Mechanisms of degradation of paraoxon in different ionic liquids

Article abstract of DOI:10.1021/jo401351v

Herein, the reactivity and selectivity of the reaction of O,O-diethyl 4-nitrophenyl phosphate triester (Paraxon, 1) with piperidine in ionic liquids (ILs), three conventional organic solvents (COS), and water is studied by ³¹P NMR, UV-vis, and GC/MS. Three phosphorylated products are identified as follows: O,O-diethyl piperidinophosphate diester (2), O,O-diethyl phosphate (3), and O-ethyl 4-nitrophenyl phosphate diester (4). Compound 4 also reacts with piperidine to yield O-ethyl piperidinophosphate monoester (5). The results show that both the rate and products distribution of this reaction depend on peculiar features of ILs as reaction media and the polarity of COS.

Full text of DOI:10.1021/jo401351v

Article
pubs.acs.org/joc
Mechanisms of Degradation of Paraoxon in Different Ionic Liquids
Paulina Pavez,* Daniela Millan
́ ́
, Javiera I. Morales, Enrique A. Castro, Claudio Lopez A.,
and Jose G. Santos
́
́
Facultad de Química, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 6094411, Chile
*
S Supporting Information
ABSTRACT: Herein, the reactivity and selectivity of the reaction of O,O-
diethyl 4-nitrophenyl phosphate triester (Paraxon, 1) with piperidine in ionic
liquids (ILs), three conventional organic solvents (COS), and water is studied
by 31P NMR, UV−vis, and GC/MS. Three phosphorylated products are
identified as follows: O,O-diethyl piperidinophosphate diester (2), O,O-diethyl
phosphate (3), and O-ethyl 4-nitrophenyl phosphate diester (4). Compound 4
also reacts with piperidine to yield O-ethyl piperidinophosphate monoester
(
5). The results show that both the rate and products distribution of this
reaction depend on peculiar features of ILs as reaction media and the polarity
of COS.
INTRODUCTION
S 2(P), is the main pathway for the reactions of Fenitrothion
N
with oximate nucleophiles in water. However, for the reactions
of Paraxon and its sulfur analogue Parathion, the attack at the
■
10
Organophosphorus pesticides (OPs) are widely used worldwide
due to their high insecticidal activity and other biological ac-
1
phosphorus center, S 2(P), has been reported as the sole
tivities. Overall, OPs compounds represent 38% of total
N
11
reaction pathway.
In the last 2 decades, ionic liquids (ILs) have been widely used
pesticides used globally. The higher toxicity of OPs insecticide
is attributed to irreversible inhibition of the acetylcholinesterase
enzyme, which is essential for central nervous system function in
vertebrates and invertebrates; thus they often lack selectivity
12,13
as alternative reaction media for many organic reactions.
They have been shown to affect rates and reaction mechanisms,
2
12a
between nontarget organisms and insect pest. On the other
as well as product distribution in some reactions. However,
hand, the growing use of these insecticides has increased the
risks of environmental contamination of soils and groundwater.
Therefore, due to the high toxicity and bioaccumulation shown
by these organophosphate compounds, many methods have
some ILs have been used to prepare a series of phosphoro-
diamides and used for phosphitylation of nucleosides and
2-deoxynucleosides, demonstrating to be a versatile procedure
with high product selectivity in comparison with their syntheses
in conventional organic solvents (COS). However, nothing has
been reported, to our knowledge, concerning the effect of ILs on
1
,3
14
been developed for their degradation. Currently, the available
approaches for OPs degradation are homogeneous and het-
4
5
erogeneous hydrolysis, photolysis, photochemical degrada-
nucleophilic substitution reactions of phosphate esters.
6
7
tion, and biodegradation, as well as chemical treatments based
on the use of strong oxidants or nucleophiles.
To investigate the effects of ionic liquids as solvents on rate
and product distribution of the nucleophilic substitution reactions
of phosphoester compounds, in this work we study the reaction of
O,O-diethyl 4-nitrophenyl phosphate triester (Paraoxon, 1) with
piperidine in ten ionic liquids, which are shown in Scheme 1. To
compare the results obtained in ILs, we have carried out the same
reaction in water, dioxane, acetonitrile, and DMSO under the
same experimental conditions. The ILs used have a variety of
cations and anions to allow investigation of the effects of the
physicochemical properties of ILs on the reactivity of 1. The
1
,3,8
Nevertheless,
some of these treatments may not be very efficient or are
unfriendly to the environment due to the formation of products
6,9
that have mild or acute toxicity.
However, it has been reported that OPs show different
pathways of degradation, depending primarily on their alkylation
or arylation state and the nature of the nucleophile. For example,
Bujan et al. studied the reactivity of O,O-dimethyl O-(3-methyl-
4
-nitrophenyl) phosphorothioate (Fenitrothion) in water with
−
−
8
several O - and N -based nucleophiles. They found competi-
tion between the nucleophilic attack at the phosphorus atom and
at the aliphatic carbon atom, S 2(P) and S 2(C), pathways,
3
1
kinetic experiments were followed through UV−vis and
P
31
NMR techniques and the product analyses by P NMR, UV−vis,
N
N
and GC/MS.
respectively, in the reactions with NH OH. Nonetheless, the
2
attack at the aliphatic carbon, S 2(C), is the main reaction
N
8
pathway when Fenitrothion reacts with BuNH . In contrast,
Received: June 24, 2013
2
Buncel et al. found that the attack at the phosphorus center,
©
XXXX American Chemical Society
A
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Scheme 1. Schematic Representation of the Reaction Studied and the Ionic Liquids (ILs) Used
Figure 1. Progressive 31P NMR spectra obtained for the reaction of 1 (0.01M) with piperidine (2.8 M) at 25 °C in [Bmim]DCA. The molar amounts
corresponding to these spectra and others for this reaction are shown in Figure S14, in Supporting Information.
RESULTS AND DISCUSSION
observed, the decrease of substrate 1 signal (−7.3 ppm) is simul-
taneous to the increase of three other signals at 8.7, 0.1, and
−5.3 ppm, which are assigned to the formation of some phosphor-
ylated species in Scheme 2: O,O-diethyl piperidinophosphate
■
Figure 1 shows the 31P NMR spectra of the reaction of 1 with
piperidine in [Bmim]DCA solution at different times. As can be
B
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Scheme 2. Nucleophilic Attack of Piperidine (PI) to 1 in ILs and COS (Dioxane, ACN, and DMSO) by Three Reaction Paths: (A)
At Phosphorus, (B) at the C-1 Aromatic Carbon, and (C) at the Aliphatic Carbon
diester (2), diethyl phosphate (3), and O-ethyl 4-nitro-
phenylphosphate diester (4), respectively. The peaks at 8.7 and
reported for degradation of 1 with different nucleophiles in
aqueous solution, where the degradation of Paraoxon, caused by
1
5
11a
0.1 were assigned by comparison with the products obtained by
alkali metal ethoxides, hydroxamate ions, and phenols and
11d
the reactions of piperidine and NaOH with O,O-diethyl chloro-
phosphate in the same IL, respectively, as shown in Scheme S1
and Figures S1 and S2, in Supporting Information. On the
amines, occur by nucleophilic attack at the phosphoryl cen-
ter as the only reaction pathway. This leads to the formation of
4
-nitrophenoxide and the corresponding phosphate derivative.
other hand, the phosphate derivative 4 was identified by 31
P
The nucleophilic attack at the aromatic and aliphatic carbons has
not been reported for the reactions of Paraoxon. To have a better
understanding of the reaction behavior in water solution, we
NMR in comparison with an authentic sample; see Figure S3 in
Supporting Information. (Synthesis details of 4 are shown in
Experimental Section).
The presence of 2 among the reaction products (see Scheme 2)
can be explained by the nucleophilic attack of piperidine to the
phosphorus atom, where also the anion 4-nitrophenoxide (6)
31
carried out a P NMR study (see Figure S18 in Supporting
Information) of this reaction using water as solvent under iden-
tical experimental conditions (temperature, concentration, and
stoichiometry). Unfortunately, under these conditions, the pH
was greater than 12 and an alkaline hydrolysis occurs, this being
the main reaction pathway. Only minor products were found
from the aminolysis reaction, which were also hydrolyzed later
(
leaving group) is formed: its presence was observed by the
increase of a band at 420 nm in the UV−vis spectra. In addition,
the nucleophilic attack to the C-1 carbon of the aromatic ring
leads to compound 3 and 1-piperidino-4-nitrobenzene (7). The
latter was determined by comparison of the UV−vis spectrum at
the end of the reaction with that at the end of the reaction of
(
see Figure S18 in SI). An external buffer was not used because
the conditions would have been different than those in ILs.
However, the S Ar pathway found in this work is in accor-
N
4-nitrochlorobenzene with piperidine at the same experimental
dance with previous investigations of nucleophilic aromatic
substitutions in ionic liquids involving less activated aromatic
conditions (in the 300−450 nm range).
The formation of 4 and N-ethylpiperidine (8) is observed
when piperidine attack occurs at the aliphatic carbon, by the
1
6
rings. They include the N-arylation of secondary cyclic amines,
17
reactions of 2-substituted 5-nitrothiophenes, and reaction of
p-fluorobenzene with p-anisidine, which reveals that S Ar reac-
SN2(C) pathway. Compound 8 was identified by GC/MS (r.t. =
18
N
17.15 min, m/z 113); see Figure S4 in Supporting Information.
tions are favored when ILs are used as solvent.
The reaction of 1 with piperidine showed a behavior similar
to that in the other ionic solvents studied. Nevertheless, in COS
the distribution of products (%) found was different. Figures S5−
It is worth mentioning that in the reaction of phosphate 1 with
3
1
piperidine a new signal at 6.4 ppm is slowly appearing in the P
NMR spectra (see Figure 1). As the reaction proceeds, the inten-
sity of this signal increases at the expense of that of compound 4,
forming O-ethyl piperidinophosphate monoester (5) and 6, due
to a new piperidine attack to the phosphorus atom of 4 (see
Scheme 2). This new compound 5 was confirmed on the basis
of the increase of the same signal (6.4 ppm) in the reaction of
O-ethyl 4-nitrophenyl phosphate monoester (4) with piperidine
in the same experimental media (see Scheme S1 and Figure S15
in Supporting Information). This result is interesting from
the toxicity point of view since it is known that phosphate
3
1
S17 in Supporting Information show the P NMR spectra
recorded at different times in these solvents (note that for
simplicity we do not show all the times recorded).
From analytical techniques (NMR, UV−vis, and GC/MS) we
found that there are three simultaneous pathways to degradation
of 1 in both COS and ILs as solvent. The three of them involve
nucleophilic attack of piperidine at the following: (i) the phos-
phoryl center, resulting in P-Oaryl cleavage, (ii) the C-1 aromatic
carbon, with aryl-O cleavage, and (iii) the aliphatic carbon, with
alkyl-O breakage. These results are different to those previously
C
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monoesters and diesters are much less lipophilic, and therefore
less toxic, than their triester precursors.
However, the formation of 4-nitrophenoxide (6) in two
different steps, as seen in Scheme 2, is evidenced by the shape of
the absorbance vs time plot when the reaction of 1 with piper-
idine was followed by UV−vis at 420 nm; see Figure 2.
Figure 3. Relative nucleophilic attack of piperidine to 1 in ILs. Attack of
piperidine at (gray columns) the phosphorus atom by S 2(P) pathway,
N
(
white columns) the C-1 aromatic carbon by the S Ar pathway, and
N
(
black columns) the aliphatic carbon by the S 2(C) pathway.
N
almost independent of the ILs used (about 20%). Our results are
very different from those reported for the same reaction in
aqueous solution, in which the only reaction pathway is the attack
11
of piperidine at the phosphorus atom.
Figure 2. Experimental plot of absorbance (at 420 nm) vs time for the
reaction of piperidine (0.4 M) with 1 in [Bmim]DCA at 25 °C. The inset
shows the time-dependent UV−vis spectra of this reaction.
Interestingly, when [Bmpy]DCA is used as solvent, the S 2(P)
pathway is the most important route for degradation of substrate
(54%). Also, we can observe that the change from [Bmpy]DCA
N
1
to [Bmim]DCA and to [Bmpyrr]DCA results in a decrease of the
percentage attack of piperidine to the phosphorus atom (from
54% to 33% and to 18%, respectively), entries 2, 9, and 10 in
It can be seen that the curve in Figure 2 is not typical of a
simple kinetic process. Its peculiar shape corresponds to at least
two kinetically relevant steps responsible for the formation of 6.
This result confirms that 4-nitrophenoxide is formed in two
consecutive steps, in agreement with the reaction scheme
proposed (Scheme 2). Similar kinetic behavior (parallel and
consecutive pathways) has been described and mathematically
Table 1. The high preference for the S 2(P) pathway when the
N
aromatic IL acts as solvent could be due to the stabilization of the
transition state (TS) of this pathway by π−π interactions of the
21
aromatic cation with the TS, in comparison with compound 1
(see kinetic results shown below).
To have control of the selectivity of this reaction, we have
included three different conventional organic solvents (COS) in
this study. Interestingly, the results of Table 1 show that, in the
less polar COS, the selectivity is enhanced markedly at the
aliphatic carbon atom and diminishes at the phosphorus atom of
the substrate. Nevertheless, when DMSO is the solvent of the
reaction, the selectivity is similar to that in ILs. This result is not
surprising because, the same as ILs, the polarity and structure
19
treated by an equation deduced by us in another system.
3
1
However, from integration of the P NMR signals of the pro-
ducts formed from piperidine attack to the different electrophilic
centers of 1 (see Figures 1 and S5−S17), the relative products
distribution was calculated in the different reaction media, as
shown in Table 1. Figure 3 shows this behavior schematically.
22
Table 1. Relative Products Distribution (%) for the
of DMSO lead to a considerable organization of the liquid state.
Nucleophilic Attack of Piperidine to 1 in the Solvent Used
A similar trend has been reported previously by other authors
when contrasting rate constants in DMF and ILs in the Kemp
solvent
% S 2(P)
% S Ar
% S 2(C)
20d
N
N
N
reaction and very recently by us in the aminolysis of aryl
23
1
2
3
4
5
6
7
8
9
1
1
1
1
[Bmim]BF4
22
33
15
16
20
17
22
18
54
18
1
19
21
28
26
30
21
23
27
12
29
13
15
23
59
46
57
58
50
62
55
55
38
53
86
76
40
acetates in DMSO and ILs.
[Bmim]DCA
However, we obtained pseudo-first-order rate coefficients
(kobsd) for all the reaction routes (S 2(P), S Ar, and S 2(C)),
[Bmim]NTf2
N
N
N
31
[Bmim]PF6
using the logarithmic plots of the P NMR area, due to degra-
dation of substrate 1 at different times, and the relative products
distribution in Table 1. The kobsd values found in the different
media used in this study are shown in Table 2.
[B mim]NTf
2
2
[B mim]BF
2
4
[E2mpAm]NTf2
[Bmpyrr]NTf2
The results of Table 2 show that the kobsd values found for the
S 2(P) and S Ar pathways in less polar solvent are lower than
[Bmpy]DCA
N
N
0
1
2
3
[Bmpyrr]DCA
dioxane
those in DMSO. These results could be rationalized in terms of
the polarity-polarizability parameter of these solvents (π* = 0.55,
24
ACN
8
0
.75, and 1.0 for dioxane, ACN, and DMSO, respectively).
DMSO
37
Although similar kobsd values were found for DMSO and ILs for
the three pathways, it is not adequate to compare these values on
These results agree with studies that report that slight modi-
the grounds of polarity parameters, such as E (30), ε, or π*,
T
fications in the ILs’ cation or anion nature would induce selec-
because the interaction of substrates with ionic solvents seems to
20
25
tivity changes of some reactions. We can observe that in most
be affected by the complex structural organization of the ILs.
of the ILs employed the S 2(C) pathway (black columns in
Figure 3) is the most important route for degradation of substrate
For the above reason, and to have a better understanding of
our kinetic results, we resolved to discuss them as a function of
the structure of the cation and anion of the IL.
N
1
(46−62%) and that the S Ar pathway (white columns) is
N
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Table 2. Pseudo-First-Order Rate Constants (kobsd) for the
Degradation Routes of 1 in Several ILs and COS
05 kobsd/s−1
SN2(P)
,
10 k /s−1
5
,
10 k /s−1
5
,
1
obsd
S Ar
obsd
solvent
SN2(C)
N
[
[
[
[
[
[
[
Bmim]BF4
2.64
4.52
0.99
1.34
0.99
0.82
0.74
2.28
2.88
1.85
2.19
1.46
1.00
0.77
7.08
6.30
3.78
4.90
2.50
3.01
1.84
Bmim]DCA
Bmim]NTf2
Bmim]PF6
B2mim]NTf2
B2mim]BF4
E2mpAm]
NTf2
[
[
[
Bmpyrr]NTf2
Bmpy]DCA
Bmpyrr]DCA
0.49
5.15
1.28
0.0064
0.17
2.38
0.73
0.95
1.80
0.083
0.33
1.48
1.50
0.34
3.34
0.55
1.65
2.58
Figure 5. Variation of the pseudo-first-order rate coefficient (kobsd) for
attack of piperidine at phosphorus by the S 2(P) pathway (gray), the
N
C-1 aromatic carbon by the S Ar pathway (white), and the aliphatic
N
Dioxane
ACN
carbon by the S 2(C) pathway (black).
N
DMSO
cation of the IL and the TS of the reaction, in comparison with
the π stacking interaction between aromatic cation and reactants.
Figure 4 shows that the kobsd values found for the S 2(P)
N
pathways with ILs that share a common cation decrease along the
In the case of [Bmim] and [B2mim] with a common anion
−
(
BF ), we found that the k value is two- to threefold greater
4
obsd
−
when [Bmim]BF4 is the reaction solvent. This result can be ex-
plained by the different hydrogen-bond donating (HBD) ability
of the cations, suggesting that [Bmim] is a stronger hydrogen-
bond donor than [B2mim], where position 2 is occupied by the
28
methyl group. In the case of [Bmim] and [B2mim], which
−
share a common NTf , we can observe a minimum effect. The
2
latter results are in accordance with the r values reported by
2
1
Armstrong et al. The r values are 0 and 0.073 for [Bmim]NTf
2
21
and [B2mim]NTf , respectively, a 40 °C. The greater r value
for the latter indicates that [B2mim] cation has a higher ability to
2
interact with π electrons in comparison with [Bmim], providing
[
B2mim] with a greater aromaticity, stabilizing therefore, the TS
Figure 4. Variation of the pseudo-first-order rate coefficient (kobsd) with
of the reaction and increasing the kobsd value. Therefore, in this
case it is evident that both HBD ability and aromaticity of the ILs’
cations must be taken into account to establish the effect of the
cations nature on the kobsd values.
the nature of anion of the ionic liquid for the S 2(P) pathway of the
N
reaction of 1 with piperidine.
series: [Bmim]DCA > [Bmim]BF > [Bmim]PF > [Bmim]-
Finally, it is clear that our analysis, by ignoring ion-pair
interactions in these organic salts, and treating anions and cations
as separate entities in these solvents, is not capable of uncovering
all the subtle factors involved in such a complex system. There-
fore, a better understanding of the ILs’ effect could be explained
taking into account the three-dimensional structure of ionic
solvents, where solute−solvent interactions are much more
4
6
NTf . The experimental trend seems to be in line with the
2
hydrogen-bond acceptor (HBA) ability of the anion (β values of
0
.708, 0.327, 0.202, and 0.23 for [Bmim]DCA, [Bmim]BF ,
4
26,20d
[
Bmim]PF , and [Bmim]NTf , respectively).
This indicates
6
2
a stabilization of the transition state of the S 2(P) pathway by the
N
interaction between the IL anion and the hydrogen on the
ammonium nitrogen of piperidine in the TS, facilitating the
25
complex.
27
nucleophilic attack at the phosphorus atom of 1. Interestingly,
for the S Ar and S 2(C) pathways the effect of the nature of the
CONCLUSIONS
N
N
■
anion on the kobsd value is less important.
An important conclusion from this study is the similar reactivity
and selectivity of this reaction in DMSO and ILs used as solvent.
Nevertheless, a marked difference exists with the behavior in less
polar COS, where the selectivity is enhanced at aliphatic carbon
atom and diminished at the phosphorus atom of the substrate.
In this study we found that both selectivity and rate constants
(kobsd) depend on the nature of ILs’ anion and cation. There is a
correlation between β values of the anion and kobsd values for the
reaction, whereas the aromaticity of the cations seems to increase
the rate of degradation of 1. Nevertheless, we have found some
exceptions, which make it necessary to take into account the
three-dimensional structures of these solvents, which cover other
factors involved in such a complex system.
As seen above, the kobsd values for PF6 and NTf − anions are
−
2
not in accordance with their β values. This could be explained by
the greater steric hindrance provided by the nitrogen anion of the
−
−
bistrifluoromethylsulfonyl group, (CF SO ) N , (NTf ) in
3
2 2
2
−
comparison with the hexafluorophosphate anion (PF ). There-
6
fore, the HBA interaction with the N−H hydrogen of the TS
would be lower.
To evidence the effect of the cation on the kobsd values found
along the three pathways for degradation of 1, we performed a
−
comparison of ILs that share a common anion (NTf ), as shown
2
in Figure 5.
From this figure it follows that the highest kobsd values are
obtained when aromatic ILs are used. These results would
suggest the highest π stacking interaction between aromatic
It is noteworthy that the second reaction shown in Scheme 2
has not been described in the Paraoxon degradation. In this
E
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Article
reaction, the original substrate mainly yields a monoester
derivative and the remaining corresponds to diethylphosphate
and diethylpiperidinophosphate diester. Therefore, in this study
it has been demonstrated that Paraoxon degradation is obtained
with efficiency, yielding phosphate products less lipophilic and
therefore less toxic to the human being.
Spectrophotometry. The products 4-nitrophenoxide (6)
and 1-piperidino-4-nitrobenzene (7), arising from the nucleo-
philic attack at the phosphoryl center and at the C-1 carbon of the
aromatic ring, respectively, were identified by comparison of
the final visible spectra of the reaction with an authentic sample
(for 6) and with the final spectra of the reaction of 4-nitro-1-
chlorobenzene with piperidine (for 7), in the ionic liquids.
Typical UV−vis bands in the ionic liquids were found for
compounds 6 and 7 at 420 and 325 nm, respectively (spectra not
shown).
EXPERIMENTAL SECTION
Materials. All ionic liquids, conventional organic solvents
COS), piperidine, O,O-diethyl chlorophosphate, and O,O-diethyl
■
(
Gas Chromatography−Mass Spectrometry (GC/MS).
GC/MS analysis was performed using a gas chromatograph fitted
with a split−splitless injector and a Elite-5MS column (30 m ×
4
-nitrophenyl phosphate triester (Paraxon) were purchased. All
ionic liquids were dried before use on a vacuum oven at 70 °C for
at least 2 h and stored in a dryer under nitrogen and over calcium
chloride. Water contents determined by Karl Fischer titration
were <200 ppm.
0
.25 mm i.d., 0.25 μm d.f). Helium was used as a carrier gas at a
flow rate of 1.0 mL/min. The injection port was maintained at
5.0 °C, and the split ratio was 19:1. Oven temperature was pro-
grammed from 70 °C for 2 min and then ramped as follows: ramp
2
O-Ethyl 4-nitrophenyl phosphate diester (4) was prepared by
29
modification of a reported method, as follows. 4-Nitrophenol
1.4 g, 10 mmol), O,O-diethyl chlorophosphate (1.72 g, 10 mmol),
1
2
, 5 °C/min to 140 °C hold for 12 min, and ramp 2, 10 °C/min to
40 °C hold for 12 min. Ionization mode was electron impact
(
and triethylamine (1.11 g, 11 mmol) were dissolved in 50 mL of
benzene. The solution was refluxed overnight and the precip-
itated triethylaminium hydrochloride was filtered. The benzene
ionization and the scanning range was from 50 to 400 amu. Mass
spectra were obtained at 0.35 s intervals. To confirm the presence
of N-ethylpiperidine (8) as a reaction product, an extraction with
diethyl ether was made from the reaction medium and this ex-
tract analyzed by GC/MS; the spectrum obtained (see Figure S4)
was matched with NIST library.
filtrate was extracted with water and dried over MgSO and the
4
benzene fraction was removed under reduced pressure to give
Paraoxon. This was dissolved in 100 mL of acetone and refluxed
for a day with dry LiBr (0.61g, 7 mmol). The solution was left at
2
5 °C overnight and the precipitate was collected and washed
ASSOCIATED CONTENT
with ether. After recrystallization from methanol/ether 1.05 g of
pure compound 4 was obtained. H NMR (400 MHz, DMSO
δ(ppm): 8.12 (d, 2H); 7.4 (d, 2H); 3.8 (“quintet”, 2H); 1.1 (t,
■
1
*
S
Supporting Information
31
Stacked P NMR plot for the reaction of 1 with piperidine in ten
ILs used and COS, GC/MS chromatogram, and mass spectrum
of compound 7. Experimental procedure, identification spectral
data for compounds 2−5. This material is available free of charge
via the Internet at http://pubs.acs.org/.
13
3H). C-NMR (400 MHz, DMSO δ (ppm): 16.6; 60.95; 120.4;
3
1
−
1
−
25.4; 141.8; 160.4. P NMR (400 MHz, [Bmim]BF ) δ (ppm):
4
5.6. Figure S3, in Supporting Information.
Kinetic Measurements. These were performed by 31P
NMR obtained on a 400 spectrometer, following the disap-
pearing of the Paraoxon (1) signal. The kinetic experiments were
carried out in ionic liquids and COS solutions at 25 °C under
pseudo-first-order conditions. Each measurement was made in
triplicate. In a typical experiment a NMR tube containing 500 μL
of the ionic liquid or COS was thermostatted at 25 °C for 10 min.
AUTHOR INFORMATION
Corresponding Author
*Tel.: +56-02-23541743. Fax: +56-02-26864744. E-mail:
ppavezg@uc.cl.
■
Present Address
−6
Then Paraoxon (7.5 × 10 mol, 15 μL of 0.5 M in ACN) and
́
Facultad de Quimica, Pontificia Universidad Catol
Av. Vicuna Mackenna 4860, Santiago 6094411, Chile.
Notes
́
ica de Chile,
−3
piperidine (2 × 10 mol, 200 μL) were added. Deuterated ACN
was used inserted in a capillary for NMR tubes. The spectra were
recorded at different reaction times and pseudo-first-order rate
̃
The authors declare no competing financial interest.
coefficients (kobsd) were found for all reaction routes, S 2(P),
N
S Ar, and S 2(C). The overall k values were obtained by
N
N
obsd
ACKNOWLEDGMENTS
This work was supported by project ICM-P10-003-F CILIS,
integration of the NMR signals for Paraoxon and plotting log
integration) vs time. To obtain the rate constants for the
■
(
granted by “Fondo de Innovacion
́
para la Competitividad” from
products formation, we multiplied kobsd by the fraction of each
product relative to the total products. The molar concentrations
of the products at the end of the reactions were obtained by
quantitative analysis of each product.
Product Studies. The product analysis was performed by
different analytical techniques, as follows.
́
Ministerio de Economia, Fomento y Turismo, Chile, and
FONDECYT, grant 1130065.
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