The structure of Alcian blue 8GX has been investigated using chemical and physical methods. Elemental analyses of the boric acid-free dye and electrophoresis suggest a phthalocyanin with an average of slightly less than four S-methylene tetramethylisothiouronium side chains per molecule. Oxidative break-down in two stages to benzene carboxylic acids, leading to the identification of benzene 1, 2, 4 tricarboxylic acid (trimellitic acid) as the main product, prove the presence of predominantly 4-substitution by the side chains in each iso-indole residue. Paper chromatography was used to resolve and identify the carboxylic acids, but final confirmation of their identity came from mass spectrometry of the mixture. Nuclear magnetic resonance spectra of the phthalimides produced in high yield during the first stage of oxidation in sulphuric acid by hydrogen peroxide confirmed and extended these findings. The ultra-violet, visible and infra-red spectra of Alcian blue and similar phthalocyanin pigments are discussed, and related to the structure.
A consideration of the possible distributions of four substituents in the eight possible positions which could be substituted leads to the conclusion that Alcian blue 8GX consists mainly of four geometrical isomers, the structures of which are presented.
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Scott, J.E. Histochemistry of Alcian blue. Histochemie 30, 215–234 (1972). https://doi.org/10.1007/BF00277593
- Nuclear Magnetic Resonance
- Carboxylic Acid
- Sulphuric Acid
- Nuclear Magnetic Resonance Spectrum