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. (C) 2003 Elsevier Science Ltd. All rights reserved.