Effect of alkali on methylene blue (C.I. basic blue 9) and other thiazine dyes

A. Mills, D. Hazafy, J. Parkinson, T. Tuttle, Michael G. Hutchings

Research output: Contribution to journalArticle

62 Citations (Scopus)

Abstract

A detailed study of the action of alkali on methylene blue (C.I. Basic Blue 9) and other thiazine dyes was carried out through a combination of UV/visible spectroscopy, thin layer chromatography, mass and NMR spectrometry and computational methods. In 0.1 M aq alkali solution, methylene blue forms a highly coloured, lipophilic species that is mainly Bernthsen's methylene violet i.e. a hydrolysis decomposition product, this being contrary to the report of a red N-hydroxy methylene blue adduct. The nature of the heterocyclic nitrogen atom in C.I. Basic Blue 9 is discussed and it is concluded there is no basis for the proposal of nucleophile addition at this site of the dye. In contrast, other thiazine dyes are deprotonated by alkali to form their neutral, highly coloured, lipophilic conjugate base forms.
Original languageEnglish
Pages (from-to)149-155
Number of pages7
JournalDyes and Pigments
Volume88
Issue number2
DOIs
Publication statusPublished - Feb 2010

    Fingerprint

Keywords

  • methylene blue
  • hydrolysis
  • thiazine
  • C.I. basic blue 9
  • methylene violet
  • DFT

Cite this