ANTIOXIDANTS AND STABILIZERS, .113. OXIDATION-PRODUCTS OF THE ANTIDEGRADANT ETHOXYQUIN

In connection with the study of the mechanism of antioxidant action of 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (ethoxyquin, I) and of its ecological responses in stabilized polymers we studied its oxidation with some selected agents and the properties of products thus obtained. The oxidation of I with silver oxide or lead dioxide proceeds by two main routes. One of them leads to 8-(6-ethoxy-2,2,4-trimethyl-1,2-dihydro-1-quinolinyl)-6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (IV), which is further oxidized to the blue compound 8-(6-ethoxy-2,2,4-trimethyl-1,2-dihydro-1-quinolinyl)-2,2,4-trimethyl-6-quinolone (IX). In the second route position 6 is attacked and 2,2,4-trimethyl-6-quinolone (VII) is formed, which is stable under the conditions used, but is oxidized further with m-chloroperbenzoic acid, giving rise to 2,2,4-trimethyl-6-quinolone-N-oxide (VIII). The oxidation of ethoxyquin with potassium permanganate also gives rise to dimer IV and not to 1,1'-bis(6-ethoxy-2, 2,4-trimethyl-1,2-dihydroquinoline) (III) reported in the literature. Potassium nitrosodisulfonate oxidizes I with formation of 6-ethoxy-2,2,4-trimethyl-8-quinolone (X). The oxidation of ethoxyquin with m-chloroperbenzoic acid gives rise to 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline-N-oxide (V) and dimer IV. Nitroxide V was obtained in the crystalline state. In the presence of acids, and particularly on the surface of silica gel it decomposes to ethoxyquin and nitrone VIII. Nitroxide V is readily reduced to the starting ethoxyquin. The transitionally formed 6-ethoxy-1-hydroxy-2,2,4-trimethyl-1,2-dihydroquinoline (XIV) readily disproportionates to I and V.