15N CP-MAS NMR Study of Azo-Hydrazone Tautomerism of Some Azo Dyes

Article abstract of DOI:10.1002/mrc.1260260614

The 20.28 MHz 15N CP-MAS NMR spectra of 15N doubly labelled 3-methyl-1-phenylpyrazole-4,5-dione 4-phenylhydrazone (1), 4-hydroxyazobenzene (2), 2-hydroxy-5-tert-butylazobenzene (3) and 1-phenylazo-2-naphthol (4) were measured and the temperature depenndence of δ(15N) was followed.For 4, representing a mixture of the azo and hydrazone forms, the hydrazone content was calculated from the 15N chemical shifts of both nitrogen atoms at various temperatures.The two calculations gave identical results.In comparison with measurements in solution, the hydrazone content in 4 is slightly h igher in the solid state.Thermodynamic data were calculated using the temperature dependence of ln K (K=/).Some hydrazone content was found in 2 in the solid state, in contrast to the meaasurements in solution.KEY WORDS 15N NMR Solid-state NMR Azo-hydrazone tautomerism.