicals, like sorbate and acrylate carboxylates to form di-ester muconates. The effect of alkyl substituents and solvents was investigated over various organometallic ruthenium-based catalysts. Conversions of up to 60% and 40% yields of the muconates were achieved with low amounts (3 mol.%) of ruthenium-based catalysts. In a subsequent step, the synthesis of diester terephthalates was achieved by a two-step and one-pot process. First, the Diels-Alder cycloaddition of muconate esters with ethylene (2.41 MPa), with no catalyst added, forms the cyclohexene dicarboxylates in high yields (&gt;95%). No separation is needed after the cycloaddition step due to the high yields achieved and the fact that no catalyst is needed. In a second step, in the same reaction batch, the aromatization of the cyclohexene dicarboxylates was catalyzed by a Pd/C catalyst to afford the formation of terephthalic acid diesters (~70% yield). Several solvents were tested for the last two-step synthesis of the terephthalates, with tetrahydrofuran resulting the best. This route can provide a sustainable alternative for the industrial production of biomass derived polyethylene terephthalate (PET).

Bio-terephthalic acid synthesis from cross metathesis of bio-sourced unsaturated carboxylic acids and consecutive one-pot cycloaddition and aromatization reactions

254th National Meeting (2017)

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