UV–Spectral Study on the Effects of Inert Salts on the Nonionic Micellar Solubilization of Phenyl Salicylate in the Absence and Presence of a Cationic Surfactant Under Alkaline Aqueous Medium

Abstract

The values of the fraction of ionizes phenyl salicylate, f_PS-, obtained from initial absorbance measurement of phenyl salicylate at 350 nm, remain unchanged with the increase in [CH₃CO₂Na] from 0.0 to 0.7 M at 0.01 M NaOH (f_PS- ≈ 0.70) and 0.02 M NaOH (f_PS- ≈ 0.93). The values of f_PS- decrease from ∼ 1.0 to 0.90 and ∼ 1.0 to 0.84 with the increase in respective [CH₃CO₂Na] and [NaBr] from 0.0 to 0.6 M at 0.01 M NaOH, 0.02 M C₁₂E₂₃(=C₁₂H₂₅(OCH₂CH₂)₂₃OH) and 0.01 M CTABr (=C₁₆H₃₃NMe₃Br).

Keywords:

• Inert salts
• micellar solubilization
• nonionic and cationic surfactants
• Phenyl salicylate
• UV–spectral study

The authors thank Universiti Malaya for financial support (Grant No. F0718=2002B) for carrying out this work.

Notes

^a [Phenyl salicylate]₀ = 2.0 × 10⁻⁴ M, 35°C, 98% (v/v) H₂O and 2% (v/v) CH₃CN.

^b The required amounts of [C₆H₅COONa] were generated into the reaction mixtures by using the stock solutions (w M) of benzoic acid in (w + 0.05) M aqueous NaOH. The stock solution (0.5 M) of NaOH was used to produce a fixed known concentration of NaOH into the reaction mixture for each kinetic run.

^c f_PS- = /A₀ where A₀ = 1.40.

^a [Phenyl salicylate]₀ = 2.0 × 10⁻⁴ M, 35°C, 98% (v/v) H₂O and 2% (v/v) CH₃CN.

^b [NaOH] = 0.01 M.

^c The required amounts of [C₆H₅COONa] were generated into the reaction mixtures by using the stock solutions (w M) of benzoic acid in (w + 0.05) M aqueous NaOH. The stock solution (0.5 M) of NaOH was used to produce a fixed known concentration of NaOH into the reaction mixture for each kinetic run.

^d f_PS- = /A₀ where A₀ = 1.40 and parenthesized values were calculated with A₀ = 1.47.