S N 2 reactions of a sulfonate ester in mixed cationic/phosphine oxide micelles

J of Physical Organic Chem

Yusoff

2001

The pseudo-first-order rate constants (k obs ) for the alkaline hydrolysis of phenyl benzoate (PB) decrease monotonically from 72.0 Â 10 À4 to 7.4 Â 10 À4 s À1 with increase in the concentration of polyoxyethylene 23 lauryl ether ([C 12 E 23 ] T ) from 0.0 to 0.01 M at 0.01 M NaOH and 35°C. The results fit satisfactorily to a pseudophase model of micelles. The values of k obs for the hydrolysis of ionized phenyl salicylate (PS À ) are almost independent of [C 12 E 23 ] T within the range 0.0-0.02 M at 0.01 and 0.03 M NaOH and 35°C. The rate of alkaline hydrolysis of PB appears to be negligible in the micellar pseudophase than in the aqueous pseudophase, which is ascribed to the extremely low concentration of HO À in the micellar region of micellized PB molecules. The values of k obs for hydrolysis of PB and PS À at 0.01 M NaOH become almost zero at !0.02 and !0.03 M C 12 E 23 , respectively. The effects of mixed C 12 E 23 -CTABr on k obs for the alkaline hydrolysis of PB reveal that mixed micelles behave like pure CTABr micelles within the [C 12 E 23 ] T range 0.0-5 Â 10 À4 M whereas an increase in [C 12 E 23 ] T from !7 Â 10 À4 to 0.02 M decreases k obs at 0.006, 0.01, 0.02 and 0.03 M CTABr. However, the values of k obs are significantly higher at [CTABr] T = 0.006, 0.01, 0.02 and 0.03 M than at [CTABr] T = 0 in the presence of [C 12 E 23 ] T in the range >5 Â 10 À4 -0.02 M. An increase in [C 12 E 23 ] T from 0.0 to 0.015 M causes nearly a twofold increase in k obs at 0.01, 0.02 and 0.03 M CTABr and 0.01 M NaOH. EFFECTS OF SURFACTANTS ON HYDROLYSIS OF PHENYL SALICYLATE AND BENZOATE 671 6.41 AE 0.07 6078 AE 23 0.074 AE 0.005 a [Phenyl salicylate] 0 = 2 Â 10 À4 M, 35°C, l = 350 nm, reaction mixture for each kinetic run contained 2% (v/v) CH 3 CN. b Error limits are standard deviations. c The absorbance value (A obs = 0.012) remained unchanged with change in the reaction time (t) from $20 s to 3 h.Figure 3. Effect of [C 12 E 23 ] T on E app for hydrolysis of PB at (◊) 0.0, (*) 0.006, (~) 0.01, (&) 0.02 and (!) 0.03 M CTABr Figure 4. Effect of [C 12 E 23 ] T on k obs for hydrolysis of PS À at (*) 0.01, (~) 0.02 and (!) 0.03 M CTABr

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Section: Effect Of C 12 E 23 ±Ctabr Mixed Micelles On K Obs For the Hmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Effects of pure non‐ionic and mixed non‐ionic–cationic surfactants on the rates of hydrolysis of phenyl salicylate and phenyl benzoate in alkaline medium

J of Physical Organic Chem

Yusoff

2001

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“…318 M. N. KHAN AND E. ISMAIL increase both the fractional micellar ionization (a) and the volume of the micellar pseudophase. [24] The mechanism by which the presence of C 12 E 23 in CTABr micelles causes the decrease in the CTABr micellar affinity of counterions may be described qualitatively as follows. It is known that the voluminous headgroup mantle of C 12 E 23 micelle is associated with considerable amount of water.…”

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