Abstract
Indophenols and indophenolates resulting from the Gibbs reaction were prepared in the pure state and their properties studied under the conditions used in the photometric reactions. The results obtained and previous investigations allowed determination of the optimum conditions for the photometric procedure. Reproducible results are obtained when 2×10−6–2×10−5 M phenol reacts with a 30–50∶1 ratio of the reagent. The optimum pH range is 8.0–10.0, obtained with a suitable buffer. It is not possible to use a glycocoll buffer (quantitative reaction with the reagent) and ammoniacal buffers cannot be used for quantitative purposes. If extraction into an organic solvent is necessary, 1-butanol should be used without previous acidification of the reaction mixture. The first step of the colour reaction is the formation of the corresponding quinoneimine. Two molecules of this reactive species react immediately with one molecule of phenol.
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