Kinetics and Mechanism of Cetyltrimethylammonium Bromide Catalyzed N-Bromosuccinimide Oxidation of D-Mannose in Acidic Medium

Abstract

The kinetics and mechanism of N-bromosuccinimide (NBS) oxidation of D-mannose in the absence and presence of cetyltrimethylammonium bromide (CTAB) in acidic media have been studied under the condition [D-mannose]_T ≫ [NBS]_T at 40°C. Under the kinetic conditions, both the slower uncatalyzed and faster catalyzed paths go on. Both the paths show the fractional and first order dependence on [D-mannose] and [NBS]_T, respectively. The rate decreased with increase in acidity. Neither succinimide (NHS) nor Hg(II) influenced the reaction rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50°C). The influence of salts on the reaction rate was also studied. CTAB accelerates the reactions and the observed effects have been explained by considering the hydrophobic and electrostatic interaction between the surfactants and reactants. In the reaction, approximately 1 mole of NBS oxidized one mole of D-mannose. A reaction scheme of the oxidation of D-mannose by NBS was found to be in consistent with the rate law and the reaction stoichiometry.

Keywords:

• CTAB
• D-mannose
• kinetics
• micellar catalysis
• oxidation

Acknowledgments

The project was supported by the Foundation of Chhattisgarh Council of Science and Technology (CGCOST), Raipur, (Chhattisgarh), India (621/CCOST/MRP/07).

The authors are grateful to Professor Laurence S. Romsted, Department of Chemistry, Wright-Rieman Laboratories, Rutgers University, New Brunswick, NJ, for valuable discussions and fruitful suggestions.

Notes

Reaction conditions: (a) [Hg(OAc)₂] = 5.0 × 10⁻⁴ mol dm⁻³; (b) [CTAB] = 1.2 × 10⁻³ mol dm⁻³, [Hg(OAc)₂] = 5.0 × 10⁻⁴ mol dm⁻³.

Reaction conditions: (a) [NBS] = 2.0 × 10⁻⁴ mol dm⁻³; [D-mannose] = 2.5 × 10⁻² mol dm⁻³; [H₂SO₄] = 0.5 × 10⁻⁴ mol dm⁻³; [Hg(OAc)₂] = 5.0 × 10⁻⁴ mol dm⁻³; acetic acid (30%(v/v)); (b) [NBS] = 2.0 × 10⁻⁴ mol dm⁻³; [D-mannose] = 2.5 × 10⁻² mol dm⁻³; [H₂SO₄] = 0.5 × 10⁻⁴ mol dm⁻³; [Hg(OAc)₂] = 5.0 × 10⁻⁴ mol dm⁻³; [CTAB] = 1.2 × 10⁻³ mol dm⁻³; acetic acid (30%(v/v)).

Reaction conditions: [NBS] = 2.0 × 10⁻⁴ mol dm⁻³; [D-mannose] = 2.5 × 10⁻² mol dm⁻³; [Hg(OAc)₂] = 5.0 × 10⁻⁴ mol dm⁻³; [H₂SO₄] = 0.5 × 10⁻⁴ mol dm⁻³; acetic acid (30%(v/v)).