Analysis of linear free-energy relationships combined with activation parameters assigns a concerted mechanism to alkaline hydrolysis of X-substituted phenyl diphenylphosphinates

Article abstract of DOI:10.1002/chem.200800553

A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1a-i). The Bronsted-type plot for the reactions of 1a-i is linear over 4.5 pK_a units with β_lg= -0.49, a typical β_lg value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with σ^o and σ^- constants are linear but exhibit many scattered points, while the corresponding Yukawa-Tsuno plot results in excellent linear correlation with ρ= 1.42 and r=0.35. The r value of 0.35 implies that leaving-group departure is partially advanced at the rate-determining step (RDS). A stepwise mechanism, in which departure of the leaving group from an addition intermediate occurs in the RDS, is excluded since the incoming HO ^- ion is much more basic and a poorer nucleofuge than the leaving aryloxide. A dissociative (D_N + A_N) mechanism is also ruled out on the basis of the small β_lg value. As the substituent X in the leaving group changes from H to 4-NO₂ and 3,4-(NO₂)₂, ΔH^≠ decreases from 11.3 kcal mol^-1 to 9.7 and 8.7 kcal mol^-1, respectively, while ΔS^≠ varies from -22.6 cal mol^-1 K^-1 to -21.4 and -20.2 cal mol^-1 K^-1, respectively. Analysis of LFERs combined with the activation parameters assigns a concerted mechanism to the current alkaline hydrolysis of 1a-i.

Full text of DOI:10.1002/chem.200800553

DOI: 10.1002/chem.200800553
Analysis of Linear Free-Energy Relationships Combined with Activation
Parameters Assigns a Concerted Mechanism to Alkaline Hydrolysis of
X-Substituted Phenyl Diphenylphosphinates
[
a]
Ik-Hwan Um,* Jeong-Yoon Han, and So-Jeong Hwang
Abstract: A kinetic study is reported
for alkaline hydrolysis of X-substituted
phenyl diphenylphosphinates (1a–i).
The Brønsted-type plot for the reac-
tions of 1a–i is linear over 4.5 pKa
units with b =ꢀ0.49, a typical b
implies that leaving-group departure is
partially advanced at the rate-deter-
mining step (RDS). A stepwise mecha-
nism, in which departure of the leaving
group from an addition intermediate
occurs in the RDS, is excluded since
the incoming HO ion is much more
basic and a poorer nucleofuge than the
leaving aryloxide. A dissociative (DN +
A ) mechanism is also ruled out on the
N
basis of the small b value. As the sub-
lg
stituent X in the leaving group changes
°
from H to 4-NO and 3,4-(NO ) , DH
2
2 2
ꢀ
1
decreases from 11.3 kcalmol to 9.7
and 8.7 kcalmol , respectively, while
ꢀ
1
lg
lg
ꢀ
°
ꢀ1
ꢀ1
value for reactions which proceed
through a concerted mechanism. The
DS varies from ꢀ22.6 calmol
K
to
ꢀ
1
ꢀ1
ꢀ21.4 and ꢀ20.2 calmol K , respec-
tively. Analysis of LFERs combined
with the activation parameters assigns
a concerted mechanism to the current
alkaline hydrolysis of 1a–i.
o
Hammett plots correlated with s and
ꢀ
s
constants are linear but exhibit
many scattered points, while the corre-
sponding Yukawa–Tsuno plot results in
excellent linear correlation with 1=
Keywords: activation parameters ·
alkaline
hydrolysis
·
reaction mechanism
1.42 and r=0.35. The r value of 0.35
Introduction
However, mechanistic (experimental and theoretical)
studies have been performed much less intensively. Accord-
ingly, the mechanisms have not been completely understood
but remain controversial (i.e., concerted vs stepwise mecha-
Certain organophosphorus compounds (e.g., soman, sarin,
paraoxon, parathion, etc.) are known to possess mammalian
toxicity as well as insecticidal properties, and to act as ace-
[13–20]
nism).
Williams et al., performed nucleophilic substitu-
[1–4]
tylcholinesterase inhibitors.
Thus, deactivation of these
tion reactions of 4-nitrophenyl diphenylphosphinate with a
toxic compounds under mild conditions has become an im-
portant task in environmental chemistry. Numerous studies
have been performed to enhance the rate of decomposition
series of aryloxides whose pK values increase the basicity
a
[13]
of the leaving 4-nitrophenoxide. The reactions have been
concluded to proceed through a concerted mechanism since
[5–12]
[13]
of toxic organophosphorus compounds.
cleophiles such as HOO , o-iodosylbenzoate and various ox-
The use of a-nu-
the Brønsted-type plot was found to be linear. Similarly,
ꢀ
Hengge et al. have found that alkaline hydrolysis of aryl di-
methylphosphinothioates exhibits much better Hammett
imate anions have been reported to be highly effective to
[5–9]
ꢀ
2
o
2
destroy such toxic materials under mild conditions.
Be-
correlation with s (R =0.991) than with s (R =0.933) or
2
[14a]
sides, various metal ions have shown significant catalytic ef-
fects as Lewis acid catalysts in reactions of various organo-
s constants (R =0.926).
Besides, reactions of 4-nitro-
phenyl dimethylphosphinothioate with aryloxides also re-
[10–12]
phosphorus compounds.
sulted in a linear Brønsted-type plot over 4.6 pK units with
a
[14a]
bnuc =0.47.
Thus, the reactions have been concluded to
proceed through a concerted mechanism with a transition-
[
14a]
[
a]Prof. Dr. I.-H. Um, J.-Y. Han, S.-J. Hwang
Division of Nano Sciences and Department of Chemistry
Ewha Womans University, Seoul 120-750 (Korea)
Fax : (+82)2-3277-2844
state (TS) structure similar to TS1.
This conclusion has
18
been further supported by studies of the primary O and
secondary N kinetic isotope effects.
1
5
[14a]
On the contrary, Haake et al. have concluded that alka-
line hydrolysis of X-substituted phenyl diphenylphosphi-
nates (X=4-MeCO, 4-Br, 4-Cl, H, 3-Me, and 4-Me) pro-
E-mail: ihum@ewha.ac.kr
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
7324
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Chem. Eur. J. 2008, 14, 7324 – 7330

FULL PAPER
which indicates that the contribution of H O to k
is negli-
obsd
2
gible. Thus, the rate law is given by Equation (1).
rate ¼ kobsd½SubŠ, where kobsd ¼ kHO
ꢀ
½HOꢀŠ
ð1Þ
The second-order rate constants (kHO
from the slopes of the linear plots of kobsd versus [HO ]and
ꢀ
) were determined
ꢀ
summarized in Tables 1 and 2. The uncertainty in kHO
ꢀ
is es-
ceeds through a stepwise mechanism on the basis of the fact
timated to be less than 3% from replicate runs. The activa-
o
°
°
that s constants exhibit a better Hammett correlation than
tion parameters (DH and DS ) were calculated from the
ꢀ
[16]
[21]
s
constants. Similar results have been reported for alka-
Eyring equation.
Kinetic conditions and results are de-
line hydrolysis of O-X-substituted phenyl dimethylphosphi-
tailed in the Supporting Information.
[17]
nothioates (X=4-NO , 4-Br, H, and 4-Me), imidazole cat-
2
alyzed hydrolysis of X-substituted phenyl diphenylphosphi-
Table 1. Summary of second-order rate constants (kHOꢀ) for alkaline hy-
drolysis of X-substituted phenyl diphenylphosphinates (1a–i) in 80 mol%
[18]
nates (X=4-NO , 3-NO , 4-MeCO, 4-Cl, and H) and alka-
2
2
line ethanolysis of X-substituted phenyl dimethylphosphi-
H O/20 mol% DMSO at 25.0Æ0.18C.
2
[10a]
nates (X=4-NO , 3-NO , 4-MeCO, 4-Cl, H, and 4-Me).
ꢀ1 ꢀ1
2
2
Entry
X
pK (X-PhOH)
kHO
ꢀ
/m
s
a
Thus, these reactions have been concluded to proceed
through a stepwise mechanism with a TS structure similar to
1
1
1c
1d
1e
1
1
1h
1i
a
b
3,4-(NO
2
)
2
5.42
7.14
7.66
7.95
8.05
9.02
9.19
9.38
9.95
200
4-NO
2
21.3
9.11
13.3
6.57
3.81
3.38
2.44
[10a,16–18]
TS2.
4-CHO
4-CN
4-COMe
3-Cl
3-COMe
4-Cl
H
o
We have recently shown that s constants result in a
better Hammett correlation than with s constants for alka-
line ethanolysis of aryl diphenylphosphinates, and aminol-
yses of aryl diphenylphosphinates
logues, O-aryl diphenylphosphinothioates.
this result has been taken as evidence for a stepwise mecha-
ꢀ
f
g
[
19]
[
20a]
and their thio ana-
[
20b]
Traditionally,
0.690
[
10a,16–18]
nism with a TS structure similar to TS2.
However, we
have concluded that the reaction proceeds through a con-
certed mechanism, since the Yukawa–Tsuno plots for the
same reactions exhibit significantly better correlation than
Effect of leaving-group basicity on reactivity: As shown in
Table 1, the second-order rate constant decreases as the
leaving group becomes more basic, that is, it decreases from
o
[19,20]
ꢀ1 ꢀ1
ꢀ1 ꢀ1
the Hammett plots correlated with s constants alone.
200m
s
to 6.57 and 0.690m
s
as the pK of the conju-
a
We have extended our study to alkaline hydrolysis of X-
substituted phenyl diphenylphosphinates (1a–i) at various
temperatures. The kinetic data have been analyzed using
various LFERs together with activation parameters (e.g.,
gate acid of the leaving aryloxide increases from 5.42 to 8.05
and 9.95, respectively. The effect of the leaving-group basici-
ty on reactivity is illustrated in Figure 1. The Brønsted-type
plot is linear over 4.5 pK units with b =ꢀ0.49Æ0.04.
a
lg
°
°
DH and DS ). Analysis of LFERꢁs combined with the acti-
vation parameters permits unambiguous assignment of the
mechanism of the phosphinyl-transfer reaction. Besides, we
have shown that deduction of reaction mechanism based
The b value determined in the current reactions is sub-
lg
stantially smaller than that reported for hydrolyses of aryl
[
22a]
phosphate dianions (b =ꢀ1.2)
and their thio analogues,
lg
[22b]
O-aryl phosphorothioate dianions (b =ꢀ1.1).
Such large
lg
o
ꢀ
just on the result from Hammett correlations with s or s
b values for the latter reactions indicate that the dissocia-
lg
constants alone can be misleading.
tion of the PꢀOAr bond is significantly advanced in the TS.
Furthermore, the resulting metaphosphate intermediate can
be stabilized through resonance interactions as shown
below. Thus, the reactions have been concluded to proceed
[22]
through a dissociative (DN + A ) mechanism.
N
Results and Discussion
However, one can exclude a (DN + A ) mechanism in
N
All reactions in this study obeyed pseudo-first-order kinetics
with quantitative liberation of X-substituted phenoxide.
Pseudo-first-order rate constants (kobsd) were determined
the current hydrolysis of 1a–i since a metaphosphate inter-
mediate is not possible and the blg of ꢀ0.49 is too small for
an (DN + A ) mechanism. In addition, it has been argued
N
from the equation ln
kobsd versus [HO ]were linear passing through the origin,
A
H
R
U
G
that metaphosphate is not an intermediate for reactions of
aryl phosphates in aqueous medium.
1
t
ꢀ
[23]
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www.chemeurj.org
7325

I.-H. Um et al.
[18]
phosphinates (X=4-NO , 3-NO , 4-MeCO, 4-Cl, and H)
2
2
and alkaline ethanolysis of X-substituted phenyl dimethyl-
phosphinates (X=4-NO , 3-NO , 4-MeCO, 4-Cl, H, and 4-
2
2
[10a]
Me).
To determine the mechanism for the reactions of 1a–i,
Hammett plots have been constructed using s and s con-
o
ꢀ
stants in Figure 2A and B, respectively. A careful examina-
o
tion of Figure 2A and B reveals that s constants exhibit
ꢀ
2
only a slightly better correlation than s constants (i.e., R =
0
o
2
ꢀ
.982 for s and R =0.974 for s constants). Thus, one
cannot obtain any conclusive information on the reaction
o
ꢀ
mechanism by the traditional method using s or s con-
stants.
Figure 1. Brønsted-type plot for alkaline hydrolysis of X-substituted
phenyl diphenylphosphinates (1a–i) in 80 mol% H O/20 mol% DMSO
2
at 25.0Æ0.18C. The identity of points is given in Table 1; blg =ꢀ0.49Æ
2
0
.04, R = 0.980.
The blg value obtained from the current reactions can be
compared with that reported for reactions which have been
suggested to proceed through a concerted mechanism, for
example, b =ꢀ0.54Æ0.04 for alkaline ethanolysis of aryl
lg
[19]
diphenylphosphinates,
b =ꢀ0.47 for alkaline hydrolysis
lg
[24]
of aryl dimethylphosphinates, b =ꢀ0.51 for reactions of
lg
ꢀ
[25]
aryl diethyl phosphates with PhO in water,
b =ꢀ0.54
lg
and ꢀ0.52 for reactions of O-aryl dimethylphosphino-
ꢀ
ꢀ
[14a]
thioates with HO and PhO , respectively,
and b =
lg
ꢀ
0.39Æ0.04 for reactions of O-aryl dimethyl phosphoro-
ꢀ
[26]
thioates with PhO in water. Since b =ꢀ0.5Æ0.1 appears
lg
to be typical for reactions which proceed through a concert-
ed mechanism, one can suggest that the current hydrolysis
of 1a–i proceeds through a concerted mechanism.
Hammett versus Yukawa–Tsuno plots: One might expect
ꢀ
that s constants would result in a better Hammett correla-
o
tion than s constants if breakdown of the PꢀOAr bond
occurs in the RDS either in a concerted mechanism with a
TS structure similar to TS or in a stepwise mechanism with
1
o
TS . On the contrary, s constants would exhibit a better
3
ꢀ
Hammett correlation than s constants if the bond rupture
o
2
Figure 2. Hammett correlations with A) s (1 = 1.60; R = 0.982) and
occurs after the RDS with a TS structure similar to TS . In
ꢀ
2
2
B) s (1 = 1.09; R = 0.974) constants for alkaline hydrolysis of X-sub-
stituted phenyl diphenylphosphinates (1a–i) in 80 mol% H O/20 mol%
fact, Haake et al. have concluded that alkaline hydrolysis of
X-substituted phenyl diphenylphosphinates (X=4-MeCO, 4-
Br, 4-Cl, H, 3-Me, and 4-Me) proceeds through a stepwise
2
DMSO at 25.0Æ0.18C. The identity of points is given in Table 1.
mechanism with a TS structure similar to TS on the basis of
2
o
the fact that s constants exhibit a better Hammett correla-
We have recently reported that the Yukawa–Tsuno equa-
tion [Eq. (2)]is highly effective to elucidate ambiguities in
ꢀ
[16]
tion than s constants.
A similar conclusion has been
drawn for hydrolysis of O-X-substituted phenyl dimethyl-
reaction mechanisms of phosphinyl transfer and related re-
[17]
[19,20,27]
phosphinothioates (X=4-NO , 4-Br, H, and 4-Me), imida-
actions.
Thus, a Yukawa–Tsuno plot has been con-
2
zole catalyzed hydrolysis of X-substituted phenyl diphenyl-
structed for the current hydrolysis of 1a–i. As shown in
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Alkaline Hydrolysis of Phosphinates
FULL PAPER
Figure 3, the Yukawa–Tsuno plot exhibits an excellent cor-
relation (i.e., R =0.996) with 1=1.42 and r=0.35. Since the
r value determined in the current reactions is neither 0 nor
for alkaline hydrolysis of aryl diphenylphosphinates. They
2
concluded that the reactions proceed through a TS structure
o
similar to TS , since s (or s) constants exhibited better
2
ꢀ
[16–18]
1
, the Yukawa–Tsuno plot results in much better linear cor-
Hammett correlations than s constants.
We suggest
o
ꢀ
relation than the Hammett plot using s or s constants
that the discrepancy in the mechanism may be due to limit-
alone.
ed numbers of substituents employed to construct a Ham-
ꢀ
mett plot with s constants (e.g., only 4-NO or 4-MeCO
2
ꢀ
has a s constant among four or six different substituents
employed by Istomin or by Haake et al., respectively), or in
the other case, to a failure of choosing a proper LFER such
as the Yukawa–Tsuno equation. In fact, we have found that
[18]
the kinetic data reported by Williams et al. result in much
2
better correlation in the Yukawa–Tsuno plot (R =0.995)
2
than in the Hammett plot using s constants (R =0.977).
The 1 value of 1.42 shown in Figure 3 is comparable to
that reported for reactions which have been suggested to
proceed through TS , for example, 1=1.17 for alkaline hy-
1
[14a]
drolysis of O-aryl dimethylphosphinothioates,
alkaline ethanolysis of aryl diphenylphosphinates, and 1=
.91 for aminolysis of aryl diphenylphosphinates and their
1=1.98 for
[19]
1
[20]
thio analogs, O-aryl diphenylphosphinothioates. However,
substantially larger 1 values have been reported for reac-
tions which proceed through a stepwise mechanism with
breakdown of intermediate being the RDS, for example, 1=
[27a]
3
.01 for aminolysis of X-substituted phenyl benzoates.
Thus, the fact that 1=1.42 in the current reactions also sup-
ports a concerted mechanism.
Figure 3. Yukawa–Tsuno plot for alkaline hydrolysis of X-substituted
phenyl diphenylphosphinates (1a–i) in 80 mol% H
at 25.0Æ0.18C; 1 = 1.42, r = 0.35, R = 0.996.
2
O/20 mol% DMSO
2
Activation parameters and reaction mechanism: To further
°
probe the above argument, activation parameters (DH and
°
DS ) have been determined from the rate constants mea-
sured at five different temperatures for reactions of 3,4-dini-
X
H
o
ꢀ
o
trophenyl, 4-nitrophenyl, and phenyl diphenylphosphinates
logk =k ¼ 1½s þ rðs ꢀs ފ
ð2Þ
ꢀ
(
1a, 1b, and 1i, respectively) with HO ion. The kinetic re-
sults are summarized in Table 2 and illustrated graphically
in Figure 4. As shown in Figure 4, the Eyring plots exhibit
The r value in the Yukawa–Tsuno equation represents the
°
resonance demand of the reaction center or the extent of
excellent linear correlations, indicating that the DH and
[28]
°
resonance contribution. The fact that r=0.35 in the cur-
rent reactions indicates that a partial negative charge devel-
ops (in the RDS) on the O
DS values determined in this study are accurate and relia-
ble.
atom of the leaving aryloxide,
Table 2. Summary of kinetic results for alkaline hydrolysis of 1a, 1b, and 1i in 80 mol% H
DMSO at five different temperatures.
2
O/20 mol%
which can be delocalized on the
substituent through reso-
X
ꢀ1 ꢀ1
k
HOꢀ/m
s
nance interactions. Thus, the
current result indicates that
breakdown of the PꢀOAr bond
°
ꢀ1
°
ꢀ1
ꢀ1
15.08C
20.08C
25.08C
35.08C
45.08C
DH /kcalmol
DS /calmol
K
1
1
a
b
116
11.9
0.344
153
16.2
0.475
200
21.3
0.690
341
38.5
1.28
543
65.5
2.52
8.7Æ0.2
9.7Æ0.1
11.3Æ0.2
ꢀ20.2Æ0.6
ꢀ21.4Æ0.4
ꢀ22.6Æ0.8
occurs in the RDS whether the 1i
reactions proceed through TS1
or TS . However, one can ex-
3
clude TS clearly in the current
The electronic nature of the substituent X in the leaving
aryloxide would influence the bond dissociation energy of
the PꢀOAr bond. Furthermore, the energy required to
3
reactions on the basis of the fact that the incoming hydrox-
ide is much more basic and a poorer nucleofuge than the
leaving aryloxide. Thus, one can suggest that the present re-
actions of 1a–i proceed through a concerted mechanism
with TS1.
°
break the PꢀOAr bond is reflected in DH . Thus, if the re-
action proceeds through a concerted mechanism as dis-
°
cussed above, DH should be strongly dependent on the
The above argument is inconsistent with the conclusion
drawn by Haake, by Istomin, and by Williams et al.
electronic nature of the substituent X. In fact, Table 2 shows
that DH increases from 8.7 kcalmol to 9.7 and 11.3 kcal
[16]
[17]
[18]
°
ꢀ1
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7327

I.-H. Um et al.
A similar result has been reported for the reactions of
morpholine with 2,4-dinitrophenyl, 4-nitrophenyl, and
[29]
phenyl acetates.
Jencks et al. have shown that the reac-
tions proceed through an addition intermediate with its
°
breakdown being the RDS (i.e., TS ), and the DH value in-
3
ꢀ1
ꢀ1
creases from 9.1 kcalmol to 10.7 and 14.3 kcalmol as the
substituent changes from 2,4-(NO ) to 4-NO and H, re-
2
2
2
[29]
°
spectively.
Thus, one might suggest that DH is even
more strongly dependent on the electronic nature of the
substituent in the leaving group for reactions which proceed
through a stepwise mechanism with leaving-group departure
being the RDS.
The fact that the Brønsted-type and Yukawa–Tsuno plots
are linear in the current hydrolysis of 1a–i indicates that the
reaction proceeds through a common TS structure (i.e., the
degree of leaving-group departure is constant regardless of
the electronic nature of the substituent X in the leaving
group). In this case, solvation of the negatively charged TS
would be more important than other factors (e.g., tightness
Figure 4. Eyring plots for alkaline hydrolysis of 1a (*, slope: ꢀ4400, in-
, slope: ꢀ4900, intercept: 13.8), and 1i ( , slope:
O/20 mol% DMSO at five differ-
tercept: 14.4), 1b (*
&
ꢀ
5700, intercept: 13.2.4) in 80 mol% H
2
ent temperatures.
°
or looseness) to determine DS .
The negative charge developing on the O atom of the
leaving aryloxide can be delocalized on the substituent X
through resonance interactions. Furthermore, as the sub-
stituent X changes from H to 3,4-(NO ) , delocalization of
ꢀ
1
mol as the substituent X changes from 3,4-(NO ) to 4-
2
°
2
NO and H. The effect of the substituent X on DH is illus-
2
2 2
trated in Figure 5, which exhibits an excellent linear correla-
such partial negative charge would be more significant,
which would cause a decrease in solvation of the TS by de-
creasing H-bonding in the aqueous medium. Thus, one can
°
expect that DS would become less negative for the reaction
of 1a (X=3,4-(NO ) ) than for that of 1i (X=H). In fact, as
2
2
°
shown in Table 2, the DS value changes from ꢀ22.6 cal
mol as the substitu-
to ꢀ21.4 and ꢀ20.2 calmol
ent X varies from H to 4-NO and 3,4-(NO ) , respectively.
ꢀ
1
ꢀ1
ꢀ1
ꢀ1
K
K
2
2 2
°
Thus, the change in DS on changing the substituent X, al-
though it is not large, is consistent with the proposed mecha-
nism.
Conclusion
The present study has allowed us to conclude the following:
1
) The reactions of 1a–i have been suggested to proceed
through a concerted mechanism on the basis of the
linear Brønsted-type plot with b =ꢀ0.49.
lg
2
) The Yukawa–Tsuno plot exhibits much better correlation
2
(
R =0.996) with r=0.35 than the Hammett plot correlat-
o
2
ed with s constants (R =0.982), indicating that depar-
°
ꢀ
Figure 5. Plot of DH versus s constants for alkaline hydrolysis of
phenyl diphenylphosphinate (1i), 4-nitrophenyl diphenylphosphinate
ture of the leaving group is advanced partially in the
ꢀ
RDS. However, TS has been excluded since HO ion is
3
(
1b) and 3,4-dinitrophenyl diphenylphosphinate (1a) in 80 mol% H
0 mol% DMSO at 25.0Æ0.18C; slope: ꢀ1.31, R = 0.995.
2
O/
more basic and a poorer nucleofuge than the leaving
phenoxide ion.
2
2
°
3
) The DH values are strongly dependent on the electron-
ic nature of the substituent X in the leaving group, indi-
cating that the leaving-group departure occurs in the
°
tion with a large slope. Such a strong dependence of DH
on the substituent X in the leaving group cannot be expect-
ed for reactions in which the departure of the leaving group
RDS.
°
4) The DS value becomes less negative as the substituent
occurs after the RDS (e.g., TS ).
X varies from H to 4-NO and 3,4-(NO ) , which has
2
2
2 2
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Chem. Eur. J. 2008, 14, 7324 – 7330

Alkaline Hydrolysis of Phosphinates
FULL PAPER
been attributed to a decrease in solvation of the nega-
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) Deduction of reaction mechanism based just on the
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Materials: X-substituted phenyl diphenylphosphinates (1a–i) were syn-
[
19,20]
thesized by modification of literature as reported previously.
concentration of NaOH stock solution was determined by titration with
potassium hydrogen phthalate. Doubly glass distilled H O was further
boiled and cooled under N to remove CO just before use. Other chemi-
cals were the highest grade available.
The
2
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6
H
4
O . All the reactions were carried
6
out under pseudo-first-order conditions in the presence of excess NaOH.
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This work was supported by the Korea Research Foundation (2005-015-
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