General procedure for the synthesis of 2,9-dicarboxy-1,10-phenanthroline from 2,9-bis(trichloromethyl)-1,10-phenanthroline: 2,9-bis(trichloromethyl)-1,10-phenanthroline (540 mg, 1.3 mmol, 1.0 eq.) was dissolved in a concentrated aqueous sulfuric acid solution (95-98%, 17 mL), and the reaction was stirred for 7 hr at 85 °C. Upon completion of the reaction, the brown reaction solution was cooled to room temperature and slowly poured onto crushed ice. After the ice was completely melted, the resulting white suspension was filtered under vacuum, washed thoroughly with water and dried in air to obtain the pure 2,9-dicarboxy-1,10-phenanthroline (360 mg, quantitative yield). The product characterization data were as follows: 1H NMR (300 MHz, DMSO-d6): δ= 8.22 (s, 2H), 8.42 (d, 3J = 8.4 Hz, 2H), 8.74 (d, 3J = 8.4 Hz, 2H); melting point 215-216 °C (decomposition).
