Mass Spectrometry of 1-Phenylazo-2-naphthols

In order to examine the azo-hydrazone tautomerism of substituted 1-phenylazo-2-naphthols and to estimate the effect of substituents on the equilibrium, mono-substituted 1-phenylazo-2-naphthols were synthesized and the spectra were compared with those of the respective acetylated derivatives and β-naphthoquinone-methylphenylhydrazone as references of the azo and hydrazone forms respectively. The spectra of acetylated derivatives show the same pattern as those of the original samples except for the molecular ion and ion at m⁄e: 43. Moreover, β-naphthoquinone-methylphenylhydrazone displays a different fragmentation process, the cleavage of the N–N bond. In conclusion, the substituted 1-phenylazo-2-naphthols exist in the gaseous state as only the azo form; this is different from the results in the liquid and solid states. The fragmentation processes, in which the reactions of M+→ (m⁄e: 171)+→ (m/e: 143)+→(m⁄e: 115)+ mainly occur, are clarified on the basis of these results. The effect of substituents on the r...