VOL. 4 (1950) 



FREE RADICALS DERIVED FROM TOCOPHEROL 



157 



Fig. I shows the absorption 

 spectrum of irradiated a-toco- 

 pherol at .iquid air tempera- 

 ture, photographed with a 

 spectrograph. 



and is irradiated with ultraviolet light through quartz windows in a Dewar vessel. Such 

 an irradiation may have two effects: one is, to raise the energy of some electron to a 



higher level. The spontaneous return of this electron to its 

 ground level will be manifested by some luminescence, 

 either fiuoiescence or phosphorescence of longer duration, 

 according to conditions discussed by Lewis. In the second 

 place, if there be an electron of sufficiently low ionization 

 potential, the electron may be knocked out altogether, a 

 process comparable to oxidation by a chemical oxidizing 

 agent. At the temperature of liquid air and in the rigid 

 medium molecular collisions are inhibited. Free radicals, 

 once created, will accumulate to a concentiation far above 

 that permissible by thermodynamics, provided the elec- 

 trons ejected are trapped in the molecules of the solvent 

 and do not re-combine with the free radicals. In this case, 

 no equilibrium in which the radical may be involved, can 

 be established. Reactions such as dismutation, or dimeri- 

 zation of the radicals cannot occur. If the radical happens to be stable in so far as not 

 to suffer a decay by a spontaneous unimolecular reaction (such as occurs in a radioactive 

 atom), it will accumulate to a thermodynamically impermissible concentration. If the 

 radical should be coloured, it could be seen in the frozen medium and remain as long as 

 the temperature is kept low. On slightly 

 warming up the solution the colour should 

 disappear. This may be taken as evidence 

 for the that fact the colour belongs to a 

 compound capable of existence to a notice- 

 able extent only under conditions where 

 the establishment of chemical equilibria is 

 inhibited*. 



The colour produced in this way can, in 

 suitable cases, be compaied with the colour 

 of free radicals produced by chemical oxida- 

 tion. In fact, the absorption spectrum of 

 the compound generated by either method 

 was found to be identical^ on working with 

 such substances as asymmetrical dimethyl- 

 p-phenylene diamine, or tritolylamine^' ^. 



In this paper we shall describe the absorp- 

 tion spectra of several coloured substances 

 considered as free semiquinone radicals pre- 

 pared in this way from substances related 



39t) 



WO 



if30 «40 ''SO 

 ^^ovelength in mfj 



Fig. 2 shows tracings, obtained w^ith a re- 

 cording micophotometer, of the spectrum of 

 irradiated a-tocopherol, and of irradiated 

 a-tocopherylhydroquinone . 



* According to Lewis and his associates, there may be still another effect: dissociation of a 

 large molecule (such as tctraphenylhydrazin) either into two free radicals, or into a positive and a 

 negative ion. Considering the structure of the compounds investigated, the possibility of such effects 

 may be disregarded here. The fact that all the spectra obtained from the various compounds are 

 similar, is further evidence as to the absence of nny essential photodecomposition. 



** The authors are indebted to the Sun Chemical Company, New York, for their permission 

 to use their recording microphotometer. 



References p. i^g. 



