Color reaction

About: Color reaction is a research topic. Over the lifetime, 1194 publications have been published within this topic receiving 19579 citations.

Investigation of the colour reaction of phenols with MBTH, II: Properties of the isolated products of the reaction with phenol, 2,6-dimethylphenol and 4-methylphenol

Abstract: The following model compounds for the study of the oxidative coupling reactions of 2-hydrazono-3-methylbenzothiazoline (MBTH) with phenolic compounds were prepared: thep-coupling products of the reagent with phenol and 2,6-xylenol and theo-coupling product withp-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 violeto-coupling product is less stable than the redp-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 andp-cresol has not hitherto been prepared. The principal spectral characteristics, γmax(ɛ), of the products in ethanol medium are: 499 nm (4.7 × 104 1·mole−1 cm−1) for the phenol derivative, 486 nm (5.0 × 104) for the 2,6-xylenol product, and γmax 540 nm for thep-cresol product.

Mechanism of the Color Reaction of Active Methylene Compounds with 1, 3, 5-Trinitrobenzene Derivatives. IV. Color Reaction of Picric Acid and Acetone under the Janovsky Conditions

Abstract: Color reaction of picric acid with acetone in an aqueous alkaline solution under the Janovsky conditions was investigated. Two main coloring matters responsible for the observed colors were prepared separately and their chemical structures were determined as a Meisenheimer compound (I-2Na) and a bicyclic compound (II-Na), respectively, as shown in Chart 2 and 3. The correlation between the coloring matters and their roles in the reaction were discussed by comparing the spectral behavior of them with the spectral changes of the reaction mixture.

2,3-Dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline as an Analytical Reagent for the Spectrophotometric Determination of Microamount of Gold(III)

Abstract: The synthesis, spectral characteristics, and analytical application of 2,3-Dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline (DCHNAQ) are described. A simple, rapid, selective, and sensitive spectrophotometric method for the determination of microgram amounts of gold, alone, or in the presence of associated metals, is developed, based on the color reaction between the metal ion and the reagent. The yellowish brown complex (λmax = 575 nm) has stoichiometric ratio (1 : 1) [metal : ligand] over the pH range 3.4 to 7.0. Beer’s law is obeyed over the concentration range 0.1—6.9 μg cm−3 of gold. The molar absorptivity and Sandell’s sensitivity of the method are 1.52 × 104 dm3 mol−1 cm−1 and 0.016 μg Au cm−1 respectively. The relative standard deviation for six replicate determination of 2.95 μg cm−3 of gold(III) is 1.37%. The interference of various ions has been studied and conditions were developed for the determination of gold in alloys and some synthetic samples without the need for extraction or he...