ESTERIFICATION OF 2,6-PYRIDINEDICARBOXYLIC ACID WITH N-BUTANOL CATALYZED BY HETEROPOLY ACID H3PW12O40 OR ITS CE(III) SALT

The liquid-phase esterification of 2,6-pyridinedicarboxylic acid (PA) with n-BuOH is efficiently catalyzed by heteropoly acid H3PW12O40 as a homogeneous catalyst and by its insoluble acidic Ce(III) salt, Ce0.87H0.4PW12O40, as a heterogeneous catalyst, yielding 100% of PA dibutyl ester. The Ce(III) salt has a lower activity than H3PW12O40 but can be easily recovered and reused. Insoluble NH4+, K+ and Cs+ salts also exhibit moderate activities. The activity of the salts decreases in the series: Ce0.87H0.4PW12O40 much greater than Cs2.5H0.5PW12O40 similar to Cs3PW12O40 similar to Cs2HPW12O40 similar to (NH4)(3)PW12O40 > K3PW12O40.