The Oxidation of 4-(4-Formylphenoxy) Phthalonitrile to 4-(4-Carboxylphenoxy) Phthalonitrile at Ambient Conditions

The substituted phthalonitriles have been used to prepare soluble phthalocyanine species in recent years. One of the most used phthalonitrile derivatives for the target product is 4-nitrophthalonitrile. In this study 4-(4-formylphenoxy) phthalonitrile was prepared as the substituted phthalonitrile derivative by the nucleophilic substitution reaction of para-hydroxybenzaldehyde with 4-nitrophthalonitrile. During the crystallization of the product by slow evaporation technique, it readily self-oxidized to 4-(4-carboxylphenoxy) phthalonitrile at ambient condition open to air. The crystal structure of the molecule was determined by XRD technique. The molecule crystalizes at triclinic space group P-1 and the unit cell parameters of crystal are a=6.3591 (10) Å, b=7.5464 (11) Å, c=13.819 (2) Å, α=88.434 (11)°, β=87.942 (12)°, γ=80.111 (12)° and Z=2. The crystal structure has intermolecular O―H∙∙∙O, C―H∙∙∙N and C―H∙∙∙O hydrogen bonds. In addition to these hydrogen bonds, C—N∙∙∙Cg and Cg∙∙∙Cg interactions are present between molecules. In the crystal, intermolecular O―H∙∙∙O hydrogen bonds occur between molecular units in a dimeric molecular form. Molecular structure, vibrational frequencies and ¹H and ¹³C NMR chemical shifts of the target compound have been calculated by using B3LYP method with 6-311++G(d, p) basis set, as well.