Spectral Characterization of Some Phenylazodihydroxy Naphthalene Derivatives

A series of azo dyes namely: 4-phenylazo-1,3-dihydroxynaphthalene 1, 4-phenylazo-1,5-dihydroxynaphthalene 2, 1-phenylazo-2,8-dihydroxynaphthalene 3, 1-phenylazo-2,3-dihydroxynaphthalene 4 and 1-phenylazo-2,7-dihydroxynaphthalene 5 have been prepared and their UV, IR, NMR and mass spectra are recorded. The spectra have been analysed to give a complete picture of the hydroxyazo-quinone hydrazone tautomerism present in these class of compounds. It is found that dyes 1, 2 and 4 exhibit quinone hydrazone tautomerism while dyes 3 and 5 exist as a mixture of hydroxyazo and quinone hydrazone tautomers. The change due to a second hydroxyl group in the naphthalene moiety is compared with azonaphthols. The fragmentation process in the mass spectra displays C-N and -N = N-cleavage and indicated that the two tautomers are present except in dye 2 which exhibits a quinone hydrazone form.