Abstract
In the reaction of phenol and xanthydrol in hydrochloric-acetic acid solution, 9-(p-hydroxyphenyl) xanthene (I) is formed as the intermediate of a pigment formation but when the reaction is allowed to proceed in glacial acetic acid solution, 9-(o-hydroxyphenyl) xanthene (II) is formed in about an equal amount with I. I and II can be separated by alumina chromatography and can be discriminated easily by the marked difference in their coloration behavior to the Gibbs reagent.When hydrochloric acid is present the reaction participated by the free-type phenol is predominant and, since its activation energy is comparatively high, difference between ortho and para substitution is thought to be rather marked. On the other hand, in the glacial acetic acid solution, the reaction participated by the phenoxide anion becomes predominant and its activation energy would be lower than that in the former case, resulting in a small difference between ortho and para substitution. This assumption is endorsed by the fact that para-substitution alone takes place in the case of anisole, which would not form a phenoxide anion, irrespective of the presence or absence of hydrochloric acid.
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