One of the world’s most widely produced polymers, poly(ethylene terephthalate) (PET), is synthesized via condensation polymerization of ethylene glycol with terephthalic acid and small amounts of isophthalic acid. Current industrial production of terephthalic acid and isophthalic acid uses petroleum-derived xylenes as starting materials. The cost and availability of petroleum varies wildly and unpredictably. In order to stabilize costs associated with the synthesis of terephthalic acid and isophthalic acid, alternative feedstocks must be made available. A reaction sequence has been elaborated that addresses this need. The starting materials, acrylic acid and isoprene, are reacted in a solvent-free cycloaddition catalyzed by an inexpensive Lewis acid catalyst. Vapor phase aromatization of the resulting cycloadducts affords para- and meta-toluic acid, which are oxidized to terephthalic acid and isophthalic acid, respectively. Both acrylic acid and isoprene are commercially synthesized from petroleum or shale gas but may also be synthesized from biobased feedstocks. Thus, by diversifying available feedstocks, costs associated with commercial terephthalic acid and isophthalic acid synthesis are stabilized. Moreover, this reaction sequence is the only one reported in the literature to produce both terephthalic acid and isophthalic acid for the manufacture of PET.
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