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I have mixed CAN in butanol and also ethanol (separately), the solution became dark red immediately but after a couple of minutes the color totally faded and turned into a transparent solution, I am curious to understand the reason behind it.

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Recall that Ce(IV) is a pretty strong oxidizing agent. So oxidation of alcohols and fading of the color is expected. The mystery lies in the immediate intense red color. It has been relatively recently studied in great detail and well known long time ago.

See these references:

  1. V. Briois, D. Lützenkirchen-Hecht, F. Villain, E. Fonda, S. Belin, B. Griesebock, and R. Frahm, "Time-Resolved Study of the Oxidation of Ethanol by Cerium(IV) Using Combined Quick-XANES, UV−Vis, and Raman Spectroscopies," J. Phys. Chem. A 2005, 109(2), 320–329 (DOI: https://doi.org/10.1021/jp046691t).

  2. Lewis Brewster Young and Walter S. Trahanovsky, "Oxidation of organic compounds with cerium(IV). VII. Formation constants for 1:1 cerium(IV)-alcohol complexes," J. Am. Chem. Soc. 1969, 91(18), 5060–5068 (DOI: https://doi.org/10.1021/ja01046a021).

Well, you can see Ce(IV), alcohols form transient 1:1 complexes with alcohols, but such complexes don't last long because of oxidation. In ref. 1, one can deduce that alcohol replaces one of monodentate ligand (nitrate), and thus absorption spectrum of this complex changes for a few seconds.

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