Effects of Cationic Micelles on the Rate of Alkaline Hydrolysis of N-(2-methoxyphenyl)phthalimide

Abstract

Pseudo-first-order rate constants (k_obs), obtained for the reaction of N-(2-methoxyphenyl)phthalimide (1) with HO⁻ at a constant [NaOH] and varying concentrations of cetyltrimethylammonium bromide ([CTABr]_T = 0.0–0.20 M), have been analyzed in terms of both pseudophase ion-exchange (PIE) model and Berezin's pseudophase (BPP) model. Although both models give the best observed data fit with least-squares values not significantly different from each other, the calculated values of K_S from BPP model appear to be more reliable compared to those from PIE model. The nonlinear decrease of k_obs with the increase of [NaBr] at the constant [NaOH] and [CTABr]_T is explained in terms of pseudophase micellar model coupled with an empirical equation which could indirectly give the measure of the ion-exchange Br⁻/HO⁻.

Keywords:

• Alkaline hydrolysis
• an empirical approach for the analysis of ion-exchange at ionic micellar surface
• BPP micellar model
• cationic surfactant
• kinetics
• N-(2-methoxyphenyl)phthalimide
• PIE micellar model
• sodium bromide

Acknowledgments

The authors thank Universiti Malaya for financial support for carrying out this work.

Notes

^a [1 ₀] = 2.0 × 10⁻⁴ M, [NaOH] = 1.0 × 10⁻³ M, 30°C, λ = 290 nm, and the reaction mixture for each kinetic run contained 98% (v/v) H₂O and 2% (v/v) CH₃CN.

^b Total concentration of CTABr.

^c Calculated from Equation (3) with kinetic parameters listed in Table 3.

^d RE = 100 (k_obs − k_cald)/k_obs.

^e Calculated from Equation (5) with kinetic parameters listed in Table 3.

^f Error limits are standard deviations.

^a [1 ₀] = 2.0 × 10⁻⁴ M, [NaOH] = 2.0 × 10⁻³ M, 30°C, λ = 290 nm, and the reaction mixture for each kinetic run contained 98% (v/v) H₂O and 2% (v/v) CH₃CN.

^b Total concentration of CTABr.

^c Calculated from Equation (3) with kinetic parameters listed in Table 3.

^d RE = 100 (k_obs − k_cald)/k_obs.

^e Calculated from Equation (5) with kinetic parameters listed in Table 3.

^f These data were obtained from Ref. 17 where kinetic runs were carried out in mixed H₂O–CH₃CN solvents at 2.0 × 10⁻⁴ M 1, 2.0 × 10⁻³ M NaOH, 290 nm, 35°C and A_∞ = δ_app [R₀] +A₀.

^g Error limits are standard deviations.

^a β = 0.8.

^b K_OH = 115 M⁻¹.

^c d_i = k_{obs i} – k_{cald i} with k_{obs i} and k_{cald i} representing observed and least-squares calculated rate constants at the i-th value of [Dn], respectively.

^d 10⁴ CMC = 7.0 M and  = 21.3 M⁻¹ s⁻¹.

^e Error limits are standard deviations.

^f 10⁴ CMC = 9.5 M and  = 29.1 M⁻¹ s⁻¹.

^a [1 ₀] = 2.0 × 10⁻⁴ M, [NaOH] = 1.0 × 10⁻³ M, 30°C, λ = 290 nm, and the reaction mixture for each kinetic run contained 98% (v/v) H₂O and 2% (v/v) CH₃CN.

^b Calculated from Equation (6) with 10² k₀ = 41.5 s⁻¹, 10³ θ = 9.86 ± 0.93 s⁻¹, K = 545 ± 89 M⁻¹.

^c RE = 100 (k_obs − k_cald)/k_obs.

^d Error limits are standard deviations.