A New Strategy for the Preparation of Terephthalic Acid by the Aerobic Oxidation of p-Xylene Using N-Hydroxyphthalimide as a Catalyst

摘要

A new methodology for the production of terephthalic acid (5) by the aerobic oxidation of p- xylene (1) using a combined catalytic system of N-hydroxyphthalimide (NHPI)/Co(OAc )2/Mn(OAc )2 was developed. The oxidation of 1 under a dioxygen atmosphere in the presence of a catalytic amount of NHPI/Co(OAc)2/Mn(OAc)2 at 100 °C for 14 h af- forded terephthalic acid in 82% yield. Removal of Mn(OAc)2 from the catalytic system resulted in con- siderable reduction in the yield of 5. When the oxi- dation of 1 was carried out under a pressure of air (50 atm) at 150 °C, the reaction was completed with- in 3 h to give 3 in 84% yield. The oxidation of p-toluic acid (2), which can be pre- vation; (~oba. ra pared by the oxidation of 1 cal~; manganese;using the NHPI/Co(OAc)2 datIon; oxygen system at room temperature, by the NHPI/Co(OAc)2/Mn(OAc)2 system under pressure of air (30 atm) at 150 °C gave 3 in 95% yield. N-Acetoxyphthalimide (NAPI) was found to require a lower catalyst loading than NHPI, but oxidation with NAPI was slower. Thus, the oxidation of 1 catalyzed by NAPI (5 mol %)/CO(OAC)2 (0.5 mol %)/Mn(OAc)2 (0.5 mol %) under a dioxygen atmosphere (1 atm) in acetic acid at 100 °C gave 3 in 80% yield.