1
4010 J. Phys. Chem. B, Vol. 114, No. 44, 2010
Campos-Rey et al.
1:1 solutions and variation of the pyrene I /I ratio with the
As soon as the micellar potential decreases, the contribution
1 3
of the stabilization is reduced. In the case of Brij 35 micelles
without effective charge, polarity and low hydration of the
interface cause the micellar effect. As we move toward more
negative potentials, the intermediate of reaction for the associa-
concentration of Brij. This material is available free of charge
via the Internet at http://pubs.acs.org.
References and Notes
tive mechanism becomes increasingly more unstable and k
m
(
1) Bentley, T. W.; Harris, H. C. J. Chem. Soc., Perkin Trans. 2 1986,
drops to lower values. The most negative micelle, STS, produces
the highest inhibition. This behavior is consistent with the
unfavorable interaction between the negative micellar surface
and the negative charge developed at the intermediate of the
reaction. We cannot exclude that the low polarity of this micelle
means additional inhibition due to the greatly limited water
accessibility.
(
4), 619–24.
(
2) Kevill, D. N.; D’Souza, M. J. J. Phys. Org. Chem. 2002, 15 (12),
8
81–888.
(3) Kevill, D. N.; Wang, W. F. K. J. Chem. Soc., Perkin Trans. 2 1998,
12), 2631–2637.
(
(4) Song, B. D.; Jencks, W. P. J. Am. Chem. Soc. 1989, 111 (22), 8470–
9
.
(5) Lindman, B.; Wennerstrom, H.; Gustavsson, H.; Kamenka, N.;
Brun, B. Pure Appl. Chem. 1980, 52 (5), 1307–1315.
Finally, as discussed previously, a modification of the water
properties at the interface cannot be excluded. Bunton et al.19
(6) Blokzijl, W.; Engberts, J. Angew. Chem., Int. Ed. 1993, 32 (11),
545–1579.
1
reported rate constants for the solvolysis of substituted benzoyl
chlorides in water/acetonitrile mixtures. If we compare the rate
constant at the micellar interface for the substrates with a highly
dissociative mechanism to the reported rate constants, we can
conclude that the polarity effect of Brij 35 micelles is similar
to that observed in a 40% water/CHCN mixture. By extrapola-
tion of the Hammett plots for that particular water/acetonitrile
(
7) Bunton, C. A.; Nome, F.; Quina, F. H.; Romsted, L. S. Acc. Chem.
Res. 1991, 24 (12), 357–364.
8) Fendler, J. F. Membrane Mimetic Chemistry; John Wiley & Sons
Ltd.: New York, 1982.
9) Otto, S.; Engberts, J. Pure Appl. Chem. 2000, 72 (7), 1365–1372.
10) Alvarez, A. R.; Garc ´ı a-R ´ı o, L.; Herv e´ s, P.; Leis, J. R.; Mejuto,
J. C.; P e´ rez-Juste, J. Langmuir 1999, 15 (24), 8368–8375.
11) Garc ´ı a-R ´ı o, L.; Herv e´ s, P.; Mejuto, J. C.; P e´ rez-Juste, J.; Rodr ´ı guez-
Dafonte, P. New J. Chem. 2003, 27 (2), 372–380.
(
(
(
(
3
mixture, the rate constant for 4-CF Bz can be interpolated as
(
12) Buurma, N. J. AdV. Phys. Org. Chem. 2009, 43, 1–37.
(13) El Seoud, O. A.; Ruasse, M. F.; Possidonio, S. J. Phys. Org. Chem.
2001, 14 (8), 526–532.
14) Buurma, N. J.; Herranz, A. M.; Engberts, J. J. Chem. Soc., Perkin
Trans. 2 1999, (1), 113–119.
15) Chiarini, M.; Gillitt, N. D.; Bunton, C. A. Langmuir 2002, 18 (10),
3836–3842.
-1
ca. 0.01-0.015 s . However, the value obtained in our study
is twice that of the calculated value. This rough estimation could
indicate the enhancement of the associative pathway of the
solvolysis due to a modification of the properties of the water.
As discussed in the previous section, the water at the Brij 35
interface is disturbed in a manner that could enhance its
nucleophilic character and therefore be more reactive in the
(
(
(
16) Buurma, N. J.; Serena, P.; Blandamer, M. J.; Engberts, J. J. Org.
Chem. 2004, 69 (11), 3899–3906.
(
17) Mu n˜ oz, M.; Rodr ´ı guez, A.; Graciani, M. D.; Moya, M. L. Int.
3
solvolysis reaction of 4-CF Bz.
J. Chem. Kinet. 2002, 34 (7), 445–451.
18) Maximiano, F. A.; Chaimovich, H.; Cuccovia, I. M. Langmuir 2006,
22 (19), 8050–8055.
19) Bunton, C. A.; Gillitt, N. D.; Mhala, M. M.; Moffatt, J. R.;
(
Conclusions
(
Solvolysis of substituted benzoyl chlorides are affected by
the presence of nonionic micelles. Both catalysis and inhibition
can be observed and related to the operating solvolysis mech-
anism. Inhibition of solvolysis can be explained by the low
polarity and water hydration of the micellar interface for the
dissociative mechanism. The catalysis of substrates reacting by
means of a highly associative mechanism can be explained in
terms of the enhanced nucleophilicity of bound water. For that
type of mechanism, a strong correlation between the charge of
the micelles and the rate constant of the solvolysis is observed
in binary mixtures of nonionic and ionic surfactants. This
observation suggests electrostatic interactions between the
surfactant charged head groups and the negatively charged
intermediate of the reaction. Cationic micelles strongly stabilize
the intermediate of the reaction and catalyze the process. This
stabilization decreases with the decrease of the charge toward
negative potentials. High negative charge presents the highest
inhibition of the solvolysis reaction due to the unfavorable
charge-charge interactions. In summary, the overall kinetic
effect results from a combination of different contributions: low
water polarity and low water content that lead to modification
of water properties and enhancement of the reactivity of water
as a nucleophile and for electrostatic interactions.
Yatsimirsky, A. K. Langmuir 2000, 16 (23), 8595–8603.
(20) Bunton, C. A. J. Phys. Org. Chem. 2005, 18 (2), 115–120.
(
21) Cabaleiro-Lago, C.; Garc ´ı a-R ´ı o, L.; Herv e´ s, P.; P e´ rez-Juste, J. J.
Phys. Chem. B 2006, 110 (16), 8524–8530.
22) Cabaleiro-Lago, C.; Garc ´ı a-R ´ı o, L.; Herv e´ s, P.; P e´ rez-Juste, J. J.
(
Phys. Chem. B 2009, 113 (19), 6749–6755.
(23) Garc ´ı a-R ´ı o, L.; Leis, J. R.; Moreira, J. A. J. Am. Chem. Soc. 2000,
22 (42), 10325–10334.
1
(
24) Cabaleiro-Lago, C.; Garc ´ı a-R ´ı o, L.; Herv e´ s, P.; P e´ rez-Juste, J. J.
Phys. Chem. B 2005, 109 (47), 22614–22622.
(25) Campos-Rey, P.; Cabaleiro-Lago, C.; Herv e´ s, P. J. Phys. Chem. B
009, 113 (35), 11921–11927.
2
(
(
26) Bunton, C. A.; Savelli, G. AdV. Phys. Org. Chem. 1986, 22, 213.
27) Romsted, L. S. Surfactants in Solution; Plenum Press: New York,
1
1
2
984.
(28) Dong, D. C.; Winnik, M. A. Photochem. Photobiol. 1982, 35 (1),
7–21.
(
29) Bentley, T. W.; Jones, R. O. J. Chem. Soc., Perkin Trans. 2 1993,
, 2351–2357.
(
30) Blandamer, M.; Burgess, J. J. Chem. Soc. ReV. 1975, 4, 55–75.
(31) Eleini, D. I. D.; Barry, B. W.; Rhodes, C. T. J. Colloid Interface
Sci. 1976, 54 (3), 348–351.
(
32) Khan, M. N.; Ismail, E.; Yusoff, M. R. J. Phys. Org. Chem. 2001,
1
4 (10), 669–676.
(33) Graciani, M. D.; Rodríguez, A.; Moya, M. L. J. Colloid Interface
Sci. 2008, 328 (2), 324–330.
34) Mu n˜ oz, M.; Rodríguez, A.; Graciani, M. D.; Moya, M. L. Langmuir
004, 20 (25), 10858–10867.
35) Freire, L.; Iglesias, E.; Bravo, C.; Leis, J. R.; Pe n˜ a, M. E. J. Chem.
(
2
(
Soc., Perkin Trans. 2 1994, (8), 1887–1894.
Acknowledgment. C.C.L. acknowledges the Isidro Parga
Pondal Program fellowship (Xunta de Galicia, Spain) and the
Swedish Research Council. This work has been supported by
the Spanish Ministerio de Educaci o´ n y Ciencia (Project CTQ2007-
(36) Gao, H. C.; Zhao, S.; Mao, S. Z.; Yuan, H. Z.; Yu, J. Y.; Shen,
L. F.; Du, Y. R. J. Colloid Interface Sci. 2002, 249 (1), 200–208.
(
37) Gao, H. C.; Zhu, R. X.; Yang, X. Y.; Mao, S. Z.; Zhao, S.; Yu,
J. Y.; Du, Y. R. J. Colloid Interface Sci. 2004, 273 (2), 626–631.
(38) Mukerjee, P.; Mysels, K. J. Critical micelle concentrations of
aqueous surfactant systems; NSRDS-NBS-36, U.S. Government Printing
Office: Washington, D.C., 1971.
6
4758).
(
(
39) Wennerstrom, H.; Lindman, B. Phys. Rep. 1979, 52 (1), 1–86.
Supporting Information Available: Dependence of surface
tension on surfactant concentration for mixed Brij 35:CTAC
40) Clint, J. H. J. Chem. Soc., Faraday Trans. 1 1975, 71 (6), 1327–
1334.