Color reaction

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

Characterization of amines by Fast Black K salt in thin-layer chromatography

Abstract: Amines were characterized on a silica gel thin-layer chromatographic (TLC) plate with the diazonium reagent Fast Black K salt (FBK) and with subsequent novel procedures: acid treatment or treatment with N-(1-naphthyl)ethylenediamine in acid solution. The differentiation of primary, secondary and tertiary aliphatic and aromatic amines was demonstrated, with special attention to drug substances. By using the N-(1-naphthyl)ethylenediamine treatment a 5-fold improvement in the detection limits for aliphatic secondary amines was achieved compared with FBK alone, allowing detection of 0.01 µg of methamphetamine and 0.04 µg of methyl phenidate. The structures of the coloured reaction products were elucidated by spectroscopic and TLC methods. An unexpected reaction was observed with dialkylanilines, which reacted by N-coupling with various diazonium salts with cleavage of an alkyl group.

Indirect spectrophotometric determination of hydrogen peroxide

Abstract: A method for the indirect spectrophotometric determination of H2O2 is based on its oxidation with chlorine in basic medium and measurement of the unreacted Cl2 by the colour reaction with o-tolidine at 438 nm. The effective molar absorptivity for H2O2 with o-tolidine is 5.37×104 mol−1 cm−1 at pH 1.7. The lower limit of determination is 1.85×10−7 mol/l or 6.29 ppb. Br−, I−, NO−2, Pb2+ and Sn2+ interfere even in small amounts, but are not present in commercial H2O2.

Studies on the mechanism of the Carr–Price blue colour reaction

Abstract: The reaction of retinoids (retinol, retinyl acetate and anhydroretinol) with Bronsted acids was studied as a model system for the Carr–Price reaction. The anhydroretinylic cation was characterised by VIS and 2D NMR spectroscopy, including an estimate of the charge distribution and region of bond inversion, observed in a mixture of identified E/Z isomers. Products obtained by quenching with NaOMe–MeOH were identified by HPLC and MS. The classical Carr–Price reaction between retinol (vitamin A) and the Lewis acid SbCl3 in saturated chloroform solution was reinvestigated by VIS, NMR, EPR, dynamic light scattering and chemical quenching. Whereas product instability and failure to provide informative NMR spectra indicated a radical cation, EPR results excluded free-radical species. Dynamic light scattering experiments, in comparison with model systems, revealed strong aggregation for the Carr–Price complex, rationalising the low stability, NMR problems and dimerisation observed by chemical quenching. The VIS data support structural similarity of the blue Carr–Price product with the delocalised anhydroretinylic cation, and a detailed structure of the antimony complex is evaluated.