158 



L. MICHAELIS, S. H. WOLLMAN 



VOL. 4 (1950) 



Red 



to tocopherol. They are all produced by irradiation of a solution in a mixture of ether, 

 ethanol and pentane*, in the volume proportions 5:2:5, respectively, with an ultra- 

 violet lamp for the duration of a few minutes to about twenty minutes. Although the 

 method is not suitable in its present form to tell anything about the yield, it may be 

 stated, that the radical of tocopherol is produced with ease to a readily recognizable 

 extent. 



Among the substances irradiated during this experimental study there is, first of 

 all, hydroquinone. It is irradiated, then the decay of the phosphorescence is awaited 

 (usually several seconds), without lifting the vessel out of the liquid air environment. 

 Now the colour in transmitted light is observed. It is yellow, its absorption spectrum 

 consists of several bands in the visible, the maxima of which are reproduced in Fig. 3. 

 The yellov/ substance is not quinone. Firstly, its absorption spectrum is different from 

 that of quinone ; secondly, this colour vanishes 

 on slightly warming up the frozen mixture. In 

 addition, a spectrum of the same character is 

 produced in this way from hydroquinone-mono- 

 methyl ether. This, of course, cannot be oxidized 

 to the level of a regular quinone but there is no 

 reason why it should not be oxidized to the level 

 of d semiquinone. 



Of the various tocopherols, samples of pure 

 a, 8, and y tocopherol** and several samples of 

 commercially available a-tocopherol were com- 

 pared. The latter showed the same behaviour as 

 the pure a-tocopherol, whereas the S and y com- 

 pound showed, after irradiation, absorption 

 bands slightly different from the a-compound. 

 Whereas the colour of the radicals from hydro- 

 quinone and its methyl-ether are yellow, that of 

 all the tocopherols is red, of slightly orange tint. This difference corresponds to the loca- 

 tion of the absorption bands in Fig. 3. 



The problem arises whether this "oxidation" by irradiation is a reversible one. Only 

 in this case the substance could serve in metabolism as something analogous to a 

 coenzyme of an oxidative enzyme. When tocopherol is chemically oxidized (say by 

 ferric chloride), the first oxidation product obtainable is a quinone, tocopherylquinone', 



360 390 UOO ^10 ^20 ^30 1>U0 «50 m^ 



Fig. 3 shows the location of the absorption 

 bands after irradiation as obtained ac- 

 cording both to photographs such as 

 Fig. I and to tracings such as Fig. z. 



1. (5-tocopherol 



2. y-tocopherol 



3. a-tocopherol 



4. a-tocopheryl hydroquinone 



5. hydroquinone monomethyl ether 



6. durohydroquinone 



7. hydroquinone 



HO. 

 H,C' 



CH3 OH 



I CH2 I 



i^^CH,— C— C,«H, 



^OH 



CH, 



CH, 



a-tocophcrol, parent substance of radical 

 No. 3 in Fig. 3 



a-tocopherylhydroquinone, parent sub- 

 stance of radical No. 4 in Fig. 3 



* G. N. Lewis recommends isopentane. We had no trouble with ordinary commercial pentane. 

 If the mixed solvent shows any inclination to crystallize at liquid air temperature, it can be corrected 

 by adding slightly more ether. 



** We owe these to the courtesy of Distillation Products Corporation, Rochester, N.Y. 



References p. i^g. 



