Abstract
Cyclopentadiene can be converted catalytically, by trichloroacetic acid, into a brown-red polycyclopentadiene–trichloroacetic acid ester, (I), the colour of which is due to conjugated double bonds1. If this ester is brought into contact with sufficiently concentrated strong acids, a dark blue, almost black, molecular compound, (II), is immediately formed. In tests in which the concentrations are small, or in which weaker acids are used, the colour of this compound is greenish-blue or green.
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References
Eisler, Farnsworth, Schnurmann and Wassermann, Nature, 168, 459 (1951).
Weiss, J. Chem. Soc., 245 (1942).
cf. Fuoss and Krauss, J. Amer. Chem. Soc., 55, 27 (1933).
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EISLER, B., WASSERMANN, A. Proton Acceptor Properties of Deeply Coloured Cyclopentadiene Polymers. Nature 172, 73–74 (1953). https://doi.org/10.1038/172073b0
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DOI: https://doi.org/10.1038/172073b0
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