Kinetics of the initiated and inhibited oxidation of methyl oleate in homogeneous and aqueous emulsion media

Abstract

The kinetics of the 2,2′-azobisisobutyronitrile-initiated oxidation of methyl oleate (MO) in the medium of the oxidized substrate itself (homogeneous system) and in an aqueous solution of cetyltrimethylammonium bromide (aqueous emulsion system, AES) was studied. The oxidation was found to occur as a nonbranched chain reaction with quadratic-law chain termination in both neat methyl oleate ([MO] ≈ 2.6 mol/l) and AES. The temperature dependence of the oxidizability parameter for methyl oleate in the temperature range from 303 to 333 K was described by the following expressions: $$\begin{gathered} in an Mo medium, log(k_2 (2k_6 )^{ - 0.5} ) = (2.0 \pm 0.5) - (27.5 \pm 3.2)\theta ^{ - 1} [l^{0.5} mol^{ - 0.5} s^{ - 0.5} ]; \hfill \\ and in the AES, log(k_2 (2k_6 )^{ - 0.5} ) = (2.4 \pm 0.4) - (29.4 \pm 2.1)\theta ^{ - 1} [l^{0.5} mol^{ - 0.5} s^{ - 0.5} ], \hfill \\ \end{gathered}$$ where θ = 2.303 × 10−3 RT kJ/mol. The apparent rate constants for the inhibition of the reaction by 2,6-di-tert-butyl-4-methylphenol, quercetin, 5-hydroxy-6-methyluracil, and α-tocopherol in an MO medium and in the AES at 333 K were measured. The values of constants fk 7 × 10−4 were 1.4 ± 0.1 and 0.9 ± 0.1, 3.0 ± 0.1 and 2.4 ± 0.3, 2.5 ± 0.1 and 1.0 ± 0.1, and 90.7 ± 19.9 and 46.5 ± 16.5 l mol−1 s−1, respectively.