Chelate Structure of o,o′-Dioxyazobenzene in Solution

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THE idea that the o-oxyazo compounds have the chelate structure is now quite convincing. It is supported by much chemical and physical evidence, such as the slight acidity, anomalous chemical reactivities referred to phenolic hydroxyl, small association factor, slight solubility in polar solvents, molecular refraction data, absorption spectra, etc. The strongest support for the chelate structure was found by Hendricks and others1 in the study of infra-red absorption spectra in carbon tetrachloride solution. On similar grounds they concluded from the absence of the absorption band at c. l.4μ corresponding to the first overtone of hydroxyl vibration that o,o′-dioxyazobenzene has the doubly chelated trans-trans configuration as (1). From the chelation of both the hydroxyl groups in (1), it may be expected that the o,o′-dioxyazobenzene, like the o-mono-oxyazo compounds, is very slightly acidic. But the former is actually found to be very easily soluble in weak alkali. It may therefore be supposed that the chelate structure of the o,o′-dioxyazobenzene is somewhat different in character from that of the o-mono-oxyazo compounds.

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  1. 1

    Hendricks, Wulf, Hilbert and Liddel, J. Amer. Chem. Soc., 58, 1991 (1936).

  2. 2

    Unpublished measurements.

  3. 3

    Jacobson and Hönigsberger, Ber., 36, 4105 (1903).

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SHINGU, H. Chelate Structure of o,o′-Dioxyazobenzene in Solution. Nature 143, 1068–1069 (1939) doi:10.1038/1431068b0

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