Kazumasa Yazu

Mechanism of lower oxidizability of eicosapentaenoate than linoleate in aqueous micelles

The aerobic oxidation kinetics of methyl eicosapentaenoate (20:5n-3) and methyl linoleate (18:2n-6) were compared in homogeneous chlorobenzene solution and in Triton X-100 aqueous micelles at 37°C. The rate of disappearance of 20:5n-3 was two times faster than that of 18:2n-6 in chlorobenzene, while the former was five times slower than the latter in aqueous micelles. It was also observed that ΔO2=Δ18:2n-6 and ΔO2=2Δ20:5n-3 in aqueous micelles. In the oxidation of a 1∶1 mixture of 20:5n-3 and 18:2n-6 in micelles, the rate of disappearance of 20:5n-3 was 3.6 times faster than that of 18:2n-6, and the rate of total substrate disappearance was reduced by a factor of 5 as compared with 18:2n-6 oxidation. These data suggest that the peroxyl radical derived from 20:5n-3 is more polar than that from 18:2n-6, and the former is likely to diffuse from the core to the micelle surface. This lowers the oxidizability for 20:5n-3 in aqueous micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more 20:5n-3 peroxyl radicals at the surface than in the micelle core.

Mechanism of lower oxidizability of eicosapentaenoate than linoleate in aqueous micelles. II. Effect of antioxidants

We have reported that the peroxyl radicals derived from methyl eicosapentaenoate (20:5n-3) are more polar than those from methyl linoleate (18:2n-6) since the former peroxyl radicals have at least two molecules of oxygen in a molecule while the latter peroxyl radical has one. This lowers the oxidizability for 20:5n-3 in aqueous Triton X-100 micelles by enhancing the termination reaction rate for peroxyl radicals and by reducing the rate of propagation since there may be more polar peroxyl radicals derived from 20:5n-3 at the surface than within the micelle core. In this study, we measured the effect of three antioxidants, di-tert-butyl-4-methylphenol (BHT), 2,2,5,7,8-pentamethyl-6-chromanol (PMC) and 2-carboxy-2,5,7,8-tetramethyl-6-chromanol (Trolox), on the oxidation of lipids in aqueous micelle. Antioxidants give a clear induction period during oxidation of 18:2n-6 initiated with a water-soluble radical initiator, and its induction length decreases in the order of BHT>PMC>Trolox. This is consistent with the proposed location of three antioxidants: being in the core of micelle, at the surface, or in aqueous phase, respectively. However, BHT does not inhibit the oxidation of 20:5n-3 efficiently, and its rate of oxidation is slower than that observed in the oxidation of 18:2n-6, supporting the idea that polar peroxyl radicals derived from 20:5n-3 are preferentially located at the surface of the micelle. Similar results were obtained when oxidation was initiated with a lipid-soluble radical initiator except antioxidants had lesser effect on the oxidation rate of 20:5n-3.

Oxidative Desulfurization of Naphtha with Hydrogen Peroxide in Presence of Acid Catalyst in Naphtha/Acetic Acid Biphasic System

Oxidative desulfurization of naphtha with H2O2 in the presence of H2SO4 in the naphtha/acetic acid (AcOH) biphasic system was investigated. All organosulfur compounds examined were smoothly oxidized in AcOH by peracetic acid effectively formed from AcOH and H2O2 in the presence of H2SO4. The order of the oxidation reactivities was sulfides, disulfides > benzothiophenes > thiophenes. The organosulfur compounds in octane were also oxidized with H2O2 in the presence of H2SO4 in the octane/AcOH biphasic system. The oxidation proceeded in the AcOH phase and most of the oxidized sulfur compounds resided in this phase, resulting in the successive removal of the sulfur compounds from the octane phase. This oxidative treatment effectively reduced the sulfur content of naphtha, and adsorption with silica gel further reduced the sulfur content to below 0.5 mass ppm. In addition, hydrodesulfurization is an effective pretreatment for this oxidative desulfurization of naphtha, resulting in further reduction of the sulfur content to below 0.1 mass ppm.

Autoxidation of Phosphatidylethanolamine Induced by Copper (II) Ions in Aqueous Dispersions

The kinetics of the aerobic oxidation of phosphatidylethanolamine (PE) induced by copper (II) ions was studied in Tween 20 micelles at 37°C. The kinetic order with respect to concentrations of PE hydroperoxides was 0.3, indicating the oxidation to be initiated by decomposition of the hydroperoxides catalyzed by copper (II) ions. The copper (II) ion-induced oxidation of PE+phosphatidylcholine (PC) in Tween 20 micelles was carried out, and the oxidation rate was noted to increase with the PE/PC mole ratio, possibly due to formation of a PE-copper (II) ion complex.

An attempt to separate nitrogen compounds

Abstract Coal liquids contain large amounts of nitrogen and oxygen compounds which make the processing of these into fuel uneconomical compared with petroleum. This paper investigates a method of separating the nitrogen compounds as sediments to provide valuable chemicals and clean fuel. Indole contained in coal liquids was photo-oxidized in carbon tetrachloride. The presence of galvinoxyl in the photo-oxidation process affected the formation of sediments in such a way as to suggest a radical reaction process. Whilst increased indole concentration led to increased sediment formation, the percentage yield was lower due to increased solubility of the sediment in highly polar solution. An optimum concentration is therefore indicated.