Micellar Effect on Kinetics of Oxidation of Acetophenone by N-Bromophthalimide in Aqueous Acetic Acid Medium

Abstract

The effect of cationic micelles of cetyl trimethyl ammonium bromide (CTAB) and anionic micelles of sodium dodecyl sulphate (SDS) on the kinetics of oxidation of acetophenone by N-bromophthalimide (NBP) was studied iodometrically at 308 K. In addition to kinetic experiments, conductivity measurements have also been done to obtain critical micelle concentration and other thermodynamic properties. The kinetic observations indicate fractional order and first order dependence, with respect to [acetophenone] and [NBP] respectively. Cationic surfactant (CTAB) strongly catalyses the oxidation of acetophenone in aqueous acetic acid medium and typical k _obs and [CTAB] profile was observed, that is, with the progressive increase in [CTAB], the reaction rate increased, at higher concentration constancy in k _obs was observed, whereas anionic surfactant (SDS) was found to show no considerable effect on reaction rate. Mercuric acetate and phthalimide exhibited nil effect on the reaction rate. The presence of inorganic salts (KCl, KBr) exhibits a severe hike in the reaction rate. The various activation parameters in presence of CTAB and SDS have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed. The rate constants k _(obs), cooperativity index (n), binding constants (Ks) with surfactants has been evaluated.

Keywords:

• Acetophenone
• cetyl trimethyl ammonium bromide
• kinetics
• N-bromophthalimide
• oxidation
• sodium dodecyl sulphate

Acknowledgments

Y. R. K. thanks the Chhattisgarh Council of Science and Technology, Chhattisgarh for the Minor Research Project Grant.

Notes

Experimental conditions: [T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, [H⁺] = 1 × 10⁻⁵ mol dm⁻³ and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³].

Experimental conditions: T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, [H⁺] = 1 × 10⁻⁵ mol dm⁻³ and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³].

Experimental conditions: T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³]. [H⁺] = 1 × 10⁻⁵ mol dm⁻³].

Experimental conditions: T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³]. [H⁺] = 1 × 10⁻⁵ mol dm⁻³].

^a Literature value of CTAB at 25°C = 9.2 × 10⁻⁴ mol dm⁻³.

Experimental conditions: T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, [H⁺] = 1 × 10⁻⁵ mol dm⁻³ and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³].

Experimental conditions: T = 308 K, 50% (v/v) acetic acid, [NBP] = 2 × 10⁻⁴ mol dm⁻³, [acetophenone] = 3 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 4.0 × 10⁻⁴ mol dm⁻³ [SDS] = 8.3 × 10⁻³ mol dm⁻³, [H⁺] = 1 × 10⁻⁵ mol dm⁻³ and [CTAB] = 9.8 × 10⁻⁴ mol dm⁻³].