Differential Reactions Between Carotene and Oils Rich in Vitamin A

Abstract

It has recently been demonstrated that carotene gives characteristic color reactions with trichloracetic acid, with chloral hydrate and with a reagent containing a mixture of sulphuric acid and formaldehyde. Tested on the rat, carotene in a biologic sense behaves in a manner similar to vitamin A. From a chemical standpoint, carotene shows a striking resemblance to vitamin A. One molecule of vitamin A is equivalent to half a molecule of carotene. Carotene and vitamin A both yield a characteristic blue color with antimony trichloride. The blue chloroform reaction mixture obtained with carotene in the presence of antimony trichloride yields, however, an absorption band at 590 mu, while the reaction mixture with vitamin A yields a wider absorption band at 610–630 mu. Recently Rosenthal and Erdelyi have demonstrated the possibility of distinguishing between carotene and vitamin A by applying the antimony trichloride test in the presence of pyrocatechol. They observed that when oil rich in vitamin A or vitamin A concentrate is dissolved in absolute chloroform and heated with antimony trichloride reagent and 0.5% pyrocatechol in chloroform solution, the blue changes to a purple or violet-red color comparable with the one characteristic of an aqueous solution of potassium permanganate. More recently Rosenthal and Erdelyi have demonstrated that in addition to pyrocatechol, hydroquinone, quaiacol and veratrole may be employed. Andersen and Levine have studied their procedure and report positive tests with antimony trichloride with vitamin Arich oils in the absence of pyrocatechol or any other phenol. They observed that pyrocatechol is even detrimental, since it inhibits the reaction and diminishes its sensitivity.