• Chelation in azophenols in relation to chromatographic adsorbability on alumina

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      https://www.ias.ac.in/article/fulltext/seca/034/06/0368-0386

    • Keywords

       

      Resorcinol; Diazonium; Orcinol; Monoazo; Caustic Soda Solution

    • Abstract

       

      The relative adsorption affinities of monoazo derivatives of phenol and resorcinol have been explained on the basis of chelation and of the availability of hydroxyl and azo groups for interaction with alumina. Since Ruggli has shown that monoazo, disazo and trisazo dyes are adsorbed in the given increasing order of strength of adsorption, an observation of special interest, explained by chelation effects, is thatp-hydroxyazobenzene is more strongly adsorbed than 2:4-bisbenzeneazophenol, and that 4-benzeneazoresorcinol is more strongly adsorbed than 2:4- or 4:6-bisbenzeneazoresorcinol.

      When phenol is coupled with a molar proportion of diazotized aniline,o-hydroxyazobenzene,p-hydroxyazobenzene and 2:4-bisbenzeneazophenol are formed in yields of 1·1, 97·9 and 1% respectively. They are separable by chromatography on alumina, the adsorption affinity being in the following decreasing order:p-hydroxyazobenzene, 2:4-bisbenzeneazophenol, ando-hydroxyazobenzene.

      2-Benzeneazoresorcinol has been prepared by coupling diazotized aniline with dimethyl resorcinol-4:6-dicarboxylate, followed by hydrolysis and decarboxylation. 4-Benzeneazoresorcinol, 4:6-bisbenzeneazoresorcinol, 2-benzeneazoresorcinol, and 2:4-bisbenzeneazoresorcinol are adsorbed on alumina in the given order of decreasing strength of adsorption. Examining the crude dye obtained by coupling resorcinol with benzenediazonium chloride by chromatography on alumina in the light of the above observations, it is shown that, contrary to statements in the literature, there is no evidence of the formation of 2-benzeneazoresorcinol.

      Although the γ- or 2-position of 5-substituted resorcinols has considerable reactivity in reactions such as carboxylation and the Fries rearrangement, the first coupling of orcinol with diazotized aniline takes place entirely in the 4-position. The second coupling takes place in the 2- or 6-position according as the pH is 5⊋ash;8 or higher.

      Resacetophenone couples with diazotized aniline to a mixture of 5-benzeneazo-and 3:5-bisbenzeneazoresacetophenone; the constitution of the former was shown by the Fries rearrangement of the diacetate to 2:4-diacetyl-6-benzeneazoresorcinol. The failure of resacetophenone to undergo the first coupling in the γ-position shows the weakness of the hydrogen bond between the carbonyl and adjacent hydroxyl groups, as well as a marked difference in the influence of such chelation on the Fries rearrangement and on diazonium coupling.

    • Author Affiliations

       

      T S Gore1 K Venkataraman1

      1. Department of Chemical Technology, University of Bombay, India
    • Dates

       
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