Diethyl pyridine-3,4-dicarboxylate can be obtained by esterification of 3,4-pyridinedicarboxylic acid with ethanol.
Concentrated sulfuric acid (12 mL) was slowly added to an ethanolic solution of 3,4-pyridinedicarboxylic acid (10.0 g, 59.8 mmol), and the mixture was heated to reflux for 2 days. After cooling the reaction mixture to room temperature, excess EtOH was first stripped. Then, the oily mixture was dissolved in ethyl acetate, neutralized with NH4OH (aqueous solution), dried over Na2SO4, and concentrated. Finally, the product was purified by silica gel column chromatography (ethyl acetate:hexane = 1:3). Yield: 9.0 g, 67%. 1H NMR (400 MHz, CDCl3, 298 K): δ 9.04 (s, 1H), 8.79 (d, JHH = 5.2 Hz, 1H), 7.47 (d, JHH = 5.2 Hz, 1H), 4.41 - 4.35 (m, 4H), 1.38 - 1.34 (m, 6H).
