| Abstrakt: |
The following model compounds for the study of the oxidative coupling reactions of 2-hydrazono-3-methylbenzothiazoline (MBTH) with phenolic compounds were prepared: the p-coupling products of the reagent with phenol and 2,6-xylenol and the o-coupling product with p-cresol. The proposed structure of the dyes was confirmed. In strongly polar and ionic media the azobetaine form of the products predominates, and in non-polar media the azine structure. The principal physico-chemical properties of the products were determined and the results contributed to formulation of the course of the coupling reaction, and to optimization of the conditions for determination of small amounts of phenolic substances. The violet o-coupling product is less stable than the red p-coupling products, and intramolecularly hydrogen-bonded six-membered ring is assumed to exist in the structure. In acid medium the dyes are mainly monoprotonated, and partly diprotonated in concentrated sulphuric acid medium. The products are stable up to about pH 11. These properties make extraction into low-polarity solvents possible. The dye derived from 2,6-xylenol and p-cresol has not hitherto been prepared. The principal spectral characteristics, γ(ɛ), of the products in ethanol medium are: 499 nm (4.7 × 10 1·mole cm) for the phenol derivative, 486 nm (5.0 × 10) for the 2,6-xylenol product, and γ 540 nm for the p-cresol product. [ABSTRACT FROM AUTHOR] |
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