Synthesis of Biobased Terephthalic Acid from Cycloaddition of Isoprene with Acrylic Acid

摘要

A reaction sequence has been elaborated that could enable the 36 × 109 kg/y of terephthalic acid currently synthesized from p-xylene and used in the manufacture of poly(ethylene terephthalate) (PET) to instead be synthesized via cycloaddition of biobased acrylic acid and biobased isoprene. A central challenge in this cycloaddition is isoprene polymerization catalyzed by acrylic acid that is accelerated by the same Lewis acid catalysts needed to improve para selectivity in the cycloaddition. Esterifying acrylic acid to avoid diene polymerization while enabling Lewis acid catalyzed cycloaddition is not atom economical. A solution has been found with TiCl4 (2 mol %) catalyzed cycloaddition of acrylic acid and isoprene. At room temperature and in the absence of solvent, cycloaddition (94% yield) gives a 23:1, para:meta selectivity. Pd(0)-catalyzed aromatization (77% yield) of the para cycloaddition product affords p-toluic acid that is converted (94% yield) into terephthalic acid with a Co~(2+) /Mn~(2+) -catalyzed O2 oxidation.