Pyridine 1 -oxide—continued reactivity

There has been continued interest in developing a process for direct esterification of terephthalic acid with ethylene glycol. It does not appear, however, that this is currently practiced on a commercial scale in the U.S. In Japan, a process was commercialized where terephthalic acid is reacted with two moles of ethylene oxide to form the dihydroxy ester in situ, as the starting material. One mole of ethylene glycol is then removed under vacuum in the subsequent condensation process. Also, it was reported that the polymer can be prepared by direct esterification at room temperature in the presence of picryl chloride. The reaction can also be performed at about 120 C in the presence of diphenyl chloro-phosphate or toluenesulfonyl chloride. This is done in solution, where pyridine is either the solvent or the cosolvent. Pyridine acts as a scavenger for HCl, that is a byproduct of the reaction, and perhaps also as an activator (by converting the acid into a reactive ester intermediate). 

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