ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2013, Vol. 87, No. 9, pp. 1462–1469. © Pleiades Publishing, Ltd., 2013. 1462 1 INTRODUCTION Various natural and synthetic chemicals are inte- grated into cosmetic, pharmaceutical and food emul- sions to furnish them with long term stability and an appropriate consistency. The most important are anti- oxidants and surfactants. The objective of antioxidants is to slow down or inhibit the chemical oxidation reac- tion long enough for the product to be used by a con- sumer whereas surfactants are the system structure stabilizing agents [1, 2]. Antioxidants are usually cate- gorized into water soluble and oil soluble groups. The main symbolic of the hydrophilic antioxidant is natu- rally occurring vitamin C (ascorbic acid, AH 2 ) [3, 4]. Vitamin C is a white crystalline substance having similar structure of glucose with the molecular for- mula of C 6 H 8 O 6 [5, 6]. It is a water-soluble com- pound, which is described by a broad spectrum of anti- oxidant activities due to its potentiality of reacting with numerous aqueous free radicals and reactive oxy- gen species [7, 8]. Strong reducing power of AH 2 is due to its small redox potential value of –0.223 V at pH 3. However the pH as well as medium in which it is solu- ble, affect the redox potential which in turn influence the rate of reaction [9, 10]. 1 The article is published in the original. Surfactants (surface active agents) are amphipathic molecules that composed of a non-polar hydrophobic portion, usually a straight or branched hydrocarbon or fluorocarbon chain containing 8–18 carbon atoms, which is attached to a polar or ionic portion (hydro- philic). The hydrophilic portion can, therefore, be nonionic, ionic or zwitterionic [11]. Nonionic surfac- tants, which may be acidic or basic in nature differ from both cationic and anionic surfactants in that the molecules are actually uncharged. Octadecylamine (ODA, C 18 H 39 N) is nonionic basic surfactant insolu- ble in water and soluble in organic solvents. Surfactant molecules colligate in water above a certain concen- tration to form colloidal particles called micelles [12, 13]. The self assembly process relies on many parame- ters such as salinity, temperature, solvent condition, and solvent architecture. Surfactants are used in vari- ous applications, from cleaning products [14–18] to nanotechnology [19–22] and are of particular rele- vance to biological cell membrane [14, 18]. The study of electron transfer processes in surfac- tant has added a new dimension to biological research [23–32]. Chemical reactions in surfactant media exhibit features that are completely different from those in non aqueous solvents. Surfactant catalyzes the reactions depending on the nature of surfac- tant/micelle being as cationic, anionic, zwitterionic or nonionic. It was found that the surfactant environ- CHEMICAL KINETICS AND CATALYSIS Factors Influencing the Mechanism of Surfactant Catalyzed Reaction of Vitamin C-Ferric Chloride Hexahydrate System 1 Muhammad Akhyar Farrukh a , Robina Kauser a , and Rohana Adnan b a Department of Chemistry, GC University Lahore, Lahore 54000, Pakistan b School of Chemical Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia e-mail: akhyar100@gmail.com Received August 24, 2012 Abstract—The kinetics of vitamin C by ferric chloride hexahydrate has been investigated in the aqueous eth- anol solution of basic surfactant viz. octadecylamine (ODA) under pseudo-first order conditions. The critical micelle concentration (CMC) of surfactant was determined by surface tension measurement. The effect of pH (2.5–4.5) and temperature (15–35°C) in the presence and absence of surfactant were investigated. Acti- vation parameters, ΔE a , ΔH # , ΔS # , ΔG ≠ , for the reaction were calculated by using Arrhenius and Eyring plot. Surface excess concentration (Γ max ), minimum area per surfactant molecule (A min ), average area occupied by each molecule of surfactant (a), surface pressure at the CMC (Π max ), Gibb’s energy of micellization ( ), Gibb’s energy of adsorption ( ), were calculated. It was found that the reaction in the presence of surfac- tant showed faster oxidation rate than the aqueous ethanol solution. Reaction mechanism has been deduced in the presence and absence of surfactant. Keywords: surfactant, vitamin C, kinetics, catalysis, thermodynamics parameters. DOI: 10.1134/S003602441309032X ΔG M ° ΔG ad °