CHEMICAL PROPERTIES OP FATS AND OILS 289 



react with each other to regenerate the three original molecules in the f ollow- 

 hig manner: AO + BO — > A + B + O2. The chain reaction is thus 

 broken and the development of rancidity is temporarily forestalled. The 

 antioxidants are gradually destroyed or are transformed to inert products. 

 During the induction period, the antioxidants break up the chain reactions 

 almost as soon as they are started. Wiien they become exhausted, as is 

 true at the end of the induction period, the oxidative reactions proceed at a 

 normal Imt greatly accelerated pace. Since the inhibitol is destroyed, 

 Stephens, **^^ and also Hamilton and Olcott,^^'' believe that the antioxidant 

 activity cannot be the result of a true anticatalyst as suggested by Moureu 

 and Dufraisse."**" 



(a) Phenols and Quinones. Phenols and quinones have been showii to 

 be especially effective antioxidants. Moureu and Dufraisse^^" reported 

 that one molecule of hydroquinone can protect 40,000 molecules of acrolein 

 from autoxidation. Olcott and MattilP^^-^*' have demonstrated that 0- 

 and p-diphenols are excellent antioxidants, while w-diphenols are inactive 

 in preventing oxidation of fats. Such a saturated hydroxybenzene deriva- 

 tive as inositol was shown to be inactive, as were aromatic compounds in 

 which the hydroxyl group was attached to the side chain. On the other 

 hand, only one h^'droxyl group is necessary in the naphthalene series to 

 provide an effective antioxidant. 



a-Naphthol was found to be a powerful reagent for preventing autoxida- 

 tion in fats, while |S-naphthol was much less effective. Quinone and ^- 

 naphthoquinone were found to be extremely effective antioxidants, but a- 

 naphthoquinone was essentially without activity. The phenolic antioxi- 

 dants were found to be acti\'e only when they were in the free state; 

 when they were combined in the form of esters, their activity was com- 

 pletely abolished. A preliminary classification of inhibitols has been 

 made by Olcott and Mattill.'^^o 



(b) Tocoyherols. The natural antioxidants were at hrst concentrated by 

 the procedures useful for the preparation of vitamin E.'*^^~^^^ It was found 

 that effective antioxidants were present in the sterol-free unsaponifiable ex- 

 tracts prepared from cottonseed, palm, and wheat germ oils. The sub- 

 stance or substances responsible for the stabilizing action were christened 

 inhibitols, *^^ since their activity, like that of the phenolic antioxidants, was 

 related to the presence of free hydroxyl groups. 



However, although it had been impossible to separate the inhibitols from 

 vitamin E, there was for some time considerable doubt that they were 

 identical, since the relationship between the antisterility and the antioxi- 



«« H. N. Stephens, J. Am. Chem. Soc, 58, 219-224 (1936). 



'^ H. S. Olcott and H. A. Mattill, J. Am. Chem. Soc, 58, 2204-2208 (1936). 



«' E. M. Bradwav and H. A. Mattill, /. Am. Chem. Soc, 56, 2405-2408 (1934). 



«2 H. S. Olcott and H. A. Mattill, J. Biol. Chem., 93, 65-70 (1931). 



«3 H. S. Olcott and H. A. Mattill, J. Biol. Chem., 104, 423-435 (1934). 



