Solvent effects on kinetics of an heteroatomic nucleophilic substitution reaction in ionic liquid and molecular solvents mixtures

Article abstract of DOI:10.1134/S0036024413120297

Rate constants, k _A, for the aromatic nucleophilic substitution reaction of 2-chloro-3,5-dinitropyridine with aniline were determined in different compositions of 2-propanol mixed with hexane, benzene, and 2-methylpropan-2-ol and 1-ethyl-3-meth

Full text of DOI:10.1134/S0036024413120297

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2013, Vol. 87, No. 12, pp. 1969–1975. © Pleiades Publishing, Ltd., 2013.
CHEMICAL KINETICS
AND CATALYSIS
Solvent Effects on Kinetics of an Heteroatomic Nucleophilic
Substitution Reaction in Ionic Liquid
and Molecular Solvents Mixtures1
Hadi Salaria, Mohsen Pedervanda, Faramarz SadeghzadehꢀDarabia, Mohammad Reza Gholamib
aYoung Researchers Club, Parsabad Mogan Branch, Islamic Azad University, Parsabad, Iran
bDepartment of Chemistry, Sharif University of Technology, Azadi Ave., Tehran, Iran
eꢀmail: gholami@sharif.ir
Received October 17, 2012
Abstract—Rate constants, kA, for the aromatic nucleophilic substitution reaction of 2ꢀchloroꢀ3,5ꢀdinitropyꢀ
ridine with aniline were determined in different compositions of 2ꢀpropanol mixed with hexane, benzene,
and 2ꢀmethylpropanꢀ2ꢀol and 1ꢀethylꢀ3ꢀmethylimidazolium ethylsulfate ([Emim][EtSO4]) with dimethyl
sulfoxide at 25°C. The obtained rate constants of the reaction in pure solvents are in the following order: 2ꢀ
methylpropanꢀ2ꢀol > dimethyl sulfoxide > 2ꢀpropanol > hexane > benzene > [Emim][EtSO4]. Molecularꢀ
microscopic solvent parameters corresponding to the selected binary mixtures were utilized to study the
kinetics of a nucleophilic substitution reaction in order to investigate and compare the effects of the solvents
on a chemical process. The influence of solvent parameters including normalized polarity (ETN ), dipolarꢀ
ity/polarizability (
π*), hydrogen bond donor acidity (
α
), and hydrogen bond acceptor basicity ( ) on the secꢀ
β
ondꢀorder rate constants were investigated and multiple linear regressions gave much better results with
regard to single parameter regressions. The dipolarity/polarizability of media has a positive effect in all mixꢀ
tures regarding zwitterionic character of the reaction intermediate and the hydrogen bond acceptor basicity
of the solvent by stabilizing of activated complex increases the reaction rate.
Keywords: nucleophilic substitution, solvent effects, rate constants dipolarity/polarizability of media.
DOI: 10.1134/S0036024413120297
1
INTRODUCTION
features have been recognized as a novel class of solꢀ
vents in recent years [3–6]. To increase the efficiency
of a process (e.g., separation, extraction, synthesis,
etc.), one would like to “tune” the solvent or solvent
mixture by adding cosolvents. It is beneficial in many
ways to understand how added cosolvents (or impuriꢀ
ties) affect the physicochemical properties of ionic liqꢀ
uids (ILs) or molecular solvents [4, 6]. When an ionic
liquid (IL) is mixed with other solvents, physical and
chemical properties will be tunable. Hence ILs can be
used as cosolvents in binary or ternary solvents mixꢀ
tures to increase the efficiency of the processes and
change physicochemical properties of the solvents.
To interpret the behavior of solvents in chemical
processes, understanding the solution interactions
with solute is necessary. Solvatochromism that is a way
to study solute–solvent interactions demonstrates
specific and nonꢀspecific solute–solvent interactions
[5]. Solvatochromic parameters and their measureꢀ
ments procedure have been reported elsewhere [6–9].
The effects of the polarity and solvophobicity on
cycloaddition reactions and the effects of polarity and
hydrogen bond donor acidity on aromatic nucleoꢀ
philic substitution (ANS) reactions have previously
Interaction with other species in solution can perꢀ
mute the energetic level of molecules. Chemical and
physical processes can be affected by solvents. Solvent
effects are related to the kind and extent of soluteꢀsolꢀ
vent interactions commonly developed in vicinity of
solutes [1, 2]. Reaction rate, selectivity, equilibria,
change in position and intensity of spectral absorption
band are some kind of obvious phenomena which are
influenced by solvents. In mixed solvents, solute–solꢀ
vent interactions are more complex than in neat solꢀ
vents because the solute can be solvated preferentially
by any species in the system. Indeed, solute–solvent
interactions can be affected drastically by solvent–solꢀ
vent interactions [3, 4].
An ideal solvent should have a very low volatility
and should be chemically and physically stable, recyꢀ
clable, reusable, and eventually, easy to handle. Moreꢀ
over, solvents that allow more selective and rapid
chemical transformations will have a significant
impact. Ionic liquids with interesting behavior and
1
The article is published in the original.
1969

1970
HADI SALARI et al.
been reported [10–13]. Therefore, it was interesting to supplied by Merck (Darmstadt, Germany) (>99%).
study the influence of the media in other ANS reacꢀ The ionic liquid was 1ꢀethylꢀ3ꢀmethylimidazolium
tions. The kinetics of nucleophilic heteroatomic subꢀ ethylsulfate synthesized according to the literature and
stitution reaction of 2ꢀchloroꢀ3,5ꢀdinitropyridine stored under anhydrous conditions [16]. Selection of
with aniline was studied in this work in 2ꢀproꢀ the room temperature ionic liquid (RTIL) was mainly
panol/hexane, 2ꢀpropanol/benzene, 2ꢀpropanol/2ꢀ based on the fact that it can be obtained using a simple
methylpropanꢀ2ꢀol and 1ꢀethylꢀ3ꢀmethylimidazolium method at a relatively low price.
ethylsulfate/dimethyl sulfoxide (DMSO) mixtures.
Kinetic measurements. A GBC UVꢀvis cintra 40
spectrophotometer coupled with a thermocell was
Electronꢀwithdrawing groups like nitro and cyano
groups assist the ANS reaction drastically. Heteroatꢀ
used to study the reaction spectrophotometrically, by
oms in heteroatomic compounds have activity as
running the reactions in the thermostatted cells of
strong as the nitro group [13–15]. With the presence of
spectrophotometer at 25°C. The absorbance variation
an electronegative nitrogen atom in the aromatic ring,
with time was recorded at = 350–360 nm in different
λ
pyridine derivatives undergo nucleophilic substitution
much easier than the corresponding benzenes [13].
This raised ability of pyridines towards the nucleoꢀ
philic attack further reflects the electronꢀattracting
character of the ring nitrogen.
solvent compositions for the product of reaction [7,
14]. The kinetics of reactions was studied under
pseudoꢀfirstꢀorder conditions. In all the cases the
infinity absorbance, A∞, was determined experimenꢀ
tally for each kinetic run, and used to calculate the
reaction rate constant from equation:
EXPERIMENTAL
.
ln A − A = −k t + ln A − A
0
(1)
(
)
(
)
∞
t
obs
∞
Materials. 2ꢀChloroꢀ3,5ꢀdinitropyridine (mp
≈
64°C) was obtained from Merck and purified by
recrystallization from methanol–light petroleum as
yellow needless. Aniline was purchased from Merck
and purified by vacuum distillation. Spectroscopic
RESULTS AND DISCUSSION
In this work, we have assumed that the reaction
grade highꢀpurity hexane, benzene, and 2ꢀmethylproꢀ proceeds by the twoꢀstep mechanism shown in
panꢀ2ꢀol, 2ꢀpropanol and dimethyl sulfoxide were Scheme 1:
k2
NH2
O2N
NO2
O2N
NO2
O2N
NO2
Cl
k1
k1
+ HCl
+
NH2Ph
–
N
N
NHPh
N
Cl
ZH
k
3[B]
Scheme 1.
The solvent effect on the reaction mechanism can kinetic form of the catalytic reaction depends on the
evaluate the validity of such a mechanism. Equation (1) relative magnitudes of
–1 and (k2 3[B]) [7].
can be achieved by applying the steady state approxiꢀ
mation for the concentration of ZH, [ZH]/ [t] = 0
k
+ k
The mechanism of both the catalyzed and the
uncatalyzed reaction has been discussed in the presꢀ
ence of the primary and secondary amines [7, 14–19].
The compound of 2ꢀchloroꢀ3,5ꢀdinitropyridine has
also a similar intermediate to 1ꢀhaloꢀ2,4ꢀdinitrobenꢀ
zene. Moreover, the reaction rate of this compound is
much faster than 1ꢀhaloꢀ2,4ꢀdinitrobenzene, because
of (a) electronꢀwithdrawing of aza group in addition to
nitro groups and (b) the possibility of intramolecular
hydrogen bonding between ammonium hydrogen and
d
d
[7, 14]. By applying steady state approximation we
obtain equation
,
(2)
kA = k1(k2 + k3 [B])/(k−1 + k2 + k3[B])
in which
k
A is the observed secondꢀorder rate constant
and B is a second molecule of the amine or an added
base [14].
The second step which is the formation or decomꢀ the aza in the intermediate (Scheme 2):
position of the intermediate in to product may be conꢀ
O
N
O2N
NO2
Cl
sidered as a rateꢀdeterminating step. If the formation of
the intermediate is the rateꢀdeterminating step, –1 Ӷ
k2 3 [B], then Eq. (2) is reduced to kA 1, and the
amine does not catalyze the reaction. But, if the conꢀ
dition is not obeyed, decomposition of the intermediꢀ
ate is rate limiting and base catalysis occurs. The
O2N
−
O
H
k
−
+
N
N
+
k
= k
N+
H
N
Cl
H
H
H
H
Scheme 2.
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013

SOLVENT EFFECTS ON KINETICS
1971
Table 1. Secondꢀorder rate constants (kA
×
10, M–1 s–1) in
The latter is confirmed with very negative activated
entropy of the reaction [15–22].
reaction of 2ꢀchloroꢀ3,5ꢀdinitropyridine with aniline in
mixtures at 25 C
°
The first step in investigating the reaction between
2ꢀchloroꢀ3,5ꢀdinitropyridine and aniline is determiꢀ
nation of the rateꢀdeterminating step. For this, various
aniline concentrations as a base on the reaction rate
were studied at different volume fraction of solvents.
The secondꢀorder rate constants of the reaction at varꢀ
ious concentration of aniline are reported in Table 1.
As it can be seen, no significant variation in the secꢀ
ondꢀorder rate constants occurred with mutation of
aniline concentration. According to our previous
works [10–12, 14] and the above explanation the reacꢀ
tion was not catalyzed by base in all mixtures and the
formation of the intermediate is the rateꢀdeterminatꢀ
ing step of the reaction.
[Aniline], mol l–1
0.030
x
0.010
0.060
Propanꢀ2ꢀol/hehane
0.3
0.6
0.9
7.52
7.80
9.11
7.52
7.50
7.80
9.14
7.84
9.15
Propanꢀ2ꢀol/benzene
0.3
0.6
0.9
1.22
2.27
5.81
1.31
2.94
5.56
1.45
2.66
5.86
The secondꢀorder rate constants of the reaction, kA
,
Propanꢀ2ꢀol/2ꢀmethylpropanꢀ2ꢀol
at 25°C in mixtures of 2ꢀpropanol with hexane, benꢀ
zene, and 2ꢀmethylpropanꢀ2ꢀol and [Emim][EtSO4]
with DMSO are summarized in Tables 2–5. The solꢀ
vatochromic parameters of media in binary mixtures
are also indicated [17, 18]. Selection of the molecular
solvents was based on the structures (2ꢀpropanol and
2ꢀmethylpropanꢀ2ꢀol as polar protic solvents, DMSO
as a polar aprotic solvent, hexane and benzene as aproꢀ
tic solvents with low polarity and [Emim][EtSO4] as a
polar ionic medium).
0.3
0.6
0.9
9.75
8.27
7.88
9.80
9.26
8.26
7.36
8.17
7.52
[Emin][EtSO4]/DMSO
(0.3)
(0.6)
(0.9)
4.50
3.50
1.26
4.57
3.59
1.30
4.50
3.63
1.26
Note:
x
is the volume fraction of propanꢀ2ꢀol and (in parentheꢀ
sis) and is the IL volume fraction.
x
IL
The data variations are plotted in Fig. 1 which
exhibits that the rate constants of reaction in 2ꢀproꢀ
panol/benzene mixtures decrease sharply with the
benzene content. The secondꢀorder rate constant of
the reaction follows the following sequence: 2ꢀmethꢀ
ylpropanꢀ2ꢀol > DMSO > 2ꢀpropanol > hexane > benꢀ
zene > [Emim][EtSO4]. A decreasing profile is demꢀ
onstrated for [Emim][EtSO4]/DMSO system by
increasing the ionic liquid content.
The normalized polarity parameter (ETN ) values of
the mixtures increase with 2ꢀpropanol content, thus it
can be expected that the reaction rate constant is
dependent on ETN . This prediction is acceptable for 2ꢀ
propanol/benzene mixtures. A singleꢀparameter corꢀ
relation of logkA versus ETN gives reasonable results.
The regression coefficient of logk
A versus ETN is 0.99.
But there is no appropriate relationships for singleꢀ
parameter correlations in other mixtures. For example
in 2ꢀpropanol–hexane mixture, the regression coeffiꢀ
cient of logkA versus ETN is 0.673. Also, there is no
1
Table 2. Secondꢀorder reaction rate constants (10
in mixtures at 25
×
M–1 s⎯ )
°
C
kA × 10,
M–1 s–1
xHex
ETN
α
β
π
*
0
6.86
9.15
9.15
11.11
7.84
7.19
6.54
7.52
7.52
5.23
4.58
0.54
0.53
0.52
0.51
0.49
0.048
0.46
0.46
0.43
–
0.67
0.66
0.66
0.65
0.65
0.66
0.66
0.71
0.75
–
0.90
0.88
0.89
0.92
0.91
0.90
0.91
0.92
0.83
0.68
0.03
0.49
0.48
0.45
0.43
0.39
0.35
0.30
0.23
0.15
0.06
–0.06
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.00
0.10
Note:
x
is the volume fraction of hexane.
Hex
acceptable correlation between logkA and dipolarꢀ
methylpropanꢀ2ꢀol, but the reaction rate constants
decrease. The increasing effect of * parameters is in
contradiction with decreasing behavior of reaction
rate constants in 2ꢀpropanol/benzene mixtures. The
data in Table 6 confirm that singleꢀparameter regresꢀ
ity/polarizability (
π
*) in any of the solutions.
π
Although value for pure [Emim][EtSO4] is the
α
highest, the obtained rate constant is lower than for the
pure DMSO in [Emim][EtSO4]/DMSO mixtures.
Other solvatochromic parameters are the same:
α
parameters increase with addition of 2ꢀpropanol to 2ꢀ sion could not give a reasonable mathematical model
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013

1972
HADI SALARI et al.
Table 3. Secondꢀorder reaction rate constants in mixtures
at 25
the standard coefficient of π* is 0.582. In mixture of 2ꢀ
propanol with 2ꢀmethylpropanꢀ2ꢀol, similar correlaꢀ
tion observes:
°
C
kA × 10,
M–1 s–1
ETN
α
β
π*
log
k
A = –2.289( 1.376) + 3.047( 0.561)
+ 0.904(2.962)
= 0.917, = 0.039,
is 0.895, and the stanꢀ
* is 0.050. In 2ꢀpropanol/benzene
β
xbenz
π
*
(4)
0
6.86
5.56
4.90
4.25
2.94
2.29
1.96
1.31
1.31
0.65
–
0.54
0.52
0.50
0.49
0.47
0.45
0.43
0.41
0.38
0.33
0.13
0.65
0.62
0.56
0.51
0.49
0.47
0.42
0.41
0.39
0.35
0.00
0.90
0.88
0.83
0.75
0.70
0.65
0.61
0.54
0.43
0.28
0.09
0.50
0.53
0.57
0.62
0.63
0.64
0.64
0.64
0.64
0.62
0.60
(
n
= 11,
R
s
F = 18.50).
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
The standard coefficient of
dard coefficient of
β
π
mixtures following equation was obtained (the stanꢀ
dard coefficient of is 0.991):
log
k
A = –1.832( 0.106) + 4.954( 0.232)ETN
(5)
(
n
= 10, = 0.991, = 0.045, = 456.78).
R
s
F
The standardized coefficient is the estimate of an analꢀ
ysis applied on variables that have been standardized,
so that they have variance of 1. This is usually benefit
to find which of the independent variables have greater
effects on the dependent variables in the multiple
regression analysis, when the variables are measured in
different units of measurements [7, 14].
Note:
x
is the volume fraction of benzene.
benz
The normalized polarity parameter is a blend of
(polarity/dipolarizability) and (hydrogen bond
donor ability) of media [14]. Thus, the correlation of
logkA versus and * was considered and the results
are demonstrated in equation:
log A = –3.650( 1.376) + 4.544( 0.436)
+ 3.058(0.842)
= 0.986, = 0.062,
The standard coefficient of
coefficient of * is 0.480.
π
*
α
Table 4. Secondꢀorder reaction rate constants in mixtures
at 25
°
C
α
π
kA × 10,
M–1 s–1
x2ꢀM
ETN
α
β
π*
k
α
π
*
(6)
0
6.86
7.52
0.53
0.52
0.51
0.51
0.50
0.49
0.48
0.46
0.45
0.42
0.39
0.66
0.62
0.61
0.61
0.57
0.54
0.51
0.49
0.45
0.39
0.33
0.87
0.89
0.90
0.90
0.91
0.92
0.93
0.93
0.94
0.95
0.94
0.50
0.50
0.51
0.51
0.51
0.51
–
(
n
= 11,
R
s
F
= 119.25).
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
α
is 1.378, and standard
8.50
π
8.50
The intermediate of the reaction has zwitterionic
character (Scheme 2), thus the activated complex of
the reaction has higher polarity than reactant. Hence,
the reaction rate increases with the polarity/dipolarizꢀ
ability of the solvent. As can be seen, the secondꢀorder
rate constant of the reaction increases with an increase
8.17
8.17
8.82
9.80
0.51
0.51
0.51
0.50
12.42
12.42
10.13
in the hydrogen bond acceptor ( ) basicity. The actiꢀ
β
vated complex leading to the zwitterionic intermediate
is stabilized through hydrogenꢀbonding interactions of
the media (solvent as acceptor with parameter) with
β
Note:
x
is the volume fraction of 2ꢀmethylpropanꢀ2ꢀol.
2ꢀM
positive charge on the activated complex of the reacꢀ
tion. The activated complex stabilizes more than the
reactant and an increase in the
the reaction rate. It is clear that in solutions of 2ꢀproꢀ
panol with 2ꢀmethylpropanꢀ2ꢀol, the effects of on
the increase in the reaction rate is higher than that of
*, because the standardized coefficient of is higher
than that of *. The activated complex has the zwitteꢀ
β
parameters accelerate
to fitting data. Therefore, multiparameter linear
regression (MLR) analysis was carried out. The dualꢀ
parameter regression and corresponding correlation
coefficients are listed in Table 6.
β
π
β
In 2ꢀpropanol/hexane mixtures dual parameter
π
correlation of log
kA versus
π
* and
β
could give a reaꢀ
rionic character with positive charge on nitrogen of
aniline and negative charge on the pyridine ring.
Hydrogen bonding interactions of media (donor and
acceptor) with the charges on the activated complex
stabilize the activated complex.
sonable mathematical equation which is summarized
in equation:
log
k
A = 0.669( 0.075) + 0.115( 0.33)
+ 0.347(0.192)
= 0.815, = 0.070,
, and
error, standard deviation, and a statistical factor,
respectively. The standard coefficient of is 0.278, and
β
π
*
(3)
In [Emim][EtSO4]/DMSO mixtures correlation
(
n
= 11,
R
s
F
= 7.91),
with ETN and
mentioned previously, ETN parameter can be divided in
π
* have the best result with R = 0.87. As
where
n,
R
,
s
F are the number of data, regression
β
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013

SOLVENT EFFECTS ON KINETICS
1973
Table 5. Secondꢀorder reaction rate constants in mixtures
at 25
two other parameters. Hence, the correlation of logkA
versus and * was done in IL mixtures. The results
are shown in equation:
log A = –2.308( 2.017) – 1.140( 0.281)
+ 2.326(1.955)
= 0.820, = 0.182,
Standard coefficient of is –0.844, and standard
coefficient of * is 0.248.
In 2ꢀpropanol/benzene
°
C
α
π
kA × 10,
M–1 s–1
xIL
ETN
α
β
π
*
k
α
π
*
(7)
0
7.18
7.18
5.55
4.57
5.55
3.92
3.59
3.59
2.28
1.30
0.98
0.44
0.52
0.55
0.57
0.6
0
0.76
0.79
0.76
0.76
0.78
0.77
0.78
0.76
0.77
0.69
0.78
1
(
n
= 11,
R
s
α
F = 8.23).
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.34
0.4
1.05
1.05
1.06
1.06
1.06
1.05
1.06
1.03
1.1
π
0.45
0.5
α
parameter has a positive
effect in reaction rate. This effect is related to stabiliꢀ
zation of activated complex via hydrogen and elecꢀ
tronic interaction between hydrogen bond donating
structure of solvent and negative charge on the interꢀ
0.61
0.63
0.67
0.67
0.68
0.69
0.54
0.58
0.66
0.68
0.66
0.76
mediate. The parameter has a dual effect on reaction
α
rate variations. Hydrogen bond donor ability of solvent
could protonate the nitrogen in aniline molecule,
hence the nucleophilic tendency of aniline decreased.
With stabilization of intermediate by hydrogen bondꢀ
0.99
ing interaction,
α
parameter could increase the rate
Note: x is the volume fraction of [Emim][EtSO ].
IL 4
constants. In 2ꢀpropanol/benzene mixtures there is no
hydrogen interaction between 2ꢀpropanol and benꢀ
zene. So, 2ꢀpropanol as a protic and polar solvent can
near the intermediate through hydrogen bonding forꢀ
mation with NO2 group in pyridine ring and ultimately
stabilize the intermediate with derealization of negaꢀ
tive charge as electronic and hydrogen interactions. By
adding small amounts of hydrogenꢀbond donor solꢀ
vent, methanol to benzene in the reaction of phenyl
2,4,6ꢀtrinitrophenyl ether with primary and secondary
amines [23] the reaction rate increased too.
In IL/DMSO, oxygen groups in the DMSO moleꢀ
cule and ethylsulfate anion can form strong hydrogen
bonding with hydrogen of NH2 group in aniline. Buttꢀ
ing to intermediate because of steric hindrance and no
hydrogen donor group in intermediate is impossible.
Furthermore, aniline is a stronger hydrogen bond
donator group more than intermediate. Hence,
solvents (binary solvents) is more probable so that
aniline cannot participate as a good nucleophile in the
ASN reaction. In 2ꢀpropanol/benzene mixtures the
effects of
α
on the reaction rate is higher than that of
π
*, because the standardized coefficient of is higher
α
than
π
* parameter.
parameter of ILs is largely affected by the
The
α
nature of the cation, but there is also a smaller anion
effect [4, 6]. It has been known that in [Emim][EtSO4]
all three imidazolium ring hydrogen atoms are acidic.
The
α
value for [Emim][EtSO4] is moderately high
compared to molecular solvents. The
β
parameter of
ILs is mainly dominated by the nature of the anion. By
adding DMSO to 1ꢀethylꢀ3ꢀmethylimidazolium ethylꢀ
sulfate, the rate constants increase signally. Despite this
hydrogen bonding interaction between aniline and variation, there is no obvious change in
π* and
β
14
4
2
1
4
−
1
x
x
0
0.4
0.8
0
0.4
0.8
14
3
9
1
4
4
−
0
0.4
0.8
x
0
0.4
0.8 xIL
Fig. 1. Secondꢀorder rate constants of reaction versus volume fraction of 2ꢀpropanol (
zene, and ( ) 2ꢀmethylpropanꢀ2ꢀol; and ( ) IL ( ) with DMSO at 25°C.
x) in its mixtures with (1) hexane, (2) benꢀ
3
4
x
IL
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013

1974
HADI SALARI et al.
Table 6. Regression coefficients in different mixtures
donor acidity relative to other molecular solvents. In
[Emim][EtSO4]/DMSO mixtures, standardized coefꢀ
ETN
ficient of
these facts and negative effect of
α
is higher than
π
* parameter. According to
parameter on reacꢀ
α
β
π
*
R
α
2ꢀPropanol/hexane
tion rate, it can be concluded that in ionic liquid, miniꢀ
mum rate constant should be obtained. Low rate conꢀ
stant for this aromatic nucleophilic substitution reacꢀ
tion was observed in 1ꢀ(1ꢀbutyl)ꢀ3ꢀmethylimidazolium
terafluoroborate ([Emim]BF4) too [14]. A study has
been done by Habibi et al. [17] showed that in
0.345
0.673
0.693
0.726
0.795
0.815
0.395
0.303
0.115
0.474
0.347
[Emim][EtSO4]/DMSO mixtures,
π* and
β
parameꢀ
ters increase and parameter decreases the rate of
reaction of 1ꢀchloroꢀ2,4ꢀdinitrobenzene with aniline
which is in resemblance with our results.
α
2ꢀPropanol/benzene
4.926
–1.516
–3.034
0.991
0.958
0.986
0.729
0.986
3.144
In order to show the efficiency of the suggested
dualꢀparameter correlations, predicted values of logkA
versus their experimental values were plotted in Fig. 2.
There is good agreement between the experimental
1.610
–4.622
3.058
4.544
and calculated values of logkA in all solvent mixtures.
2ꢀPropanol/2ꢀmethylpropanꢀ2ꢀol
0.818
0.828
0.891
0.414
0.917
–0.651
2.922
CONCLUSIONS
Solvent effects on the aromatic nucleophilic substiꢀ
tution reaction of 2ꢀchloroꢀ3,5ꢀdinitropyridine are
similar to those of aromatic nucleophilic substitution
reaction of 1ꢀhaloꢀ2,4ꢀdinitrobenzene. The reaction
mechanism is also similar to ANS reaction of haloniꢀ
trobenzens, and it confirms the suggested mechanism
in Scheme 2. In all mixtures, formation of the zwitteꢀ
rionic intermediate is the rateꢀdetermining step of the
reaction. Normalized polarity, hydrogen bond donor
acidity, and hydrogen bond acceptor basicity of media
have different effects on the rate of the reaction. Solꢀ
vatochromic parameters of media can describe solvent
effects on the reaction rate and represent a theoretical
model for similar cases in the 2ꢀpropanol and
[Emim][EtSO4] mixed with other molecular solvents.
The results of dualꢀparameter correlations of logkA
6.857
3.047
0.904
[Emim][EtSO4]/DMSO
0.828
0.784
0.409
0.044
0.820
–1.059
4.391
0.411
2.326
–1.140
parameters in IL system. The anion of [Emim][EtSO4]
is known to have a compact structure, possessing
much weaker basicity in comparison to alcohols.
Then, [Emim][EtSO4] has higher hydrogen bond
versus
π
* and
β
(also
α
and ) in all of the solutions
β
show some improvement with regard to the singleꢀ
parameter models.
Theoritical
1.5
REFERENCES
1. M. R. Gholami and A. HabibiꢀYangjeh, J. Chem. Res.
(S), 226 (1999).
0.7
2. M. R. Gholami and A. HabibiꢀYangjeh, J. Phys. Org.
Chem. 13, 468 (2000).
3. M. KhodadadiꢀMoghadam, A. HabibiꢀYangjeh, and
M. R. Gholami, Monatsh Chem. 140, 329 (2009).
−
0.1
4. A. R. HarifiꢀMood. A. HabibiꢀYangjeh, and
M. R. Gholami, J. Phy. Chem. B 110, 7073 (2006).
−
0.1
0.3
0.7 1.1
Experimental
5. C. Rafols, M. Rosés, and E. Bosch, J. Chem. Soc. Perꢀ
kin Trans. 2, 243 (1997).
6. H. Salari, M. KhodadadiꢀMoghadam, A. R. Harifiꢀ
Fig. 2. Plot of the calculated values of log
experimental values of it in mixtures of 2ꢀpropanol and IL
at 25°C.
k versus the
A
Mood, and M. R. Gholami, J. Phys. Chem. B 114
,
9586 (2010).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013

SOLVENT EFFECTS ON KINETICS
1975
7. A. R. HarifiꢀMood, M. Sadat Masumpour, and 15. E. A. Hamed, Int. J. Chem. Kinet. 29, 515 (1997).
M. R. Gholami, Prog. React. Kinet. Mech. 31, 117
16. E. Gomez, B. Gonzalez, E. Calvar, E. Tojo, and
A. Dominguez, J. Chem. Eng. Data 51, 2096 (2006).
17. A. HabibiꢀYangjeh, Y. JafariꢀTarzanag, and
(2006).
8. H. Salari, A. R. HarifiꢀMood, and M. R. Gholami,
J. Sol. Chem. 39, 1509 (2010).
A. R. Banaie, Int. J. Chem. Kinet. 41, 153 (2009).
9. A. R. HarifiꢀMood, A. HabibiꢀYangjeh, and
18. M. Rosés, C. Ràfols, J. Ortega, and E. Bosch, J. Chem.
M. R. Gholami, J. Phys. Org. Chem. 21, 783 (2008).
Soc. Perkin. Trans. 2, p. 1607 (1995).
10. M. R. Gholami and A. HabibiꢀYangjeh, Int. J. Chem.
19. D. J. Cram, B. Rickborn, C. A. Kingsbury, and P. Habꢀ
Kinet. 32, 431 (2001).
11. M. R. Gholami and A. HabibiꢀYangjeh, Int. J. Chem.
Kinet. 33, 118 (2001).
12. M. R. Gholami and B. A. Talebi, J. Phys. Org. Chem.
erfield, J. Am. Chem. Soc. 83, 3678 (1961).
20. M. Orozco and F. J. Luque, Chem. Rev. 100, 4178
(2000).
21. E. A. Hamed, A. A. ElꢀBardan, E. F. Saad,
G. A. Gohar, and G. M. Hassan, J. Chem. Soc. Perkin
Trans 2, p. 2415 (1997).
16, 369 (2003).
13. A. R. HarifiꢀMood, M. Sadat Masumpour, and
M. R. Gholami, Prog. React. Kinet. Mech. 31, 117
(2006).
22. F. M. Hegazy, A. Z. A. Fattah, E. A. Hamed, and
S. M. Sharaf, J. Phys. Org. Chem. 13, 549 (2000).
14. A. R. HarifiꢀMood, A. HabibiꢀYangjeh, M. R. Gholꢀ
ami, and A. HabibiꢀYangjeh, Int. J. Chem. Kinet. 39
,
23. O. Banjoko and I. A. Babatunde, Tetrahedron 60, 4645
681 (2007).
(2004).
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 87
No. 12
2013