Deep eutectic solvent as an operative media on structure-reactivity relationships

Article abstract of DOI:10.1002/kin.21273

Deep eutectic solvents seem to be environmentally friendly solvents, particularly because they are prepared easily and have very low-vapor pressures under ambient conditions. They are suitable candidates as green solvents for reaction media with special properties. To present this behavior, substitution reactions of some para- and meta-substituted anilines with 1-fluoro-2,4-dinitrobenzene have been spectrophotometrically investigated in varying mole fractions of ethaline as a deep eutectic solvent in dimethyl sulfoxide (DMSO). The measured rate coefficients of the reaction demonstrated a noticeable variation with the increasing mole fraction of ethaline in ethaline-DMSO mixtures. The linear free energy relationship (LFER) of second-order rate coefficients based on Hammett's substituent constants demonstrates a reasonably linear straight line with a negative slope in different mole fractions of ethaline-DMSO mixtures. Another LFER investigation based on the polarity parameters of the media showed a good agreement with hydrogen bond donor and acceptor abilities of the solvent. Non-LFER assay according to the preferential solvation model confirmed differences between the microsphere solvation of the solute molecules and the bulk composition of the solvents.

Full text of DOI:10.1002/kin.21273

Received: 12 July 2018
DOI: 10.1002/kin.21273
Revised: 25 February 2019
Accepted: 28 February 2019
A R T I C L E
Deep eutectic solvent as an operative media on
structure-reactivity relationships
Ali Reza Harifi-Mood
Hasan Khorshahi
Department of Physical Chemistry, Faculty of
Chemistry, Kharazmi University, Tehran, Iran
Abstract
Deep eutectic solvents seem to be environmentally friendly solvents, particularly
because they are prepared easily and have very low-vapor pressures under ambient
conditions. They are suitable candidates as green solvents for reaction media with
special properties. To present this behavior, substitution reactions of some para- and
meta-substituted anilines with 1-fluoro-2,4-dinitrobenzene have been spectrophoto-
metrically investigated in varying mole fractions of ethaline as a deep eutectic sol-
vent in dimethyl sulfoxide (DMSO). The measured rate coefficients of the reaction
demonstrated a noticeable variation with the increasing mole fraction of ethaline in
ethaline-DMSO mixtures. The linear free energy relationship (LFER) of second-order
rate coefficients based on Hammett's substituent constants demonstrates a reasonably
linear straight line with a negative slope in different mole fractions of ethaline-DMSO
mixtures. Another LFER investigation based on the polarity parameters of the media
showed a good agreement with hydrogen bond donor and acceptor abilities of the
solvent. Non-LFER assay according to the preferential solvation model confirmed
differences between the microsphere solvation of the solute molecules and the bulk
composition of the solvents.
Correspondence
AliReza Harifi-Mood, DepartmentofPhysical
Chemistry, Facultyof Chemistry, Kharazmi
University, 15719-14911, Tehran, Iran.
Email:harifi@khu.ac.ir;
alireza.harifi@gmail.com
Fundinginformation
Kharazmi University, Grant/Award Number:
D/2043
K E Y W O R D S
aromatic nucleophilic substitution, deep eutectic solvent, 1-fluoro-2,4-dinitrobenzene, Hammett equation,
preferential solvation
of molecules as a solute.5 The effects of both the molecular
structure of reactants and solvent on the rate of the aromatic
1
INTRODUCTION
Methodical studies of the substituent effects of the chemi-
cal reactions in solution have been carried out comprehen-
sively by many researchers since the proposal of Hammett's
equation.1 In some studies, the relationships between the pro-
portionality constant, ꢀ, values and the environmental changes
have also been the major subject of the reports.2–4 It has been
confirmed that a solvent as environment in chemical reactions
plays an important role in many chemical and physical pro-
cesses. It is a determinative factor in the chemical equilibrium
constant and rate coefficient values in chemical reactions.
Solvents might also influence the selectivity in the reactions
and the position and intensity of spectral absorption bands
reactions in different binary solvent compositions have been
explained using Hammett's equation.5,6 These two effects can
also be investigated to find a probable correlation among dis-
crete properties.
New solvent media have novel capacity to present observ-
able results in chemical kinetics. Deep eutectic solvents
(DESs) are now widely introduced as a new class of ionic
media like ionic liquids (ILs) and are noticed as an alternative
to ILs.7–9 They are easily prepared by mixing and heating of
two components to produce a composite with a melting point
lower than either of its individual components.10 Many recent
studies have focused on bulk physical properties, including
Int J Chem Kinet. 2019;1–9.
wileyonlinelibrary.com/journal/kin
© 2019 Wiley Periodicals, Inc.
1

2
HARIFI-MOOD AND KHORSHAHI
phase diagrams information,11–14 viscosity, density, and elec-
trical conductivity data,15–18 and the effect of molecular struc-
ture on the physical properties of DESs.19 A few academic
reports can be found about the investigation of microscopic
physical properties of DESs and the prediction of their influ-
ence on chemical reaction rates.20 Such studies provide deep
insights into the necessary information to design new DESs
with desirable properties.
360 nm, according to the product absorbance of each reac-
tion, at constant concentration of substituted anilines (Figure
S1 in the Supporting Information). The reaction kinetics was
studied under pseudo–first-order condition. The pseudo–first-
order and the second-order rate coefficients were obtained
from the absorbance values of product at t and infinity accord-
ing to the procedure reported elsewhere.6 Figure S2 in the
Supporting Information shows a representative outcome of
the rate coefficient from experimental data. All experiments
were carried out at least in triplicate, and the results are aver-
aged.
In this contribution, we have chosen the reaction of
1-fluoro-2,4-dinitrobenzene (FDNB) with meta- and para-
substituted anilines in ethaline-dimethyl sulfoxide (DMSO)
mixtures to study the solvent and substituent effects, simul-
taneously, on the reaction rate coefficient. Ethaline is a well-
known DES prepared by mixing choline chloride and ethylene
glycol. In addition, the rate coefficient data variations were
investigated according to linear and nonlinear free-energy
relationship models such as the Hammett equation, solvent
effect, and preferential solvation.
3
RESULTS AND DISCUSSION
As a known mechanism, the most aromatic compounds
undergo electrophilic aromatic substitution reaction with
electrophiles. Some aryl halides consisting of electron-
withdrawing groups are capable of participating in nucle-
ophilic substitution reaction so that increasing the number of
substituents groups increases the reactivity of the aryl halide.
Nucleophilic aromatic substitution occurs with a variety of
strong nucleophiles such as primary or secondary amines.
On the other hand, other characteristics such as the elec-
tronegativity of the halogen and the location of the electron-
withdrawing group greatly affect the rate of nucleophilic aro-
matic substitution. The effective charge delocalization can be
observed when the electron-withdrawing groups are located
ortho or para to the halogen. The aromatic nucleophilic substi-
tution reaction occurs through an addition-elimination mech-
anism including a zwitterionic intermediate, which can be
converted to a product spontaneously or by a base-catalyzed
mechanism.21 The nucleophile usually plays catalyst's role in
the reaction.
2
EXPERIMENTAL
2.1 Materials
Aniline and its derivatives were purchased from Merck. The
former was purified by vacuum distillation, and the latter were
of analytical grade. Solid compounds were recrystallized from
◦
water/ethanol and water/acetone. FDNB (m.p. 26–28 C) was
obtained from Fluka. Choline chloride (≥98%) and ethylene
glycol (≥99.8%) were purchased from Sigma-Aldrich and
Merck, respectively (all materials were of high-purity grade).
Analytical reagent-grade DMSO (≥99.9%; Merck) was used
for the preparation of solutions. Choline chloride was dried for
48 h at 313 K with a high-vacuum oven. Ethylene glycol and
˚
FDNB is a good candidate for a nucleophilic aromatic sub-
stitution with the addition-elimination mechanism. In contin-
uing our recent study of solvent effects on organic reactions20
and similar studies,22 we were interested in studying effects
of mixtures on DESs with molecular solvents. The reaction of
DMSO were dried over a 3-A molecular sieve. The water con-
tent of the dried compounds was determined by coulometric
Karl Fischer titration, yielding <500 ppm residual water for
ethylene glycol and DMSO and <800 ppm for choline chlo-
ride.
◦
FDNB with some substituted anilines was studied at 25 C in
Ethaline was obtained by mixing choline chloride and ethy-
lene glycol at the molar ratio of 1:2 in an inert atmosphere and
subsequent stirring under heating up 353.15 K until a homo-
geneous, colorless liquid was formed.14 Binary mixtures of
DES and DMSO over the entire range of ethaline mole frac-
tions were prepared gravimetrically before each kinetic run.
binary mixtures of ethaline and DMSO mixtures. The evalu-
ation of the reaction mechanism (shown in Figure 1) demon-
strates a second-order rate law with an apparent rate coeffi-
cient, k , according to Equation 1 where B refers to substi-
A
tuted aniline as a base catalyst:
(
)
ꢁ1 ꢁ2 + ꢁ3 [B]
ꢁ−1 + ꢁ2 + ꢁ3 [B]
ꢁA =
.
(1)
2.2 Kinetic measurements
The reaction kinetics of FDNB with substituted anilines was
measured spectrophotometrically using a UV-vis Cintra 101
The second-order rate coefficients of the reactions under
pseudo–first-order conditions with excess of substituted
aniline were determined over the whole range of mole
◦
spectrophotometer at 25 C. The kinetic runs were carried out
by measuring the absorbance of reaction media from 350 to

HARIFI-MOOD AND KHORSHAHI
3
F I G U R E 1 The reaction mechanism of 1-fluoro-2,4-dinitrobenzene and substituted anilines
−1
TA B L E 1 Second-order coefficients (k / M
s
−1) for the reaction of substituted anilines with 1-fluoro-2,4-dinitrobenzene in various mole
A
◦
fraction of DMSO in ethaline at 25 C
Mole fraction of DMSO
Substituents in aniline
p-NH2
0
0.1
0.2
0.3
6.78
0.4
7.08
0.5
7.76
0.6
8.51
0.7
0.8
0.9
1
12.3
5.14
0.310
2.06
1.08
5.01
2.65
1.66
1.15
4.21
6.60
1.01
0.92
0.67
5.62
1.22
2.16
1.47
5.43
3.50
5.02
2.72
8.53
8.12
4.23
1.82
1.13
6.25
1.38
2.37
1.73
6.11
4.16
5.73
3.16
9.22
8.67
6.62
2.95
3.38
9.33
10.2
11.2
p-OH
1.89
2.42
1.92
6.71
5.75
6.01
4.03
2.05
2.94
2.07
8.20
6.41
7.13
4.82
2.54
3.55
2.17
8.73
6.62
7.52
6.22
2.68
3.66
2.21
9.49
6.85
7.65
6.63
2.92
4.08
2.24
3.32
3.29
3.51
p-OMe (10 × k )
4.49
2.53
4.63
2.52
5.51
3.20
A
p-CH3 (10 × k )
A
m-CH3 (102 × k )
10.1
10.5
11.8
12.7
A
None (102 × k )
7.01
8.12
7.01
7.30
9.01
7.04
7.46
9.53
7.26
2.61
9.03
12.0
7.71
29.2
A
p-NHCOMe (102 × k )
A
m-OH (102 × k )
A
p-Br (103 × k )
10.1
10.8
16.0
20.4
24.1
25.0
A
p-Cl (103 × k )
9.82
8.33
4.12
4.64
10.1
10.0
14.0
10.2
16.3
14.8
17.9
18.1
21.6
18.9
10.2
10.6
31.2
39.5
24.7
13.1
12.8
A
m-Cl (103 × k )
20.0
11.4
11.0
p-COOH (103A× k )
5.39
7.06
8.92
9.58
A
p-COCH3 (103 × k )
5.17
7.03
8.16
10.1
A
fractions of DMSO in ethaline, and the results are summa-
rized in Table 1.
3.1 Structural LFER
The well-known Hammett equation is applied for the calcula-
The energy changes for a reaction are also linearly asso-
ciated with the energy changes for a reference reaction. The
relationships can be ascertained between substituent or sol-
vent parameters and varied substituent- or solvent-dependent
processes within the sort of a linear Gibbs energy relation-
ship, often still mentioned as a linear free-energy relationship
(LFER).5
tion of substituent effects on reaction rates.1
log ꢁ = log ꢁ0 + ꢀꢂ,
(2)
where k is the rate coefficient of the reaction. The symbol
k denotes the rate coefficient corresponding to reaction of
u0nsubstituted aniline with FDNB, ꢂ is substituent constant,
presumably dependent only on the nature and position of the
second substituent (at the meta or para position). The Ham-
mett constant (ꢂ) reflects the effects of both inductive and res-
onance effects on substituents. Their values are summarized
in some reviews.23 ꢀ is a reaction constant dependent only on
the nature of the side chain, the center of the reaction, and
the conditions (reagent, solvent, catalyst, temperature) under
which the reaction occurs.
For this evaluation in present report, the mentioned reac-
tions were considered including only small changes in the
molecular structure or media properties that are involved from
one reaction to another. These changes are structural includ-
ing a series of differently substituted aniline as reactants in the
same media, and environment consisting of a single reaction
carried out in a series of different binary ethaline-DMSO mix-
tures. Such relationships will be useful in not only the study of
reaction mechanisms but also the prediction of reaction rates
coefficients depending on substituent or solvent changes.5 On
the other hand, the use of DES as reaction media might affect
both structure and solvent-reactivity correlations. Therefore,
the relationships were studied for the reaction between FDNB
and some substituted aniline in binary mixtures of ethaline-
DMSO as follows.
The LFER investigations according to the Hammett equa-
tion were performed for the reaction between FDNB with sub-
stituted anilines in the solvent mixtures. Results, which are
summarized in Table 2, demonstrate a good linear behavior
with a negative slope. Figure 2 shows a representative linear
relationship in three different compositions of binary solvent
mixtures. The negative values of the Hammett slope imply

4
HARIFI-MOOD AND KHORSHAHI
TA B L E 2 Hammett's reaction parameters (ꢀ) and regression coefficients (r2) for the reaction of 1-fluoro-2,4-dinitrobenzene with substituted
◦
anilines in the mixture of DMSO and ethaline at 25 C
xDMSO
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
ꢀ
−3.318
(0.100)
0.990
−3.148
(0.105)
0.989
−2.928
(0.141)
0.975
−2.886
(0.163)
0.966
−2.837
(0.168)
0.963
−2.837
(0.173)
0.963
−2.671
(0.182)
0.951
−2.623
(0.192)
0.944
−2.639
(0.193)
0.945
−2.643
(0.185)
0.949
−2.593
(0.174)
0.953
r2
Uncertainty values are presented in parenthesis.
influenced by the solvent effect; therefore, the investigation of
corresponding correlations would be reasonable.
3.2 Environmental LFER
As stated in many papers, both specific and nonspecific
solute-solvent interactions can influence the reactivity. To
determine the influence of solute-solvent interactions on the
kinetics of the reaction, LFER correlations between the acti-
vated free energy of reaction and polarity parameters were
investigated. These methods are based on single-parameter
regression including normalized polarity, ꢃꢅꢄ , or multiparam-
eter regression consisting of Kamlet, Abboud, and Taft (KAT)
hypothesis.25,26 Although the finding of a reasonable relation-
ship with ꢃꢅꢄ produces a simple equation, the interpretation
of the solvent effects on the reaction rate involves inevitable
complexity. The KAT model is based on the multiparameter
F I G U R E 2 Typical Hammett plot of log k versus constant ꢂ for
A
the reaction in the solvent mixtures (x is the mole fraction of DMSO)
correlation between the log k of the reaction and the solva-
A
that electron-donating substituents accelerate the reaction
rate. It can be attributed to the increasing nucleophile charac-
teristic of substituted anilines and positive charge developed
on the N-atom of the transition state structure. As regards
the confirmed mechanism, it is expected that the mechanism
results in nucleophilic substitution reactions. The high magni-
tude of ꢀ values suggests preferable influence of nucleophilic-
ity of the substituted anilines on the reaction rate.24 The order
of magnitude of the ꢀ value depends on both the molecu-
lar structure of reactants and solvent effects. For instance,
the reaction of 2-chloro-5-nitropyridine or benzenesulfonyl
chloride with substituted anilines in binary molecular sol-
vents exhibits low values for ꢀ about ten times less than the
values in this study.3,4 However, the similar ꢀ values have
been observed for the studied reaction in binary mixtures of
methanol and ethyl acetate.6 The decreasing the ꢀ value about
20% from ethaline to DMSO will be interesting because of
two aspects. The former is related to its higher value when the
reaction is performed in DES. It can be attributed to specific
interactions such as strong ion-molecule interactions in this
novel media, which might amplify the substituent effects on
the reaction rate. Therefore, it is expected that the ethaline as a
common DES can distinguish the little difference of structural
reactivity in these reactions. The latter case implies the adjust-
ment of substituent effects on the reaction by solute-solvent
interactions when the mole fraction of DES decreases. Above
interpretations show that the substituent effects are definitely
tochromic parameters of the media (Equation 3):
log ꢁA = ꢆ0 + ꢇꢈ∗ + ꢉꢊ + ꢋꢌ,
(3)
where ꢈ* is an index of solvent dipolarity/polarizability mea-
suring the ability of the solvent to interact through a perma-
nent or induced dipole by virtue of its dielectric effect, ꢊ is
the solvent hydrogen bond donor (HBD) acidity, which refers
the ability of the solvent to donate a proton, ꢌ is the solvent
hydrogen bond acceptor (HBA) basicity, which describes the
ability to accept a proton in a solute-solvent interaction, and
A is the regression value of the solute property in a refer-
0
ence solvent (such as n-hexane) with zero values of solva-
tochromic parameters. Constants of s, a, and b are regression
coefficients, which are calculated by data essay. The solva-
tochromic parameters for ethaline-DMSO mixtures used in
the present study are obtained from our previous report.27
The data derived from experimental data and Equation 3
are presented in Table 3. Although several single or dual-
parameter relationships have been found for all reactions in
the whole range of solvent mole fractions, it seems that the
dual-parameter relationships between log k with ꢊ and ꢌ
A
are reasonable in the reactions according to their statistical
parameters (Table 3). Figures S3-S5 in the Supporting Infor-
mation present the ability of this dual-parameter regression in
reproduction of the reaction rate coefficients. As can be seen,
the HBD and HBA abilities of media have opposite effects

HARIFI-MOOD AND KHORSHAHI
5
◦
TA B L E 3 Statistical (r2, s, F) and correlation (e, p, a, and b) coefficients for correlation of log k with solvatochromic parameters at 25 C
A
Substituents in aniline
r2
102 × sa
Fa
47.43
Intercept
0.798
eb
pb
ab
bb
0.395
p-NH2
0.922
3.9
–
–
−0.352
(0.076)
–
(0.163)
1.117
(0.146)
0.349
(0.163)
2.539
(0.105)
2.646
(0.149)
2.671
(0.157)
0.375
(0.172)
0.979
(0.1)
0.914
0.985
0.986
0.987
0.918
0.915
0.943
0.982
0.942
0.921
0.982
0.943
0.926
0.919
0.911
0.937
0.936
0.982
0.935
0.982
0.968
0.985
4.1
4.0
4.0
4.0
4.7
3.8
3.3
1.8
3.4
3.9
1.9
3.3
4.2
4.4
5.1
4.5
4.6
3.1
6.0
3.3
4.9
3.5
42.51
582.15
292.09
300.19
44.70
−0.722
(0.166)
–
–
–
–
–
–
–
(0.239)
−1.857
(0.090)
−1.999
(0.167)
−2.096
(0.230)
−0.511
(0.193)
−1.525
(0.085)
2.545
p-OH
–
–
0.078
(0.078)
–
0.180
(0.160)
–
p-OMe
p-CH3
−0.441
(0.090)
–
96.66
–
65.60
−0.44
(0.138)
–
−2.791
(0.601)
–
–
–
(0.56)
221.94
64.74
−1.168
(0.076)
2.545
−0.196
(0.036)
−0.208
(0.066)
3.07
0.710
(0.068)
–
–
−2.958
(0.567)
–
(0.565)
2.212
46.73
−6.961
(1.642)
−0.408
(0.076)
−0.440
(0.138)
–
–
(0.616)
−0.983
(0.109)
2.545
(0.834)
–
212.64
65.60
–
0.680
(0.074)
–
−2.791
(0.601)
–
–
(0.56)
m-CH3
49.90
−1.303
(0.176)
−0.991
(0.256)
−2.311
(0.113)
−2.021
(0.187)
−1.881
(0.264)
−2.714
(0.070)
7.111
−0.345
(0.082)
–
0.530
(0.157)
0.484
(0.174)
1.266
(0.132)
1.048
(0.167)
1.029
(0.180)
1.813
(0.082)
–
45.648
91.67
−0.706
(0.178)
–
–
–
–
–
–
None
–
59.60
–
−0.160
(0.087)
–
58.02
−0.323
(0.184)
–
p-NHCOMe
m-OH
490.80
130.16
221.85
269.16
265.89
–
–
–
–
–
–
−7.899
(0.692)
–
(0.082)
−2.672
(0.137)
−3.099
(0.108)
−8.397
(1.724)
−0.023
(0.064)
–
1.781
(0.122)
2.088
–
(0.127)
3.010
4.304
–
(1.399)
(0.313)
(Continues)

6
HARIFI-MOOD AND KHORSHAHI
TA B L E 3 (Continued)
Substituents in aniline
p-Br
r2
102 × sa
8.2
Fa
48.89
Intercept
−2.823
(0.339)
−2.461
(0.485)
−1.161
(0.068)
−0.391
(0.129)
−1.687
(0.250)
−0.884
(0.368)
−4.772
(0.158)
−4.449
(0.283)
−4.314
(0.401)
−4.701
(0.237)
−4.032
(0.377)
−3.724
(0.538)
−3.099
(0.108)
−8.397
(1.724)
eb
pb
ab
bb
1.479)
0.924
–
–
−0.409
(0.158)
–
(0.304)
1.430
(0.330)
–
0.921
0.927
0.936
0.954
0.949
0.972
0.977
0.976
0.922
0.950
0.947
0.968
0.985
8.4
7.2
6.7
6.0
6.4
7.1
6.8
6.9
10.7
9.0
9.3
4.9
3.5
46.59
114.16
131.20
82.566
73.92
−0.832
(0.337)
–
–
–
–
–
–
–
–
–
–
–
–
–
p-Cl
−1.037
(0.097)
–
−2.051
(0.179)
–
–
−0.859
(0.116)
–
0.483
(0.224)
0.355
−1.779
(0.256)
–
(0.251)
3.256
m-Cl
306.85
168.42
163.26
106.55
75.74
–
(0.186)
3.013
–
−0.178
(0.131)
–
(0.253)
3.003
−0.345
(0.279)
–
(0.273)
2.874
p-COOH
p-COCH3
–
(0.278)
2.370
–
−0.368
(0.175)
–
(0.337)
2.335
72.19
−0.736
(0.374)
–
(0.366)
2.088
269.16
265.89
–
–
(0.127)
3.010
–
4.304
(1.399)
(0.313)
as and F are the standard deviation and statistical Fischer factor, respectively.
be, p, a, and b are the coefficients of ꢃꢅꢄ , ꢈ*, ꢊ, and ꢌ, respectively.
on the reaction rate in the most of regressions. The pres-
ence of ethaline decreases the rate of reactions because of its
high HBD character compared with DMSO. In fact, the strong
solvent-nucleophile interactions in a HBD solvent would play
an important role in the reaction rate. On the other side, the
HBA interactions of solvent with the reactants and interme-
diate increase the rate coefficient of the reactions. It can be
attributed to the both increasing of the nucleophilicity of the
substituted anilines and facilitating of the intermediate break.
The negative and positive effects of HBD and HBA, respec-
tively, abilities in dual-parameter regressions show that this
reaction would be not only accelerated in HBA solvents but
also decelerated in HBD media.
vated parameters in chemical reactions. Moreover, nonlinear
relationship models might be used to investigate the solvent
effects on the reactions. One of the well-known hypotheses
is the preferential solvaion model, which has drawn atten-
tion of scientists in recent years.28–30 While the LFER mod-
els provide useful information about the effective factors on
the chemical kinetics of the reactions, preferential solvation
models as a nonlinear equation may provide valuable solute-
solvent and solvent-solvent structural information. The pref-
erential solvation model is based on a physical exchange of
two solvents in a microsphere solvation layer of an indicator
(solute) according to the following equations:
I(S1)2 + 2S2 ⇌ I(S2)2 + 2S1
(4)
(5)
I(S1)2 + S2 ⇌ I(S12)2 + S1,
3.3 Preferential solvation
Solvent and structure reactivity correlations are the sam-
where I stands for the solute, S1 and S2 for the pure sol-
ples of linear relationships to interpret the variations of acti-
vents, and S12 for the solvent formed due to solvent-solvent

HARIFI-MOOD AND KHORSHAHI
7
TA B L E 4 The preferential solvation parameters of
DMES-ethaline mixtures calculated by fitting second-order rate
coefficient of the reaction in Equation 6 (Y , Y , and Y are log k in
1
2
12
A
ethaline, DMSO, and mixed solvents, respectively)
Substituents
in aniline
p-NH2
p-OH
Y1
Y2
Y12
f2/1 f12/1 103 × s r2
1.09 0.72 0.89 1.01 1.75 0.3
0.56 −0.51 0.38 0.33 3.16 3.2
−0.29 −0.70 −0.51 0.83 1.03 0.8
−0.51 −0.97 −0.63 1.06 6.29 0.7
−0.90 −1.31 −1.13 0.45 1.17 0.3
−1.09 −1.58 −1.18 0.24 1.09 1.2
0.989
0.980
0.977
0.970
0.991
0.972
0.995
0.983
0.953
0.990
0.965
0.992
0.980
p-OMe
p-CH3
m-CH3
None
p-NHCOMe −0.93 −1.77 −1.17 0.14 4.22 0.4
m-OH
p-Br
−1.12 −1.94 −1.17 0.50 2.63 1.9
−1.54 −2.30 −1.52 1.80 2.46 5.6
−1.40 −2.16 −2.0 0.70 2.24 1.0
−1.65 −2.89 −1.87 0.50 2.56 9.5
−1.91 −3.02 −2.05 0.68 2.21 1.8
−1.91 −3.19 −2.10 0.41 1.47 6.1
p-Cl
F I G U R E 3 The typical plot of log k versus the mole fraction
m-Cl
ethaline (x ). The solid curves are calculatAed from coefficients of
Et
p-COOH
p-COCH3
Equation 6 given in Table 4, and the points are experimental data
composite solvent in the microsphere solvation of molecules,
it has a slight effect on the rate of the reactions.
interaction (yielding a composite structure). I(S1), I(S2), and
I(S12) represent the solute solvated by the S1, S2, and S12
species, respectively. According to a previous study,28 the
physical properties (Y) in the solvent mixtures are calculated
as an average of these properties in pure solvents S1, S2, and
S12 (Y , Y , and Y , respectively), according to the mole frac-
Consequently, solvent reactivity correlations and preferen-
tial solvation data indicate the strong solvation of reactants
and activated complex of the reactions in the solvents. Since
DMSO is the preferential solvent in microsphere of the ani-
lines and activated complex of the reaction, it shows a relative
alignment effect on the nucleophilicity of substituted anilines.
However, the ethaline as a protic DES has a high HBD interac-
tion with substituted anilines. Therefore, it can show the dif-
ferent solvation ability and highlighting the nucleophilicity of
various anilines. It will appear that the Hammett parameter
(ꢀ) obviously decreases from DES to DMSO.
2
12
tions o1f each solvent in the mixture (푥20), as follows:
(
)
(
)
(
)
푌1 1 − 푥02 + 푌2푓2∕1 푥02 + 푌2푓12∕1 1 − 푥02 푥0
푌 =
2 , (6)
(
)
(
)
(
)
1 − 푥20 2 + 푓2∕1 푥02 + 푓12∕1 1 − 푥20 푥02
where f and f
are the thermodynamic equilibrium con-
2/1
12/1
stants of Equations 4 and 5, respectively. Their numerical val-
ues refer to the difference of solvent composition between
microsphere solvation of solute and the bulk of media.
4
CONCLUSIONS
However, the solute-solvent interactions have been widely
investigated by using the physical property Y as a solva-
tochromic parameter,27,31–33 the use of this model as a non-
linear relationship between activation free energy of chemical
reactions and solvent composition (non-LFER) has demon-
strated interesting results.20,33,34 Equation 6 was applied for
The solvent and structure reactivity investigations of the reac-
tion of FDNB with the substituted anilines in ethaline-DMSO
mixtures showed that the reaction rate changes by a factor of
0.4–0.04, according to the substituted anilines of each reac-
tion, when the ethaline as a DES was added to the media.
Ethaline-DMSO mixtures showed the minimum and maxi-
mum solvent effects on the reaction rate of anilines with p-
NH2 and m-Cl substituents, respectively. On the other hand,
ethaline as a solvent increases the substituent effects on the
reaction rate. The kinetic studies of the reaction demonstrate
that the main factors that affect the rate coefficient are HBD
and acceptor abilities of the media in ethaline-DMSO mix-
tures. Solvation data based on the preferential solvation model
log k , and the results are summarized in Table 4. Statistical
A
parameters and good agreement shown in Figure 3 confirm
the ability of Equation 6 in reproducing the reaction rate coef-
ficients. In the most of reactions, data show that f2/1 values are
less than a unit. It means that the reactions are preferentially
influenced by DMSO. On the other hand, the reactants and
activated complex of the reactions are preferentially solvated
by DMSO and the decreasing of DMSO in solvent compo-
sition has a dramatic effect on the reaction rate. In addition,
showed that the nonideal behavior of log k in solvent mix-
A
the low f
values reveal that in spite of the presence of the
tures can be related to the difference between the microsphere
12/1

8
HARIFI-MOOD AND KHORSHAHI
solvation of the solutes and the bulk composition of the sol-
vents. The reactants and activated complex of the reactions
were preferentially solvated by DMSO in the solvent mixtures.
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ACKNOWLEDGMENT
The authors gratefully acknowledge the financial support of
15. Harifi-Mood AR, Buchner R. Density, viscosity, and conductiv-
ity of choline chloride + ethylene glycol as a deep eutectic sol-
vent and its binary mixtures with dimethyl sulfoxide. J Mol Liq.
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Kharazmi University (Grant Number: D/2043).
ORCID
Ali Reza Harifi-Mood
https://orcid.org/0000-0002-7172-1660
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How to cite this article: Harifi-Mood AR, Khor-
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on structure-reactivity relationships. Int J Chem Kinet.
2019;1-9. https://doi.org/10.1002/kin.21273
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