The general procedure for the synthesis of N,N-bis(4-formylphenyl)aniline from triphenylamine and N,N-dimethylformamide was as follows: a solution of POCl3 (56.0 mL, 0.53 mol) was added slowly and dropwise to a stirred solution of anhydrous DMF (38.0 mL, 0.5 mol) of triphenylamine (12.3 g, 0.05 mol) under ice-bath conditions. Subsequently, the reaction mixture was heated to 95 °C and stirred continuously for 5 hours. Upon completion of the reaction, the resulting solution was poured into water and neutralized with 20% NaOH solution to pH 8. The product was extracted with ethyl acetate (3 x 200 mL), the organic phase was washed with water, dried over anhydrous MgSO4, and concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography using ethyl acetate/cyclohexane (1:5, v/v) as eluent to afford the target product N,N-bis(4-formylphenyl)aniline (yellow solid, 11.45 g, 76% yield, melting point 120-123 °C). The product was confirmed by IR (KBr, cm-1): 3044, 3038, 2816, 2745, 1691, 1601, 1584, 1508, 1336, 828, 772, 758; 1H NMR (400 MHz, CDCl3, δ ppm): 9.90 (s, 2H, CHO), 7.7-7.8 (m, 6H). 7.3-7.4 (m, 3H), 7.1-7.3 (m, 4H); 13C NMR (101 MHz, CDCl3, δ ppm): 191.05, 151.72, 145.56, 131.70, 130.58, 130.21, 129.34, 126.48, 125.62; EI-MS (m/z): 302.1131 [M+H]+ (calculated value C20H15NO2: 301.1121).
