Kinetic and mechanistic studies on quinuclidinolysis of Y-substituted-phenyl picolinates: Effect of amine nature on reactivity and transition- state structure

Article abstract of DOI:10.1002/bkcs.10272

Second-order rate constants (k_N) have been measured spectrophotometrically for reactions of Y-substitutedphenyl picolinates (7a-7i) with a series of quinuclidines in 80 mol% H₂O/20 mol% DMSO at 25.0 ± 0.1 °C. The Bronsted-type plot f

Full text of DOI:10.1002/bkcs.10272

Article
DOI: 10.1002/bkcs.10272
BULLETIN OF THE
I.-H. Um et al.
KOREAN CHEMICAL SOCIETY
Kinetic and Mechanistic Studies on Quinuclidinolysis of Y-substituted-
Phenyl Picolinates: Effect of Amine Nature on Reactivity and Transition-
State Structure
*
Ik-Hwan Um, Min-Young Kim, and Yeseul Kang
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
*E-mail: ihum@ewha.ac.kr
Received December 15, 2014, Accepted January 13, 2015, Published online April 24, 2015
Second-order rate constants (kN) have been measured spectrophotometrically for reactions of Y-substituted-
phenyl picolinates (7a–7i) with a series of quinuclidines in 80 mol% H2O/20 mol% DMSO at 25.0 0.1 ꢀC.
The Brønsted-type plot for the reactions of 7a–7i with quinuclidine is linear with βlg = −0.80. The Yukawa-
Tsuno plot exhibits an excellent linear correlation with ρY = 2.37 and r = 0.52, indicating that a negative charge
develops partially on the O atom of the leaving group in the rate-determining transition state (TS). The
Brønsted-type plot for the reactions of 2-chloro-4-nitrophenyl picolinate (7a) with a series of quinuclidines
is also linear with βnuc = 0.83. Thus, it was concluded that the reactions proceed through a stepwise mechanism,
in which expulsion of the leaving group occurs in the rate-determining step. Comparison of the current kinetic
datawiththosereportedpreviouslyforthecorrespondingreactionswithpiperidinerevealed thatquinuclidineis
ca. 102-fold less reactive than piperidine. This is in contrast to the reports that quinuclidines are more reactive
than isobasic secondary amines toward diaryl carbonates and related esters. Effects of amine nature on reac-
tivity and TS structures are discussed.
Keywords: Y-substituted-phenyl picolinates, Quinuclidinolysis, Brønsted-type plot, Yukawa-Tsuno plot,
Rate-determining step
Introduction
A similar result has been reported for the reactions of 2a
and 2b, e.g., aminolysis of phenyl 4-nitrophenyl carbonate
(2a) proceeds through a stepwise mechanism with a change
in the RDS while the corresponding reaction of O-phenyl
O-4-nitrophenylthionocarbonate (2b, a thio analog of 2a)pro-
ceeds via a stepwise mechanism with two intermediates (i.e.,
T and T−).8 However, reactions of 2,4-dinitrophenyl diphe-
nylphosphinate (3a) and diphenylphosphinothioate (3b, a thio
analog of 3a) with primary and cyclic secondary amines have
been reported to proceed through a concerted mechanism on
the basis of linear Brønsted-type plots with βnuc = 0.4 0.1.9
Aminolysesofestershave been intensively investigated dueto
their importance in biological processes (e.g., enzyme actions
and peptide biosynthesis) as well as in synthetic applica-
tions.1–10 Nucleophilic substitution reactions of esters with
amines have been reported to proceed through a concerted
mechanism or via a stepwise pathway with one or two inter-
mediates (e.g., a zwitterionic tetrahedral intermediate T
and its deprotonated form T−) depending on the reaction con-
ditions (e.g., nature of the reaction medium and electrophilic
center).2-10
Reactions of 2,4-dinitrophenyl benzoate (1a) with a series
of cyclic secondary amines in 80 mol% H2O/20 mol% DMSO
have been suggested to proceed through a stepwise mechan-
ism with a change in the rate-determining step (RDS) on the
basis of a curved Brønsted-type plot.6a However, the corre-
sponding reactions carried out in an aprotic solvent MeCN
have been concluded to proceed via a concerted mechanism
NO
NO
2
2
X
C
X
X
NO
Ph
O
NO
PhO C
O
Ph
P
O
NO
2
2
2
Ph
X = O(1a), S(1b).
X = O(2a), S(2b).
X = O(3a), S(3b).
We have reported that intramolecular H-bonding interac-
tion is also an important factor that controls the reaction mech-
anism. Reactions of 4-pyridyl X-substituted-benzoates (4)
with cyclic secondary amines in MeCN have been suggested
to proceed through a stepwise mechanism with one or two
intermediates depending on the electronic nature of the sub-
stituent X in the benzoyl moiety (e.g., with T and T− when
the substituent X is a strong electron-withdrawing group such
as 4-NO2 or 4-CN, but with T only when Xis a weak electron-
withdrawing group or an electron-donating group).10a In con-
trast, the corresponding reactions of 2-pyridyl X-substituted-
on the basis of a linear Brønsted-type plot with βnuc
=
0.40,6b indicating that the reaction mechanism is dependent
on the nature of the reaction medium. In contrast, reactions
of O-2,4-dinitrophenyl thionobenzoate (1b, a thio analog of
1a) with cyclic secondary amines have been reported to pro-
ceed through a stepwise mechanism with two intermediates
(i.e., T and T−) in H2O as well as in MeCN on the basis of
an upward curvature found in the plots of kobsd vs. [amine].7
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Quinuclidinolysis of Y-substituted-Phenyl Picolinates
KOREAN CHEMICAL SOCIETY
benzoates (5) have been proposed to proceed through a forced
concerted mechanism with an unstable cyclic intermediate as
modeled by 6.10b It is noted that the H-bonding interaction
shown in 6 could decrease the basicity of the leaving group
dramatically by changing the nucleofuge from a strongly basic
2-pyridyloxide (pKa of its conjugate acid is 11.62 in H2O) to a
weakly basic 2-pyridinium oxide (pKa of its conjugate acid is
0.75 in H2O) or its tautomer 2-pyridone. Thus, we have pro-
posed that the intramolecular H-bonding interactions in 6
shorten its lifetime and force the reaction to proceed through
a concerted mechanism by decreasing the basicity of the leav-
ing group over 10 pKa units.10b
Tables 1 and 2 for the reactions of Y-substituted-phenyl
picolinates (7a–7i) with quinuclidine and for those of 2-
chloro-4-nitrophenyl picolinate (7a) with a series of quinucli-
dine derivatives, respectively.
Effects of Leaving Group Basicity on Reactivity. As shown
in Table 1, the kN value for the reactions of 7a–7i with quinu-
clidine decreases as the basicity of the leaving group increases,
e.g., it decreases from 8.70 M−1 s−1 to 0.217 and 0.00280 M−1
s−1 as the pKa of the conjugate acid of the leaving aryloxide
increases from 5.45 to 7.95 and 9.95, respectively. A similar
result is demonstrated for the reactions with piperidine,
although the cyclic secondary amine is ca. 102-fold more reac-
tive than the similarly basic tertiary amine. The effect of amine
nature on reactivity will be discussed subsequently.
The effect of amine basicity on reactivity is illustrated in
Figure 1. The Brønsted-type plot for the reactions of 7a–7i with
quinuclidine is linear with βlg = −0.80. A similarly linear plot
isdemonstratedforthecorrespondingreactionswithpiperidine,
although the slope for the piperidinolysis is larger (βlg = −1.04)
than that for the quinuclidinolysis. The linear Brønsted-
typeplotsinFigure 1areincontrasttothecurved Brønsted-type
plot reported by Gresser and Jencks for the reactions of phenyl
Y-substituted-phenyl carbonates with quinuclidine (i.e., βlg
changes from −1.3 to −0.2 as the leaving group becomes less
basic than quinuclidine by 3–5 pKa units).13
O
O
O
O
Ar
C
N
δ
C O
δ
C O
N
N
N
X
H
X
4
5
6
We have now extended our study to reactions of Y-substi-
tuted-phenyl picolinates (7a–7i) with a series of quinuclidines
in 80 mol% H2O/20 mol% DMSO to obtain further informa-
tion on the reaction mechanism (Scheme 1). The kinetic data
obtained from the current study have been compared with
those reported previously for the corresponding reactions with
a series of cyclic secondary amines10c to investigate the effects
of amine nature (e.g., secondary amines vs. tertiary amines) on
reactivity and transition-state (TS) structures.
Table 1. Summary of kinetic data for the reactions of Y-substituted-
phenyl picolinates (7a–7i) with quinuclidine and piperidine in
80 mol% H2O/20 mol % DMSO at 25.0 0.1 ꢀC.
Results and Discussion
kN (M−1 s−1
)
The kinetic study was carried out under pseudo-first-order
conditions in which the concentration of quinuclidine was
kept in excess of the substrate concentration. All the reactions
in this study obeyed pseudo-first-order kinetics and proceeded
with quantitative liberation of Y-substituted-phenoxide ion
(and/or its conjugate acid). Pseudo-first-order rate constants
(kobsd) were calculated from the equation, ln(A∞ − At) =
Piperidineb
a
Entry
Y
pKa
Quinuclidine
7a
7b
7c
7d
7e
7f
7g
7h
7i
2-Cl-4-NO2
4-NO2
4-CHO
4-CN
4-COMe
4-COOEt
3-Cl
5.45
7.14
7.66
7.95
8.05
8.50
9.02
9.38
9.95
8.70
0.829
0.161
0.217
—
211
49.5
—
0.0610
0.0601
0.0125
0.00811
0.00280
18.0
12.7
2.34
0.783
0.230
−kobsdt + C. The plots of ln(A − At) vs. t were linear over
∞
90% of the total reaction. The uncertainty in the kobsd values
is estimated to be less than 3% from replicate runs. The plots
of kobsd vs. [quinuclidine] were linear. Thus, the second-order
rate constants (kN) were calculated from the slope of the linear
plots. The kN values calculated in this way are summarized in
4-Cl
H
a The pKa data of Y-substituted-phenols were taken from Ref 11.
b The kinetic data for the reactions with piperidine were taken from
Ref 10c.
O
C
O
C
O
N
N
O
Table 2. Summary of kinetic data for the reactions of 2-chloro-4-
nitrophenyl picolinate (7a) with quinuclidines in 80 mol % H2O/20
mol % DMSO at 25.0 0.1 ꢀC.
N
N
Y
Y
7a-7i
a
Y = 2-Cl-4-NO2(7a), 4-NO2(7b), 4-CHO(7c), 4-CN(7d),
4-COMe(7e), 4-COOEt(7f), 3-Cl(7g), 4-Cl(7h), H(7i).
Entry
pKa
kN (M−1 s−1
)
1.
2.
3.
4.
5.
Quinuclidine
3-Hydroxyquinuclidine
3-Chloroquinuclidine
1,4-Diazabicyclo[2.2.2]octane
3-Quinuclidinone
11.4
9.8
9.0
8.9
7.5
8.70
0.888
0.0732
0.176
0.00593
Z
N
=
;
W
Z = CH and W = CH2 (quinuclidine)
N
Z = CH and W = CHOH (3-hydroxyquinuclidine)
Z = CH and W = CHCl (3-chloroquinuclidine)
Z = N and W = CH2 (1,4-diazabicyclo[2.2.2]octane)
Z = CH and W = CO (3-quinuclidinone).
a pKa data were taken from Ref 12.
Scheme 1. Quinuclidinolysis of 7a-7i.
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Quinuclidinolysis of Y-substituted-Phenyl Picolinates
KOREAN CHEMICAL SOCIETY
The βlg value obtained in this study is a little smaller than
To obtain more conclusive information on the RDS of the
current reactions, the Yukawa-Tsuno equation has been
employed. Eq. (1) was originally derived to account for the
kinetic results obtained from solvolysis of benzylic systems
in which a positive charge develops partially at the reaction
center.14 We have shown that Eq. (1) is also highly effective
to elucidate uncertainties in reaction mechanisms for nucleo-
philic substitution reactions of esters with various nucleo-
philes (e.g., neutral amines as well as anionic nucleophiles
that reported previously for reactions that proceed through a
stepwise mechanism with breakdown of an addition interme-
diate being the RDS (e.g., βlg = −1.1 0.2) but is much larger
than that for reactions in which expulsion of the leaving group
occurs after the RDS (e.g., βlg = −0.3 0.1).2,12,13 Besides, the
current βlg value of −0.80 is also larger than that reported for a
concerted mechanism (e.g., βlg = −0.5 0.1 for aminolysis of
Y-substituted-phenyl diphenylphosphinates and diphenyl-
phosphinothioates).2,9 Accordingly, the linear Brønsted-type
plot with βlg = −0.80 alone does not lead to a conclusion
whether the current reactions proceed through a stepwise
mechanism or via a concerted pathway.
such as OH−, N3 , and CN−).5,9,10,15
−
logkY=kH = ρY½σYo + rðσY −– σY Þꢁ
ð1Þ
o
It is well known that Hammett plots correlated with σ− and
σo constants give useful information on the reaction mechan-
ism including the RDS. If the reactions of 7a–7i with quinu-
clidine proceed through a concerted mechanism or via a
stepwise pathway with expulsion of the leaving group being
the RDS, a negative charge would develop partially on the
O atom of the leaving Y-substituted-phenoxide. Since such
a negative charge can be delocalized to the substituent
In fact, the Yukawa-Tsuno plot shown in Figure 3 for the
quinuclidinolysis of 7b–7i exhibits excellent linearity (R2 =
0.991) with ρY = 2.37 and r = 0.52. This is comparable with
the linear Yukawa-Tsuno plot for the corresponding reactions
1
0
1
0
(b)
(a)
−
7b
7b
Y through resonance interactions, one might expect that σY
constants should result in a better Hammett correlation than
σYo constants. In contrast, if the reactions proceed through a
stepwise mechanism, in which expulsion of the leaving group
occurs after the RDS, nonegative charge woulddeveloponthe
O atom of the leaving group in the rate-determining TS. In this
case, σYo constants should result in a better Hammett correla-
tion than σY− constants. Thus, Hammett plots have been con-
structed using σYo and σY− constants. As shown in Figure 2,
theHammettplotcorrelatedwithσYo constantsexhibitshighly
7d
7d
7c
7e
7f
7c
–1
–2
–3
–4
7f
–1
–2
–3
–4
7e
7g
7h
7g
7h
7i
7i
ρY = 3.1 0.5
R2= 0.936
ρ
Y = 1.8 0.2
R
2 = 0.978
1.0
0.0
0.5
1.5
0.0
0.5
σYο
1.0
σY−
scattered points (R2 = 0.936). The plot correlated with σY
−
constants results in a slightly better correlation (R2 = 0.978),
but it still exhibits many scattered points. Accordingly, one
cannot obtain useful information on the RDS from these Ham-
mett plots.
Figure 2. Hammett plots correlated with σY− (a) and σYo (b) for the
reactions of Y-substituted-phenyl picolinates (7b–7i) with quinucli-
dinein80 mol%H2O/20 mol%DMSO at25.0 0.1 ꢀC. Theidentity
of points is given in Table 1.
1
0
4
3
(a)
(b)
2
0
4
2
(a)
(b)
7b
7a
7b
7b
7c
7d
2
7b
7c
7c
7e
–1
–2
–3
–4
7f
7e
7d
7f
7e
7f
1
7f
7c
7g
7g
7h
7g
7h
7e
7g
7h
7h
7i
0
–2
–4
0
7i
7i
7i
ρY = 2.37
r = 0.52
ρY = 2.76
r = 0.62
β
= −1.04
–1
–2
β
= −0.80 0.05
lg
lg
2
R2 = 0.991
R2 = 0.994
2
R
= 0.994
R
= 0.988
–2
0.0
0.5
1.0
0.0
0.5
1.0
4
6
8
10
6
7
8
9
10 11
σYo + r (σY− − σYo)
σYo + r (σY− − σYo)
pK
pK
a
a
Figure 1. Brønsted-type plots for the reactions of Y-substituted-
phenyl picolinates (7a–7i) with quinuclidine (a) and piperidine (b)
in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 ꢀC. The identity
of points is given in Table 1.
Figure 3. Yukawa-Tsuno plots for the reactions of Y-substituted-
phenyl picolinates (7b–7i) with quinuclidine (a) and piperidine (b)
in 80 mol % H2O/20 mol % DMSO at 25.0 0.1 ꢀC. The identity
of points is given in Table 1.
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Quinuclidinolysis of Y-substituted-Phenyl Picolinates
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with piperidine (e.g., ρY = 2.76, r = 0.62, and R2 = 0.994). The
r value in Eq. (1) represents the resonance demand of the reac-
tion center or the extent of resonance contribution, while the
term (σY− − σYo) is the resonance substituent constant that
measures the capacity for π-delocalization of the π-electron
acceptor substituent.14,16 The r value of 0.52 found for the
reactions with quinuclidine clearly indicates that a negative
charge develops partially on the O atom of the leaving group,
which can be delocalized to the substituent Y through reso-
nance interactions.
Effect of Amine Basicity on Reactivity. To obtain further
information on the reaction mechanism, second-order rate
constants for reactions of 2-chloro-4-nitrophenyl picolinate
(7a) with a series of quinuclidines have been measured. As
shown in Table 2, the kN value for the reaction of 7a decreases
with decreasing basicity of quinuclidines, e.g., it decreases
from 8.70 M−1 s−1to 0.888 and 0.00593 M−1 s−1 as the pKa
of the conjugate acid of quinuclidine decreases from 11.4 to
9.8 and 7.5, respectively.
3b and quinuclidinolysis of methyl 2,4-dinitrophenyl carbo-
nate).9,12b Thus, one can conclude that the current reactions
proceed through a stepwise mechanism in which expulsion
of the leaving group occurs in the RDS.
EffectofAmineNatureonReactivityandTSStructure. As
shown in Table 1, quinuclidine is ca. 102-fold less reactive
than the similarly basic piperidine. One might suggest that
steric hindrance exerted by quinuclidines is responsible for
the decreased reactivity, since tertiary amines are bulkier than
cyclic secondary amines. However, we propose that amine
nature is also responsible for the kinetic result that quinucli-
dines are much less reactive than isobasic secondary amines
on the basis of the following reason. We have previously pro-
posed that reactions of 7a–7i with cyclic secondary amines
proceed through a cyclic intermediate as modeled by 8, which
could gain great stability through intermolecular H-bonding
interactions.10c However, such cyclic intermediate is structur-
ally not possible for the reactions with quinuclidines (e.g.,
intermediate 9). Stabilization of the intermediate through such
H-bonding interactions would lead to stabilization of the TS
onthebasisofHammondpostulate.18 Thus, onemight suggest
that the enhanced stability of intermediate 8 through the H-
bonding interactions is primarily responsible for the kinetic
result that piperidine is much more reactive toward 7a–7i than
the similarly basic quinuclidine.
The effect of nucleophile basicity on reactivity is illustrated
in Figure 4. The statistically corrected Brønsted-type plot for
the reactions of 7a with quinuclidines results in an excellent
linear correlation with βnuc = 0.83, which is comparable with
that reported previously for reactions proceeding through a
stepwise mechanism with expulsion of the leaving group
being the RDS (e.g., βnuc = 0.86 for the reactions of methyl
O
C
N
O
C
N
4-nitrophenyl carbonate with quinuclidines12b and βnuc
=
O
O
δ
0.78 for the reactions of 4-nitrophenyl picolinate (7b) with a
series of cyclic secondary amines10c). However, a βnuc value
of 0.83 observed in this study is much larger than a βnuc value
0.5 0.1 reported previously for reactions that proceed
through a concerted mechanism (e.g., aminolysis of 3a and
N
N
δ
H
Y
Y
8
9
It has generally been understood that βnuc represents a rel-
ative degree of bond formation between the nucleophile and
the electrophilic center, while βlg stands for a relative degree
of leaving group expulsion. The βnuc value of 0.83 0.06
shown in Figure 4 for the reactions of 7a with quinuclidines
is almost the same as that reported previously for the reactions
of 7a with cyclic secondary amines (βnuc = 0.78 0.04),10c
indicating that the degree of bond formation between the
nucleophile and electrophilic center is practically the same
for both series of the reactions. In contrast, βlg for the reactions
of 7a–7i with quinuclidine is −0.80 0.05, which is smaller
than the βlg value of −1.04 0.05 for the reactions with piper-
idine (Figure 1). This indicates that expulsion of the leaving
group in the rate-determining TS is clearly less advanced
for the reactions with quinuclidines than that for the reactions
with piperidine.
Scrutiny of the proposed intermediates 8 and 9 reveals that
the positive charge on the N atom of their aminium moiety is
different, i.e., a partial positive charge in 8 and a full positive
one in 9. One might expect that expulsion of the leaving group
from 9, in which the N atom bonded to the reaction center is
fully charged, would be more difficult than from 8, where
the N atom is partially charged. This idea accounts for the
fact that βlg is smaller for the reactions proceeding through
intermediate 9 than for those proceeding via 8.
2
1
1
2
0
4
–1
3
–2
–3
–4
5
nuc= 0.83 0.06
β
R2 = 0.991
6
8
10
12
pK + log (p/q)
a
Figure 4. Brønsted-type plot for the reactions of 2-chloro-4-
nitrophenyl picolinate (7a) with quinuclidines in 80 mol % H2O/
20 mol % DMSO at 25.0 0.1 ꢀC. The plot was statistically corrected
using p and q (i.e., p = 1 and q = 1 except q = 2 for 1,4-diazabicyclo
[2.2.2]octane).17 The identity of points is given in Table 2.
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BULLETIN OF THE
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Quinuclidinolysis of Y-substituted-Phenyl Picolinates
Conclusions
KOREAN CHEMICAL SOCIETY
reaction mixtures was ca. (5–100) × 10−3 M, while the con-
centration of the substrate was ca. 4 × 10−5 M. Pseudo-first-
order rate constants (kobsd) were calculated from the equation,
ln(A∞ − At) = −kobsdt + C. The plots of ln(A−At) vs. time were
linear over 90% of the total reaction.
Thecurrentstudyhasallowedustoconcludethefollowing:(1)
The Brønsted-type plot for the reactions of 7a–7i with quinu-
clidine is linear with βlg = −0.80 0.05, which is smaller than
that reported for the corresponding reactions with piperidine
(i.e., βlg = −1.04 0.05). (2) The Yukawa-Tsuno plot results
in excellent linearity with ρY = 2.37 and r = 0.52, indicating
that a partial negative charge develops on the O atom of the
leaving group in the rate-determining TS. (3) The Brønsted-
type plot for the reactions of 7a with a series of quinuclidines
is linear with βnuc = 0.83 0.06, which is practically the same
as that reported previously for the corresponding reactions
with secondary amines (i.e., βnuc = 0.78 0.04). (4) The reac-
tions with quinuclidines proceed through a stepwise mechan-
ism, in which expulsion of the leaving group occurs in the
RDS. (5) Analysis of βnuc and βlg values suggests that expul-
sion of the leaving group from the intermediate in the rate-
determining TS is less advanced for the reactions with quinu-
clidines than that for the reactions with secondary amines,
while bond formation between the nucleophile and electro-
philic center is practically the same for both reactions. (6)
Piperidine is ca. 102-fold more reactive than quinuclidine
toward 7a–7i. This supports the proposal that the reactions
of 7a–7i with secondary amines proceed through a stabilized
cyclic intermediate, which is structurally not possible for the
reactions with quinuclidines.
Products Analysis. Y-substituted-phenoxide ion (and/or its
conjugate acid) was liberated quantitatively and identified
as one of the products by comparison of the UV–vis spectrum
after completion of the reaction with that of an authentic sam-
ple under the same reaction condition.
Acknowledgments. Publication cost of this article was sup-
ported by the Korean Chemical Society.
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Experimental
Materials. Y-substituted-phenyl picolinates (7a–7i) were
readily prepared from the reaction of picolinic acid with Y-
substituted-phenol in methylene chloride under the presence
of N,N0-dicyclohexylcarbodiimide (DCC) as reported pre-
viously.10c The crude product was purified by column chro-
matography and the purity was checked by their melting
point and spectral data such as 1H and 13C NMR spectra. Dou-
ble glass distilled H2O was further boiled and cooled under
nitrogen just before use. DMSO and other chemicals were
of the highest quality available.
Kinetics. The kinetic study was carried out using a UV–vis
spectrophotometer equipped with a constant temperature cir-
culating bath to maintain the reaction mixture at 25.0 0.1 ꢀC.
The reactions were followed by monitoring the appearance of
Y-substituted-phenoxide ion. All the reactions in this study
were performed under pseudo-first-order conditions, in which
the concentration of quinuclidine was kept in excess of the
substrate concentration. Owing to low solubility of 7a–7i in
pure water, aqueous DMSO (i.e., 80 mol% H2O/20 mol%
DMSO) was used as the reaction medium.
Typically, the reaction was initiated by adding 5 μL of a
0.02 M solution of the substrate in acetonitrile to a 10-mm
quartz UV cell containing 2.50 mL of the thermostated reac-
tionmixture madeupofsolventand aliquot ofthequinuclidine
stock solution. All solutions were transferred by gastight syr-
inges. Generally, the concentration of quinuclidines in the
Bull. Korean Chem. Soc. 2015, Vol. 36, 1405–1410
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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BULLETIN OF THE
Article
Quinuclidinolysis of Y-substituted-Phenyl Picolinates
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Bull. Korean Chem. Soc. 2015, Vol. 36, 1405–1410
© 2015 Korean Chemical Society, Seoul & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.bkcs.wiley-vch.de 1410