Improved method for preparing 4-phenyl-cyanophenyl

The invention relates to a method for preparing 4-phenyl-cyanophenyl. The method mainly comprises the steps of: carrying out Friedel-Crafts acylation on biphenyl which is a starting material to obtain 1-chloroacetyl-4-phenyl-benzene; carrying out ammonolysis reaction on the 1-chloroacetyl-4-phenyl-benzene to obtain 4-phenyl-benzamide; and carrying out dehydration reaction on the 4-phenyl-benzamide in the presence of a dehydrating agent to obtain the target product. The method is characterized in that (1) a catalyst used in the Friedel-Crafts acylation reaction is imidazole ionic liquid; and (2) the dehydrating agent used in the dehydration reaction is a mixture of triphosgene and ammonium salt, the molar ratio of the triphosgene to the ammonium salt is 1:(0.05-0.1), and the ammonium salt is organic ammonium salt or/and inorganic ammonium salt. The method for preparing the 4-phenyl-cyanophenyl with better commercial value is provided by the invention.