Reactivity of arenesulfinic acids as nucleophiles in the addition reaction to 2-haloacrylonitriles

Article abstract of DOI:10.1002/jccs.200700062

The nucleophilic addition reactions of both the non-substituted and p-substituted benzenesulfinic acids with 2-chloro- and 2-bromoacrylonitriles have been studied. The structures of the 3-benzenesulfonyl-2- halogenopropanenitriles thus obtained were confi

Full text of DOI:10.1002/jccs.200700062

Journal of the Chinese Chemical Society, 2007, 54, 447-452
447
Reactivity of Arenesulfinic Acids as Nucleophiles in the Addition Reaction
to 2-Haloacrylonitriles
D. Zvezdova,* S. Stoeva and D. Aleksiev
Department of Organic Chemistry, Bourgas Assen Zlatarov University, 8010 Bourgas, Bulgaria
The nucleophilic addition reactions of both the non-substituted and p-substituted benzenesulfinic ac-
ids with 2-chloro- and 2-bromoacrylonitriles have been studied. The structures of the 3-benzenesulfonyl-
2-halogenopropanenitriles thus obtained were confirmed by microanalytical and spectral methods. The
basic kinetic parameters of the reactions were determined and some local electronic descriptors concern-
ing the reaction centers were calculated. For the interaction with benzenesulfinic acids, 2-bromoacrylo-
nitrile was found to have higher reactivity as a Michael acceptor than 2-chloroacrylonitrile. The higher re-
activity of 2-bromoacrylonitrile is associated with the higher electrophilicity of its b-carbon atom, which
was proved by its pronounced acceptor delocalizability and increased reaction rate values with the corre-
sponding benzenesulfinic acids.
Keywords: 2-Chloro(bromo)acrylonitriles; Benzenesulfinic acids; Nucleophilic addition.
INTRODUCTION
RESULTS AND DISCUSSION
The interaction of sulfinic acids with alkenes, con-
taining electron-withdrawing functional groups such as
COCH3, CONH2, COOCH3, CN, SO2CH3, NO2, etc., has
been studied by a number of authors.1-8 Regardless of their
strong acidities, sulfinic acids act mostly as S-nucleophiles
rather than O-nucleophiles because of the presence of an
unshared electron pair at the sulfur atom.9 The addition of
sulfinic acids to a,b-unsaturated nitriles is known to result
in the preparation of b-cyanosulfones.1 The high reactivity
of acrylonitriles corresponds to their high polarity and,
hence, participation as reactants in similar non-catalytic re-
actions.1,9-11 On the other hand, haloacrylonitriles represent
a special group of Michael acceptors, which is due to the
additional effect exerted by the halogen atom on the reac-
tivity of an unsaturated system.12-15 Therefore, we have ob-
tained some adducts of non-substituted and substituted
benzenesulfinic acids with 2-chloro(bromo)acrylonitriles.
The aim of the present study was to make quantitative esti-
mation of the reactivity of these compounds, particularly
the haloacrylonitriles with respect to their interaction with
benzenesulfinic acids. This task was accomplished by de-
termining some basic kinetic parameters of the nucleo-
philic addition reactions studied, and the results were juxta-
posed to the reactivity indexes of haloacrylonitriles.
The interaction of sodium arenesulfinates with halo-
acrylonitriles occurs according to the following reaction
Scheme I.
The adducts 3a-f were prepared in water-alcohol me-
dium by using 0.04 M acetate buffer with an ionic strength
of 0.24 at pH 4.22. Maintaining certain acidity of the reac-
tion medium hindered the elimination of hydrogen halide
during the synthesis.9 Moreover, catalytic amounts of
hydroquinone were added to the reaction mixture in order
to avoid polymerization of the haloacrylonitriles, which
usually takes place as a side reaction during the nucleo-
philic addition of an anion by a Michael-type reaction.16
The composition and structure of the 3-arenesulfo-
nyl-2-halogenopropanenitriles prepared were confirmed
by elemental microanalysis, IR and 1H-NMR spectroscopy
(Tables 1 and 2). The absorption bands, corresponding to
the asymmetric and symmetric stretching vibrations of the
sulfonyl group, were registered at 1315-1300 cm-1 and
1140-1130 cm-1, respectively.9 A medium-intensity band at
1090-1080 cm-1 can be assigned to the S-aryl stretching vi-
brations. Absorption bands within 1640-1440 cm-1 corre-
sponding to skeletal-type vibrations for aromatic nucleus
were also observed. The bending C-H aryl vibration within
the 830-790 cm-1 region indicated the presence of a p-sub-
* Corresponding author. E-mail: dzvezdova@yahoo.com

448 J. Chin. Chem. Soc., Vol. 54, No. 2, 2007
Zvezdova et al.
Scheme I
Table 1. Physical and analytical data for compounds 3a-f
Yield
(%)
Tm
Molecular
formula
Molar mass
(g mol-1)
Analysis, calcd (found) (%)
No
Compound
(°C)
C
H
N
S
Cl
47.06
3.51
6.10
13.96
SO2 CH2
CH
SO2 CH2
SO2 CH2
3a
3b
3c
3d
3e
3f
74
80
91
85
82
94
102-103 C9H8ClNO2S
229.68
243.71
264.13
274.13
288.16
308.58
(46.80) (3.25) (5.97) (13.55)
49.28 4.14 5.75 13.16
(48.95) (4.03) (5.51) (12.89)
40.93 2.67 5.30 12.14
(39.92) (2.39) (5.01) (11.89)
39.43 2.94 5.11 11.70
(39.10) (2.63) (4.80) (11.40)
41.68 3.50 4.86 11.13
(41.40) (3.20) (4.51) (10.82)
35.03 2.29 4.54 10.39
CN
Cl
H3C
Cl
CH
80-81
92-93
C10H10ClNO2S
C9H7Cl2NO2S
CN
Cl
CH
CN
Br
SO2 CH2
CH
SO2 CH2
SO2 CH2
133-134 C9H8BrNO2S
122-123 C10H10BrNO2S
CN
Br
H3C
Cl
CH
CH
CN
Br
CN
97-98
C9H7BrClNO2S
(34.90) (2.32) (4.30) (9.84)
Table 2. Spectroscopic data for compounds 3a-f
IR data
n (cm-1)
1H-NMR (CDCl3)
No
Compound
d (ppm)
as
Cl
1310 (n ); 1130 (nSsO );
3a
SO2
3.80 (d, 2H, CH2); 4.93 (t, 1H, CH);
7.26-7.99 (m, 5H, Ar-H)
2
SO2 CH2
CH
CN
1090 (nAr-S ); 2235 (nCºN
)
as
1312 (n ); 1135 (nSsO );
3b
3c
3d
3e
3f
Cl
SO2
2.40 (s, 3H, CH3); 3.75 (d, 2H, CH2);
2
SO2 CH2
H3C
Cl
CH
CN
4.90 (t, 1H, CH); 7.20-7.80 (m, 4H, Ar-H)
1085 (nAr-S ); 2233 (nCºN
)
as
Cl
1305 (n ); 1140 (nSsO );
SO2
3.87 (d, 2H, CH2); 4.90 (t, 1H, CH);
7.26-7.99 (m, 4H, Ar-H)
2
SO2 CH2
CH
CN
1080 (nAr-S ); 2230 (nCºN
)
as
1315 (n ); 1140 (nSsO );
Br
SO2
3.80 (d, 2H, CH2); 4.90 (t, 1H, CH);
7.30-7.91 (m, 5H, Ar-H)
2
SO2 CH2
CH
CN
1080 (nAr-S ); 2235 (nCºN
)
as
Br
1310 (n ); 1135 (nSsO );
SO2
2.40 (s, 3H, CH3); 3.85 (d, 2H, CH2);
2
SO2 CH2
SO2 CH2
H3C
Cl
CH
CH
CN
4.90 (t, 1H, CH); 7.30-7.90 (m, 4H, Ar-H)
1090 (nAr-S ); 2235 (nCºN
)
as
1315(n ); 1135 (nSsO );
Br
SO2
3.79 (d, 2H, CH2); 4.89 (t, 1H, CH);
7.28-7.88 (m, 4H, Ar-H)
2
CN
1090 (nAr-S ); 2235 (nCºN
)

Reactivity of Arenesulfinic Acids as Nucleophiles
J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 449
stituted benzene ring for compounds 3b, c, e, f. The stretch-
ing C-H aryl vibrations were observed in the interval 3100-
3000 cm-1. In the same interval, a characteristic multiplet
with decreasing intensities of higher frequencies was regis-
tered. A series of overtone and composite frequencies were
observed in the range 2000-1650 cm-1 and were found to be
rather more selective towards the type of substitution in the
ring. The stretching vibrations for the carbon-halogen bond
were registered at 680-640 cm-1. An absorption maximum
characteristic for the stretching vibrations of cyano group
was observed at 2235-2230 cm-1. The presence of a halogen
atom at the a-position towards the cyano group decreased
significantly the band intensity (Table 1).
der the influence of the electron-withdrawing effect of sul-
fonyl group. The chemical shift of these protons was not af-
fected by the type of substituent (electron-donating or elec-
tron-withdrawing) located at p-position in the aromatic
ring. Methyne protons were the least shielded ones (d
4.89-4.93 ppm). This was determined by the presence of
halogen atoms (Cl, Br), a cyano group and benzenesulfonyl
fragment, regardless of the fact that the latter was not di-
rectly bound to the methyne carbon. For comparison,
chemical shifts of protons in bromo- and chloroacetoni-
triles are known to correspond to d 3.7 and 4.1 ppm, respec-
tively.17 If the compounds studied were regarded as struc-
tural analogues of the abovementioned haloacetonitriles, in
which one hydrogen was replaced by a benzenesulfonyl-
methyl fragment, this would result in chemical shift of the
resonance signal towards the weaker field by approxi-
mately a unity (Table 2).
Resonance signals for methyl (3H), methylene (2H),
methyne (1H) and aromatic (Ar-H) protons were observed
in the 1H-NMR spectra of the compounds studied17 (Table
2). Under the influence of the negative inductive effect of
the aromatic ring, the chemical shift of methyl protons was
registered at d 2.40 ppm. Methylene protons gave a reso-
nance signal even in a weaker field (d 3.79-3.85 ppm) un-
The principal kinetic parameters for the interaction of
non-substituted and substituted arenesulfinic acids with
2-chloro(bromo)acrylonitriles are presented in Table 3.
Table 3. Basic kinetic parameters related to the addition reaction of benzenesulfinic acids to 2-chloro- and 2-
bromoacrylonitriles
¹
Temperature
(K)
Rate constant
(M-1s-1 ´ 104)
E
DH
(kJ mol-1)
Nucleophile
Substrate
(kJ mol-1)
298
303
308
313
318
298
303
308
313
318
298
303
308
313
318
298
303
308
313
318
298
303
308
313
318
0.58
0.99
1.35
1.88
3.28
0.79
1.11
2.09
2.80
3.43
0.46
0.72
1.20
1.90
2.83
0.95
1.47
1.99
3.63
4.35
0.61
1.13
1.60
2.80
3.59
1a
2a
64.71
61.37
73.00
62.93
70.99
62.15
58.81
70.44
60.37
68.43
1b
1c
1a
1c
2a
2a
2b
2b

450 J. Chin. Chem. Soc., Vol. 54, No. 2, 2007
Zvezdova et al.
The measurements conducted at 298 K showed that this
was a second-order reaction, i.e., of the first order towards
each of the reactants within the concentration range of 0.01
M-1 M. The exact experimental values of the reaction order
for the interaction between benzenesulfinic acid and 2-
bromoacrylonitrile were 1.62 (determined by Van’t Hoff’s
method) and 1.72 (calculated by the half-time method). For
the nucleophilic addition of benzenesulfinic acid to 2-chlo-
roacrylonitrile, these values were 1.62 and 1.77, respec-
tively.
same nucleophile was determined by the differences in the
electrophilicity of their b-carbon (Cb or C3) atom. As can be
seen from Table 4, the C3 in 2-bromoacrylonitrile was a
stronger electrophilic center than the corresponding carbon
in 2-chloroacrylonitrile which was proved by both the high
value of its acceptor delocalizability (SN(C3) = 0.254
(a.u.)2/eV) and low negative value of its atomic charge
(q(C3) = -0.123 a.u.). Generally, the electrophilicity of the
C3 atom in haloacrylonitriles was higher than that of the C3
atom in non-substituted acrylonitrile, and this was associ-
ated with the electronic effects of chlorine and bromine at-
oms (-I, +M). Bearing in mind the higher electronegativity
of a chlorine atom (3.0) compared to bromine (2.8),22 one
should expect stronger polarizability of the double bond in
2-chloroacrylonitrile. However, there is more effective
conjugation of the unshared electrons at chlorine with the
2p orbital of a carbon atom, compared to the bulkier bro-
mine. As a result, the acceptor delocalizability value of C3
atom in 2-chloroacrylonitrile became lower than that of
2-bromoacrylonitrile (SN(C3) = 0.248 (a.u.)2/eV). There-
fore, the ability of the C3 (b-carbon) atom in 2-chloro-
acrylonitrile to bind to nucleophilic reactants was less pro-
nounced than that of 2-bromoacrylonitrile, regardless of
the lower C2-C3 bond order for the latter (Table 4). Appar-
ently, the local electrophilicity of a b-carbon atom in 2-
haloacrylonitriles was mainly determined by conjugation
rather than inductive effects of the halogen atoms attached.
The kinetic studies for the compounds listed in Table
3 were carried out within the temperature range of 298-318
K. An analysis of the second-order rate constants showed
that a temperature increase of 10 K resulted in values 2 to
2.5 times higher than the basic ones, which corresponded to
Van’t Hoff’s empirical rule.18 The values of rate constants
depended mainly on the electron density at the reaction
centers such as the sulfonyl group of the benzenesulfinate
ion and the b-carbon atom of haloacrylonitriles. Depending
on the structure of the substrate and the reactant, the fol-
lowing trends in the change of the rate constants should be
noted:
1. With the same substrate (e.g., 2-chloroacryloni-
trile), higher rate constants were associated with benzene-
sulfinic acid containing an electron-donating substituent
such as a methyl group as compared to non-substituted
benzenesulfinic acid or acid containing an electron-with-
drawing substituent (chlorine). The increased nucleophil-
icity of 4-methylbenzenesulfinate ion was also confirmed
by the higher value of the donor delocalizability of its sul-
fur atom (SE(S) = 0.2496 (a.u.)2/eV) compared to that of
the sulfur atom in benzenesulfinate ion (SE(S) = 0.2444
(a.u.)2/eV). These parameters were calculated by employ-
ing the MOPAC 93 quantum-chemical method.19,20 As a re-
sult, the activation energy for the addition reaction of 4-
methylbenzenesulfinate ion with 2-chloroacrylonitrile had
the lowest value (E = 61.37 kJ mol-1).
EXPERIMENTAL
Apparatus
Elemental microanalyses of the compounds studied
were performed using a Carlo Erba 1104 instrument (Italy).
Infrared spectra were recorded with a Specord 75 IR instru-
ment (Germany). The samples were prepared as KBr pel-
2. The interaction of sodium benzenesulfinate (1a)
with 2-bromoacrylonitrile (2b) took place at a higher rate
than the reaction with 2-chloroacrylonitrile (2a) at the
same temperature within the interval studied. This was also
observed in the presence of sodium 4-chlorobenzenesul-
finate (1c) as nucleophilic reactant. Similar reactivity pat-
terns were found earlier for the reaction of sodium arene-
sulfinates with 2-bromo-2-nitroethenylbenzenes.21
Apparently, the difference in the reactivity of 2-bro-
mo- and 2-chloroacrylonitriles for their reaction with the
Table 4. Reactivity indices of acrylonitrile and its halogenated
derivatives determined by MOPAC 93 program
SN(C3)
((a.u.)2/eV)
q(C3)
(a.u.)
p-order of
Compound
C2-C3 bond
2
3
CH2
1
CN
0.237
0.248
-0.156
-0.155
1.928
1.887
CH
Cl
C
CH2
CN
Br
C
CH2
0.254
-0.123
1.894
CN

Reactivity of Arenesulfinic Acids as Nucleophiles
J. Chin. Chem. Soc., Vol. 54, No. 2, 2007 451
1
lets. H-NMR spectra were recorded at 250 MHz with a
The concentrations of sulfones thus obtained were deter-
mined by measuring their absorptions at 315 nm on a Specol
spectrometer. Consequently, the concentrations of ben-
zenesulfinic acids reacting under the selected conditions
were calculated. The experimental data obtained were con-
sistent with a second-order kinetic equation and were pro-
cessed by employing linear regression analysis with corre-
lation coefficients exceeding 0.90, which proved the rele-
vancy of the linear approximation.
Bruker DRX-250 spectrometer in CDCI3 solution. Chemi-
cal shifts were expressed in ppm with reference to tetra-
methylsilane (TMS) as an internal standard. The melting
temperatures (Tm) were determined from the thermogravi-
metric (TG) scans obtained in air (static atmosphere) by us-
ing MOM Derivatograph OD-102 (Hungary) at a heating
rate of 6 K/min. For the purpose of kinetic studies, a Specol
HACH DR 2000 spectrophotometer (Germany) was used.
The second-order rate constants, the activation en-
ergy and enthalpy of activation were calculated according
to known procedures.18
Materials
All the substituted and non-substituted sodium ben-
zenesulfinates were prepared by known procedures, em-
ploying reduction of the corresponding benzenesulfonyl-
chlorides with 50% excess of sodium sulfite.23 2-Chloro-
and 2-bromoacrylonitriles were obtained by dehydrohalo-
genation of the corresponding 2,3-dichloro- or 2,3-dibro-
moacrylonitriles in the presence of sodium acetate as cata-
lyst.24,25 The composition and the structure of the com-
pounds were proved by elemental microanalysis and IR
spectroscopy data.
Calculation of Electronic Descriptors
Molecular geometry of the corresponding sodium
benzenesulfinates, acrylonitrile and 2-haloacrylonitriles
were optimized. Then the quantum-chemical descriptors
were calculated using the AM1 Hamiltonian method of the
MOPAC 93 program, a semi-empirical molecular model-
ing routine.19,20 The following local electronic descriptors
were determined: donor delocalizibility of a sulfur atom
(SE(S)) for some benzenesulfinate ions; acceptor delocali-
zibility of a C3 atom (SN(C3)) in acrylonitrile and its halo-
genated derivatives; charges of a C3 atom (q(C3)) for the
same acrylonitriles. The higher values of SE and SN corre-
sponded to stronger nucleophilicity and electrophilicity of
the atomic reaction center, respectively.27
General Procedure for Preparation of Compounds
3a-f
To a solution of 0.01 mol sodium arenesulfinate in 10
cm3 distilled water, 0.01 mol of glacial acetic acid was
added. Then, a solution of 0.01 mol 2-chloro or 2-bromo-
acrylonitrile in 15 cm3 ethanol and a catalytic amount of
hydroquinone were introduced into the reaction mixture.
Haloacrylonitriles were allowed to react with the corre-
sponding benzenesulfinic acids for 48 hours at 291-293 K.
The crystalline products obtained were filtered and purified
by recrystallization from ethanol. These products were
found to be stable on prolonged storage in air and were sol-
uble in chloroform, acetone and 1,4-dioxane but insoluble
in water, n-hexane and petroleum ether. The yields ob-
tained varied within the range of 74-94% (Table 1).
ACKNOWLEDGEMENTS
The authors wish to thank Prof. O. Mekenyan (Head
of the Laboratory of Mathematical Chemistry, Bourgas
Assen Zlatarov University) for the opportunity to apply the
MOPAC 93 software for evaluation of the reactivity of the
compounds under study.
Rate Measurements
Received November 23, 2005.
The reaction mixtures for the kinetic measurements
were prepared as described above. The mixtures were ther-
mostated at the desired temperature and aliquots were
taken at certain time intervals and were diluted with etha-
nol. An excess of aqueous solution of p-benzoquinone was
then added in order to convert the unreacted benzenesul-
finic acids into 2,5-dihydroxydiphenyl sulfones or 2,5-di-
hydroxy-4¢-substituted diphenyl sulfones respectively.26
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