4,5-Dichlorophthalonitrile (4,5-dichloro-1,2-dicyanobenzene) is a phthalonitrile derivative. It has been synthesized from 4,5-dichloro-1,2-benzenedicarboxamide and characterized by ¹H ,¹³C-NMR and IR. 4,5-dichlorophthalonitrile undergoes base catalyzed nucleophilic aromatic substitution reaction with O-, S- nucleophiles and acidic -CH containing compounds to form corresponding phthalonitrile derivatives, which are the precursors in the synthesis of phthalocyanines.

4,5-Dichlorophthalonitrile is suitable as a reactant in the synthesis of 4,5-bis(3,4-dimethoxyphenyl) phthalonitrile and 4,5-bis(2,6-dimethoxyphenoxy) phthalonitrile. It may be used in the synthesis of 4,5-diphenoxyphthalonitrile.