Effect of Cationic Micelle on the Kinetics of Oxidation of Citric Acid by N-Bromophthalimide in Acidic Medium

Abstract

Kinetics of the oxidation of citric acid (CA) by N-bromophthalimide (NBP) has been studied in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) at 35°C. The CMC value is lower than those given in the literature for aqueous solutions of CTAB without added electrolyte. The reaction is strongly catalyzed by cationic micelle, CTAB with a progressive increase in CTAB concentration the reaction rate increased, at higher concentration constancy in the rate constant was observed. The reaction follows first and fractional order kinetics in NBP and citric acid, respectively. The reaction follows inverse fractional order with respect to perchloric acid. The Arrhenius equation is found to be valid for the reaction. A detailed mechanism with the associated reaction kinetics is discussed. The catalytic role of CTAB micelles is discussed in terms of the Menger and Portnoy model.

Keywords:

• Binding constant
• cetyltrimethylammonium bromide
• citric acid
• kinetics
• micellar catalysis
• N-bromophthalimide
• oxidation

Y. R. K. thanks the University Grants Commission, New Delhi for the Research Project Grant. The authors also thank Professor Laurence S. Romsted, Department of Chemistry, Wright–Rieman Laboratories, New Jersey (USA) for valuable discussions and fruitful suggestions.

Notes

Literature value at 25°C is 9.2 × 10⁻⁴ mol dm⁻³ [CA] = 2 × 10⁻² mol dm⁻³; [NBP] = 2 × 10⁻⁴ mol dm⁻³; [Hg (OAc)₂] = 7.5 × 10⁻³ mol dm⁻³ [HClO₄] = 1 × 10⁻³ mol dm⁻³; Temperature at 35°C.

[CTAB] = 9 × 10⁻⁴ mol dm⁻³, [Hg(OAc)₂] = 7.5 × 10⁻⁴ mol dm⁻³, Temperature at 35°C.

[CA] = 2 × 10⁻² mol dm⁻³; [NBP] = 2 × 10⁻⁴ mol dm⁻³, [Hg (OAc)₂] = 7.5 × 10⁻⁴ mol dm⁻³, [HClO₄] = 1 × 10⁻³ mol dm⁻³, acetic acid 30% (v/v); temperature at 35°C.