Dephosphorylation of paraoxon by hydroxamate ions in micellar media

Article abstract of DOI:10.1016/j.tetlet.2004.10.023

The rate-surfactant concentration profiles for the reaction of the insecticide paraoxon with hydroxamate ions (R(CO)?NHO^-, R = CH₃, R = C₆H₅, R = 2-HOC₆H ₄) in aqueous solutions of cetyltri

Full text of DOI:10.1016/j.tetlet.2004.10.023

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 9103–9105
Dephosphorylation of paraoxon by hydroxamate ions in
micellar media
*
Kallol K. Ghosh, Manmohan Lal Satnami and Daliya Sinha
School of Studies in Chemistry, Pt. Ravishankar Shukla University, Raipur (C.G.) 492010, India
Received 24 July 2004; revised 26September 2004; accepted 5 October 2004
Abstract—The rate–surfactant concentration profiles for the reaction of the insecticide paraoxon with hydroxamate ions
ꢀ
ꢀ ꢀ
6 5 6 4
H , R = 2-HOC H ) in aqueous solutions of cetyltrimethylammonium salts, CTAX (X = Br ,
(
R(C@O)ÆNHO , R = CH
3
, R = C
H ) have been measured at pH11.0 at 30ꢀC. All these profiles are typical of micelle-assisted bimolecular reactions involv-
ing interfacial ion exchanges. The salicylhydroxymic acid–CTACl combination is most reactive.
2004 Elsevier Ltd. All rights reserved.
ꢀ
ꢀ
Cl , SO
3
ꢁ
Hydroxamate ions are a-effect nucleophiles, that is, their
reactivity is greater than that expected from the basicity
1
–3
of the nucleophile. It has been known for many years
that a nucleophiles are excellent deacylating and de-
phosphorylating agents. Despite several decades of re-
4
–13
search,
the need for new and improved methods
Scheme 1. Reagents: R = C
CH
mic acid, SHA), CTAX = n-C16
6 5
H (benzohydroxamic acid, BHA), R =
for the detoxification of organophosphates, phospho-
nates and phosphinates continues. These are persistent
acetylcholinesterase inhibitors and neurotoxic agents
and are used as pesticides and chemical warfare
3
(acetohydroxamic acid, AHA), R = 2-HOC
6
H
4
ꢀ
(salicylhydroxa-
ꢀ
+
ꢀ
H
33N (Me)
3
X ; X = Br (CTAB),
ꢀ
ꢀ
ꢀ
ꢀ
X
= Cl (CTACl), X = SO
3
H
(CTAP).
1
4,15
agents.
Nucleophile-aided hydrolysis and oxidation
To our knowledge there is no report describing the
detoxification reaction of paraoxon catalyzed by
hydroxamate ions in the presence of surfactants. How-
are the preferred methods for their detoxification. In this
report we focus on a new method for the decomposition
of simulants of the G-type agents (RO(P@O)XY),
RO = (CH ) CCH(CH )O, X = F, Y = CH (Soman,
1
6
17
ever, Brown and co-workers and Um et al. recently
reported an improved method for environmental decon-
tamination of paraoxon using La(OCH ) and alkali
3
3
3
3
GD); RO = (CH ) CHO, X = F, Y = CH (Sarin, GB);
2
3
3
3
3
RO = (CH ) N, X = CN, Y = C H (Tabun, GA) and
3
2
2
5
ꢀ
+
+
metal ethoxides (EtO M ; M = Li, Na, K). Similarly
the significant contributions of Buncel and co-work-
the pesticide paraoxon (RO = Y = OC H , X = OC H
4-
2
5
6
NO ) (Scheme 1) using hydroxamate ions in the pres-
2
7,18,19
4
ꢀ
ꢀ
ꢀ
ers
and Morales-Rojas and Moss deserve special
ence of cationic surfactants (CTAX; X = Br , Cl ,
SO H ). The least toxic structural analogues that di-
ꢀ
mention in this context. In our previous studies, we ob-
served large rate enhancements in hydroxamic acid–cat-
ionic surfactant systems for the hydrolysis of carboxylic
3
rectly mimic or imitate the actual chemical warfare
agents are called simulants. The use of simulants make
it easier to isolate the variables that effect the agentꢀs
chemistry.
2
0,21
esters.
It is very desirable to replace current, prob-
lematic and environmentally harmful corrosive decon-
taminants, like hypochlorite.
The first order rate constant, kobs for the reaction of para-
oxon with the three hydroxamate ions (a-nucleophiles)
and p-chlorophenol (normal nucleophile) have been
measured spectrophotometrically under pseudo-first
order conditions in water at 30ꢀC, with the nucleophiles
in large excess over the substrate in each case. The pH
Keywords: Hydroxamate ions; paraoxon; Dephosphorylation; The
a-effect.
Corresponding author. Tel.: +91 7712262249; e-mail: kallolkghosh@
yahoo.com
*
0
040-4039/$ - see front matter ꢁ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.10.023

9104
K. K. Ghosh et al. / Tetrahedron Letters 45 (2004) 9103–9105
Table 1. Kinetic data for the reaction of paraoxon with hydroxamate ions in micellar media at pH11.0 and 30ꢀC, l = 0.1M KCl
3
4
ꢀ1
[
Surfactant] · 10 M
k
obs · 10 (s
)
6
p-ClC H
4
OH
AHA
BHA
SHA
CTAB
CTAB
CTACl
CTAB
CTACl
CTAB
CTACI
CTAP
0
1
2
3
5
7
9
1
1
1
1
.0
0.76
2.57
3.11
0.76
4.42
4.80
2.67
5.81
7.66
2.67
9.47
10.2
2.67
4.15
6.35
.8
0.75
1.18
1.27
1.83
1.85
.6
.61.10
.0
1.51
1.90
3.40
5
5.10 10.5
8.6 7.25
1.20
––
1.65
1.80
1.87
1.75
1.65
1.60
1.45
1.95
2.00
2.15
2.05
1.85
1.82
1.76
3.75
4.10
4.28
4.20
4.10
3.95
3.71
5.20
5.40
5.52
5.30
5.10
5.00
4.97
8.20
7.15
6.23
5.50
5.00
4.55
4.08
10.0
9.00
8.32
7.70
7.20
6.60
6.45
6.90
5.75
3.63
.0
.1
1.30
1.20
––
2.0
4.0
6.0
8.2
0.90
0.60
2
8
was kept constant at 11.0. All the reactions followed rate
Eq. 1.
of bimolecular micellar assisted reactions. The ob-
served first order rate constant, k increased very shar-
w
ply with increasing [CTACl] and then decreased for
SHA. Rate–surfactant profiles for other hydroxamic
acids are similar but the above system was most reactive.
SHA is seven times more reactive than AHA toward
paraoxon, and reaches its maximum reactivity at a lower
concentration of CTAX. These observations reflect
the greater hydrophobicity of SHA, which affords en-
hanced binding to the CTAX micelles and more efficient
reaction with the bound substrate. The marked increase
kobs ¼ k þ k ½NuŠ
ð1Þ
0
Nu
ꢀ
where k = k
0
+ kOH [OH ] + k [Nu].
H O
2
2
It is assumed that catalysis by the nucleophile (HA) is
dependent upon the ionization state of the hydroxamic
acid. Questions regarding the structure of the hydrox-
ꢀ
ꢀ
amic acid anions (N or O acids) have been the subject
2
2–26
of several computational investigations.
known whether they are N-acids or O-acids in micellar
It is not
ꢀ
ꢀ
in micellar effects observed when Cl replaced Br is ex-
pected since Cl is known to be more readily exchange-
able than Br . Moreover, the high nucleophilicity of
2
7
ꢀ
medium. The N-acid form is less nucleophilic than
the O-acid form. This argument is supported by the fact
that the O-acylated product (C H CONHOCOMe) was
ꢀ
hydroxamate ions is typical behavior of a nucleophiles.
The interfacial ion exchange and the binding constant of
the substrate are the key factors at the origin of micellar
catalysis. It is now recognized that accelerations in surf-
actant solutions arise not because of an increase in the
6
5
2
identified by Um et al. Eq. 1 may be written to describe
kHA; [HA]T is the analytical concentration of hydrox-
amic acids and aHA is the fraction of [HA]T ionized
(
Eq. 2).
micellar rate constant, k , as compared to those in
m
k
obs ¼ k
0
þ kHA½HAŠ ꢁ aHA
ð2Þ
T
water, but because of large reagent concentrations in
the small interfacial volume in which the reaction
occurs. In most cases, the pseudo-phase ion exchange
model utilizing the kobs versus surfactant concentration
profiles works fairly well and gives access to the micellar
reagent concentrations and rate constants.
The observed rate constants increase with varying pH
values (9.0–12.4); the reaction was very fast in solutions
of higher pH (Scheme 1). However, we did not have a
stopped flow spectrophotometer available, so we were
restricted to conditions in which reactions could be
followed using a UV spectrophotometer (pH11.0).
The pK
.8, and 7.50, respectively, exceeding that (2.0) of the
s of catalysts AHA, BHA, and SHA are 9.30,
a
8
2
9
Rate–surfactant profiles for reactions in solutions of
various cationic surfactants (Table 1, Fig. 1) are typical
surfactant p-nitrophenoxide leaving group. It is con-
sidered that nucleophilicity is governed not only by the
basicity but also by the strength of interaction between
the nucleophile and surfactant aggregate. Work is now
in progress to study the nucleophilicity of hydroxamate
CTAB (AHA)
1
1
2
0
8
6
4
2
0
CTACl (AHA)
CTAB (BHA)
CTACl (BHA)
CTAB (SHA)
CTACl (SHA)
CTAP (SHA)
30
ions in reaction with organophosphorus esters.
Acknowledgements
Support of this research by the Council of Scientific and
Industrial Research (Grant No 01(1825/02/EMR-II 07.
0
8 02), Govt. of India, New Delhi, is gratefully acknowl-
edged. The authors are thankful to Professor G. L.
Mundhara, Head, School of Studies in Chemistry for
providing facilities. The authors are deeply indebted to
Professor J. R. Leis, University of Santiago deCompost-
ela, Spain, for his suggestions.
0
5
10
15
M
20
-
3
[Surfactant].10
Figure 1. Rate–surfactant concentration profiles for the reaction of
paraoxon with hydroxamate ions at pH11.0 and 30ꢀC.

K. K. Ghosh et al. / Tetrahedron Letters 45 (2004) 9103–9105
9105
References and notes
16. Tsang, J. S.; Neverov, A. A.; Brown, R. S. J. Am. Chem.
Soc. 2003, 125, 7602–7607.
1
1
1
2
2
2
2
2
2
7. Um, I. H.; Jeon, S. E.; Baek, M. H.; Park, H. R. Chem.
Commun. 2003, 22, 3016–3017.
8. Terrier, F.; Guevel, E. L.; Chatrousse, A. P.; Moutiers, G.;
Buncel, E. Chem. Commun. 2003, 600–601.
9. Buncel, E.; Negelkerke, R.; Thatcher, G. R. J. Can. J.
Chem. 2002, 81, 53–63.
0. Ghosh, K. K.; Simanenko, Y.; Satnami, M. L.; Sar, S. K.;
Indian J. Chem., in press.
1. Ghosh, K. K.; Sinha, D.; Satnami, M. L. J. Surface Sci.
Technol. 2003, 19, 159–166.
2. Bagno, A.; Comuzzi, C.; Scorrano, G. J. Am. Chem. Soc.
1
2
3
. Bunton, C. A.; Gillitt, N. D.; Foroudian, H. J. Langmuir
1
998, 14, 4415–4421.
. Um, I. H.; Yoon, H. W.; Lee, J. S.; Moon, H. J.; Kwon,
D. S. J. Org. Chem. 1997, 62, 5939–5944.
. Nucleophilicity, Advances in Chemistry Series 215; Harris,
J. M., McManus, S. P., Eds.; ACS: Washington, DC,
1
987.
. Morales-Rojas, H.; Moss, R. A. Chem. Rev. 2002, 102,
497–2521, and references cited therein.
. Yang, Y. C.; Baker, J. A.; Ward, J. R. Chem. Rev. 1992,
2, 1729–1743.
4
5
6
7
8
9
2
9
1
994, 116, 916–924.
3. Kakkar, R.; Grover, R.; Chadha, P. Org. Biomol. Chem.
003, 1, 2200–2206.
4. Bohm, S.; Exner, O. Org. Biomol. Chem. 2003, 1, 1176–
180.
. Chemical Warfare Agents; Somani, S. M., Ed.; Academic:
New York, 1992, Chapter 2.
2
. Buncel, E.; Cannes, C.; Chatrousse, A. D.; Terrier, F.
J. Am. Chem. Soc. 2002, 124, 8766–8767.
1
. Ouarti, N.; Marques, A.; Blagoeva, I.; Ruasse, M. F.
Langmuir 2000, 16, 2157–2163.
5. Senent, M. L.; Nino, A.; Caro, C. M.; Ibeas, S.; Garcia,
B.; Leal, J. M.; Secco, F.; Venturini, M. J. Org. Chem.
. Dubey, D. K.; Gupta, A. K.; Sharma, M.; Prabha, S.;
Vaidhyanathaswami, R. Langmuir 2002, 18, 10489–
2
003, 68, 6535–6542.
2
2
6. Remko, M. J. Phys. Chem. A. 2002, 106, 5005–5010.
7. Blasko, A.; Bunton, C. A.; Gillitt, N. D. Langmuir 1997,
1
0492.
1
1
1
0. Katritzky, A. R.; Duell, B. L.; Durst; Knier, B. L. J. Org.
Chem. 1988, 53, 3972–3978.
1
3, 6439–6446.
2
8. Bunton, C. A. Kinetic and Catalysis in Microheterogene-
ous Systems. In Surfactants in Science Series; Gratzel, M.,
Kalyanasundaran, K., Eds.; Dekker: New York, 1991;
Vol. 28.
1. Kirby, A. J.; Lima, M. F.; da Silva, D.; Nome, F. J. Am.
Chem. Soc. 2004, 126, 1350–1352.
2. Bunton, C. A.; Gillitt, N. D. J. Phys. Org. Chem. 2002, 15,
2
9–35.
2
3
9. Kotchevar, A. T.; Moss, R. A.; Scrimin, P.; Tecilla, P.;
Zhang, H. Tetrahedron Lett. 1994, 35, 4927–4930.
0. Simanenko, Y. S.; Prokopꢀeva, T. M.; Popov, A. F.;
Bunton, C. A.; Karpichev, E. A.; Savyolova, V. A.;
Ghosh, K. K. Russ. J. Org. Chem., in press.
1
1
3. Menger, F. M.; Rourk, M. J. Langmuir 1999, 15, 309–313.
4. Emsley, J.; Hall, D. The Chemistry of Phosphorus; Wiley:
New York, 1976, p 494.
1
5. Wagner, G. W.; Yang, Y. C. Ind. Eng. Chem. Res. 2002,
4
1, 1925–1928.