Structural characterisation of Nitrazine Yellow by NMR spectroscopy.

Nitrazine Yellow is an indicator used in microscopy with variations of absorption visible spectrum in pH range 6.0–7.0. The stated structure, deriving from the attack of 2′,4′-dinitrobenzenediazonium salt to ortho hydroxy position of 1-naphthol-3,6-disulphonic acid, appears incoherent with the alochromic behaviour. Nmr analysis and, in particular, HMQC and HMBC two-dimensional techniques showed that the real structure comes from an attack of the diazonium salt to para hydroxy position. [Copyright &y& Elsevier]