Carr-Price reaction

Some conversion into the anhydrovitamin (112) occurs during silica gel t.l.c. of retinyl palmitate in non-polar solvents. Some new colour reactions of vitamin A are reported to be better than the Carr-Price reaction. The kinetics and mechanism of acid-catalysed isomerization of retinyl acetate into the trans-retro-derivative (113) have been studied. Oppenauer oxidation of kitol (39) results in specific cyclopentanol-cyclopentanone oxidation. ... 

B. Carr-Price Reaction (See Chromatography, Appendix IIA.) Prepare a small chromatography column by filling a 200- x 7-mm glass tube, stoppered with glass wool, with alumina (80- to 200-mesh) slurried in toluene so that the settled alumina fills about 2/3 of the tube. Using a rubber outlet tube and clamp, adjust the flow rate to about 30 drops/min. 

Initial bioassay techniques were too time consuming to be employed on a routine basis and were superseded by physicochemical methods based on colorimetry, e.g., after reaction with antimony trichloride (Carr-Price reaction), or trifluoroacetic acid, or based on ultraviolet (UV) spectrophotometry or fluo-rimetry. However, these procedures cannot readily discriminate molecular species with different vitamin A activities (e.g., cis-trans isomers, retinyl esters, or oxidative degradation products). 

The Carr-Price reaction for the colorimetric determination of retinoids, which has long been in use, is based on colored cations formed via antimony (III) chloride (Hubbard et aL, 1971 Blatz and Estrada, 1972 Bridges and Alvarez, 1982). In the same way, the protonation of retinoids with trifluoroacetic acid has been used for colorimetric analysis (Dugan et aL, 1964). 

The addition product of an oxygen, atom from monoperphthalic acid with retinol (1) was named chromogen 574 on the basis of its characteristic UV absorbence in the Carr-Price reaction chromogen 574 was long thought to be 5,6-epoxyretinol (68) or 7,8-epoxyretinol (69), and only later investigations have shown that it has the structure (75) (Welch et aL, 1980). 

Vitamin A reacts with antimony trichloride in chloroform to give a blue colour (the Carr-Price reaction). 

Kildahl-Andersen G, Anthonsen T, and Liaaen-Jensen S. 2007. Studies on the mechanism of the Carr-Price blue color reaction. Organic Biomolecular Chemistry 5 3027-3033. 

Water-Soluble Annatto Extracts Transfer 2 mL or 2 g of sample into a 50-mL separatory funnel, and add sufficient 2 N sulfuric acid to make the solution acidic to pH test paper (pH 1 to 2). Dissolve the red precipitate of norbixin by mixing the solution with 50 mL of toluene. Discard the water layer, and wash the toluene phase with water until it no longer gives an acid reaction. Remove any undissolved norbixin by centrifugation or filtration, and dry the solution over anhydrous sodium sulfate. Transfer 3 to 5 mL of the dry solution to the top of an alumina column prepared as described above. Elute the column with toluene, three 10-mL volumes of dry acetone, and 5 mL of Carr-Price Reagent (see Solutions and Indicators) added to the top of the column. The orange-red band of norbixin immediately turns blue-green. 

Compound 2, m.p. 134 - 135°C, showed a M at m/e 414. The NMR, UV, and JR spectra suggested the presence of a steroid. The color reactions developed with the Liebermann-Burchard and Carr-Price reagents were also in accord with a steroid structure. Compound 2 was identified as sitosterol by comparing its m.p. and NMR, IR, UV, and MS spectra data with those of an authentic sample (Aldrich Chemical Company, Inc., Milwaukee, WI). 

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