4.3.1 Synthesis of 4'-methyl-4-aminobiphenyl (4a): 5-nitro-2-(p-tolyl)pyridine (3a, 2.54 mmol, 541 mg) was dissolved in a solvent mixture of EtOH/EtOAc (1:1, 50 mL). The hydrogenation-reduction reaction was carried out in all-hydrogen mode in the presence of Raney Nickel catalyst at a reaction temperature of 65 °C and a hydrogen flow rate of 0.8 mL/min. Upon completion of the reaction, the resulting solution was concentrated under reduced pressure to give 480 mg of yellow solid. The crude product was purified by silica gel column chromatography using hexane/CH2Cl2 (1:1) as eluent, resulting in 440 mg of the pure target product 4'-methyl-4-aminobiphenyl (4a) as an off-white solid in 95% yield.
