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Published March 1988 | public
Journal Article

Ozone fading of natural organic colorants: mechanisms and products of the reaction of ozone with indigos

Abstract

Indigo, dibromoindigo, and colorants containing thioindigo and tetrachlorothioindigo were exposed in the dark to dry, purified air containing ozone (10 ppm) for 4 days, and the exposed samples were analyzed by mass spectrometry. Under the conditions employed, indigo and dibromoindigo were entirely consumed, and the major reaction products were isatin and isatoic anhydride from indigo and bromoisatin and bromoisatoic anhydride from dibromoindigo. Thioindigo and its chloro derivative also reacted with ozone, though at a slower rate; the corresponding substituted isatins and anhydrides were tentatively identified as reaction products. These results can be rationalized in terms of a mechanism involving electrophilic addition of ozone onto the unsaturated carboncarbon bond. This mechanism adequately describes the observed loss of chromophore (fading) for all indigos studied and presumably applies to other indigo compounds as well. The reaction products of indigo, isatin and isatoic anhydride, were not ozone fugitive under our conditions.

Additional Information

© 1988 by the American Chemical Society. Received for review January 28, 1987. Accepted September 17, 1987. This work was supported by a contract with The Getty Conservation Institute, Marina del Rey, CA.

Additional details

Created:
August 19, 2023
Modified:
October 26, 2023