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.