15N, 13C and 1H NMR spectra and azo-hydrazone tautomerism of some dyes prepared by coupling of 1-naphthalenediazonium salt

Abstract

2-(1-Naphthyl)azo-5-tert.butylphenol ( 1), 3-methyl-1-phenylpyrazole-4,5-dione 4-(1-naphthyl)hydrazone ( 2), 1-(1-naphthyl)azo-2-naphthol ( 3), and 4-(1-naphthyl)azo-1-naphthol ( 4) were prepared by coupling naphthalene-diazonium chloride with the appropriate passive components and their 1H, 13C and 15N NMR spectra were measured and analysed. Two-dimensional NMR experiments were used to assign 1H and 13C chemical shifts unambiguously. The values of 1J( 15N, 1H) and 15N chemical shifts show that compounds 1 and 4 exist almost completely in azo tautomeric forms, whilst compound 2 exists completely in the hydrazone form and compound 3 predominantly in the hydrazone form. The increase of hydrazone content in compound 3 compared with the hydrazone content in 1-phenylazo-2-naphthol is in the range 1–2.7%, calculated from δ( 15N a) and δ( 15N b) chemical shifts and 1.2–1.6% using 1J( 15N, 1H), i.e. the annelation of the benzene ring in the active component has, contrary to the annelation of the benzene ring in the passive component, practically negligible influence on the azo-hydrazone equilibrium in compounds studied.