Effect of cationic surfactants on limonene oxidation

Abstract

Kinetic regularities of free radical formation during limonene oxidation with molecular oxygen in a chlorobenzene solution at 60 °С were studied by the inhibitor method under autooxidation conditions and with additives of surfactants (cetyltrimethylammonium chloride and bromide) using dimer 2,2´ bis[2 (p dimethylaminophenyl)indane 1,3 dione] and α toco pherol as acceptors of radicals. In the presence of the surfactants, the rates of radical generation and oxidation increase sharply. The catalytic activity of cetyltrimethylammonium chloride is much higher than that of the corresponding bromide.Key words: 2,2´ bis[2 (p dimethylaminophenyl)indane 1,3 dione], α tocopherol, oxida tion of limonene, catalysis, formation of free radicals, cetyltrimethylammonium chloride, cetyltrimethylammonium bromide.Limonene (4 isopropenyl 1 methyl 1 cyclohexene, LH) is a natural cycloolefin of the terpene series contain ing two unsaturated bonds. Limonene is found in almost all essential oils, and it is readily oxidized with molecular oxygen via the free chain radical mechanism. 1-3 The oxi dation products at moderate temperatures are isomeric hydroperoxides (LOOH), whose composition depends on oxidation conditions. 4 The rate of oxygen absorption (W O 2 ) during limonene oxidation is proportional to W i 0.5 (W i is the chain initiation rate), indicating a square chain termination, and is described by the known 5 equation of the theory of liquid phase oxidation of hydrocarbons (RH)where k p and k t are the apparent rate constants of chain propagation and termination, respectively. The recent studies 6-11 showed that additives of sur factants can affect substantially the rate and mechanism of hydrocarbon oxidation. Surfactant molecules form as sociate microaggregates in a nonpolar hydrocarbon me dium in which polar oxidation products, viz., water, alcohols, hydroperoxides, and others, are concentrated. The character of this influence depends on the nature of a surfactant and oxidized hydrocarbon.Quaternary ammonium salts are known to accelerate the oxidation of hydrocarbons and fats 10-12 and possess a bactericidal effect. 13 The same effect is inherent in some phosphonium, sulfonium, selenium, and arsenic salts. 10 Several authors call the catalysis of oxidation with cat ionic surfactants as "halide catalysis" 14,15 ; these surfac tants are believed 16-18 to activate oxygen. The bacteri cidal effect is explained by binding cationic surfactants with membrane proteins. 13 We found 19,20 that the cata lytic effect of cetyltrimethylammonium bromide (CTAB) on the oxidation of ethylbenzene is caused by the acceler ated decomposition of ROOH in surfactant microreactors with escape of RO 2 • radicals to the solvent bulk followed by the chain radical oxidation of ethylbenzene.We have previously 19,20 used the inhibitor method and dimer 2,2´ bis[2 (p dimethylaminophenyl)indane 1,3 dione] (FF) as an acceptor of free radicals to study the kinetics of free radical formation during the oxidation of ethylbenzene with molecular oxygen initiated by an...

Lipid Oxidation in Homogeneous and Micro-Heterogeneous Media in Presence of Prooxidants, Antioxidants and Surfactants

“…It affects peroxide bond, weakens it and facilitates decomposition into free radicals. Apparent activation energies of hydroperoxide decay decrease to 50-60 kJ/mol in mixed micelles from ~ 100 kJ/mol for thermal decay [51].…”

“…The ethylbenzene is oxidized selectively into acetophenon and water catalyzed with the combination of CTAB and cobalt acetylacetonate [53]. Under similar conditions limonene is oxidized with the primary formation of a carbonyl compound (carvon) [51].…”