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
Mn. Khan et al., 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 PHYS ORG, 14(10), 2001, pp. 669-676
The pseudo-first-order rate constants (k(obs)) for the alkaline hydrolysis
of phenyl benzoate (PB) decrease monotonically from 72.0 x 10(-4) to 7.4 x
10(-4) s(-1) with increase in the concentration of polyoxyethylene 23 laury
l ether ([C12E23](T)) from 0.0 to 0.01 M at 0.01 M NaOH and 35 degreesC. Th
e results fit satisfactorily to a pseudophase model of micelles. The values
of k(obs) for the hydrolysis of ionized phenyl salicylate (PS-) are almost
independent of [IC12E23](T) within the range 0.0-0.02 M at 0.01 and 0.03 M
NaOH and 35 degreesC. The rate of alkaline hydrolysis of PB appears to be
negligible in the micellar pseudophase than in the aqueous pseudophase, whi
ch is ascribed to the extremely low concentration of HO- in the micellar re
gion of micellized PB molecules. The values of k(obs) for hydrolysis of PB
and PS- at 0.01 M NaOH become almost zero at greater than or equal to0.02 a
nd greater than or equal to0.03 m C12E23, respectively. The effects of mixe
d C12E23-CTABr on k(obs) for the alkaline hydrolysis of PB reveal that mixe
d micelles behave like pure CTABr micelles within the [C12E23](T) range 0.0
-5 x 10(-4) M whereas an increase in [C12E23](T) from greater than or equal
to7 x 10(-4) to 0.02 M decreases k(obs) at 0.006, 0.01, 0.02 and 0.03 M CT
ABr. 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 [C1
2E23](T) in the range >5 x 10(-4) 0.02 M. An increase in [C12E23](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. Copyright (C) 2001 John Wiley & Sons, Ltd.