Oligomers from Hydroxymethylfurancarboxylic Acid

Polycondensation of 5-hydroxymethyl-2-furancarboxylic acid (1) was studied. Oligoesters of 1 were prepared by using 2-chloro-l-methylpyridinium iodide (2) as a polycondensation agent. The solution polycondensation in pyridine at a 2 / 1 molar ratio more than 1.2 at 60°C gave selectively the macrocyclic oligoesters at a total yield more than 91 % : cyclic trimer (>33%), tetramer (>35%), pentamer (>13%) and higher oligomers (> 9%). The polycondensation in n-hexane in place of pyridine with tri-n-butylamine as a scavenger of hydrogen halide produced selectively the linear oligoesters from trimer to hexamer. That in toluene instead of n-hexane yielded the polyester, the cyclic and linear oligoesters. A mechanism is proposed for the formation of the cyclic oligoesters.