Azo Coupling Reactivity and Photolysis Characteristics of Diazonium Hexafluorophosphates

Abstract

Diazonium hexafluorophosphate (Diazonium PF₆ salt) is virtually water-insoluble diazonium salt. Coupling reactivity and photolysis characteristics of four kinds of diazonium PF₆ salts were investigated. Coupling rate constant (k_c) in acetonitrile with N-(3-morpholinopropyl)3-hydroxy-2-naphthalenecarboxamide (coupler: No.5) increased with increasing infrared absorption frequency for the N-N stretching mode (ν(_-N2)) of the diazonium salts. This relationship was similar to that observed in an aqueous medium. The solubility in water of diazonium PF₆ salt was 1∼4×10^-4 mol⋅dm^-3: about one tenth of that of diazonium tetrafluoroborate (Diazonium BF₄ salt). The photolysis rate constant (k_p) in the film specimen containing diazonium PF₆ salts was obtained using UV fluorescent lamp as a light source. The k_p decreased with increasing the vν(_-N2), in contrast to the case of k_c. Self-catalysis effect was found in the coupler No.5. The coupler reacted with diazonium PF₆ salts in acetonitrile without the addition of base. It is suggested that the c oupler is in the naphtholate ion state in acetonitrile via intramolecular proton-transfer process.