Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 94

Table 4 Effect of surfactants on dissociation constants
Surfactant a Conc. T (°C) Chemical D p K a (obs) b Reference

HDTMA Br 3.7 mM 30 4-Nitrophenol −0.59 Seguchi (1979)

3-Methyl-4-nitrophenol −0.56

4-Nonylphenol −1.61

1.2 mM 25 Methyl 4-hydroxybenzoate −0.29 Loh and Volpe (1992)

10 mM 25 Benzoic acid −0.56 Gerakis et al. (1993)

2-Acetyloxybenzoic acid −0.21

DAC 40 mM 30 3-Hydroxybenzoic acid −1.01 Isoda et al. (1997)

2-Methylbenzoic acid −0.91

SDS 5 w/w% 25 4-Methylaniline +1.58

∼

Drummond et al. (1989)

1.91

9.6 mM 25 Methyl 4-hydroxybenzoate +0.23 Loh and Volpe (1992)

10 mM 25 Benzoic acid −0.19 Gerakis et al. (1993)

2-Acetyloxybenzoic acid −0.14

20 mM 25 Benzimidazole +1.30 Saha et al. (1994)

SDBS 3.7 mM 30 4-Nitrophenol +0.01 Seguchi (1979)

3-Methyl-4-nitrophenol +0.06

4-Nonylphenol +2.58

Tween 80 10 mM 25 Benzoic acid +0.40 Gerakis et al. (1993)

2-Acetyloxybenzoic acid +0.15

2-Nitrophenol +0.39

20 mM 25 Benzimidazole −0.60 Saha et al. (1994)

Brij-35 3.7 mM 30 4-Nitrophenol +0.01 Seguchi (1979)

3-Methyl-4-nitrophenol −0.01

4-Nonylphenol +1.05

C 12 E 8 5 w/w% 25 4-Methylaniline −0.43 Drummond et al. (1989)

4- tert -Butylphenol +1.65
a DAC, dodecylammonium chloride, C 12 E 8 , C 12 H 25 O(CH 2 CH 2 O) 8 H.
b

∆ p K a (obs) = p K a (obs) (in the presence of surfactant) − p K a (obs) (water).

electrostatic effect is calculated to be approximately −1.7 from the surface potential
of the HDTMA Br micelle of about 100 mV (Drummond et al. 1989), the nonelec-
trostatic effect by HDTMA Br micelle may be much greater than that of Tween 80.
Isoda et al. (1997) reported similar electrostatic effects of ionic micelles on p K a obs
by using the ultrasonic relaxation absorption method. Similar trends were observed
for simple phenols with variations caused by the substituent effects through inductive
and resonance terms, whereas the introduction of a long alkyl chain markedly
enhanced the difference of p K a by 1-2 (Seguchi 1979). Therefore, the hydrophobic
effect is considered to be one of the dominant factors controlling the p K a obs value.
The p K a values of anilines and hetero-aromatics including nitrogen atom(s) in
anionic micelles were oppositely increased by the electrostatic effects among the
protonated solubilizate and anionic head groups of surfactants (Saha et al. 1994;
Sarpal and Dogra 1993). The p K a values of organic chemicals in Table 4 are those
specific to the constant concentration of surfactants and are known to vary with