Reaction of aniline with ammonium persulphate and concentrated hydrochloric acid: Experimental and DFT studies

Article abstract of DOI:10.2478/s11696-012-0163-1

In this paper, the reaction of aniline with ammonium persulphate and concentrated HCl was studied. As a result of our experimental studies, 2,4,6-trichlorophenylamine was identified as the main product. This shows that a high concentration of HCl does not favour oxidative polymerisation of phenylamine, even though the ammonium persulphate/HCl system is widely used in polyaniline synthesis. On the basis of the experimental data and density functional theory for reaction path modelling, we proposed a mechanism for oxidative chlorination of aniline. We assumed that this reaction proceeded in three cyclically repeated steps; protonation of aniline, formation of singlet ground state phenylnitrenium cation, and nucleophilic substitution. In order to confirm this mechanism, kinetic, thermochemical, and natural bond orbital population analyses were performed.

Full text of DOI:10.2478/s11696-012-0163-1

Chemical Papers 66 (7) 699–708 (2012)
DOI: 10.2478/s11696-012-0163-1
ORIGINAL PAPER
Reaction of aniline with ammonium persulphate and concentrated
hydrochloric acid: Experimental and DFT studies
Maciej Przyby ꢀl ek*, Jerzy Gaca
Department of Chemistry and Environmental Protection, Faculty of Chemical Technology and Engineering,
University of Technology and Life Sciences, 85-326 Bydgoszcz, Poland
Received 31 October 2011; Revised 11 February 2012; Accepted 14 February 2012
In this paper, the reaction of aniline with ammonium persulphate and concentrated HCl was
studied. As a result of our experimental studies, 2,4,6-trichlorophenylamine was identified as the
main product. This shows that a high concentration of HCl does not favour oxidative polymerisation
of phenylamine, even though the ammonium persulphate/HCl system is widely used in polyaniline
synthesis. On the basis of the experimental data and density functional theory for reaction path
modelling, we proposed a mechanism for oxidative chlorination of aniline. We assumed that this
reaction proceeded in three cyclically repeated steps; protonation of aniline, formation of singlet
ground state phenylnitrenium cation, and nucleophilic substitution. In order to confirm this mech-
anism, kinetic, thermochemical, and natural bond orbital population analyses were performed.
ꢀ
c 2012 Institute of Chemistry, Slovak Academy of Sciences
Keywords: oxidative chlorination, 2,4,6-trichloroaniline, DFT
Introduction
When considering the reaction of aromatic amine
with peroxides and aqueous HCl (HClaq), two main
pathways should be generally taken into account:
oxidative chlorination and oxidative polymerisation.
It is commonly known that aniline is very unstable
in the presence of oxidants. The ammonium persul-
phate ((NH4)2S2O8)/HClaq system is widely used in
polyaniline synthesis (Chiang & MacDiarmid, 1986;
MacDiarmid et al., 1987, 1991; Mattoso et al., 1994).
However, some of the N- and C-substituted aniline
−
The presence of oxidants, Cl and many differ-
ent kinds of organic compounds in the reaction mix-
ture can contribute to the formation of chloro–organic
species. Oxidative chlorination reactions have a great
significance in modern organic synthesis and the nat-
ural environment (Sasson, 1995; Gribble, 2003). In
general, the mechanisms for the formation of chloro–
organic compounds are very diverse because there are
−
−
many kinds of chlorinating agents such as Cl , Cl2,
HCl, HOCl, Cl . This is why so many organic species
derivatives can be chlorinated by Cl in the pres-
.
ence of peroxides without yielding large amounts
of oxidation by-products, e.g. oxidative chlorina-
tion of N-phenylacetamide (acetanilide) is an effec-
tive method of obtaining 2,4,6-trichlorophenylamine
can be converted into chloro–organic compounds.
The reaction mechanism can be quantitatively and
qualitatively described by means of experimental and
theoretical tools. Probably mainly due to the low com-
putation cost, density functional theory (DFT) calcu-
lations are very common in reaction path modelling.
Nevertheless, the results of studies of reactions ob-
tained with the use of DFT methods are often in very
good agreement with experimental data (Zheng et al.,
˙
(2,4,6-trichloroaniline, 2,4,6-TCA) (Gaca & Zak,
1997). It is worth noting that C-substituted pheny-
lamine (aniline) derivatives can be chlorinated with
a good yield (up to 80 %) in the presence of
HClaq and H2O2 (Vyas et al., 2003). Studies on
the oxidative chlorination of p-nitrophenylamine (p-
nitroaniline) with the use of many different peroxides
2
010; Szaleniec et al., 2006; Dračínský et al., 2010).
*Corresponding author, e-mail: przybylek@mail.utp.edu.pl

7
00
M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
like M2S2O8 (where M = NH4, Na, K) and H2O2
showed that the yield of chlorinated products is the
highest when the reaction proceeds in the presence of
In order to obtain accurate results in reactions involv-
ing protonation and deprotonation, Gibbs free energy
of hydrated H (∆G(H )aq) was calculated from the
+
+
(NH4)2S2O8 (Kowalska & Gaca, 2002).
Eqs. (1) and (2).
It is commonly accepted that the oxidative poly-
+
+
+
merisation of aniline is usually carried out in diluted
HClaq (Chiang & MacDiarmid, 1986; MacDiarmid et
al., 1987, 1991; Mattoso et al., 1994). To the best of
our knowledge, there is no information in the litera-
ture about the reaction of non-substituted aniline with
Ggas(H ) = Hgas(H )−T Sgas(H )
(1)
(2)
+
+
+
∆
G(H )aq=Ggas(H )+∆Ghydr(H )
+
−1
Where Hgas(H ) = 2.5RT (6.19 kJ mol ) and
(
NH4)2S2O8 in the presence of concentrated HClaq.
+
−1
TSgas(H ) = 32.47 kJ mol (Tawa et al., 1998; Topol
The purpose of this paper is to contribute towards fill-
ing this gap by presenting the results of our empirical
and theoretical studies.
et al., 2000; Pokon et al., 2001; Liptak & Shields,
001), R is gas constant, T represent temperature,
Hgas(H ) is gas-phase enthalpy of H , Sgas(H ) is
gas-phase entropy of H , and Ggas(H ) is gas-phase
Gibbs free energy of H We used the experimental
value of Gibbs free energy of hydration ∆Ghydr(H )
–1104.58 kJ mol , which is accepted as the most
accurate (Camaioni & Schwerdtfeger, 2005; Palascak
2
+
+
+
+
+
Theoretical
+
+
All DFT calculations reported in this paper were
performed with the use of a Gaussian03 computer
software package (Frisch et al., 2004). The natural
bond orbital (NBO) charge distribution and opti-
mised molecular structures presented here were visu-
alised using GaussView 3.0 program (Dennington et
al., 2003).
−1
=
&
Shields, 2004; Król et al. 2006).
Experimental
Geometry optimisation, single point, and frequen-
cies calculations for all reactants, intermediates, tran-
sition states, and product were performed using the
Becke three-parameter (B3) hybrid method (Becke,
All reagents, standards and solvents were pur-
chased from commercial suppliers. Ammonium per-
sulphate (purity ≥ 97 %), hydrochloric acid (37 %),
benzene (purity ≥ 99.5 %), and hexane (purity
≥ 99.0) from POCH (Poland). Aniline (purity ≥
99.5 %), 2,4,6-TCA (purity ≥ 98.0 %), tetramethyl-
silane (TMS), and zinc powder from Sigma–Aldrich
(USA). Chloroform-d (purity 99.96 %) from Deutero
GmbH (Germany) and used without purification ex-
cept aniline which was purified by distillation over
1
988, 1993) with the Lee–Yang–Parr (LYP) func-
tional (Lee et al., 1988) and 6-311++G(2d,p) basis
set (McLean & Chandler, 1980; Krishnan et al., 1980;
Frisch et al., 1984; Clark et al., 1983). In order to
evaluate the reliability of the B3LYP method, addi-
tional G3MP2 (Curtiss et al., 1998) calculations were
performed for selected steps of the aniline oxidative
chlorination process. Because the reaction studied pro-
ceeds in an aqueous environment, the self-consistent
reaction field (SCRF) method with the polarised con-
tinuum model (PCM) of solvation (Miertuš et al.,
1
zinc powder before use. H NMR (200 MHz) and
13
C NMR (50 MHz) spectra were recorded on a Var-
ian Gemini 200 spectrometer (Varian, USA), the IR
spectrum on a Bruker Alpha-PFT-IR spectrometer
(Bruker, Germany) with a diamond attenuated total
reflection (ATR) crystal, and the MS (EI) spectrum
on a Bruker 320-MS spectrometer (Bruker, Germany).
Thin-layer chromatography (TLC) was performed on
silica-gel plates (Merck 60 F254, Merck, Germany).
The reaction of aniline with (NH ) S O and con-
1
981; Miertuš & Tomasi, 1982) and Bondi-type atomic
radii were applied. Boys–Bernardi counterpoise cal-
culations (Boys & Bernardi, 1970), which are neces-
sary for ion pair species, cannot be combined with
the PCM model. Therefore, basis set superposition er-
ror (BSSE) corrections were calculated in vacuum for
structures optimised in the PCM model according to
the approach presented in the paper (Hunter & Wet-
more, 2007). Vibrational analysis was performed in
order to confirm that reactants, product and interme-
diates were local minima (zero imaginary frequencies)
and transitional states are saddle points on the po-
tential energy surface of the molecules (one imaginary
frequency). Furthermore, the structures of the tran-
sitional states were verified by intrinsic reaction co-
ordinate (IRC) calculations (Fukui, 1981; Gonzales &
Schlegel, 1990). Gibbs free energy changes (∆G), and
the pK values derived from them, were calculated for
the standard conditions of 101.325 kPa and 298.15 K.
4
2
2
8
centrated HClaq was carried out at ambient temper-
ature and under atmospheric pressure conditions, ac-
cording to the following procedure. First, a solution of
phenylammonium chloride was prepared by the addi-
tion of aniline (0.91 mL, 10.00 mmol) to concentrated
HClaq (50 mL, 37 %) with vigorous magnetic stirring.
Then, (NH ) S O (3.5 g, 15.35 mmol) was added to
4
2
2
8
this solution. The mixture was stirred for an hour and
then poured into 1500 mL of water. The precipitated
product was filtered and washed copiously with wa-
ter until the filtrate was colourless. After drying in
air, 2,4,6-TCA was obtained as a pinkish–white solid.
◦
The yield was 20.1 %; m.p. 75 C. TLC, eluent ben-
−
1
zene/hexane (ϕ = 2 : 3); R = 0.88. IR, ν˜ /cm
r
f
:

M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
701
Fig. 1. Oxidation reactions of aniline and 2,4,6-TCA.
3
1
456 (NH), 3367 (NH), 3075 (CH), 1610 (NH2),
first of these reactions (Fig. 1) can take place under
conditions of the oxidative polymerisation of aniline
(Wei et al., 1990, 1989; Gospodinova & Terlemezyan,
571 (Ph), 1391 (Ph), 1296 (C—N), 1072 (NH2), 783
1
(C—Cl), 555 (C—Cl). H NMR (CDCl3), δ: 7.19 (s,
13
´
2H, benzene ring), 4.43 (bs, 2H, NH2). C NMR
1998; Ciri ´c -Marjanovi ´c et al., 2008a). The product
(
1
CDCl3), δ: 139 (Car—N), 127.6 (CH), 121.8 (C—Cl),
19.7 (C—Cl). UV-VIS/nm (methanol): 304, 242, 218.
of the latter reaction was identical with the prod-
uct obtained by electrochemical oxidation of 2,4,6-
TCA (Jaworski & Kalinowski, 2007; Pusztai et al.,
2004).
MS (EI) signals of 2,4,6-TCA in the recorded spec-
trum, m/z (Ir/%): 48.6 (6), 52.0 (10), 61.8 (15), 65.0
(
1
1
13), 73.3 (4), 79.5 (7), 87.8 (12), 96.8 (21), 106.8 (3),
24 (29), 133.1 (4), 158.7 (7), 167.3 (3), 194.9 (100),
98.5 (25), 200.9 (10). We also identified peaks of m/z
Studies on oxidative chlorination of p-nitroaniline
(Kowalska & Gaca, 2002) and anodic chlorination of
aniline (Matsuda et al., 1984) suggest that Cl is the
−
values greater than those characteristic of 2,4,6-TCA
Stein, 2011; AIST, 2011), m/z (Ir/%): 274.7 (7) and
55.1 (4).
most probable chlorinating agent. It appears obvious
that, although Cl2 is formed under reaction condi-
tions, it cannot act as a chlorinating agent in o- and
p-chlorination of aniline. According to Henderson–
Hasselbalch equation:
(
3
Results and discussion
At the first stage of our studies, we sought to
pKa = pH + log([BH]/[B])
(3)
establish what type of reaction occurred under ex-
perimental conditions and to propose a mechanism
for the main product formation. The main goal of
the experimental part of this study was to resolve
whether the oxidative chlorination of aniline occurred
in the presence of reagents which are typical of aniline
polymerisation. We found that a high concentration
of HCl did not favour the oxidative polymerisation
of aniline. Furthermore, good agreement with avail-
able spectral data (Stein, 2011; AIST, 2011; Badawi
et al., 2009; Davis, 2009) indicates that, in the re-
action of aniline with (NH4)2S2O8 and concentrated
HClaq, 2,4,6-TCA is mainly produced. We found that
the yield of chlorination of aniline and the purity of
obtained 2,4,6-TCA was most satisfactory when the
reaction was carried out according to the procedure
presented in “Experimental”, i.e. in the presence of a
maximal concentration of chloride ions, in contrast to
polymerisation which was carried out in diluted HCl.
However, the pinkish-white colour of the precipitate
and some mass spectrum peaks suggest that 2,4,6-
TCA is probably contaminated with small amounts
of aniline trimerisation (m/z = 274.7) and 2,4,6-
TCA dimerisation (m/z = 355.1) by-products. The
in the presence of concentrated HClaq (pH < 1) almost
all of aniline, pKa = 4.57 (Hall et al., 1972), exists in
a protonated form and NH3 substituent directs elec-
+
trophilic attack on the meta position.
According to many papers, the oxidation of ani-
line with (NH4)2S2O8 in an acidic medium leads
´
to the formation of phenylnitrenium cation (Ciri ´c -
Marjanovi ´c et al., 2006, 2008a, 2008b; Kovaľchuk et
al., 2001; Kulkarni et al., 2011). This species may
react with various nucleophiles (McClelland et al.,
1996; Tordeux & Wakselman, 1995; Borodkin & Shu-
bin, 2005). It is worth emphasising that only the sin-
glet ground state phenylnitrenium cation exhibits elec-
−
trophilic properties in the reaction with Cl (McClel-
land et al., 1996). Based on these facts, we assumed
that the oxidative chlorination of aniline consisted
of three steps which were cyclically repeated; proto-
nation of aniline, formation of singlet ground state
phenylnitrenium cation, and nucleophilic substitution
(Fig. 2).
At the next stage of our studies, DFT reaction
path modelling was performed. The results of the ther-
mochemical analysis of p-chloroaniline (p-CA), 2,4-

7
02
M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
Fig. 2. Proposed mechanistic pathway for oxidative chlorination of aniline.
Table 1. Results of thermochemical analysis of proposed aniline oxidative chlorination steps: in the cases of K1, K5, K9, K13, pK
values are equal to negative logarithm of equilibrium constant of deprotonation reaction (pKa); values in parentheses are
calculated at G3MP2 level
∆
G
pK
Reaction
−
1
kJ mol
Calc.
Exp.
K1
23.01
4.03
C6H5NH +3 ←→ C6H5NH2 + H+
4.57a
(30.51)
(5.35)
–20.51
(–15.4)
K2
–117.07
–
–
C6H5NH +3 + S2O8 ←→ C6H5NH + 2HSO4
2−
+
−
(
–87.90)
–140.58
–108.91
18.03
K3
C6H5NH +3 Cl + S2O8 ←→ C6H5NH+Cl + 2HSO4
−
2−
−
−
–24.63
–19.08
3.16
–
K4
C6H5NH +3 Cl ←→ p−CA
−
–
3.99a
–
K5
p-CAH+ ←→ p-CA + H
+
K6
p-CAH+ + S2O8 ←→ p-Cl-C6H4NH + 2HSO4
2−
+
−
–127.78
–125.56
–22.39
–22.00
K7
p-CAH+Cl +S2O
−
2−
←→ p-Cl-C6H4NH+Cl + 2HSO4
−
−
–
8
K8
p-Cl-C6H4NH+Cl ←→ 2,4-DCA
−
–122.93
6.07
–21.54
1.06
(3.04)
–22.98
(–17.60)
–
K9
+
2.05a
2
,4-DCAH+ ←→ 2,4-DCA + H
(17.35)
K10
–131.17
–100.50)
,4-DCAH+ + S2O8 ←→ 2,4-di-Cl-C H3NH + 2HSO4
2−
+
−
–
2
6
(
K11
,4-DCAH+Cl +S2O
−
2−
←→ 2,4-di-Cl-C H3NH+Cl + 2HSO4
−
−
–130.75
–124.93
–9.54
–22.91
–21.89
–1.67
–
–
2
2
2
8
6
K12
, 4-di-Cl-C6H3NH+Cl ←→ 2,4,6-TCA
−
K13
,4,6-TCAH+ ←→ 2,4,6-TCA + H
+
–0.03b
a) pKa value from (Hall et al., 1972); b) pKa value from (Angioi et al., 2005); Calc. – calculated, Exp. – experimental.
dichloroaniline (2,4-DCA), and 2,4,6-TCA formation
are given in Table 1.
In this paper we compared two different compu-
tational methods: B3LYP/6-311++G(2d,p) based on
the density functional theory and G3MP2 based on
second order M ¨o ller–Plesset perturbation theory. ∆G
values calculated at these two levels of computational
theory vary from each other. Nevertheless, the results

M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
703
Fig. 3. Visual representation of optimised structures of ammonium cation/Cl : C6H5NH3 Cl (A); p-CAH+ Cl (C); 2,4-DCAH+
−
+
−
−
Cl (E) and phenylnitrenium/Cl : C6H5NH+Cl (B); p-Cl-C6H4NH+ Cl (D); 2,4-di-Cl-C6H3NH Cl (F); ion pair
−
−
−
−
+
−
intermediates.
obtained with both of these methods confirmed that
the process studied could proceed under experimen-
tal conditions. The theoretical values of pK for K1,
K5, K9, and K13 reactions are found to be close to
the experimental data (Hall et al., 1972; Angioi et
al., 2005). However, the pK1 value calculated by the
G3MP2 method is slightly less accurate than by the
DFT method. All acid–base equilibria except for K13
favour the phenylammonium cation. This is obvious
because 2,4,6-TCA has a very weak basic character
dation of chlorinated anilines, because ion pair inter-
mediates do not affect the values of pK significantly.
The structures of complexes involved in the proposed
mechanism are summarised in Fig. 3.
Energy of interaction (Eint) (Krygowski et al.,
2005; Szaty ꢀl owicz et al., 2007) of phenylammonium/
−
−1
,
Cl A, C, and E adducts is –8.33 kJ mol
−
1
−1
–8.95 kJ mol , and –10.00 kJ mol , respectively.
The negative values of Eint indicate that an ion pair
has lower energy than the sum of separate energies
of individual ions. It is worth noting that the forma-
tion of complex A was proved via various NMR spec-
(pKa < 0), and hence a large amount of water added
to the reaction mixture leads to precipitation of the
neutralised product.
−
troscopy techniques (Suezawa et al., 1991). Cl · · ·C
−
−
With a high concentration of Cl , phenylammo-
interaction in B, D, and F is the cause of the increased
−
nium/Cl , and phenylnitrenium/Cl ion pairs forma-
tion seems to be probable and so it should be taken
into consideration. DFT calculations showed that the
K3 reaction was more thermodynamically favourable
than the K2 reaction, which meant that ion-pairing
was advantageous for the non-substituted aniline ox-
idation step. The same cannot hold true for the oxi-
tetrahedral character of orto- and para-carbon atoms
−
in phenylnitrenium/Cl complex. This loss of pla-
narity is probably due to charge transfer and can be il-
lustrated by the value of C-3 C-4 C-5 C-6 dihedral an-
◦
gle in B (Fig. 3) which is equal to –0.346 . Eint values
−
1
calculated for B, D, F complexes are –39.29 kJ mol
–12.72 kJ mol , –14.77 kJ mol , respectively. This
,
−
1
−1

7
04
M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
Fig. 4. NBO charges in phenylnitrenium cation and its chlorinated derivatives.
−
shows that the formation of phenylnitrenium/Cl
ion pair intermediates is energetically favourable.
BSSE error calculated for A–F ion pair species
Table 2. Geometrical parameters of selected intermediates and
transitional states
Cl—H
˚A
Cl—H—N
Cl—C
˚A
−
1
−1
−1
is 1.92 kJ mol , 3.97 kJ mol , 1.88 kJ mol ,
Structure
− −1 −1
1
◦
4
.48 kJ mol , 2.26 kJ mol , 4.73 kJ mol , respec-
tively. This means that the BSSE error is generally
−
A
B
2.136
–
–
–
–
176.302
–
higher for phenylnitrenium/Cl complexes than in the
–
–
–
–
–
1.887
1.815
1.890
1.811
1.859
–
−
case of phenylammonium/Cl ion pairs. Interaction
TS1
D
TS2
TS4
E
−
between phenylnitrenium cation and Cl seems to be
fundamental in K4, K8, and K12 substitution steps.
NBO charge distribution in phenylnitrenium cation
–
2.104
175.929
(
Fig. 4) indicates that chloride ion would be likely
to interact with ortho- and para-carbon atoms. Be-
cause there is lower electron density in para-position
in C6H5NH+ than in ortho-position, our studies do
not include o-chlorination of non-substituted aniline,
as we sought to present only the most favourable path-
way for 2,4,6-TCA formation. It is worth noting that,
according to the similar mechanism of electrochemi-
cal oxidative chlorination proposed by Matsuda et al.
in the inter-molecular and intra-molecular proton-
transfer steps. The high positive values of Gibbs free
energy of activation suggest that inter-molecular pro-
ton transfers in D and F intermediates (Figs. 5d and
5e) are kinetically unfavourable, hence the formation
of TS2 and TS3 (Figs. 5b and 5c) in the alternative
pathway is preferred. Although TS3 is formed with
a relatively high value of Gibbs free energy of acti-
vation, this barrier can be overcome by the energy
released in the TS2 decomposition step. Summarising
these considerations, in accordance with our DFT cal-
culations, the most reasonable reaction path consists
of the intra-molecular proton transfers presented in
Figs. 5a–5c.
(1984), aniline is chlorinated to p-CA and then p-CA
is chlorinated to 2,4-DCA.
High negative values of pK indicate that all oxida-
tion and substitution steps equilibria favour the prod-
ucts (Table 1). This means that the formation of chlo-
rinated aniline derivatives is probable, as our thermo-
chemical modelling predicts but, in order to confirm
that the proposed mechanism can really take place, ki-
netic calculations were also performed. The values of
Gibbs free energy of activation and transitional state
The geometrical parameters of selected intermedi-
ates and transitional states are presented in Table 2.
C—Cl bond distances in transitional states are longer
than in intermediates. However, the differences be-
tween values in this geometrical parameter are not
significantly high. Interactions of phenylammonium
(
TS) decomposition are presented in Fig. 5.
Protonation of the nitrogen atom in the transi-
tional state plays a key role in the kinetics of the nu-
cleophilic attack on the phenylnitrenium cation (Mc-
Clelland et al., 1996). Our calculations showed that
Gibbs free energy barriers of proton addition to B
and D intermediates (Figs. 5a and 5b) were the lowest
in comparison with other reaction paths. It is worth
noting that 2,4-DCA and 2,4,6-TCA can be formed
−
−
cation/Cl and phenylnitrenium cation/Cl interme-
diates can be characterised by Cl—H and Cl—C bond
distances. It is worth noting that Cl—H and Cl—C
values calculated for A–F are lower than the sum of

M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
705
Fig. 5. Transitional states formation and decomposition in substitution steps of oxidative chlorination of aniline. Gibbs free energy
−
1
values are given in kJ mol
.
◦
the appropriate van der Waals radii. Moreover, the
Cl—H—N bond angle in these complexes is close to
180 . Both of the geometrical parameters referred to
above (bond distances and angles) suggest relatively

7
06
M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
good stability of the ion pairs studied.
energies. Some procedures with reduced errors. Molecular
Physics, 19, 553–566. DOI: 10.1080/00268977000101561.
Camaioni, D. M., & Schwerdtfeger, C. A. (2005). Comment on
Conclusions
“
Accurate experimental values for the free energies of hydra-
tion of H , OH , and H3O+ ”. Journal of Physical Chem-
+
−
The reaction between aniline, (NH4)2S2O8, and
concentrated HClaq has never been studied before. As
a result of our experimental investigations, we found
that, in a large excess of concentrated hydrochloride
acid, nucleophilic attack of chloride anion to phenyl-
nitrenium cation was more probable than chemical
polymerisation of aniline, although (NH4)2S2O8 and
HClaq are reagents widely used in polyaniline syn-
thesis. Oxidative chlorination of aniline under exper-
imental conditions results in the formation of 2,4,6-
TCA. Unfortunately, the reaction studied is not a
very effective method of chlorination of aniline be-
cause 2,4,6-TCA is formed in rather low yield and
it is contaminated with small amounts of probably
oxidative dimerisation and trimerisation by-products.
In order to establish the mechanism of the chlori-
nation of aniline with the use of (NH4)2S2O8 and
HClaq, B3LYP/6-311++G(2d,p) reaction path cal-
culations were performed. The results of this study
showed that formation of 2,4,6-TCA by the proposed
pathway (protonation of aniline, formation of phenyl-
istry A, 109, 10795–10797. DOI: 10.1021/jp054088k.
Chiang, J. C., & MacDiarmid, A. G. (1986). ‘Polyaniline’: Pro-
tonic acid doping of the emeraldine form to the metallic
regime. Synthetic Metals, 13, 193–205. DOI: 10.1016/0379-
6779(86)90070-6.
Clark, T., Chandrasekhar, J., Spitznagel, G. W., & von Ragué
Schleyer, P. (1983). Efficient diffuse function-augmented ba-
sis sets for anion calculations. III. The 3-21+G basis set for
first-row elements, Li–F. Journal of Computational Chem-
istry, 4, 294–301. DOI: 10.1002/jcc.540040303.
Curtiss, L. A., Raghavachari, K., Redfern, P. C., Rassolov, V.,
&
Pople, J. A. (1998). Gaussian-3 (G3) theory for molecules
containing first and second-row atoms. Journal of Chemical
Physics, 109, 7764–7776. DOI: 10.1063/1.477422.
Ciri ´c -Marjanovi ´c , G., Konyushenko, E. N., Trchová, M., & Stej-
skal, J. (2008a). Chemical oxidative polymerization of anilin-
ium sulfate versus aniline: Theory and experiment. Synthetic
Metals, 158, 200–211. DOI: 10.1016/j.synthmet.2008.01.005.
´
´
Ciri ´c -Marjanovi ´c , G., Trchová, M.,
& Stejskal, J. (2006).
MNDO-PM3 study of the early stages of the chemical ox-
idative polymerization of aniline. Collection of Czechoslovak
Chemical Communications, 71, 1407–1426. DOI: 10.1135/
cccc20061407.
Ciri ´c -Marjanovi ´c , G., Trchová, M., & Stejskal, J. (2008b).
Theoretical study of the oxidative polymerization of ani-
line with peroxydisulfate: Tetramer formation. Interna-
tional Journal of Quantum Chemistry, 108, 318–333. DOI:
´
−
nitrenium cation/Cl ion pair intermediate, and nu-
cleophilic substitution involving intra-molecular pro-
ton transfer) appears to be thermodynamically and
kinetically feasible.
10.1002/qua.21506.
Davis, M. C. (2009). Chlorination of aniline and methyl car-
banilate by N-chlorosuccinimide and synthesis of 1,3,5-
trichlorobenzene. Synthetic Communications, 39, 1100–1108.
DOI: 10.1080/00397910802499542.
Dračínský, M., Casta n˜ o, O., Kotora, M., & Bouř, P. (2010).
Rearrangement of Dewar benzene derivatives studied by
DFT. Journal of Organic Chemistry, 75, 576–581. DOI:
Acknowledgements. The authors gratefully acknowledge the
help received from the Academic Computer Centre in Gda n´ sk
in providing its facility to perform all the calculations published
in this study.
References
10.1021/jo902065n.
Dennington, R., II, Keith, T., Millam, J., Eppinnett, K., Hov-
ell, W. L., & Gilliland, R. (2003). GaussView 03, [computer
software], University park, PA, USA: Semichem Inc.
Frisch, M. J., Pople, J. A., & Binkley, J. S. (1984). Self-
consistent molecular orbital methods 25. Supplementary
functions for Gaussian basis sets. Journal of Chemical
Physics, 80, 3265–3269. DOI: 10.1063/1.447079.
AIST, National Institute of Advanced Industrial Science and
Technology (2011). Spectral database for organic com-
pounds, SDBS No. 1500. Retrieved October 18, 2011, from
http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct frame
top.cgi
Angioi, S., Polati, S., Roz, M., Rinaudo, C., Gianotti, V., &
Gennaro, M. C. (2005). Sorption studies of chloroanilines
on kaolinite and montmorillonite. Environmental Pollution,
Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E.,
Robb, M. A., Cheeseman, J. R., Montgomery, J. A., Jr.,
Vreven, T., Kudin, K. N., Burant, J. C., Millam, J. M.,
Iyengar, S. S., Tomasi, J., Barone, V., Mennucci, B., Cossi,
M., Scalmani, G., Rega, N., Petersson, G. A., Nakatsuji, H.,
Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J.,
Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H.,
Klene, M., Li, X., Knox, J. E., Hratchian, H. P., Cross, J. B.,
Bakken, V., Adamo, C., Jaramillo, J., Gomperts, R., Strat-
mann, R. E., Yazyev, O., Austin, A. J., Cammi, R., Pomelli,
C., Ochterski, J. W., Ayala, P. Y., Morokuma, K., Voth, G.
A., Salvador, P., Dannenberg, J. J., Zakrzewski, V. G., Dap-
prich, S., Daniels, A. D., Strain, M. C., Farkas, O., Malick, D.
K., Rabuck, A. D., Raghavachari, K., Foresman, J. B., Ortiz,
J. V., Cui, Q., Baboul, A. G., Clifford, S., Cioslowski, J., Ste-
fanov, B. B., Liu, G., Liashenko, A., Piskorz, P., Komaromi,
I., Martin, R. L., Fox, D. J., Keith, T., Al-Laham, M. A.,
Peng, C. Y., Nanayakkara, A., Challacombe, M., Gill, P. M.
W., Johnson, B., Chen, W., Wong, M., Gonzalez, W. C., &
134, 35–43. DOI: 10.1016/j.envpol.2004.07.018.
Badawi, H. M., F ¨o rner, W., & Al-Saadi, A. A. (2009). Struc-
tural stability, NH2 inversion and vibrational assignments of
2
,4,6-trichloroaniline and 2,3,5,6-tetrachloroaniline. Journal
of Molecular Structure, 938, 41–47. DOI: 10.1016/j.molstruc.
009.09.001.
2
Becke, A. D. (1988). Density-functional exchange-energy ap-
proximation with correct asymptotic behavior. Physical Re-
view A, 38, 3098–3100. DOI: 10.1103/PhysRevA.38.3098.
Becke, A. D. (1993). Density-functional thermochemistry III.
The role of exact exchange. Journal of Chemical Physics,
98, 5648–5652. DOI: 10.1063/1.464913.
Borodkin, G. I., & Shubin, V. G. (2005). Nitrenium ions and
problem of direct electrophilic amination of aromatic com-
pounds. Russian Journal of Organic Chemistry, 41, 473–504.
DOI: 10.1007/s11178-005-0193-z.
Boys, S. F., & Bernardi, F. (1970). The calculation of small
molecular interactions by the differences of separate total

M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
707
Pople, J. A. (2004). Gaussian 03, Revision D.02 [computer
software]. Wallingford, CT, USA: Gaussian, Inc.
tion methods. Journal of the American Chemical Society,
123, 7314–7319. DOI: 10.1021/ja010534f.
Fukui, K. (1981). The path of chemical reactions - the IRC
approach. Accounts of Chemical Research, 14, 363–368. DOI:
MacDiarmid, A. G., Chiang, J. C., Richter, A. F., & Epstein,
A. J. (1987). Polyaniline: a new concept in conducting poly-
mers. Synthetic Metals, 18, 285–290. DOI: 10.1016/0379-
6779(87)90893-9.
MacDiarmid, A. G., Manohar, S. K., Masters, J. G., Sun, Y.,
Weiss, H., & Epstein, A. J. (1991). Polyaniline: Synthesis
and properties of pernigraniline base. Synthetic Metals, 41,
621–626. DOI: 10.1016/0379-6779(91)91145-z.
Matsuda, Y., Nishiki, T., Sakota, N., & Nakagawa, K. (1984).
Anodic chlorination of aniline in N,N-dimethylformamide
and N,N-dimethylacetamide. Electrochimica Acta, 29, 35–39.
DOI: 10.1016/0013-4686(84)80034-1.
1
0.1021/ar00072a001.
˙
Gaca, J., & Zak, S. (1997). Oxidative chlorination of ac-
etanilides by metal chlorides – hydrogen peroxide in acid-
aqueous medium systems. Synthetic Communications, 27,
3291–3299. DOI: 10.1080/00397919708004189.
Gonzales, C., & Schlegel, H. B. (1990). Reaction path following
in mass-weighted internal coordinates. Journal of Physical
Chemistry, 94, 5523–5527. DOI: 10.1021/j100377a021.
Gospodinova, N.,
& Terlemezyan, L. (1998). Conducting
polymers prepared by oxidative polymerization: polyani-
Mattoso, L. H. C., MacDiarmid, A. G., & Epstein, A. J. (1994).
Controlled synthesis of high molecular weight polyaniline and
poly(o-methoxyaniline). Synthetic Metals, 68, 1–11. DOI:
line. Progress in Polymer Science, 23, 1443–1484. DOI:
10.1016/s0079-6700(98)00008-2.
Gribble, G. W. (2003). The diversity of naturally produced
organohalogens. Chemosphere, 52, 289–297. DOI: 10.1016/
s0045-6535(03)00207-8.
10.1016/0379-6779(94)90140-6.
McClelland, R. A., Kahley, M. J, Davidse, P. A., & Hadzialic,
G. (1996). Acid–base properties of arylnitrenium ions. Jour-
nal of the American Chemical Society, 118, 4794–4803. DOI:
Hall, W. E., Higuchi, T., Pitman, I. H., & Uekama, K.
(1972). Aminolysis of acid anhydrides in water. II. Nonlinear
10.1021/ja954248d.
structure-reactivity relations in the aminolyses of phthalic
and succinic anhydrides. Journal of the American Chemical
Society, 94, 8153–8156. DOI: 10.1021/ja00778a035.
Hunter, K. C., & Wetmore, S. D. (2007). Environmental ef-
fects on the enhancement in natural and damaged DNA nu-
cleobase acidity because of discrete hydrogen-bonding inter-
actions. Journal of Physical Chemistry A, 111, 1933–1942.
DOI: 10.1021/jp066641j.
McLean, A. D., & Chandler, G. S. (1980). Contracted Gaussian
basis sets for molecular calculations. I. Second row atoms,
Z=11–18. Journal of Chemical Physics, 72, 5639–5648. DOI:
10.1063/1.438980.
Miertuš, S., Scrocco, E., & Tomasi, J. (1981). Electrostatic in-
teraction of a solute with a continuum. A direct utilizaion
of AB initio molecular potentials for the prevision of solvent
effects. Chemical Physics, 55, 117–129. DOI: 10.1016/0301-
Jaworski, J. S., & Kalinowski, M. K. (2007). Electrochemistry
of anilines. In Z. Rappoport (Ed.), The chemistry of anilines
0104(81)85090-2.
Miertuš, S., & Tomasi, J. (1982). Approximate evaluations of
the electrostatic free energy and internal energy changes
in solution processes. Chemical Physics, 65, 239–245. DOI:
(pp. 871–926). Chichester, UK: Wiley.
Kovaľchuk, E. P., Whittingham, S., Skolozdra, O. M., Zavalij,
P. Y., Zavaliy, I. Yu., Reshetnyak, O. V., & Seledets, M.
10.1016/0301-0104(82)85072-6.
(2001). Co-polymers of aniline and nitroanilines. Part I.
Palascak, M. W., & Shields, G. C. (2004). Accurate experimen-
Mechanism of aniline oxidation polycondensation. Materials
Chemistry and Physics, 69, 154–162. DOI: 10.1016/s0254-
+
−
tal values for the free energies of hydration of H , OH , and
+
H3O . Journal of Physical Chemistry A, 108, 3692–3694.
0584(00)00393-x.
DOI: 10.1021/jp049914o.
Pokon, E. K., Liptak, M. D., Feldgus, S., & Shields, G. C.
Kowalska, M., & Gaca, J. (2002). Chlorides as the potential
agents contributing to formation of chloroorganic compounds
in oxidation of amines. Polish Journal of Environmental
Studies, 11(Supplement I), 41–44.
Krishnan, R., Binkley, J. S., Seeger, R., & Pople, J. A. (1980).
Self-consistent molecular orbital methods. XX. A basis set
for correlated wave functions. Journal of Chemical Physics,
(2001). Comparison of CBS-QB3, CBS-APNO, and G3 pre-
dictions of gas phase deprotonation data. Journal of Physical
Chemistry A, 105, 10483–10487. DOI: 10.1021/jp012920p.
Pusztai, S., Pánczél, J., Dankházi, T., & Farsang, G. (2004).
The electrodimerization mechanism of 2,4,6-trichloro- and
tribromoanilines in unbuffered acetonitrile. Journal of Elec-
troanalytical Chemistry, 571, 233–239. DOI: 10.1016/j.
jelechem.2004.04.020.
Sasson, Y. (1995). Formation of carbon–halogen bonds (Cl, Br,
I). In S. Patai, & Z. Rappoport (Eds.), Supplement D2. The
chemistry of halides, pseudo-halides and azides, (Part 2, pp.
72, 650–654. DOI: 10.1063/1.438955.
Król, M., Wrona, M., Page, C. S., & Bates, P. A. (2006). Macro-
scopic pKa calculations for fluorescein and its derivatives.
Journal of Chemical Theory and Computation, 2, 1520–1529.
DOI: 10.1021/ct600235y.
Krygowski, T. M., Zachara, J. E., & Szatylowicz, H. (2005).
Molecular geometry as a source of chemical information. Part
535–628). Chichester, UK: Wiley.
Stein, S. E. (2011). NIST Chemistry WebBook. Retrieved Oc-
tober 18, 2011, from http://webbook.nist.gov/cgi/cbook.cgi?
Name=2%2C4%2C6-trichloroaniline&Units=SI
Suezawa, H., Horiike, N., Yamazaki, S., Kamachi, H., & Hi-
rota, M. (1991). Multinuclear NMR spectroscopic studies on
ionic interactions. Interactions between nitrogen cations and
halide ions. Journal of Physical Chemistry, 95, 10787–10796.
DOI: 10.1021/j100179a049.
Szaleniec, M., Witko, M., Tadeusiewicz, R., & Goclon, J. (2006).
Application of artificial neural networks and DFT-based pa-
rameters for prediction of reaction kinetics of ethylbenzene
dehydrogenase. Journal of Computer-Aided Molecular De-
sign, 20, 145–157. DOI: 10.1007/s10822-006-9042-6.
2—An attempt to estimate the H-bond strength: the case
of p-nitrophenol complexes with bases. Journal of Physical
Organic Chemistry, 18, 110–114. DOI: 10.1002/poc.875.
Kulkarni, S. B., Joshi, S. S., & Lokhande, C. D. (2011).
Facile and efficient route for preparation of nanostructured
polyaniline thin films: Schematic model for simplest oxida-
tive chemical polymerization. Chemical Engineering Jour-
nal, 166, 1179–1185. DOI: 10.1016/j.cej.2010.12.032.
Lee, C., Yang, W., & Parr, R. G. (1988). Development of the
Colle-Salvetti correlation-energy formula into a functional of
the electron density. Physical Review B, 37, 785–789. DOI:
10.1103/PhysRevB.37.785.
Liptak, M. D., & Shields, G. C. (2001). Accurate pKa cal-
culations for carboxylic acids using complete basis set and
Gaussian-n models combined with CPCM continuum solva-
Szaty ꢀl owicz, H., Krygowski, T. M., & Zachara-Horeglad, J. E.
(2007). Long-distance structural consequences of H-bonding.
How H-bonding affects aromaticity of the ring in variously

7
08
M. Przyby lꢀ ek, J. Gaca/Chemical Papers 66 (7) 699–708 (2012)
substituted aniline/anilinium/anilide complexes with bases
and acids. Journal of Chemical Information and Modeling,
7, 875–886. DOI: 10.1021/ci600502w.
Tawa, G. J., Topol, I. A., Burt, S. K., Caldwell, R. A., & Rashin,
A. A. (1998). Calculation of the aqueous solvation free energy
of the proton. Journal of Chemical Physics, 109, 4852–4863.
DOI: 10.1063/1.477096.
Topol, I. A., Tawa, G. J., Caldwell, R. A., Eissenstat, M. A., &
Burt, S. K. (2000). Acidity of organic molecules in the gas
phase and in aqueous solvent. Journal of Physical Chemistry
A, 104, 9619–9624. DOI: 10.1021/jp001938h.
Tordeux, M., & Wakselman, C. (1995). The Bamberger reaction
in hydrogen fluoride: the use of mild reductive metals for the
preparation of fluoroaromatic amines. Journal of Fluorine
Chemistry, 74, 251–254. DOI: 10.1016/0022-1139(95)03257-
e.
Wei, Y., Jang, G. W., Chan, C. C., Hsueh, K. F., Hariharan,
R., Patel, S. A., & Whitecar, C. K. (1990). Polymerization of
aniline and alkyl ring-substituted anilines in the presence of
aromatic additives. Journal of Physical Chemistry, 94, 7716–
7721. DOI: 10.1021/j100382a073.
Wei, Y., Tang, X., Sun, Y., & Focke, W. W. (1989). A study of
the mechanism of aniline polymerization. Journal of Polymer
Science Part A: Polymer Chemistry, 27, 2385–2396. DOI:
10.1002/pola.1989.080270720.
Zheng, S., Xiong, Y., & Wang, J. (2010). Theoretical studies on
identity SN2 reactions of lithium halide and methyl halide:
A microhydration model. Journal of Molecular Modeling, 16,
1931–1937. DOI: 10.1007/s00894-010-0688-6.
4
Vyas, P. V., Bhatt, A. K., Ramachandraiah, G., & Bedekar, A.
V. (2003). Environmentally benign chlorination and bromi-
nation of aromatic amines, hydrocarbons and naphthols.
Tetrahedron Letters, 44, 4085–4088. DOI: 10.1016/s0040-
4039(03)00834-7.