The Protective Action of Some Antioxidants II. The Metal Halide Compounds of Some Protective Agents against Aging, with Special Reference to Aldol-Alpha-Naphthylamine

The results described in the present paper can be summarized as follows: 1. Certain antioxidants containing nitrogen, like aldol-α-naphthylamine and Stabilite Alba, give in alcoholic solution with higher halides of certain metals, especially those of iron and copper, unstable intense blue-violet as well as stable carmine-red colorations, which may be regarded as more or less stable complex compounds of these antioxidants. A series of other heavy metal halides of which similar behavior would be expected (for example, SnCl4, CoCl3, etc.) give no color reactions of this kind. 2. Both the chemical and the optical behavior of these colored solutions indicate that they contain complexes of ferric chloride and cupric chloride groups attached to tertiary nitrogen, as in the haemin of blood pigment. 3. Of the antioxidants studied here, aldol-α-naphthylamine reacts quickest with the metal halides named above, Agerite the slowest and Stabilite Alba somewhere between the two. The reaction with cupric chloride occurs in every case much more rapidly than that with ferric chloride. It is obvious that this behavior might be utilized to distinguish analytically small quantities of these substances. 4. The complex metal halide compounds show strong oxygen-transporting action, as does the haemin of the blood, which contains iron. This is many times greater with the compounds of antioxidants which contain copper than with those which contain iron compounds, and this agrees with the similar behavior of compounds of these metals with rubber, as has long been known. 5. Since the antioxidants are oxidized in the course of time, as the result of autoöxidation, they protect an autoöxidizable substance like rubber only so long as they are not rendered inactive. Since traces of soluble heavy metal compounds, especially of iron, are invariably present in rubber compounding ingredients, it can be understood why rubber mixtures containing protective agents are more or less strongly and more or less rapidly discolored as a result of the formation of dark-colored metal complex compounds and their oxidation products. 6. Finally it was possible to show that the complex metal halide compounds of the antioxidants studied are remarkably sensitive toward certain catalytic poisons such as hydrocyanic acid, in quite an analogous fashion to known biological oxygen carriers. It is entirely possible that this phenomenon may also be of significance in the use of protective agents in technical rubber mixtures.