Phthalonitrile is an organic compound with the formula C6H4(CN)2, which is an off-white crystal solid at room temperature.

The compound is used as a precursor to phthalocyanine and other pigments, fluorescent brighteners, and photographic sensitizers.

Phthalonitrile is produced industrially in a single-stage continuous process, by the ammoxidation of o-xylene at 480 °C.

It was noted as a byproduct of the synthesis of ortho-dicyanodiazoamidobenzene via the reaction of ortho-amidobenzonitrile hydrochloride, sodium nitrite, and hydrochloric acid.

[3] The first intentional synthesis involved dehydration of phthalamide by boiling in acetic anhydride.