Fading of Organic Artists' Colorants by Atmospheric Nitric Acid: Reaction Products and Mechanisms

Daniel Grosjean, Lynn G. Salmon, and Glen R. Cass
Environmental Science and Technology, 26 (1992) 952--959


The reaction products formed upon exposure of selected artists' colorants to gas phase nitric acid have been identified using chemical ionization mass spectrometry. The two organic colorants that were most nitric acid- fugitive were triphenylmethane derivatives: the chloride cationic dye basic fuchsin yielded the corresponding nitrate salt, and the carbinol pararosaniline yielded the corresponding organic nitrate ester. Both also yielded small amounts of benzophenones. Other colorants studied yielded only small amounts of oxidation (but not nitration) products, i.e. phenols and/or ring-opening products: benzoic acid and hydroxyquinacridone from acridones, isatin and isatoic anhydride from indigo, trihydroxyanthraquinone from alizarin, and phthalic acid from Alizarin Crimson. The corresponding reaction mechanisms are outlined. The results are discussed in terms of possible damage to colorants in museum collections resulting from exposure to atmospheric nitric acid.

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Article about my work in Caltech On Campus, October, 1990

Another article in Science News of the Week, July 14, 1990: Pigments take thier NOx

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Lynn Garry Salmon <>{