(b) Synthesis of di(2-pyridyl) carbonate: Under argon protection, triethylamine (10.5 mL, 75 mmol) was slowly added dropwise to a solution of anhydrous dichloromethane (500 mL) containing triphosgene (3.0 g, 10 mmol) and 2-hydroxypyridine (5.7 g, 60 mmol), keeping the reaction temperature at 0°C. The reaction mixture was then gradually warmed to room temperature and stirred continuously overnight. Subsequently, the reaction mixture was gradually warmed to room temperature and stirred continuously overnight. Upon completion of the reaction, the solvent was removed by distillation under reduced pressure and the resulting residue was dissolved in ethyl acetate (500 mL). The organic phase was washed sequentially with saturated aqueous sodium bicarbonate (2 x 150 mL) and brine (200 mL), and then dried over anhydrous sodium sulfate. After filtration, the filtrate was concentrated to give an orange colored oil. Crystallization by mixed ethyl acetate/hexane solvent resulted in an off-white crystalline solid of bis(2-pyridyl) carbonate (3.70 g, 57% yield). The nuclear magnetic resonance hydrogen spectrum (1H NMR) data were as follows: δ 8.42 (2H, dd, J = 4.8, 1.1 Hz), 7.83 (2H, ddd, J = 7.8, 7.7, 1.8 Hz), 7.30-7.23 (4H, m).
