Kinetic study on reactions of O-Y-substituted phenyl thionobenzoates with quinuclidine: Factors governing reactivity and reaction mechanism

Article abstract of DOI:10.1002/bkcs.10207

Second-order rate constants (k_quin) for the reactions of O-Y-substituted phenyl thionobenzoates (3a-3i) with quinuclidine have been measured spectrophotometrically. Comparison of k_quin with the rate constants reported previously for the corresponding reactions with benzylamine (k_BzNH2) has revealed that quinuclidine is less reactive than benzylamine toward 3a-3i although the former is 2.1 pK_a units more basic than the latter. Steric hindrance exerted by quinuclidine has been suggested to be responsible for the decreased reactivity of the tertiary amine. The Bronsted-type plot for the reactions of 3a-3i with quinuclidine is linear with β_lg = -0.37. The Hammett plot correlated with σ(Formula presented.) constants exhibits many scattered points (R² = 0.982). In contrast, the Yukawa-Tsuno plot results in an excellent linear correlation (R² = 0.9992) with ρ_Y = 0.96 and r = 0.51, indicating that a negative charge develops partially on the O atom of the leaving group. Thus, the reactions of 3a-3i with quinuclidine have been concluded to proceed through a concerted mechanism in which expulsion of the leaving group is advanced only a little in the rate-determining transition state.

Full text of DOI:10.1002/bkcs.10207

Article
DOI: 10.1002/bkcs.10207
BULLETIN OF THE
E.-J. Yang et al.
KOREAN CHEMICAL SOCIETY
Kinetic Study on Reactions of O-Y-substituted Phenyl Thionobenzoates
with Quinuclidine: Factors Governing Reactivity and Reaction
Mechanism
†,‡
†
†,*
Eun-Ji Yang, Min-Young Kim, and Ik-Hwan Um
†
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 120-750, Korea.
E-mail: ihum@ewha.ac.kr
Department of Chemistry, Duksung Women's University, Seoul 132-714, Korea
Received November 20, 2014, Accepted December 4, 2014, Published online March 11, 2015
*
‡
Second-order rate constants (kquin) for the reactions of O-Y-substituted phenyl thionobenzoates (3a–3i) with
quinuclidine have been measured spectrophotometrically. Comparison of kquin with the rate constants reported
previously for the corresponding reactions with benzylamine (kBzNH2) has revealed that quinuclidine is less
reactive than benzylamine toward 3a–3i although the former is 2.1 pK units more basic than the latter. Steric
a
hindrance exerted by quinuclidine has been suggested to be responsible for the decreased reactivity of the ter-
tiary amine. The Brønsted-type plot for the reactions of 3a–3i with quinuclidine is linear with β = −0.37. The
lg
o
Y
2
Hammett plot correlated with σ constants exhibits many scattered points (R = 0.982). In contrast, the
Yukawa-Tsuno plot results in an excellent linear correlation (R = 0.9992) with ρ = 0.96 and r = 0.51, indicat-
2
Y
ing that a negative charge develops partially on the O atom of the leaving group. Thus, the reactions of 3a–3i
with quinuclidine have been concluded to proceed through a concerted mechanism in which expulsion of the
leaving group is advanced only a little in the rate-determining transition state.
Keywords: Quinuclidinolysis, O-Aryl thionobenzoates, Rate-determining step, Concerted mechanism,
Steric hindrance
Introduction
Aminolysis of thione esters have been reported to proceed
Nucleophilic substitution reactions of esters with amines have
intensively been investigated due to their importance in
biological processes as well as in synthetic applications.
through a stepwise mechanism with one or two intermediates
±
(e.g., a zwitterionic tetrahedral intermediate T and its depro-
1–10
− 8
tonated form T ). We have reported that reactions of O-4-
nitrophenylthionobenzoate (3b) with primary amines proceed
through a stepwise mechanism with a change in the RDS on
Aminolysis of esters has been reported to proceed through a con-
certed mechanism or via a stepwise pathway depending on reac-
tion conditions (e.g., nature of the electrophilic center, amines,
8a
the basis of a curved Brønsted-type plot. In contrast, the cor-
responding reactions with secondary amines have been pro-
posed to proceed through a stepwise mechanism with two
2–10
and reaction medium).
Reactions of 2,4-dinitrophenyldiphe-
nylphosphinate (1) with primary and secondary amines have
been reported to proceed through a concerted mechanism on6
the basis of a linear Brønsted-type plot with βnuc = −0.4 ± 0.1.
The reactions of 2,4-dinitrophenyl benzoate (2) with a series
of cyclic secondary amines in MeCN have also been suggested
to proceed through a concerted mechanism on the basis of a lin-
±
−
intermediates (i.e., T and T ) as plots of k
curved upward.
vs. [amine]
obsd
8b,c
This study has now been extended to reactions of a series of
O-Y-substituted phenyl thionobenzoates (3a–3i) with quinucli-
dine (a tertiary amine) to obtain further information on the reac-
tion mechanism (Scheme 1). The kinetic data in this study have
7a
ear Brønsted-type plot with βnuc = 0.40. In contrast, the corre-
8b,9
sponding reactions of 2 in 80 mol% H O/20 mol% dimethyl
been compared with those reported previously for the reac-
2
−
3
−
sulfoxide (DMSO) havebeen reportedto proceed through a step-
wise mechanism with a change in the rate-determining step
tions of 3a–3i with benzylamine, N , and OH to investigate
factors governing reactivity and reaction mechanism.
(RDS) on the basis of a curved Brønsted-type plot (e.g., the slope
decreasesfrom0.74to0.34astheattackingaminebecomesmore
Results and Discussion
7b
basic than the leaving group by ca. 4.5 pK units).
a
The kinetic study was carried out spectrophotometrically
under pseudo-first-order conditions in which the concentra-
tion of quinuclidine was kept at least 20 times in excess of
the substrate concentration. All the reactions in this study
obeyed first-order kinetics and pseudo-first-order rate
Bull. Korean Chem. Soc. 2015, Vol. 36, 1120–1125
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Quinuclidinolysis of O-Y-substituted Phenyl Thionobenzoates
KOREAN CHEMICAL SOCIETY
constants (kobsd) were calculated from the equation, ln(A −
benzylamine is quite an unexpected result. Because quinucli-
dines have been reported to be more reactive than isobasic
cyclic secondary amines toward methyl chloroformate and
diaryl carbonates. Furthermore, cyclic secondary amines
have been reported to be even more reactive than isobasic pri-
mary amines.
Steric hindrance exerted by quinuclidine would not be so
significant for the reactions of phenyl Y-substituted phenyl
carbonates, although quinuclidine (a tertiary amine) is bulkier
than piperidine (a secondary cyclic amine) and benzylamine (a
primary amine). However, one might expect that steric hin-
drance is an important factor that influences reactivity of qui-
nuclidine in the current reactions of thione esters 3a–3i.
Because the C S bond in 3a–3i is much larger than the
C O bond in phenyl Y-substituted phenyl carbonates. Fur-
thermore, steric hindrance exerted by the Ph group in 3a–3i
would be more significant than that shown by the PhO group
∞
At) = −kobsdt + C. Theplotsof kobsd vs. quinuclidine concentra-
tion were linear. Accordingly, the second-order rate constants
for the quinuclidinolysis of 3a–3i (kquin) were calculated from
the slope of the linear plots. The kquin values calculated in this
way are summarized in Table 1 together with those reported
10
8
b,9
previously
for the corresponding reactions with benzyla-
−
−
mine (BzNH ), N , and OH for comparison. The uncertainty
2
3
in the kquin values is estimated to be less than ±3% based on the
replicate runs.
Factors Influencing Reactivity of Thione Esters. As shown
in Table 1, the reactivity of substrates 3a–3i decreases as the
basicity of the leaving group increases, e.g., the k value for
N
the reactions of 3a–3i with quinuclidine decreases from
−
1 −1
3
.01 to 0.301 and 0.0465 M s as the pK of conjugate acid
a
of the leaving aryloxide increases from 5.42 to 8.05 and 10.19,
in turn. Similar results are demonstrated for the corresponding
−
3
−
reactions with benzylamine (BzNH ), N , and OH . However,
inthediaryl carbonatesonthebasisoftheirE
values(i.e., E =
s s
2
−
2.55 for Ph and the E value for PhO is not available but
the reactivity of these nucleophiles toward substrates 3a–3i is
s
13
would be similar to E = −0.38 for PhCH ). Thus, one might
independent of their basicity, e.g., quinuclidine is less reactive
s
2
−
suggest that steric hindrance is responsible for the kinetic
result that quinuclidine is less reactive than the less basic ben-
zylamine toward the C S centered esters 3a–3i.
than BzNH and N , although it is 2.1 and 6.7 pK units more
2
3
a
−
−
basic than BzNH and N , respectively. Furthermore, N is
more reactive than OH toward substrates possessing an elec-
2
3
3
−
−
3
−
As shown in Table 1, N is more reactive than OH toward
tron-withdrawing group in the leaving group (e.g., 3a–3d),
substrates 3a–3d, althoughtheformeris11pK unitslessbasic
than the latter. This is in contrast to the report that N is 383-
fold less reactive than OH toward 2. It is well known that a
C S bond is significantly more polarizable than a C O bond
because the overlap between 2p and 3p orbitals in a C S bond
is not as strong as that between 2p and 2p orbitals in a C O
bond. Besides, N was reported to be a highly polarizable base
while OH is a nonpolarizable one. Thus, the high polariz-
ability of N could be responsible for the enhanced reactivity
of N toward the highly polarizable C S esters at least in part.
although the former is 11 pK units less basic than the latter.
a
a
−
3
The fact that quinuclidine is less reactive than less basic
−
14
−
3
−
14
−
3
−
3
Another factor that might affect reactivity of 3a–3i is nature
of the reaction mechanism. Nucleophilic substitution reac-
tions of esters have been reported to proceed through a
Scheme 1. Quinuclidinolysis of 3a–3i.
−
Table 1. Summary of the kinetic data for the reactions of O-Y-substituted phenyl thionobenzoates (3a–3i) with quinuclidine, benzylamine, N ,
3
−
ꢀ
and OH in 80 mol% H O/20 mol% DMSO at 25.0 ± 0.1 C.
2
a
−1 −1
b
−1 −1
c
−1 −1
d
−1 −1
Y
pKa
kquin/M
s
kBzNH2/M
s
kN3–/M
s
kOH–/M s
3
3
3
3
3
3
3
3
3
a
b
c
d
e
f
g
h
i
3,4-(NO
4-NO2
4-CHO
4-COMe
3-NO2
3-COMe
H
4-Me
4-MeO
2
)
2
5.42
7.14
7.66
8.05
8.35
9.19
9.95
10.19
10.20
3.01
12.7
3.71
—
183
11.0
2.50
1.39
—
10.5
1.87
0.735
0.360
0.301
—
0.846
0.650
1.46
0.489
0.210
0.161
0.172
2.14
—
0.165
0.0645
0.0465
0.0442
1.87
—
0.915
0.871
—
0.0122
0.00509
0.00544
a
b
c
a
pK data taken from Ref. 11.
Kinetic data taken from Ref. 8b.
Kinetic data taken from Ref. 9.
Kinetic data taken from Ref. 12.
d
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Quinuclidinolysis of O-Y-substituted Phenyl Thionobenzoates
KOREAN CHEMICAL SOCIETY
concerted mechanism or via a stepwise pathway depending on
A linear Brønsted-type plot with β = −0.37 is typical for
lg
2–10
reaction conditions.
Reactions of 3a–3i with benzylamine
reactions reported previously to proceed through a stepwise
have been reported to proceed through a stepwise mechanism
mechanism with formation of an intermediate being the
±
−
2–10
with one or two intermediates (e.g., T and T when the sub-
stituent Y in the leaving group is an electron-donating group
such as 4-Me but the deprotonation process is absent when
RDS.
Thus, one might suggest that the quinuclidinolysis
of 3a–3i proceeds through a stepwise mechanism in which
expulsion of the leaving group occurs after the RDS.
8
b
−
Y is an electron-withdrawing group). Reactions of 3a–3i
It is well known that Hammett plots correlated with σ and
−
3
−
o
with N and OH have also been reported to proceed through
σ constants give useful information on reaction mechanism
a stepwise mechanism, in which the RDS is dependent on the
particularly on the RDS. If the quinuclidinolysis of 3a–3i pro-
ceeds through a stepwise mechanism, in which expulsion of
the leaving group occurs after the RDS, no negative charge
would develop on the O atom of the leaving group in the
−
3
nucleophiles (e.g., the RDS for the reactions with N changes
from formation of an addition intermediate to its breakdown as
−
the leaving group becomes 1.6 pK units more basic than N ,
a
3
−
o
while the RDS for the reactions with OH is formation of an
rate-determining TS. In this case, σ constants should result
9,12
−
intermediate regardless of the leaving-group basicity).
in a better Hammett correlation than σ constants. In contrast,
if the reactions of 3a–3i with quinuclidine proceed either
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
group. Assucha negative chargecan be delocalizedto thesub-
stituent Y in the leaving group through resonance interactions,
Deduction of Reaction Mechanism. To investigate the reac-
tion mechanism, Brønsted-type plots for the reactions with
−
3
quinuclidine and N have been constructed. As shown in
Figure 1, the Brønsted-type plot for the reactions of 3a–3i with
quinuclidine is linear with β = −0.37. This is in contrast to the
lg
curved Brønsted-type plot for the corresponding reactions
−
−
3
−
3
one might expect that σ constants should result in a better
with N . The reactions of 3a–3i with N have previously been
o
Hammett correlation than σ constants. In fact, Figures S1
reported to proceed through a stepwise mechanism with a
change in the RDS on the basis of the curved Brønsted-type
plot, i.e., from formation of an addition intermediate to its
o
and S2 in the Supporting Information demonstrate that σ con-
−
stants result in a much better correlation than σ constants for
the reactions of 3a–3i with benzylamine and hydroxide ion,
respectively.
breakdown as the leaving group becomes 1.6 pK units more
a
−
3
9
basic than N . The linear Brønsted-type plot for the quinucli-
Thus, Hammett plots for the reactions of 3a–3i with quinu-
dinolysis of 3a–3i indicates that the reaction proceeds without
changing the reaction mechanism including the RDS.
o
−
clidine have been constructed using σ and σ constants to
Y
Y
investigate the nature of the RDS. As shown in Figure 2, the
Hammett plot correlated with σ constants results in a poor
correlation (R = 0.982). The one correlated with σ constants
results in a slightly better correlation but with many scattered
o
Y
2
−
Y
2
points (R = 0.991). Accordingly, one cannot obtain conclu-
sive information on the RDS from these Hammett plots.
To obtain more conclusive information on the RDS of the
current reactions, the Yukawa-Tsuno equation has been
employed, which was originally derived to account for the
15
kinetic results obtained from solvolysis of benzylic systems.
However, we have shown that Eq. (1) is highly effective to
clarify ambiguities in reaction mechanisms for nucleophilic
substitution reactions of esters with various nucleophiles
(
e.g., neutral amines as well as anionic nucleophiles such as
−
−
−
5,9,12
OH , N , and CN ).
3
Â
À
ÁÃ
Y
H
o
−
Y
o
logk =k = ρ σ + r σ – σ
ð1Þ
Y
Y
Y
As shown in Figure 3, the Yukawa-Tsuno plot for the qui-
2
nuclidinolysis of 3a–3i exhibits excellent linearity (R =
0
.9992) with ρ = 0.96 and r = 0.51. The r value in Eq. (1)
Y
represents the resonance demand of the reaction center or
the extent of resonance contribution, while the term
−
o
(
σ −σ ) is the resonance substituent constant that measures
Y Y
the capacity for π-delocalization of the π-electron acceptor
Figure 1. Brønsted-type plots for the reactions of O-Y-substituted
15,16
−
substituent.
The r value of 0.51 observed for the quinucli-
phenyl thionobenzoates (3a–3i) with quinuclidine (●) and N (○)
3
ꢀ
in 80 mol% H
2
O/20 mol% DMSO at 25.0 ± 0.1 C. The identity of
dinolysis of 3a–3i clearly indicates that a partial negative
points is given in Table 1.
charge develops on the O atom of the leaving group, which
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Quinuclidinolysis of O-Y-substituted Phenyl Thionobenzoates
KOREAN CHEMICAL SOCIETY
(
a)
(b)
o
−
Figure 2. Hammett plots correlated with σ (a) and σ (b) for the reactions of O-Y-substituted phenyl thionobenzoates (3a–3i) with quinuclidine
Y
Y
ꢀ
2
in 80 mol% H O/20 mol% DMSO at 25.0 ± 0.1 C. The identity of points is given in Table 1.
However, we propose that the current reactions of 3a–3i with
quinuclidine proceed through a concerted mechanism as a βlg
value of −0.37 is too small for a stepwise mechanism in which
expulsion of the leaving group occurs in the RDS.
Effect of Steric Hindrance on Reaction Mechanism. As
mentioned inthe precedingsection, thereactions of3a–3iwith
quinuclidine would experience significant steric hindrance.
Steric hindrance would be more significant on going from
the ground state (GS) to the zwitterionic tetrahedral interme-
±
diate (T ). Because the dihedral angle of the reaction center
ꢀ
2
decreases from 120 (an sp hybridization in the GS) to ca.
ꢀ
3
1
09 (an sp hybridization in the intermediate). Consequently,
±
a plausible intermediate T formed from the reactions of 3a–3i
with quinuclidine would be highly unstable due to the
enhanced steric hindrance.
One might expect that expulsion of the leaving group from
the plausible intermediate diminishes the steric hindrance sig-
ꢀ
nificantly by increasing the dihedral angle from ca. 109 (an
3
ꢀ
2
sp hybridization in the intermediate) to 120 (an sp hybrid-
ization in the product). Accordingly, we propose that the±
enhanced steric hindrance in the plausible intermediate T
forces the reactions to proceed through a concerted mechan-
ism with a TS structure similar to a zwitterionic tetrahedral
intermediate, in which expulsion of the leaving group is
advanced only a little.
Figure 3. Yukawa-Tsuno plot for the reactions of O-Y-substituted
phenyl thionobenzoates (3a–3i) with quinuclidine in 80 mol%
ꢀ
H
2
O/20 mol% DMSO at 25.0 ± 0.1 C. The identity of points is given
in Table 1.
Conclusion
This study has led us to conclude the following:
can be delocalized to the substituent Y through resonance
interactions. This case is possible for reactions that proceed
either through a concerted mechanism or via a stepwise path-
way with expulsion of the leaving group being the RDS.
1
. Quinuclidine is less reactive than less basic benzyla-
mine. Steric hindrance is responsible for the decreased
reactivity of quinuclidine toward 3a–3i.
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Quinuclidinolysis of O-Y-substituted Phenyl Thionobenzoates
KOREAN CHEMICAL SOCIETY
2
. The Brønsted-type plot for the reactions with quinucli-
2. Reviews: (a) E. A. Castro, Pure Appl. Chem. 2009, 81, 685; (b)
E. A. Castro, J. Sulfur Chem. 2007, 28, 401; (c) E. A. Castro,
Chem. Rev. 1999, 99, 3505; (d) W. P. Jencks, Chem. Rev.
1985, 85, 511; (e) W. P. Jencks, Chem. Soc. Rev. 1981, 10, 345.
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J. Phys. Org, Chem. 2014, 27, 265; (b) P. Pavez, D. Millan,
J. I. Morales, E. A. Castro, J. Org. Chem. 2013, 78, 9670; (c)
R. Aguayo, F. Arias, A. Canete, C. Zuniga, E. A. Castro,
P. Pavez, J. G. Santos, Int. J. Chem. Kinet. 2013, 45, 202; (d)
E. A. Castro, D. Ugarte, M. F. Rojas, P. Pavez, J. G. Santos,
Int. J. Chem. Kinet. 2011, 43, 708; (e) E. Castro, M. Aliaga, P.
R. Campodonico, M. Cepeda, R. Contreras, J. G. Santos,
J. Org. Chem. 2009, 74, 9173; (f ) E. A. Castro, M. Ramos,
J. G. Santos, J. Org. Chem. 2009, 74, 6374.
dine is linear with β = −0.37, which is in contrast to the
lg
−
3
curved plot for the corresponding reactions with N .
3. The Yukawa-Tsuno plot exhibits an excellent linear
correlation with ρ = 0.96 and r = 0.51, indicating that
Y
a partial negative charge develops in the leaving group
in the rate-determining TS.
4
5
6
. The reactions of 3a–3i with quinuclidine proceed
through a concerted mechanism in which expulsion of
the leaving group is advanced only a little.
. Steric hindrance exerted by quinuclidine forces the cur-
rent reactions to proceed through a concerted
mechanism.
. Reactivity of nucleophiles toward 3a–3i is independent
of their basicity. Steric hindrance, polarizability and
nature of reaction mechanism affect their reactivity.
4. (a)H. K. Oh, J. Y. Oh, D. D. Sung, I. Lee, J. Org. Chem. 2005, 70,
5624; (b) H. K. Oh, Y. C. Jin, D. D. Sung, I. Lee, Org. Biomol.
Chem. 2005, 3, 1240; (c) I. Lee, D. D. Sung, Curr. Org. Chem.
2
9
3
1
004, 8, 557; (d) J. F. Kirsch, A. Kline, J. Am. Chem. Soc. 1969,
1, 1841; (e) T. H. Fife, L. Chauffe, J. Org. Chem. 2000, 65,
579; (f ) W. J. Spillane, C. Brack, J. Chem. Soc. Perkin Trans.
998, 2, 2381.
Experimental Section
Materials. Substrates 3a–3i were readily prepared from the
reaction of dithiobenzoic acid with Y-substituted phenol in
5
6
. I. H. Um, J. S. Min, J. A. Ahn, H. J. Hahn, J. Org. Chem. 2000,
5, 5659.
. (a)I. H. Um, J. Y. Han, Y. H. Shin, J. Org. Chem. 2009, 74, 3073;
b) I. H. Um, K. Akhtar, Y. H. Shin, J. Y. Han, J. Org. Chem.
0
the presence of N,N -dicyclohexylcarbodiimide (DCC) in
6
1
7
methylene chloride as reported previously. The crude com-
pounds were purified by recrystallization. The purity was con-
(
1
13
firmed by melting points and H and C NMR spectra. The
stock solutions of quinuclidine was prepared by adding two
equivalent of quinuclidine hydrochloride and one equivalent
of standardized NaOH to make a self-buffered solution just
2007, 72, 3823; (c) I. H. Um, Y. H. Shin, J. Y. Han, M. Mishima,
J. Org. Chem. 2006, 71, 7715.
7. (a) I. H. Um, S. E. Jeon, J. A. Seok, Chem. Eur. J. 2006, 12, 1237;
b) I. H. Um, K. H. Kim, H. R. Park, M. Fujio, Y. Tsuno, J. Org.
(
Chem. 2004, 69, 3937.
. (a)I. H. Um, S. E. Lee, H. J. Kwon, J. Org.Chem. 2002, 67, 8999;
before use. Doubly glass distilled H O was further boiled
2
8
and cooled under N gas. Due to low solubility of substrates
2
(
b) I. H. Um, S. J. Hwang, S. R. Yoon, S. E. Jeon, S. K. Bae,
3
a–3i in pure water, 80 mol% H O/20 mol DMSO was used
2
J. Org. Chem. 2008, 73, 7671; (c) I. H. Um, J. A. Seok, H. T.
Kim, S. K. Bae, J. Org. Chem. 2003, 68, 7742.
as the reaction medium.
Kinetics. The kinetic study was performed using a UV–Vis
spectrophotometer equipped with a constant-temperature cir-
culating bath. The reactions were followed by monitoring the
appearance of the leaving Y-substituted-phenoxide ion. Reac-
tions were followed generally for 9–10 half-lives and kobsd
values were calculated using the equation, ln(A − A ) =
9
. I. H. Um, A. R. Bae, T. I. Um, J. Org. Chem. 2014, 79, 1206.
1
0. (a) E. A. Castro, M. Aliaga, P. R. Campodonico, J. R. Leis, L.
Garcia-Rio, J. G. Santos, J. Phys. Org. Chem. 2008, 21, 102;
(b) E. A. Castro, M. Aliaga, P. Campodonico, J. G. Santos,
J. Org. Chem. 2002, 67, 8911; (c) E. A. Castro, M. Aliaga, P.
R. Campodonico, J. R. Leis, L. Garcia-Rio, J. G. Santos, J. Phys.
Org. Chem. 2006, 19, 683.
∞
t
−kobsdt + C. Typically, the reaction was initiated by adding
1
1. W. P. Jencks, J. Regenstein, In Handbook of Biochemistry, 2nd
ed., H. A. Sober Ed., Chemical Rubber Publishing Co., Cleve-
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