Effect of the nucleophile structure on the relative mobility of the nitro group and fluorine atom in reactions of 3,5-dinitro- and 3-fluoro-5-nitrobenzotrifluorides with phenols in the presence of potassium carbonate

Article abstract of DOI:10.1023/A:1015346507161

The relative mobility of the nitro group and fluorine atom in 3,5-dinitro- and 3-fluoro-5-nitrobenzofluorides was estimated by the competing reaction technique using phenols in the presence of potassium carbonate (DMF, 65-95°C). Correlation analysis of th

Full text of DOI:10.1023/A:1015346507161

Russian Journal of Organic Chemistry, Vol. 38, No. 1, 2002, pp. 47 58. Translated from Zhurnal Organicheskoi Khimii, Vol. 38, No. 1, 2002,
pp. 56 67.
Original Russian Text Copyright
2002 by Khalfina, Vlasov.
Effect of the Nucleophile Structure on the Relative Mobility
of the Nitro Group and Fluorine Atom in Reactions
of 3,5-Dinitro- and 3-Fluoro-5-nitrobenzotrifluorides*
with Phenols in the Presence of Potassium Carbonate
I. A. Khalfina and V. M. Vlasov
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
Received October 27, 2000
Abstract The relative mobility of the nitro group and fluorine atom in 3,5-dinitro- and 3-fluoro-5-nitro-
benzofluorides was estimated by the competing reaction technique using phenols in the presence of potassium
carbonate (DMF, 65 95 C). Correlation analysis of the relative rate constants k (NO )/k (F) and of the dif-
2
ferences in the activation parameters ( H and
S ) of competing reactions showed the existence of two
reaction series for the examined phenols. The higher mobility of the nitro group was found to result from the
entropy control of the reactivity of arenes. The mechanism of these reactions is discussed.
It is known [1, 2] that ipso-substitution in S Ar
subsequent S Ar reaction, and desorption of the prod-
N
N
reactions of meta-substituted nitrobenzenes with
various charged nucleophiles becomes possible due
to high mobility of the nitro group and fluorine atom,
whose reactivities are comparable [3]. However, such
reactions are fairly rare cases [1, 2, 4 10] because
of not only insufficient substrate activation but also
the existence of equilibrium between different kinds
ucts [17, 18]. Clearly, such heterogeneous processes
are difficult to study by direct kinetic methods. On the
other hand, the competing reaction technique may be
useful for studying substrates possessing comparable
reactivities, since the apparent reaction rate should
weakly depend on the rates of particular stages other
than the replacement stage [19]. As applied to hetero-
geneous processes, the competing reaction technique
makes it possible to estimate the effect of nucleofuge
on the substrate reactivity with regard to phenol struc-
ture; also, the series of appropriate nucleophiles can
be extended. The choice of a nitro group and fluorine
atom as a couple of nucleofuges for competing reac-
tions ensures mild conditions of the substitution. We
showed in [15] that 1,3-dinitro- and 1-fluoro-3-nitro-
benzenes react with phenol and 3-nitrophenol in DMF
in the presence of K CO under fairly mild conditions
of -complexes [10, 11]. As a result, S Ar-replace-
N
ment of the nitro group or fluorine atom in meta-sub-
stituted nitrobenzenes in reactions with various
nucleophiles usually requires drastic conditions, the
yields of the target products are low, and the process
is accompanied by side reactions [5, 6, 9]. Phenoxide
ions are among such nucleophiles, and substitution
reactions with participation of phenoxide ions can
be complicated by formation of C-arylation products
[
10, 12]. As was shown in [13 16], phenols smoothly
react with meta-substituted nitrobenzene derivatives
in dipolar aprotic solvents in the presence of alkali tative yields; it was also found that the mobilities
2
3
to give the corresponding products in almost quanti-
metal carbonates, yielding products of replacement of
the nitro group by phenoxy. The proposed reaction
scheme includes preliminary chemisorption of the
reactants on the surface of deprotonating agent, the
of the nitro group and fluorine atom in competing
reactions are comparable. In the present work, using
the competing reaction technique, we have studied
the relative reactivity of the nitro group in 3,5-dinitro-
benzotrifluoride (I) and of the fluorine atom in
3-fluoro-5-nitrobenzotrifluoride (II) toward phenols
III IX whose acidity varies over a wide range. The
reactions were carried out in DMF in the presence of
_
*
___________
This study was financially supported by the Russian Founda-
tion for Basic Research in the framework of the Leading
Scientific School Program (project no. 96-15-97562).
1
070-4280/02/3801-0047$27.00 2002 MAIK Nauka/Interperiodica

4
8
KHALFINA, VLASOV
Scheme 1.
(
1 3)
I, R = NO [reaction (1)]; II, R = F [reaction (2)]; R = NO /F [competing reactions (3)]; III, IIIa, X, Ar = 4-MeC H ;
2
2
6
4
IV, XI, Ar = Ph; V, XII, R = 4-ClC H ; VI, XIII, R = 3-NO C H ; VII, XIV, R = 4-AcC H ; VIII, XV, R = 4-NCC H ;
6
4
2
6
4
6
4
6
4
IX, IXa, XVI, R = 3-NO -5-BrC H .
2
6
3
K CO in the temperature range from 65 to 95 C
bis(trifluoromethyl)diphenyl ether (XVII) as by-prod-
uct (see Experimental) via reaction of I and II with
the released ambident nitrite ion. The latter is known
to compete with phenoxide ions at elevated tempera-
ture [16, 20].
Electron-acceptor substituents in the substrate are
known to accelerate replacement of the nitro group in
meta-activated nitro compounds by the action of
phenols in DMF in the presence of potassium carbo-
nate [18, 21, 22]. Introduction of electron-donor sub-
stituents into the aromatic ring of phenols accelerates
reactions (1) and (2) (see Experimental). These facts
indicate that the rate-determining stage is formation
of -complex. The data in Table 1 show that the
2
3
(
Table 1). In addition, we have determined the relative
rate constants for replacement of the nitro group and
fluorine atom in compounds I and II in reactions
with weakly and strongly acidic phenols (compounds
III and IX) in the presence of potassium and cesium
carbonates (heterogeneous conditions) and with potas-
sium phenoxides IIIa and IXa (homogeneous condi-
tions) in DMF with the goal of estimating the effect
of adsorption on the reaction kinetics.
The selected temperature range ensured quantitative
yields of the target products and the absence of by-
products. For example, competing reaction (3) with
phenols III VI above 98 C or with phenols VII IX
above 80 C resulted in formation of 3,3 -dinitro-5,5 -
k(NO )/k(F) ratio is greater than unity and that it
2
Table 1. Relative rate constants k(NO )/k(F) and differences in the activation parameters of competing reactions of
2
compounds I and II with phenols III IX in the presence of K CO (Cs CO ) and with potassium phenoxides IIIa
2
3
2
3
and IXa in DMF
k(NO )/k(F)a
2
H ,b
kJ/mol
b
Comp.
no.
S ,
J mol 1 K 1
6
5 C
70 C
75 C
80 C
90 C
95 C
III
III
1.05 0.05
1.05 0.03
1.23 0.06
1.41 0.05
1.52 0.04
1.50 0.03
15.4 0.2
45.3 0.6
c
IIIa
IV
V
1.06 0.03
1.35 0.02
1.51 0.02
1.86 0.02
3.23 0.02
3.55 0.05
4.25 0.01
1.00 0.02
1.58 0.01
1.84 0.01
1.11 0.01
1.20 0.01
1.38 0.02
1.53 0.02
1.58 0.02
1.66 0.02
1.70 0.02
2.02 0.02
18.1 0.5
21.8 0.4
27.6 0.8
75.0 0.4
80.3 1.1
91.6 6.2
52.9 1.4
64.0 1.2
83.6 2.5
225.5 0.6
241.3 3.4
275.3 9.4
VI
2.39 0.02
2.66 0.06
d
d
VII
VIII
IX
1.04 0.04
1.05 0.05
1.05 0.01
2.24 0.02
2.34 0.01
d
d
d
d
2.54 0.01
c
e
IX
2.29 0.01
3.72 0.02
2.50 0.05
e
IXa
2.40 0.01
a
Average value from no less than two parallel runs.
The differences in the activation parameters for competing reaction (3)
b
H
=
H (NO2)
H (F) and
S
=
S (NO2)
S (F) were calculated by the Eyring equation: log[k(NO )/k(F)] = (
H /T + S )/4.576 [23].
2
c
d
e
In the presence of Cs CO .
2
3
When the reaction time was 3 h, compound XVII was formed as by-product (see Experimental).
The relative rate constant was not determined because of the low rate of formation of product XVI (see Experimental).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

EFFECT OF THE NUCLEOPHILE STRUCTURE
increases both as the temperature rises and as the
49
acidity of phenols III IX increases. The phenols
under study give rise to linear relations between
log[k(NO )/k(F)] and 1/T (r = 0.999) (Fig. 1), which
2
means that the Arrhenius equation is valid for reac-
tions (1) and (2). Taking into account that nucleophilic
substitution in compounds I and II by the action of
phenols in the presence of potassium carbonate is
a multistage process, the fulfilment of the Arrhenius
equation for competing reactions (3) indicates that
the ratio of rates of replacement of the nitro group
and fluorine atom is determined by the effective rate
constants of reactions (1) and (2).
As follows from Fig. 1, the isoselective temperature
Tiso at which the rate constants of reactions (1) and (2)
Fig. 1. Plots of log[k(NO )/k(F)] versus 1/T for reactions
are equal [k(NO ) = k(F)] is below the experimental
2
2
(
3) with phenols III IX in the presence of K CO .
2
3
temperature range (Texp > T ) for all the examined
iso
phenols: Tiso = 42 69 C for weakly acid phenols
III VI and Tiso = 63 64 C for strongly acid phenols
VII IX. In keeping with the generally accepted views
on the relations between internal (enthalpy) and
external (entropy) reactivity factors [24], the nitro
group is more reactive than fluorine atom in com-
peting reactions (3) under conditions of entropy
control. Therefore, the difference in the effective
a lower rate than in reactions with phenols of the
second series, which are more acidic. The same
tendency is observed for the log[k(NO )/k(F)]
2
(
or pK ) relations, since the Hammett and Br o/ nsted
a
equations for competing reactions (3) are valid for
each phenol series (III VI and VII IX) separately
(
Table 3). The resulting log[k(NO )/k(F)] (pKa)
2
dependences for all phenols have a V-like shape with
activation parameters ( H and
lated by the modified Eyring equation for competing
reactions. The H and S values thus obtained
Table 1) are linearly related with each other (r =
S ) can be calcu-
equal
(
Nuc) values for both branches, which
indicates some perturbation of the mechanism of
reaction (1) and/or (2) in going from phenols III VI
to VII IX [28].
(
0
.999; Table 2); this indicates that isokinetic relation-
ship should be observed for the whole series of
The positive values of
the difference in the Br o/ nsted coefficients
and negative values of
[at
phenols III IX. The isokinetic temperature
the slope of the linear dependence between
(i.e.,
H
Nuc
Nuc(NO ) > 0 and Nuc(F) > 0] throughout the
2
and
sign of
S ) is equal to 331 K (Table 2). The positive
H and S for reaction (3) (Table 1)
examined temperature range (Table 3) suggest greater
sensitivity of the replacement of fluorine atom to
suggests that the substitution of the nitro group in
I is favored by the entropy factor while the substitu-
tion of the fluorine atom in II is favored by the
enthalpy factor. Here, the effects of these factors
become stronger as the acidity of phenol increases.
Table 2. Isokinetic temperatures
ferent dependences
calculated from dif-
Dependence
, K
r
s
n
Despite the existence of a common linear relation
between
divided into two series differing by the values of
and S . Phenols III VI are characterized
by considerably smaller H and S values, as
compared to VII IX (Table 1). The same division
follows from Fig. 1: the pair cross points of the
H
and
S , phenols III IX can be
H
= f ( S )
331 1
0.999
0.999
0.999
0.250
0.266
0.333
7
4
3
4
3
4
4
4
3
17 1a
3
3
b
H
33 1
a
log[k(NO )/k(F)] =
322 2
338 1
2
b
f (1/T)
= f (1/T)
322 1a 0.998
0.005
0.062
0.001
0.009
b
dependences log[k(NO )/k(F)] = f(1/T) for phenols
338 1
322 1
0.960
0.997
2
a
III VI are located at 322 2 K, whereas the corre-
sponding points for phenols VII IX are located at
= f (1/T)
Nuc
338 1b 0.963
3
38 1 K (Table 2). In reactions with weakly acidic
a
phenols the relative mobility of the nitro group and
fluorine atom increases with rise in temperature at
Phenols III VI.
Phenols VII IX.
b
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

5
0
KHALFINA, VLASOV
Table 3. Parameters of the Hammett {lg[k(NO )/k(F)] = + a} and Br o/ nsted equations {log[k(NO )/k(F)] =
2
2
a
p
K
+
b
}
f
o
r
c
o
m
p
e
t
i
n
g
r
e
a
c
t
i
o
n
s
(
3
)
i
n
t
h
e
p
r
e
s
e
n
c
e
o
f
K
C
O
Nuc
a
2
3
Parameter
65 C
70 C
75 C
80 C
90 C
0.259 0.019
0.200
95 C
0.276 0.022
0.235
b
c
0
.134 0.006
0.130 0.03
0.047
0.202 0.013
0.44 0.14
0.130
0
.017 0.007
0.003
0.200 0.06
0.180
b
a
c
a
0.07
0.996
0.968
0.006
0.130
0.995
0.952
0.009
b
r
r
s
s
0.994
0.994
c
0.924
0.953
b
0.013
0.014
c
0.001
0.006
0.010
0.030
b
0
.0264 1
0.020 0.001
0.520
0.040 0.001
0.067 0.008
0.841
0.051 0.001
1.110
0.054 0.001
1.207
Nuc
c
0
.0021 0.005
0.048
0.031 0.003
0.78
Nuc
b
b
c
b
0.460
1.439
b
r
r
s
s
0.999
0.999
0.999
0.999
c
0.832
0.998
0.994
0.994
b
0.001
0.003
0.004
0.005
c
0.002
0.001
0.004
0.01
a
The relative rate constants k(NO )/k(F) were taken from Table 1;
= 0.17 (4-CH ), 0 (H), 0.19 (4-Cl), 0.84 (4-Ac), 1.00 (4-CN);
3
2
p
=
0.71 (3-NO ), 1.10 (3-NO -5-Br) [25]; pK of phenols III IX in DMSO: 18.9 (4-CH ), 18.0 (H), 16.75 (4-Cl), 14.4 (3-NO ),
m
2
2
a
3
2
1
4.0 (4-Ac), 13.2 (4-CN), 12.2 (3-NO -5-Br) [26]; pK values of phenols in DMF correlate with pK in DMSO by the equation
2
a
a
pK (DMF) = 1.56 + 0.96pK (DMSO) [27].
Phenols III VI.
Phenols VII IX.
a
a
b
c
the substituent in phenol, as compared to the replace-
ment of nitro group. This trend becomes stronger in
reactions of I and II with more acidic phenols VII
IX. The transition state in the stage of formation of
presence of potassium carbonate is later than in the
reactions of compound I [29]. Both phenol series
conform to the reactivity selectivity principle, accord-
ing to which the selectivity of substitution of the nitro
group increases as the reactivity of phenoxide ion
decreases [30].
-complex in the reactions of II with phenols in the
The parameters
and
for competing reac-
Nuc
tion (3) increase as the temperature rises, exhibiting
a linear relation with 1/T for each phenol series
(
Table 3, Fig. 2). The isokinetic temperatures calcu-
lated from the dependence (or Nuc) 1/T are as
= 322 K (phenols III VI) and = 338 K
follows:
1
2
(phenols VII IX) (Table 2, Fig. 2).
Thus the existence of linear
H
S relations
implies a common isokinetic relationship for all
phenols III IX; however, analysis of the dependences
log[k(NO )/k(F)] 1/T and
(or
Nuc) 1/T led
2
us to distinguish two phenol series, III VI and
VII IX, each having its own isokinetic relationship.
This discrepancy can be eliminated by analyzing the
relations between
series. Calculation of the isokinetic temperatures gave
the values = 317 K for phenols III VI and
H and
S for each phenol
Fig. 2. Plots of
phenols (1) III VI and (2) VII IX in the presence of
potassium carbonate.
versus 1/T for reaction (3) with
Nuc
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

EFFECT OF THE NUCLEOPHILE STRUCTURE
333 K for phenols VII IX (Table 2, Fig. 3). We
51
=
2
can conclude that a combination of known methods
for identification of isokinetic relationships yields
consistent results [28], since all values satisfactorily
agree with each other (Table 2).
It should be noted that the existence of isokinetic
relationship for reaction (3) implies that isokinetic
relationships for reactions (1) and (2) also exist. Here,
the isokinetic temperatures for reactions (1), (2), and
(
3) coincide. At the isokinetic temperature, the rates
of replacement of the nitro group and fluorine atom
do not depend on the nature of substituent in phenol
[
(NO ) = (F) = 0], and the relative mobilities of
2
the nitro group and fluorine atom are similar for all
the examined phenols; they are determined by the
difference in the free terms of the isokinetic relation-
ships of reactions (1) and (2). Insofar as the isokinetic
temperature approaches the range of isoselective tem-
peratures, the rates of replacement of the nitro group
and fluorine atom at that temperature are similar
Fig. 3. Plots of
phenols (1) III VI and (2) VII IX in the presence of
potassium carbonate.
H
versus
S for reaction (3) with
(
with phenols III and IX in the presence of K CO ).
2
3
The way of generation of nucleophilic species
insignificantly affects the relative mobility of the nitro
group and fluorine atom in reactions with weakly
acidic phenols, whereas the same effect in reactions
with more acidic phenols is much stronger (Table 1).
(
Fig. 1). The isokinetic relationships for reactions (1)
and (2) are characterized by similar proportionality
coefficients and free terms, which means that reac-
tions (1) and (2) follow a common mechanism; this
is supported by fairly small
values calculated for
It was presumed in [17, 18] that a necessary condi-
tion for aromatic nucleophilic substitution by phenols
in dipolar aprotic solvents in the presence of potas-
sium carbonate is chemisorption of the reactants on
reaction (3) with phenols of both series (Table 3) [31].
The mechanism of reaction (1) and/or (2) changes
in going from one phenol series to the other. The
character of the
H ( S T) pK dependence
a
the K CO surface. However, addition of 3,5-dinitro-
suggests that this change is jumpwise (Fig. 4). The
magnitude of distortion of isokinetic relationships
in going from one phenol series to the other suggests
perturbation of the corresponding reaction mechanism
rather than its radical change. Therefore, transition
states in the reactions of I and II with phenols III IX
in the presence of K CO in DMF are likely to be
2
3
benzotrifluoride (I) to a solution, prepared by heating
at 70 C potassium carbonate and 3-bromo-5-nitro-
phenol (IX) in DMF under stirring with subsequent
removal of the undissolved material, gave 18% of
2
3
similar.
In the reaction of I and II with potassium 5-bromo-
-nitrophenoxide (IXa) at 95 C ether XVI was
3
formed in 87% yield, whereas an analogous hetero-
geneous reaction with 5-bromo-3-nitrophenol (IX) in
the presence of potassium carbonate gave product
XVI in quantitative yield even at 65 C. In the pres-
ence of Cs CO as deprotonating agent in reaction (3)
2
3
with 5-bromo-3-nitrophenol (IX) ether XVI was
obtained in quantitative yield only at 80 C. Thus,
there is a relation between the rates of reactions (1)
and (2) and nucleophile nature. The relative rate
constants of reaction (3) with 4-cresol (III) and
5
2
-bromo-3-nitrophenol (IX) in the presence of Cs CO3
Fig. 4. Plots of
S T (light circles and squares) versus pK for reaction
(3) with phenols III VI and VII IX in the presence of
H
(dark circles and squares) and
occupy an intermediate place between those deter-
mined under homogeneous (using potassium phen-
oxides IIIa and IXa) and heterogeneous conditions
a
K CO at 70 C.
2
3
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

5
2
KHALFINA, VLASOV
Table 4. Reaction conditions and yields, melting points, and analytical data of compounds X XVI and XIX
Initial compoundsa
Tempera-
ture,
Yield,b mp,
C
Calculated
Product
Found M+
Formula
C
%
(solvent)
M
substrate phenol
I
I
II
II
I
III
IV
98
4 -Methyl-3-nitro-
5-trifluoromethyl-
diphenyl ether (X)
100
92
100
91
100
88
100
87
100
85
88
84
98
65
85
63
99
52
99
51
98
51 52
(MeOH)
297.06161 C H F NO
3
297.06127
1
4
10 3
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
98
70
70
98
70
70
3-Nitro-5-trifluoro-
methyldiphenyl
ether (XI)
21 21.5c
I
II
II
I
V
4 -Chloro-3-nitro-
5-trifluoromethyl-
diphenyl ether (XII)
47 48
(MeOH)
317.00697 C H ClF NO
3
317.00665
328.03070
325.06127
310.0165
1
3
7
3
I
II
II
I
VI
3,3 -Dinitro-5-tri-
fluoromethyldi-
70 70.5 328.03089 C H F N O
13 7 3 2
(EtOH)
5
4
3
I
II
II
I
phenyl ether (XIII)
d
d
d
d
d
VII
VIII
IX
4 -Acetoxy-3-nitro-5-
trifluoromethyldi-
phenyl ether (XIV)
78 79
(EtOH)
325.06161 C H F NO
15 10 3
I
II
II
I
3-Nitro-5-trifluoro-
methyl-4 -cyanodi-
phenyl ether (XV)
63 64
(EtOH)
310.0167 C H F N O
14 7 3 2
I
38
96
38
98
23
18
95
21
II
II
I
I
I
II
II
II
3 -Bromo-3,5 -dinitro-
5-trifluoromethyldi-
phenyl ether (XVI)
70 71
(EtOH)
405.94231 C H BrF N O
3 2 5
405.94126
1
3
6
d
XVIII
3-Nitro-5-trifluoro-
methyl-4 -fluorodi-
phenyl ether (XIX)
100
50 51
(MeOH)
300.54997 C H F NO
3
300.55013
1
3
7 4
a
b
c
Molar ratio I(II):ArOH:K CO3 1:1:1.2.
2
Method a; preparative yield; reaction time 3 h.
Published data [16]: mp 21 21.5 C.
Reaction time 5 h.
d
diaryl ether XVI in 3 h at 70 C. By reaction of I with
-bromo-5-nitrophenol (IX) in the presence of K CO3
(IXa). This means that reaction (1) with 3-bromo-5-
nitrophenol (IX) in the presence of potassium carbo-
nate cannot be described only as the one occurring on
the K CO surface and that it also differs from the re-
3
2
ether XVI was obtained in 23% yield (70 C, 3 h;
Table 4). Therefore, the rate of replacement of the
nitro group in homogeneous reaction of compound I
with 3-bromo-5-nitrophenol (IX) is close to the rate
of the corresponding heterogeneous reactions but is
considerably higher than the reaction rate of com-
2
3
action of I with 3-bromo-5-nitrophenoxide ion (IXa).
4-Cyanophenol is known to smoothly react with
nitrobenzene derivatives in DMSO in the presence of
KF to afford products of replacement of the nitro
pound I with potassium 3-bromo-5-nitrophenoxide group by 4-cyanophenoxy group. Here, the nucleo-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

EFFECT OF THE NUCLEOPHILE STRUCTURE
53
Table 5. 19F NMR spectra of the reaction mixture obtained from 3-fluoro-5-nitrobenzotrifluoride (II), 4-fluorophenol
(
XVIII), and K CO in DMF
2
3
Signal intensity ratioa ( , ppm)
F
Temperature,
C
Sample no.
CF3
3-F
4-F
4 -F
1b
2
3
4
5
25
25
70
70
70
3.0 (101.46)
3.0 (101.46)
3.0 (101.46)
3.0 (101.36)
3.0 (101.33)
1.0 (56.92)
1.0 (56.92)
0.9 (56.92)
0.7 (56.92)
0.5 (56.92)
1.0 (36.28)
1.0 (34.97)
0.9 (34.27)
0.7 (34.05)
0.5 (33.96)
0 (45.91)
0 (45.91)
0.1 (45.91)
0.3 (45.91)
0.5 (45.91)
c
a
3
-F denotes the fluorine atom in position 3 of compound II; 4-F stands for the 4-fluorine atom in 4-fluorophenol (XVIII); 4 -F is
the fluorine atom in position 4 of ether XIX; and CF corresponds to the overall signal of the CF group in compounds II and XIX.
Sample no. 1 was withdrawn immediately after mixing the reactants, and the other samples were withdrawn each 20 min.
After withdrawal of sample no. 3, the mixture was heated to 70 C.
3
3
b
c
philic species is a complex of 4-cyanophenol with KF,
which was characterized by IR spectroscopy [32].
Comparison of the IR spectrum of a sample, prepared
rather than on the K CO surface. The upfield shift
2 3
of the signal from 4-fluorophenol at room temperature
suggests higher rate of complex formation, as com-
by keeping potassium carbonate with 4-cyanophenol pared to the rate of substitution (Table 5).
(
VIII) in DMF at 70 C and subsequent filtration,
Taking into account that potassium carbonate is
very poorly soluble in DMF [21], the relatively high
rate of formation of the corresponding complex may
be explained by processes occurring on the K CO
with the IR spectra of solutions of 4-cyanophenol and
potassium 4-cyanophenoxide in DMF suggests that
such a complex is actually formed. Stretching vibra-
tions of the cyano group in 4-cyanophenol and
4
2
3
surface. Probably, initially chemisorbed phenol mole-
cule irreversibly leaves the K CO surface together
1
-cyanophenoxide ion appear at 2222 and 2185 cm ,
2
3
respectively. In the spectrum of the assumed complex
two bands at 2206 and 2189 cm were present, while
with potassium carbonate molecule, i.e., as a complex
with the deprotonating agent [33]. This assumption
can explain a satisfactory correlation between the rate
1
absorption typical of OH stretching vibrations in
1
4
-cyanophenol (3077 cm ) was absent. The greater of replacement of the nitro group in 4-nitrophthalo-
shift of the (CN) band in going from 4-cyanophenol
to its complex with K CO , as compared to the com-
nitrile by phenols in the presence of alkali metal
carbonates M CO and the energy of their crystal
2
3
2
3
plex with KF, indicates greater charge delocalization
lattice [21]. Obviously, coordination of phenol at the
K CO surface should affect mutual orientation of
in the former complex [32].
2
3
The 19F NMR spectrum of a solution, prepared by
the phenol and potassium carbonate molecules in the
corresponding complex. Irreversible desorption is
typical of strong chemisorption bonds; therefore, the
complex thus formed should be fairly stable. Dorogov
et al. [18] presumed formation of a cyclic adsorption
complex via phenol coordination at an active part
of the M CO surface. An analogous cyclic structure
keeping potassium carbonate and 4-fluorophenol
(
XVIII) in DMF at 70 C with subsequent filtration
from undissolved material, contains a singlet at
3.36 ppm (t.t). This value is intermediate between
3
F
1
9
the F chemical shifts of 4-fluorophenol and potas-
sium 4-fluorophenoxide in DMF, 36.28 (t.t) and
1.64 ppm (br.s), respectively. Using F NMR spec-
2
3
F
1
9
may be assigned to the complex [ArOH K CO ],
3
2 3
as well as to [4-CNC H OH KF] [32].
troscopy, it was also shown that during the reaction
of 3-fluoro-5-nitrobenzotrifluoride (II) with 4-fluoro-
phenol in the presence of potassium carbonate signals
corresponding to compound II and 4-fluorophenol dis-
6
4
Assuming a common mechanism of reactions (1)
and (2), the reactions of compounds I and II with
phenols III IX and XVIII in the presence of K CO
2
3
appear at equal rates coinciding with the rate of ap- in DMF can be considered to occur as replacement of
pearance of the signal at 45.34 ppm which belongs
to 4 -F in diaryl ether XIX; here, the intensity of the
the nitro group and fluorine atom by the action of the
corresponding phenol potassium carbonate complex
[ArOH K CO ] in solution. Then, chelate structures
F
CF signal remains unchanged (Table 5). These data
3
2
3
indicate that the reaction proceed mainly in solution
A and B may be proposed for transition states (TS)
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

5
4
KHALFINA, VLASOV
at the stage of formation of -complex in reactions
similar but high entropies of activation [39]. Analysis
of the
H and S values for reaction (3) with
(2) and (1), respectively:
strongly acidic phenols VII IX from the viewpoint
of the possibility for synchronous mechanism shows
that the stage of formation of -complex in reaction
(
2) requires much lower enthalpy of activation and
a strictly definite mutual orientation of the reactants,
as compared to the corresponding stage of reaction (1).
In going to reactions (3) with weakly acidic phenols
III VI, the
H
and
S
values suggest closer
activation parameters for the formation of -complex
in reactions (1) and (2) as the acidity of phenol
decreases. Obviously, a synchronous mechanism is
hardly probable for the reactions of I and II with
the [ArOH K CO ] complexes.
2
3
It should be specially emphasized that in stepwise
bimolecular reactions the efficiency of coordination
catalysis is determined mainly by the possibility for
formation of an intermediate complex with rigorous
mutual reactant orientation. This factor favors the
reactions via increased activation entropy [40].
The apparent rate constants of reactions (1) and (2)
with stepwise formation of transition states A and B
include not only the rate constant of nucleophilic
attack but also the corresponding complex formation
On the basis of the relation between the stability
of coordination compounds and their structure, transi-
tion states A and B are expected to be stabilized to
a sufficient extent, structure B being stabilized better
than A. Formation of a chelate ring is known to
increase the stability of coordination compounds, and
increase in the number of chelate rings enhances this
tendency [34]. Therefore, the transition states can
be stabilized additionally via formation of chelate-like
cyclic structures A and B. It should be noted that
coordination compounds with small chelate rings are
more stable than analogous carbocycles, since the
atoms and bonds in the former are not similar [35].
Five-membered chelate rings are more stable than
four-membered; therefore, structure B should be more
stable than A [34]. Presumably, the reactions of I
and II with the complexes [ArOH K CO ] follow
constant. Therefore, the parameters
H ,
S ,
,
and are composite quantities describing the
Nuc
overall process (complex formation stage and nucleo-
philic attack). In this case, the fulfilment of the
Br o/ nsted and Hammett dependences for reactions (1)
and (2) implies that they are also valid for each stage
taken separately.
Structures A and B suggest that in the course of
nucleophilic attack the dative bond between the
phenolic oxygen atom and potassium cation becomes
+
2
3
weaker while the bond between K and fluorine atom
a coordination catalysis mechanism, according to
which nucleophilic attack on the complex is possible
due to additional assistance by complex formation
preceding or occurring simultaneously with the rate-
determining stage (formation of -complex [36]).
Stepwise mechanism includes intramolecular nucleo-
philic attack which is more favorable than inter-
molecular [37]. In the case of a concerted mechanism,
the corresponding transition state is stabilized by
considerable electron density delocalization via elec-
tron transfer [38]. In both cases, complex formation
not only creates favorable steric conditions for forma-
tion of transition states but also enhances the reac-
tivity of the components [38].
(
in compound II) or oxygen atom of the nitro group
in I strengthens. It is known that complex formation
exerts some effect on bonds neighboring to the dative
ones [40]; therefore, the positive charge on the elec-
trophilic center in II may increase due to cyclic
charge transfer. This should reduce the enthalpy of
formation of -complex, i.e., the H (F) value.
Simultaneously, the entropy of TS decreases, and
S (F) increases. A combination of these factors is
equivalent to introduction of an additional electron-
acceptor substituent into the corresponding phenol and
shift of TS along the reaction coordinate toward later
states. Clearly, a necessary condition is sufficiently
late TS and fairly high nucleophilicity of the reagent.
Thus, in terms of the proposed scheme we should
expect (a) similar transition states in reactions (1)
and (2) for each phenol and (b) jumpwise perturbation
Reactions following a coordination catalysis
mechanism with synchronous formation of TS are
characterized by very low energies of activation and
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

EFFECT OF THE NUCLEOPHILE STRUCTURE
55
of the mechanism of reaction (2) (due to cyclic charge
transfer) in going to more acidic phenols. These
expectations are well consistent with the results
of analysis of correlations obtained for competing
reactions (3).
Table 6. Product ratios in the reactions of compounds I
and II with KNO2 and KF in the presence and in the
a
absence of K CO (DMF, 95 C, 3 h)
2
3
Composition of the
b
Comp.
no.
reaction mixture, mmol
The following conclusions can be drawn: (1) Sub-
stitution of the nitro group in compound I and of the
fluorine atom in II by the action of [ArOH K CO ]
KNO2 KF K CO3
2
I
II
XVII
2
3
in the examined temperature range includes initial
complex formation stage and subsequent intramole-
cular nucleophilic attack; (2) In reaction (2) additional
stabilization via cyclic charge transfer is possible;
I
I
I
I
II
II
+
+
+
+
0.450
0.485 0.010
0.500
0.495 0.005
0.010 0.480
0.040 0.460
0.050
0.005
+
+
(
3) The higher reactivity of the nitro group in I, as
compared to the fluorine atom in II, is explained
in terms of the entropy control whose contribution
increases as the nucleophilicity of the reagent rises
+
+
+
0.010
(Fig. 4); (4) The effect of the substituent in phenol on
a
Initial reactant ratio, mol: I (or II) : KNO (or KF):K CO ,
2
2
3
the relative reactivity of the nitro group and fluorine
atom is determined by the overall sensitivity of the
nucleophilic attack and complex formation stages to
that factor. Taking into account that complexing
power of eight-electron cations increases as their
radius decreases [41], the proposed mechanism is less
probable in the presence of cesium carbonate.
5
:1:1.2.
b
GLC data.
The IR spectra of 2% solutions in DMF and CCl4
were obtained on a Specord M-80 instrument. GLC
analysis of the reaction mixtures was performed on
an LKhM-72 chromatograph (heat conductivity de-
tector; 4000 4-mm column packed with 15% of
SKTFT-803 on Chromaton-W; carrier gas helium;
linear oven temperature programming from 70 to
270 C at a rate of 10 deg/min). The components were
quantitated by the absolute calibration technique using
preliminarily plotted calibration curves and were
identified by addition of authentic samples. The mass
spectra (70 eV) were run on a Finnigan MAT-8200
spectrometer (ion source temperature 100 220 C).
Silufol UV-254 plates were used for thin-layer chrom-
atography (eluent CCl4).
We also tried to reveal the effect of K CO on the
2
3
reactivity of nitrite and fluoride ions released in com-
peting reactions (3). For this purpose we examined
reactions of compounds I and II with KNO and KF
2
in the presence and in the absence of potassium car-
2
bonate (Table 6). The results showed that K CO3
clearly affects only the rate of reactions of I and II
with ambident nitrite ion as O-nucleophile. The
observed effect may be explained by preliminary
coordination of nitrite ion to potassium carbonate in
a way similar to coordination of phenol in the com-
plex [ArOH K CO ] and formation of a cyclic transi-
2
3
Commercial dimethylformamide was dried over
tion state.
4
-
molecular sieves and distilled under reduced
Thus meta,meta-activated arenes containing highly
nucleofugic substituents such as nitro group and
fluorine atom react with phenols in the presence of
potassium carbonate in a stepwise mode involving
formation of a cyclic transition state with participation
of K CO at the stage of nucleophilic attack. Ob-
pressure over CaH . Commercial phenols III IX and
XVIII were purified by standard procedures. Com-
mercial KNO , KF, and K CO were dehydrated by
calcination and were then ground. 3,5-Dinitrobenzotri-
fluoride (I) and 3-fluoro-5-nitrobenzotrifluoride (II)
were synthesized as described in [16], mp 47 48 C (I)
and bp 67 68 C (4 mm; II); their constants coincided
with published date. 3-Bromo-5-nitrophenol (IX) was
prepared by demethylation of 3-bromo-5-nitroanisole
by the action of HBr [42], mp 145 C [43]; 3-bromo-
2
2
2
3
2
3
viously, an analogous mechanism could be expected
not only for neutral nucleophiles (such as phenols,
alcohols, thiols, and amines) but also for charged
species (such as nitrite and azide ions).
5-nitroanisole was in turn synthesized by replacement
EXPERIMENTAL
of one nitro group in 1-bromo-3,5-dinitrobenzene by
methoxy [2]. Potassium phenoxides IIIa, VIIIa,
IXa, and XVIIIa were synthesized by the procedure
reported in [44].
The H and 19F NMR spectra of 10% solutions
1
in CCl were recorded on a Bruker WP 200SY spec-
trometer using HMDS and C F as internal references.
4
6
6
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

5
6
KHALFINA, VLASOV
Table 7. 1H and 19F NMR and IR spectra of compounds X, XII XVI, and XIXa
Comp.
no.
19F NMR spec-
trum, F, ppm
1H NMR spectrum, , ppm (J, Hz)
2.40 s (3H, CH ), 6.88 6.98 d.m (2H, 2 -H, 6 -H, 8.0), 7.17
IR spectrum,b , cm 1
X
98.41 s (CF3) 1545 s, 1350 s (NO ); 1230 s,
3
2
7
.27 d.m (2H, 3 -H, 5 -H, 8.0), 7.48 m (1H, 6-H), 7.84 m
1086 m (C O C); 655 m
(
1H, 2-H), 8.08 m (1H, 4-H)
(C F)
XII 6.97 7.10 d.m (2H, 2 -H, 6 -H, 9.0), 7.30 7.43 d.m (2H, 98.41 s (CF3) 1545 s, 1350 s (NO ); 1232 s,
2
3
(
-H, 5 -H, 9.0), 7.43 7.48 m (1H, 6-H), 7.85 7.90 m
1H, 2-H), 8.16 m (1H, 4-H)
XIII 7.32 7.42 d.m (1H, 6 -H, 7.0), 7.58 m (1H, 6-H), 7.56
.70 m (1H, 5 -H), 7.88 7.94 m (1H, 2 -H), 7.94 7.99 m
1H, 2-H), 8.06 8.16 d.m (1H, 4 -H, 9.2), 8.26 m (1H,
-H)
XIV 1.23 s (3H, COCH ), 7.06 7.14 d.m (2H, 2 -H, 6 -H, 9.0), 98.41 s (CF3) 1706 s (C O); 1504 s, 1345 s
1087 m (C O C); 687 m
(C F); 681 m (C Cl)
98.43 s (CF3) 1537 s, 1344 s (NO ); 1231 s,
2
7
(
4
1087 m (C O C); 697 m
(C F)
3
7
.55 m (1H, 6-H), 7.95 8.09 m (3H, 2-H, 3 -H, 5 -H),
(NO ); 1233 s, 1085 m
2
8
.22 m (1H, 4-H)
(C O C), 695 m (C F)
XV
7.10 7.15 d.m (2H, 2 -H, 6 -H, 8.5), 7.58 m (1H, 6-H), 7.72
.75 d.m (2H, 3 -H, 5 -H, 8.5), 7.99 m (1H, 2-H), 8.27 m
1H, 4-H)
98.38 s (CF3) 2213 s (CN); 1500 s, 1348 s
7
(
(NO ); 1238 s, 1087 m
2
(C O C); 685 m (C F)
XVI 7.50 7.51 m (1H, 5 -H), 7.59 m (1H, 6-H), 7.80 7.81 m 98.41 s (CF3) 1540 s, 1342 s (NO ); 1231 s,
2
(
1H, 4 -H) , 8.00 m (1H, 2-H), 8.25 8.26 m (1H, 2 -H),
1085 m (C O C); 692 m
8
.32 m (1H, 4-H)
(C F); 683 m (C Br)
XIX 6.95 7.18 m (4H, 2 -H, 3 -H, 5 -H, 6 -H), 7.49 m (1H, 6-H), 98.40 s (CF3), 1546 s, 1353 s (NO ); 1232 s,
2
7
.87 m (1H, 2-H), 8.15 m (1H, 4-H)
45.34 m (4 -F)
1089 m (C O C); 685 m
(C F)
a
The spectral parameters of compounds XI and XVII were reported in [16].
In CCl4.
b
Reaction of compounds I and II with phenols
Determination of the relative reactivity of com-
pounds I and II toward phenols III IX in the
presence of K CO and Cs CO . Phenol III IX and
III IX in the presence of potassium carbonate in
DMF (Method a) (Table 4). To a 10% solution of
compound I or II in DMF we added phenol III IX
or XVIII, and freshly calcined K CO , and the
2
3
2
3
freshly calcined K CO or Cs CO were added to
2
3
2
3
a 10% solution of compounds I and II in DMF, and
the mixture was stirred on heating. It was then cooled,
and the precipitate was filtered off and washed with
methylene chloride on a filter. The solvent was
distilled off from the filtrate, and the residue was
analyzed by GLC. The conditions and results of
typical experiments are available from the authors.
2
3
mixture was stirred on heating. The progress of the
reaction was monitored by TLC. The mixture was
cooled, the precipitate was filtered off and washed
with methylene chloride on a filter, and the filtrate
was evaporated. The products (Table 7) were isolated
by chromatography on a 35 150-mm column charged
with Al O of activity grade II (40/250 m) using
2
3
Determination of the relative reactivity of
compounds I and II toward potassium 4-methyl-
phenoxide (IIIa) and potassium 3-bromo-5-nitro-
phenoxide (IXa) in DMF. Potassium phenoxide IIIa
or IXa was added to a 10% solution of compounds
I and II in DMF, and the mixture was stirred on
heating. It was then cooled, the precipitate was filtered
off and washed with methylene chloride on a filter,
the filtrate was evaporated, and the residue was
analyzed by GLC. The conditions and results are
available from the authors.
CCl as eluent and were additionally purified by
4
recrystallization.
Reaction of compound I with 3-bromo-5-nitro-
phenol IX in the presence of K CO in DMF
2
3
(Method b) (Table 4). Potassium carbonate was added
to a 10% solution of 3-bromo-5-nitrophenol in DMF,
the mixture was stirred for 3 h at 70 C and cooled,
and the precipitate was filtered off. Compound I was
added to the filtrate, and the mixture was stirred for
3
h at 70 C, cooled, and analyzed by GLC.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 38 No. 1 2002

EFFECT OF THE NUCLEOPHILE STRUCTURE
57
Reactions of 4-cyanophenol (VIII) and 4-fluoro-
7. Gitis, S.S. and L’vovich, I.G., Zh. Obshch. Khim.,
phenol (XVIII) with K CO in DMF. Potassium
1964, vol. 34, no. 7, pp. 2250 2254.
2
3
carbonate, 0.083 g (0.6 mmol), was added to a 2% so-
lution of 0.06 g (0.5 mmol) of phenol VIII or XVIII
in DMF, and the mixture was stirred for 3 h at 70 C.
The resulting suspension was cooled, and the precip-
itate was filtered off. The filtrate was examined by
8
.
Kornblum, N., Cheng, L., Kerber, R.C., Kest-
ner, M.M., Newton, B.N., Pinnick, N.W.,
Smith, R.G., and Wade, P.A., J. Org. Chem., 1976,
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9
.
Plakhtinskii, V.V., Dorogov, M.V., Khokhlov, A.L.,
and Krasovskaya, G.G., Izv. Akad. Nauk SSSR, Ser.
Khim., 1996, vol. 39, no. 3, pp. 3 7.
1
9
F NMR spectroscopy (for 4-fluorophenol) or IR
spectroscopy (for 4-cyanophenol); the spectral param-
eters were then compared with those of the corre-
sponding phenols and their potassium salts.
1
1
0. Buncell, E. and Manderville, R.A., J. Phys. Org.
Chem., 1993, vol. 6, no. 1, pp. 71 82.
1
9
F NMR study of the reaction of compound II
with 4-fluorophenol (XVIII) in DMF in the pres-
ence of K CO . Phenol XVIII, 0.123 g (1.1 mmol),
1. Terrier, F., Nucleophilic Aromatic Displacement:
The Influence of the Nitro Group, Weinheim: VCH,
1991, part. 1, pp. 85 94.
2
3
and freshly calcined potassium carbonate, 0.183 g
1
1
2. Stahly, G.P., J. Org. Chem., 1985, vol. 50, no. 17,
(
(
1.3 mmol), were added to a 10% solution of 0.152 g
1.1 mmol) of compound II in DMF, and the mixture
pp. 3091 3094.
3. Shevelev, S.A., Dutov, M.D., Vatsadze, I.A., Serush-
kina, O.V., Rusanov, A.L., and Andrievskii, A.M.,
Mendeleev Commun., 1995, no. 4, pp. 157 158;
Shevelev, S.A., Dutov, M.D., and Serushkina, O.V.,
Izv. Akad. Nauk, Ser. Khim., 1995, no. 12, pp. 2528
was stirred. Samples were withdrawn at specified time
1
9
intervals and were analyzed by F NMR spectroscopy
(see Table 5).
Reactions of compounds I and II with KNO2
and KF in DMF in the presence and in the absence
of potassium carbonate. Freshly calcined potassium
nitrite or potassium fluoride and, if necessary, potas-
sium carbonate were added to a 10% solution of com-
pound I or II (0.5 mmol) in DMF, and the mixture
was stirred at 95 C. It was then cooled, the precipitate
was filtered off and washed with methylene chloride
on a filter, the filtrate was evaporated, and the residue
was analyzed by GLC. The conditions and results of
these experiments are summarized in Table 6.
2
529.
1
4. JPN Patent no. 07-118212, 1995; Chem. Abstr.,
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1
995, vol. 123, no. 82943; EU Patent no. 193358,
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