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The chemical estimation of vitamin-E activity in cereal products. IV.—ε-tocopherol

1956; Wiley; Volume: 7; Issue: 7 Linguagem: Inglês

10.1002/jsfa.2740070706

1097-0010

P. W. Russell Eggitt, F. W. Norris,

Analytical Chemistry and Chromatography

Abstract ϵ‐Tocopherol has been isolated from wheat bran and some of its properties and its reactions have been studied. Its absorption spectrum, and that of nitroso‐ϵ‐tocopherol, are almost identical with the corresponding spectra for β‐tocopherol. ϵ‐Tocopherol, when oxidized with the Emmerie‐Engel reagents, yields a tocopheroxide, which may be converted into the isomeric ϵ‐tocopherylquinone. The latter shares a characteristically shaped absorption spectrum with β‐tocopherylquinone. With nitric acid in ethanol ϵ‐tocopherol forms a red o ‐quinone and other products with a reaction spectrum again very like that for β‐tocopherol. Only the β‐ and ϵ‐homologues produce a brilliant violet unstable colour (not the quinone) with nitric acid in chloroform. In these reactions the new tocopherol behaves as if it is 5‐methyltocol and this structure is confirmed by the fact that ϵ‐tocopherol yields 5: 7‐dimethyltocol (ζ‐tocopherol) under conditions that convert β‐tocopherol to α‐tocopherol. Difficulties encountered in applying the Quaife rdtrosation technique to the tocopherols are discussed. The factor converting depth of colour to concentration when ϵ‐tocopherol is assayed by the modified Emmerie‐Engel method described previously 1, 2 is 96.