Dimethyl sulfoxide/deep eutectic solvents mixtures as media in the reaction of 1-fluoro-2,4-dinitrobenzene with piperidine: A solvent effect study

Article abstract of DOI:10.1002/poc.3787

Aromatic nucleophilic substitution reaction of 1-fluoro-2,4-dinitrobenzene with piperidine was kinetically investigated in ethylene glycol-choline chloride and glycerol-choline chloride as 2 deep eutectic solvents (DESs) mixed with dimethyl sulfoxide, in

Full text of DOI:10.1002/poc.3787

Received: 8 June 2017
DOI: 10.1002/poc.3787
Revised: 1 October 2017
Accepted: 16 October 2017
R E S E A R C H A R T I C L E
Dimethyl sulfoxide/deep eutectic solvents mixtures as
media in the reaction of 1‐fluoro‐2,4‐dinitrobenzene with
piperidine: A solvent effect study
Ali Reza Harifi‐Mood
| Samira Sadrzadeh
Department of Chemistry, Kharazmi
University, Tehran, Iran
Abstract
Aromatic nucleophilic substitution reaction of 1‐fluoro‐2,4‐dinitrobenzene
Correspondence
with piperidine was kinetically investigated in ethylene glycol‐choline chlo-
ride and glycerol‐choline chloride as 2 deep eutectic solvents (DESs) mixed
with dimethyl sulfoxide, in whole mole fractions, at room temperature. The
investigation of the reaction in different concentrations of the piperidine
shows that the reaction follows the base‐catalyzed mechanism. The measured
rate coefficients of the reaction demonstrated a sharp decreasing in all mix-
tures with the increasing mole fraction of DESs. Linear free energy relation-
ship investigations confirm that hydrogen bond donor ability in addition to
polarity‐polarizability of the media has a major effect on the reaction rate.
The decrease in the rate coefficient is attributed to not only hydrogen‐
bonding donor interactions of the media with piperidine as both reactant and
catalyst but also the preferential solvation of reactants by DES compared with
the intermediate of the reaction.
Ali Reza Harifi‐Mood, Department of
Chemistry, Kharazmi University, Tehran,
Iran.
Email: harifi@khu.ac.ir; alireza.
harifi@gmail.com
KEYWORDS
deep eutectic solvent, 1‐fluoro‐2,4‐dinitrobenzenelinear free energy relationshipsolvent effect
1 | INTRODUCTION
As mentioned earlier, solvent effects are closely
related to the nature and extent of solute‐solvent interac-
Solvents play an important role in determining chemical
reactivity. In particular, the rate and/or mechanism of a
chemical reaction may change when the solvent is
changed.[1] Kinetics solvent effects on chemical reactions
in different media are usually correlated in terms of
solvent polarity which sums up all the specific and non‐
specific interactions of the media with initial and
transition states, in the other words, “solute‐solvent inter-
actions”.[2] However, the interpretation of the kinetic
results on the basis of the solvent polarity on the medium
sometimes fails and sometimes succeeds. A large effort
has been directed toward understanding such solvent
effects, and a great deal of progress has been made both
theoretically[3–7] and experimentally.[8–15]
tions. In many physical and chemical processes taking
place in a solution, binary mixtures of solvents are fre-
quently used as media in which solvent‐solvent interac-
tions as well as solute‐solvent interactions are
considered. Solute‐solvent interactions are much more
complex in mixed solvents than in pure solvents owing
to the possibility of preferential solvation by any of sol-
vents present in the mixture.[16] Moreover, the solvent‐
solvent interactions produced in solvent mixtures can
affect the solute‐solvent interactions; therefore, they can
also affect preferential solvation.[17,18]
For a few years, we have studied the aromatic nucleo-
philic substitution reactions in binary solvent mix-
tures.[10–12] Aromatic nucleophilic substitution reactions
J Phys Org Chem. 2017;e3787.
wileyonlinelibrary.com/journal/poc
Copyright © 2017 John Wiley & Sons, Ltd.
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HARIFI‐MOOD AND SADRZADEH
have been proposed to proceed through an addition‐
elimination mechanism (SNAr) involving the formation
of an intermediate complex.[8] This mechanism causes
that the reaction shows specific behavior based on
solvent effects.
2 | RESULTS AND DISCUSSION
As we have been mentioned in several contributions,[10,11]
the confirmed reaction mechanism of this reaction, as an
aromatic nucleophilic substitution, is given in Scheme 1
Some of our previous reports have been in non‐
conventional binary solvent media based on using an
ionic liquid as a moiety of mixed solvent systems.[10]
The complexity of even simple reactions in ionic liquids
is significantly greater than those of reactions in molecu-
lar solvents. In spite of that the ionic liquids have
recently attracted greater attention as environmentally
with
apparent
rate
coefficient
according
to
Equation (1).[10]
k1ðk2 þ k3½BꢀÞ
kA ¼
(1)
k−1 þ k2 þ k3½Bꢀ
where kA is the apparent second‐order rate coefficient and
B is piperidine as a base catalyst. The breakdown of the
zwitterionic intermediate can occur spontaneously (if
the formation of the product from intermediate is fast)
or by a base‐catalyzed mechanism (if the decomposition
of the intermediate to products is slow). In the former,
Equation (1) reduces to kA = k − 1, and in the latter,
Equation (1) is simplified to Equation (2).
benign alternatives to conventional organic solvents in
[19]
a variety of physical and chemical processes
and also
which their properties can be fine‐tuned by altering the
cationic or anionic moieties,[20] some ionic liquids suffer
from more or less some drawbacks such as toxicity,
preparation, and high cost in the process for use.[21]
Traditional ionic liquid and protic ionic liquid are highly
cost and toxic (in some case) for applied engineering
research.
ꢀ
ꢀ
k1
k1
kA ¼ k2
þ
k3
½Bꢀ
(2)
k−1
k−1
Deep eutectic solvents (DESs) are as an alternative
approach to the formation of ionic fluids that can be sim-
ply prepared via mixing of a quaternary ammonium salt
(eg, choline (2‐hydroxyethyl‐trimethylammonium) chlo-
ride that is vitamin B4) with salts or a hydrogen bond
donor (HBD) compound.[22] These liquids have physical
and solvent properties that are similar to ionic liquids
formed with discrete ions. DESs which are also called
ionic liquid analogues can be prepared using cheap and
non‐toxic materials. DESs not only have special properties
compared with traditional organic solvents, but also their
mixtures with other ordinary organic solvents may show
improved and favorable characteristics.[23–28] In this con-
tribution and in continuing our previous studies on chem-
ical kinetics in solvent mixtures,[10–12] we report here a
kinetic study of the reaction between 1‐fluoro‐2,4‐dinitro-
benzene (FDNB) and piperidine performed in various
compositions of ethylene glycol‐choline chloride
(ethaline), and glycerol‐choline chloride (glyceline) as 2
DESs mixed with dimethyl sulfoxide (DMSO) as a com-
mon aprotic molecular solvent at 25°C. These binary sys-
tems have demonstrated specific solvent‐solvent and
solute‐solvent interactions.[29] The correlation between
the kinetic data and the molecular‐microscopic solvent
parameters has been investigated and discussed using
the general linear free energy relationship (LFER) model.
2.1 | Reaction mechanism
In order to determine the catalyzed or non‐catalyzed
mechanism of the reaction, the influence of piperidine
concentration as a base on the reaction rate was studied
at different compositions of ethaline and glyceline mixed
with DMSO as solvent media. The variation of second‐
order rate coefficients of the reaction at various concen-
trations of piperidine is shown in Figures 1 and 2. The
plots show that the reaction follows the base‐catalyzed
mechanism in the solvent mixtures. A partly linear signif-
icant acceleration in apparent rate coefficient occurred
with the increase in piperidine concentration. A similar
base‐catalyzed mechanism has been also reported for aro-
matic nucleophilic substitution reactions in aprotic sol-
vents and their mixtures,[8] whereas we can find some
researches with non‐catalyzed mechanism in pure or
mixed protic solvents. [9–12] Although the hydrogen donor
groups of ethylene glycol are involved in strong interac-
tion with chloride anion in DES to stabilize the deep
eutectic mixtures and prevent them from solidifying,
ethaline and glyceline show high HBD abilities (Table 1)
and act as active DESs. It can be contributed to the
ammonium hydrogen of choline cation with minimum
electron density. Therefore, we expect that DESs show a
non‐catalyzed mechanism like protic solvents while they
k2
F
H
N
H
NO2
k1
+
N
N
HF
_
O2N
+
+
O2N
k-1
F
k3[B]
SCHEME 1 The reaction mechanism of
1‐fluoro‐2,4‐dinitrobenzene and piperidine
NO2
NO2
NO2

HARIFI‐MOOD AND SADRZADEH
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TABLE 1 The second‐order rate coefficients of the reaction (at
2.0 × 10−4 M of piperidine) and solvatochromic parameters in
ethaline‐DMSO mixtures at 25°C
xethaline
kA (M−1 s−1
)
ETN
π*
α
β
0.0
425
0.44
1.01
0.13
0.98
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.1
1.0
88.0
44.3
16.3
10.3
5.80
5.95
5.60
3.81
2.76
2.59
0.61
0.63
0.66
0.71
0.73
0.76
0.78
0.81
0.83
0.84
1.03
1.04
1.04
1.05
1.05
1.05
1.04
1.06
1.06
1.12
0.46
0.49
0.57
0.67
0.71
0.77
0.81
0.86
0.91
0.88
0.92
0.91
0.91
0.91
0.88
0.86
0.84
0.79
0.76
0.53
FIGURE 1 Base‐catalyzed behavior of the second‐order rate
coefficient of the reaction in various concentrations of piperidine
and different compositions of the ethaline‐DMSO. Inset curve shows
the slope of Equation (2) as a catalytic factor
the reaction is controlled by the catalytic rate coefficient,
k3, of the mechanism. Moreover, the sharper variation in
glyceline‐DMSO systems compared with ethaline‐DMSO
media can be attributed to the effect of more numbers of
free DMSO molecules which don't attend in solvent‐sol-
vent interactions.[29] Based on preferential solvation, the
presence of complex molecules, produced from interac-
tion between DMSO and DES, is more observable in
ethaline‐DMSO than those in glyceline‐DMSO.[29] This
different behavior can predict that DMSO will appear as
a more effective portion in glyceline‐DMSO compared
with ethaline‐DMSO mixtures.
2.2 | Solvent‐reactivity correlations
In order to investigate and evaluate the solvent effects on
the reaction in DMSO‐DES mixtures and interpret above
results, the second‐order rate coefficients, kA, of the reac-
tion were obtained at 25°C by the experimental pseudo‐
first‐order rate coefficients and are summarized in
Tables 1 and 2 in different compositions of mixed sol-
vents. Results show that the second‐order rate coefficient
decreases in ethaline and glyceline while its value is con-
siderably higher in DMSO. In the solvent mixtures, the
rate coefficient of the reaction decreases sharply with
the DES content. Negative deviation from ideal behavior,
consisting of the dramatic decrease of the rate coefficient
in low concentration of DES and then its smooth varia-
tions to its corresponding value in neat DES, proves that
the molecules are preferentially solvated by DES. To
determine the incidence of each type of solvent properties
on the kinetics of the reaction, LFER correlations based
on specific and non‐specific solute‐solvent interactions
were investigated. This model is based on the single or
FIGURE 2 Base‐catalyzed behavior of the second‐order rate
coefficient of the reaction in various concentrations of piperidine
and different compositions of the glyceline‐DMSO. Inset curve
shows the slope of Equation (2) as a catalytic factor
demonstrate a weak based‐catalyzed mechanism for this
reaction. It seems that the DMSO moiety of the solvent
enhances the base‐catalyzed characterization of the reac-
tion as an aprotic solvent in mixtures.
The upward trends of the rate coefficients in the inves-
tigated mixed solvent compositions demonstrate an expo-
nential increase in slope with increasing of the DMSO
mole fraction (inset curves of Figures 1 and 2). It can be
claimed that the special molecular characteristic of DMSO
is the most important factor to control the reaction mech-
anism. According to Equation (2), the catalytic slope of

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HARIFI‐MOOD AND SADRZADEH
TABLE 2 The second‐order rate coefficients of the reaction (at
2.0 × 10−4 M of piperidine) and solvatochromic parameters in
glyceline‐DMSO mixtures at 25°C
decreases as HBD acidity of the media increases. Because
of the base‐catalyzed mechanism of the reaction, the exis-
tence of free piperidine molecules is a necessity in the
reaction media, and therefore HBD interactions reduce
the available piperidine molecules as catalyst.
xglyceline
kA (M−1 s−1
)
ETN
π*
α
β
0.0
425
0.44
1.01
0.13
0.98
The activated complex leading to the zwitterionic
intermediate (Scheme 1) is expected to have the zwitter-
ionic character and to be favored by the increase in the
normalized polarity parameter, because zwitterionic mol-
ecules were more stabilized in high‐polar media than in
the media with lower polarity. In spite of our expectation,
it is interesting that a reverse result was observed. This is
in contrast to previous researches in ionic liquids
media.[10] In spite of that reline and glyceline as 2 com-
mon DESs have ionic characterization like ionic liquids,
they don't show similar effects on this SNAr reaction as
a solvent. It might be due to weak solute‐solvent interac-
tion in zwitterionic intermediate on one hand and the
strong interaction of the solvent with reactants and also
preferentially solvating by DES on the other hand.
Among dual‐parameter correlations, it seems that all
of them except 1 case show similar acceptable results. A
meticulous investigation in data, especially in all mix-
tures, confirms that the best correlation with reasonable
statistical factor consisting of regression coefficient, stan-
dard deviation, Fischer factor, and the significant values
of the parameters is between logkA with π* and α. It is
exactly compatible with single parameter correlations that
showed the best correlated data of logkA with ENT and α,
individually and separately. Because the normalized
polarity parameter is a blend of dipolarity‐polarizability
and the HBD acidity of the media,[1] we can claim that
the correlation of logkA with π* and α is the pure model
based on LFER method. Figures 3 and 4 show the ability
of mentioned dual‐parameter correlation in the reproduc-
tion of the reaction‐rate coefficients.
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.1
1.0
43.9
19.5
5.90
5.85
3.67
2.83
2.80
2.82
2.97
3.03
0.61
0.65
0.69
0.72
0.75
0.77
0.79
0.80
0.83
0.85
1.07
1.09
1.10
1.10
1.10
1.10
1.10
1.10
1.10
1.09
0.43
0.50
0.59
0.66
0.71
0.75
0.80
0.82
0.88
0.94
0.94
0.94
0.88
0.86
0.81
0.77
0.73
0.67
0.65
0.59
multi‐parameter correlations between the logkA of the
reaction and the solvatochromic parameters of the media.
Multi‐parameter regression can be usually used when
combination of some of the solvent properties can affect
the rate coefficient. The solvatochromic parameters for
solutions of DMSO with ethaline and glyceline at various
compositions have been determined in our laboratory
(Tables 1 and 2).[29]
The hydrogen bond acceptor (HBA) ability, β, values
of the solvents decrease slowly with increasing of the
mole fraction of DES; thus, it can be expected that the
reaction rate coefficient depends on β. Despite this agree-
ment, the comparative statistical data of Table 3 demon-
strate a weak correlation between logkA and β in all
mixtures. While a different trend is observed in the π*
parameter, the correlations of logkA with π* show a little
bit better results than those with β but not reasonable.
On the other hand, solvatochromic parameter data in
Tables 1, 2 demonstrate an increasing trend, but sharply,
in ENT and α values. In contrast to this variation, the rate
coefficients of the reaction show a sharp decreasing to
its corresponding value in DES in all mixtures. These var-
iations accompany with a smooth positive and negative
deviation in ENT and α values and rate coefficients data,
respectively. Statistical data show the better correlation
of logkA with these parameters than the others, and there-
fore it can be demonstrated that the empirical polarity
and HBD of the media play an important role in DMSO‐
DES mixtures. As can be seen, the second‐order rate coef-
ficient of the reaction decreases with the increase in the
normalized polarity parameter and HBD of the media.
In the presence of piperidine, DESs are known to act
as HBD, and therefore, piperidine is stabilized via hydro-
gen‐bonding interactions with HBD and the reaction rate
On the other hand, standardized coefficients of the
solvent properties in dual‐parameter correlation show
that the HBD ability of the media as a specific interaction
of the solvent is a preferable and effective parameter,
compared with nonspecific interactions such as
dipolarity‐polarizability of the media. This different effect
is considerable in ethaline‐DMSO mixtures.
3 | EXPERIMENTAL
3.1 | Materials
Choline chloride (>99%), ethylene glycol (99.8%, anhy-
drous), glycerol (>99.5% spectrophotometric grade), and
spectroscopic grade of DMSO were purchased from Merck
(all materials in high purity grade). FDNB was available

HARIFI‐MOOD AND SADRZADEH
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HARIFI‐MOOD AND SADRZADEH
FIGURE 3 The calculated values of logkA, according to its
correlation with π* and α, versus the experimental values in
ethaline‐DMSO mixtures
FIGURE 4 The calculated values of logkA, according to its
correlation with π* and α, versus the experimental values in
glyceline‐DMSO mixtures
from Fluka and was used without further purification.
Piperidine was supplied by Merck and used freshly after
distillation.
In order to obtain ethaline and glyceline, choline
chloride was mixed with ethylene glycol and glycerol,
respectively, in a molar ratio of 1:2 and stirred under
heating (near 80°C) until a homogeneous colorless liquid
was formed.
3.2 | Kinetic measurements
The stability of the product (prepared by addition of
piperidine and the alcoholic solution of FDNB and

HARIFI‐MOOD AND SADRZADEH
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recrystallized from ethanol) was tested in all solvent com-
positions for 24 hours. The reaction kinetics were studied
spectrophotometerically in different mixtures of DESs
with DMSO, which had been gravimetrically prepared
(0.1 mg), by running the reaction in the thermostatted
cells of a spectrophotometer at 25°C. A GBC Cintra 101
spectrophotometer coupled with a thermocell was used
with 1.00‐cm silica cells. The absorbances of media were
measured at a wavelength around 370 to 380 nm, corre-
sponding to product absorbance and depending on the
type of solvent. Other components such as solvents, reac-
tants, and intermediates were not absorbed at these wave-
lengths. Concentrations of FDNB and piperidine were
selected 2.0 × 10−6 and 2.0 × 10−4 M, respectively. There-
fore, the reaction was studied under pseudo‐first‐order
conditions. All experiments were carried out at least in
triplicate and the results averaged.
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Mixture of ethaline and glyceline as 2 common DESs with
DMSO showed different behavior compared with ionic
liquid‐molecular solvents mixtures used as reaction
media. HBD and dipolarity‐polarizability of the solvent
affect the reaction rate. It seems that the preferential sol-
vation of the reactants by DES and also the stabilization
of the piperidine because of HBD interactions lead the
reaction to low rate in high polar and HBD mixtures.
Normalized polarity, dipolarity‐polarizability, and HBD
ability of media have parallel and negative effects on the
rate of the reaction. On the other hand, the reaction
follows the catalyzed mechanism by piperidine in the
solvent mixtures. HBD interactions decrease easy access
to free piperidine molecules in order to attend in the
reaction mechanism. Thus, HBD ability of the solvent is
an important factor to control the reaction rate.
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How to cite this article: Harifi‐Mood AR,
Sadrzadeh S. Dimethyl sulfoxide/deep eutectic
solvents mixtures as media in the reaction of 1‐
fluoro‐2,4‐dinitrobenzene with piperidine: A
solvent effect study. J Phys Org Chem. 2017;e3787.
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