Interrelation of the chemical structure and inhibiting activity of sterically hindered phenols in methyl oleate oxidation in homogeneous and microheterogeneous systems

Specific features of the inhibiting activity of sterically hindered phenolic antioxidants (AOs) 3, 5-Bu^t₂-4-OHC₆H₂(CH₂)₂C(O)O(CH₂)₂N⁺Me₂R·X⁻ (R = H, Me, C₈H₁₇, C₁₀H₂₁, C₁₂H₂₅, C₁₆H₃₃; X = Br, I), being phenosan derivatives containing the ethanolamine residue substituted at the N atom by an alkyl substituent, were studied. The action of these AOs was studied in the initiated oxidation of homogeneous solutions of methyl oleate in chlorobenzene and an aqueous emulsion medium in the presence of the surfactant sodium dodecyl sulfate. Phenolic AOs act in two directions: they react with peroxy radicals with a rate constant of 0. 98·10⁴ L mol⁻¹ s⁻¹ and decompose hydroperoxides to form molecular products. The effect of hindered phenols as AOs depends substantially on their chemical structure and oxidation conditions. In lipid solutions, they efficiently hinder the oxidation of methyl oleate, outperforming the action of α-tocopherol, dibunol, phenosan K, and its methyl ester taken in comparative concentrations. The inhibiting activity of the AOs decreases substantially with the chain elongation of the R substituent. For oxidation in an aqueous emulsion medium, the inhibition effect of the AOs under study weakens compared to oxidation in a homogeneous solution, which is accompanied by the disappearance of differences in efficiency of different AOs.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 323–328, February, 2005.