41.4 g of N,N′-diphenyl-p-phenylenediamine, 66 g of iodobenzene, 100 ml of nitrobenzene, 45 g of K2CO3, 10.8 g of copper powder, and I2 (trace) were put in a four-neck flask of 300-milliliter volume, and were refluxed gently over 24 hours by stirring the same while removing generated water by reflux. Subsequently, steam distillation was carried out, and when a distillate no longer came out, residues were filtered out after cooling, washed with water, and extracted using toluene. After removing toluene by distillation, ethanol was added to the residues, and the mixture was filtered. Recrystallization was carried out using a solvent of toluene and ethanol (toluene:ethanol=4:1 (by volume)), whereby 36.5 g of N,N,N′,N′-tetraphenyl-p-phenylenediamine was obtained. It had a melting point of 200° C. to 202° C.
