Trichloroisocyanuric acid in 98% sulfuric acid: A superelectrophilic medium for chlorination of deactivated arenes

Article abstract of DOI:10.1016/j.apcata.2011.05.017

Trichloroisocyanuric acid (TCCA) reacts with arenes and its reactivity is highly affected by the acid strength of the reaction medium. Deactivated arenes are efficiently chlorinated by TCCA in H₂SO₄. Our results, along with DFT calculations and ¹³C NMR spectrometry suggest the formation of a monoprotonated TCCA superelectrophile as the reactive species that can efficiently transfer electrophilic Cl⁺ to even very weak nucleophiles, such as m-dinitrobenzene.

Full text of DOI:10.1016/j.apcata.2011.05.017

Applied Catalysis A: General 401 (2011) 176–181
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Trichloroisocyanuric acid in 98% sulfuric acid: A superelectrophilic medium for
chlorination of deactivated arenes
Gabriela Fonseca Mendonc¸ a, Mônica Rufino Senra, Pierre M. Esteves∗, Marcio C.S. de Mattos∗
Instituto de Química, Departamento de Química Orgânica, Universidade Federal do Rio de Janeiro, Cx Postal 68545, 21945-970, Rio de Janeiro, Brazil
a r t i c l e i n f o
a b s t r a c t
Article history:
Trichloroisocyanuric acid (TCCA) reacts with arenes and its reactivity is highly affected by the acid
strength of the reaction medium. Deactivated arenes are efficiently chlorinated by TCCA in H2SO4. Our
results, along with DFT calculations and 13C NMR spectrometry suggest the formation of a monoproto-
nated TCCA superelectrophile as the reactive species that can efficiently transfer electrophilic Cl+ to even
very weak nucleophiles, such as m-dinitrobenzene.
Received 13 March 2011
Received in revised form 12 May 2011
Accepted 14 May 2011
Available online 23 May 2011
© 2011 Elsevier B.V. All rights reserved.
Keywords:
Trichloroisocyanuric acid
DFT Calculations
Arenes
Superelectrophilic species
Aromatic chlorination
1. Introduction
Rearrangement utilizing trichloroisocyanuric acid was described
[18]. Furthermore, the use of TCCA also shows quite advantageous
The interaction of reactive intermediates with the reaction
medium could cause significant changes in the reactivity of cer-
tain species and this topic has attracted great interest. Based on
this concept, the protosolvation (protolytic solvation), which led to
the concept of superelectrophiles [1], has been successfully used in
the reaction with substrates of low reactivity [2]. Superelectrophilic
species are formed upon the activation of electrophiles with Bron-
sted or Lewis acids via coordination or solvation. Through this
interaction, the reactivity of these (super)electrophiles is greatly
enhanced compared to the original electrophile. Acyl and nitron-
ium cations are good examples of intermediates that have their
reactivity increased by using a superacid medium, leading to the
formation of the dications RCOH2+ and NO2H2+ [3].
Trichloroisocyanuric acid (TCCA, Fig. 1) is a stable and inexpen-
sive solid, easily available in pool supplies and frequently used
as swimming-pool disinfectant and bleaching agent. It is an effi-
cient source of the electrophilic chlorenium ion (“Cl+ꢀꢀ ), which has
been used for chlorination of alkenes [4] and carbonyl compounds
[5,6], cohalogenation of alkenes [7] and alkynes [8], preparation of
esters [9], amides [9], nitriles [10], epoxides [11], N-chloro com-
pounds [12–15], chlorofluoro compounds [16], and also in diverse
oxidation reactions [17]. Recently, a very interesting Hofmann
compared to several similar N-chlorinated compounds (such as
1,3-dichloro-5,5-dimethyl hydantoin, NCS, N-chlorosaccharin, and
chloramine-T) as it is able to transfer three equivalents of chlorine
atoms to the substrate, which is of up to 45.5% of its mass, a value
greater than those of the N-chloro analogues.
Several reagents are known for the chlorination of acti-
vated arenes [19]. On the other hand, the direct chlorination
of deactivated aromatic compounds is frequently disappointing.
Trichloroisocyanuric acid also reacts smoothly with activated
arenes to produce chloroarenes [20], but this reaction is not effec-
tive with deactivated substrates [20], even in ionic liquids [21,22].
An efficient electrophilic chlorination of deactivated aromatic com-
pounds using NCS in the superelectrophilic media BF3/H2O was
published [23]. Recently, the system NCS/pTsOH was successfully
used for chlorination of phenol and analogues [24].
Continuing our interest in electrophilic halogenations using
trihaloisocyanuric acids [25–30] and related N-halo compounds
[31–33], herein we communicate our results on the behavior of
the system TCCA/98% H2SO4 in electrophilic aromatic chlorination
of deactivated arenes.
2. Experimental
2.1. General
∗
Corresponding author. Tel.: +55 21 25627142; fax: +55 21 25627142.
E-mail addresses: pesteves@iq.ufrj.br (P.M. Esteves), mmattos@iq.ufrj.br
Arenes, TCCA (99%), and 98% H2SO4 were purchased from
commercial suppliers and used as received. All reactions were
(M.C.S. de Mattos).
0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2011.05.017

G.F. Mendonc¸ a et al. / Applied Catalysis A: General 401 (2011) 176–181
177
13C NMR spectra of TCCA were recorded on a Bruker AC-
200 spectrometer at 75 MHz. HRGC-MS analyses were performed
on a Shimadzu GCMS-QP2010S gas chromatograph with electron
impact (70 eV) by using a 30 m DB-5 silica capillary column. GC
analyses were performed on a HP-5890-II gas chromatograph with
FID by using a 30 m RTX-5 silica capillary column and He (flow rate
50 cm/s) as carrier gas (split 1:20).
Fig. 1. Structure of trichloroisocyanuric acid (TCCA).
The geometries of the studied species were optimized at the
B3LYP/6-31++G** level by using standard techniques [34]. All
calculations were carried out using GAUSSIAN 09 package [35].
Vibrational analysis on the optimized geometries of selected points
on the potential energy surface was carried to determine whether
the resulting geometries are true minima or transition states,
by checking the existence of imaginary frequencies. Single-point
performed using a single-necked flask and were monitored by GC.
After workup, the solvent was evaporated on a rotatory evapora-
tor at reduced pressure and controlled heating. The reactions were
analyzed by GC and the products were identified by co-injection
with authentic samples and mass spectrometry.
Table 1
Results of the reaction of anisole with TCCA (0.34 mol equiv).
.
Solvent
Time (min)
Yield (%)a
Selectivity (%)b
(o/p)
CH3CN
98% H2SO4
HOAc
90
5
20
20
20
20
91
28
100 (1/1)
–
95(1/2.7)
71 (1/2)
90 (1/2.5)
92(1/2.5)
–
–
5
29
10
8
–
100
–
–
–
c
–
98% H2SO4/HOAc (1:1)d
98% H2SO4/HOAc (1:10)d
98% H2SO4/HOAc (1:20)d
–
c
c
–
c
–
–
a
Yield of pure product, based on anisole.
Determined by HRGC.
Not determined.
Molar.
b
c
d
Table 2
Results of the reaction of toluene with TCCA (0.34 mol equiv).
.
Solvent
Time (h)
Yield (%)a
Selectivity (%)b
(o/p)
CH3CN
98% H2SO4
HOAc
120c
0.3
168
5
24
48
50
–
65
85
81
80
100 (1/1)
57(1.5/1)
100 (2/1)
100 (2/1)
100 (2/1)
100 (2/1)
–
14
–
–
–
–
29
–
–
–
d
98% H2SO4/HOAc (1:1)e
98% H2SO4/HOAc (1:10)e
98% H2SO4/HOAc (1:20)e
–
–
a
Yield of pure product, based on toluene.
Determined by HRGC.
Incomplete reaction.
Not determined.
b
c
d
e
Molar.

178
G.F. Mendonc¸ a et al. / Applied Catalysis A: General 401 (2011) 176–181
Table 3
Results of the reaction of chlorobenzene with TCCA (0.34 mol equiv).
.
Solvent
Time (days)
Yield (%)a
Selectivity (%)b
(o/p)
CH3CN
98% H2SO4
HOAc
7
1
7
7
7
7
0
–
0
68
65
44
–
–
32
–
–
–
c
68 (1/2)
–
100(1/1.7)
100(1/1.4)
100(1/1.4)
98% H2SO4/HOAc (1:1)d
98% H2SO4/HOAc (1:10)d
98% H2SO4/HOAc (1:20)d
–
a
Yield of pure product, based on chlorobenzene.
Determined by HRGC.
Not determined.
Molar.
b
c
d
energy calculations were performed at B3LYP/6-311++G** level
at the B3LYP/6-31++G** geometries [36–38]. Energy differences
correspond to enthalpy differences at 298.15 K and 1 atm and con-
sider zero-point energy and thermal expansion to 298.15 K from
B3LYP/6-31++G** vibrational frequencies.
2.2.2. General procedure for chlorination of nitroarenes using 98%
H2SO4
To a magnetically stirred solution of the nitroarene (2 mmol) in
98% H2SO4 (2 mL) was added TCCA (0.67 mmol) at the temperature
depicted in Tables 4 and 5. After 2 h, the reaction was cooled, poured
onto crushed ice and extracted with CH2Cl2. The combined organic
layers were washed with 10% NaHCO3, 15% NaHSO3, water and
dried (Na2SO4). After filtration and evaporation of the solvent, the
residue was analyzed by HRGC.
2.2. Chlorination of arenes with TCCA
2.2.1. General procedure for chlorination of arenes using 98%
H2SO4/HOAc
To a magnetically stirred solution of TCCA (2 mmol) in 98%
H2SO4/HOAc (5 mL, molar ratios of 1:0, 1:1, 1:10, 1:20, 0:1) was
added the arene (6 mmol) at room temperature. After completion
(HRGC), the reaction was poured onto crushed ice and extracted
with CH2Cl2. The combined organic layers were washed with 10%
NaHCO3, brine and dried (Na2SO4). After filtration and evaporation
of the solvent, the residue was analyzed by GC.
- m-Chloro-nitrobenzene. MS: m/z 159 (M++2), 157 (M+), 129, 127,
113, 111 (100%), 101, 99, 87, 85, 75, 74, 50.
- 3-Chloro-4-nitrotoluene. MS: m/z 173 (M++2), 171 (M+), 143, 141,
127, 125, 115, 113, 101, 99, 91, 89 (100%), 77, 63, 51.
- 3,4-Dichloro-nitrobenzene. MS: m/z 195 (M++4), 193 (M++2), 191
(M+), 165, 163, 161,137, 135, 133, 149, 147, 145, 111, 109 (100%),
75, 74, 50.
- 4-Chloro-2,6-dinitrotoluene. MS: m/z 218 (M++2), 216 (M+), 200,
199 (100%), 184, 182, 171, 169, 153, 124, 11, 97, 89, 75, 63, 51.
- 1-Chloro-3,5-dinitrobenzene. MS: m/z 204 (M++2), 202 (M+), 158,
156, 128, 126, 112, 110, 75 (100%), 74, 63, 50.
- p-Chloroanisole. MS: m/z 144 (M++2), 142 (M+), 129, 127, 113, 111,
101, 99 (100%), 77, 75, 73, 63, 50.
- o-Chloroanisole. MS: m/z 144 (M++2), 142 (M+), 129, 127, 113, 111,
101, 99 (100%), 77, 75, 73, 63, 50.
- 2,4,6-Trichloroanisole. MS: m/z 216 (M++6), 214 (M++4), 212
(M++2), 210 (M+), 201, 199, 197, 195, 173, 171, 169, 167 (100%),
136, 134, 132, 111, 109, 99, 97, 74, 62, 61.
Table 4
Results of the reaction of nitrobenzene with TCCA (0.34 mol equiv).
- p-Chlorotoluene. MS: m/z 128 (M++2), 126 (M+), 99, 91 (100%), 89,
75, 65, 63, 52.
- o-Chlorotoluene. MS: m/z 128 (M++2), 126 (M+), 99, 91 (100%), 75,
65, 63, 52.
- 2,4-Dichlorotoluene. MS: m/z 164 (M++4), 162 (M++2), 160 (M+),
127, 125 (100%), 99, 89, 73, 63, 50.
- 2,4,6-Trichlorotoluene. MS: m/z 200 (M++6), 198 (M++4), 196
(M++2), 194 (M+), 163, 161, 159 (100%), 125, 123, 97, 89, 73, 63,
50.
.
Conditions
Time (h)
Yield (%)a
- p-Dichlorobenzene. MS: m/z 150 (M++4), 148 (M++2), 146 (M+)
(100%), 113, 111, 75, 74, 50.
CH3CN, r.t.
168
168
168c
5
0
0
45
80
98% H2SO4/HOAc (1:1)b, r.t.
98% H2SO4, r.t.
- o-Dichlorobenzene. MS: m/z 150 (M++4), 148 (M++2), 146 (M+)
(100%), 113, 111, 75, 74, 50.
98% H2SO4, 80 ◦
C
a
Yield of pure product, based on nitrobenzene.
Molar.
Incomplete reaction.
- 1,2,4-Trichlorobenzene. MS: m/z 186 (M++6), 184 (M++4), 182
(M++2), 180 (M+) (100%), 149, 147, 145, 111, 109, 86, 84, 74, 50.
b
c

G.F. Mendonc¸ a et al. / Applied Catalysis A: General 401 (2011) 176–181
179
Table 5
2,4,6-trichloroanisole as the unique product in 28% yield in only
5 min (82% yield, based on unreacted anisole), indicating the higher
reactivity of TCCA in 98% H2SO4 than in acetonitrile. Similar
results, i.e., the formation of trihalo compounds, is also observed
in other electrophilic chlorination reactions of anisole [39,40] and
related activated arenes [41–43]. In fact, the formation of 2,4,6-
trichloroaniline from aniline and NCS is almost inevitable [44].
Bagmanov suggests that the introduction of an halogen atom into
the activated aromatic nucleus activates the aromatic ring for fur-
ther substitution reactions [45].
On the other hand, reaction of TCCA with anisole in a weak acid
(HOAc) led to the exclusive formation of o- and p-chloroanisole,
along with small amount of 2,4-dichloroanisole. Furthermore,
reducing the acidity strength of the reaction medium by dilution
of H2SO4 with HOAc led to the total consumption of the sub-
strate in 20 min and exclusive formation of chloroanisoles and
2,4-dichloroanisole. This shows that less acidic medium favors the
monochlorinated product. Table 1 summarizes the results.
The results clearly show that the reactivity of trichloroisocya-
nuric acid can be regulated by the acid strength of the reaction
media. Similar behavior was observed in the reactions of TCCA
with the less reactive arenes toluene (Table 2) and chlorobenzene
(Table 3). The reaction of toluene with TCCA in acetonitrile to pro-
duce o- and p-chlorotoluene was incomplete after 5 days at room
temperature, but took only 20 min in 98% H2SO4 to produce a mix-
ture of several chlorinated products. As expected, dilution of H2SO4
with HOAc led to the monochlorinated product in lower yields and
higher reaction times. On the other hand, chlorobenzene was not
reactive with TCCA in acetonitrile or in HOAc after several days,
but reacted in 98% H2SO4 in 24 h at room temperature. Once more,
diluting H2SO4 with HOAc led to o- and p-dichlorobenzene specif-
ically, but the yield decreased with dilution.
Results of the reaction of nitroarenes with TCCA (0.34 mol equiv) in 98% H2SO4.
.
Substrate
Product
T (◦C)
r.t.
Yield (%)a
54
130
130
130
74
68
50
a
Yield of pure product, based on nitroarene.
3. Results and discussion
Finally, the reaction of nitrobenzene (the less reactive arene
tested) with TCCA was only effective in 98% H2SO4 after 5 h at 80 ◦C
to produce m-chloronitrobenzene in 80% yield (Table 4).
Based on the above results we studied the chlorination of
some deactivated nitroarenes with TCCA in 98% H2SO4. The reac-
tions were carried out stirring together the nitroarene with TCCA
(0.34 mol equiv) in 98% H2SO4 for 2 h and the results are show in
Table 5. As expected, p-nitrotoluene (the most reactive nitroarene
tested) reacted at room temperature, while more deactivated sub-
In our study, we initially tested the reaction of trichloroiso-
cyanuric acid with arenes with different nucleophilic degrees
(in decreasing order of reactivity with an electrophile): anisole,
toluene, chlorobenzene, and nitrobenzene. The reactions were car-
ried out stirring together the arene (6 mmol) and TCCA (2 mmol) in
3 ml of the chosen solvent.
Anisole reacted smoothly with TCCA in acetonitrile at room
temperature to produce a mixture of o- and p-chloroanisole (91%)
in 1.5 h. The same reaction carried out in 98% H2SO4 produced
Table 6
Enthalpy difference for protonation of TCCA and for single Cl+ loss.a
Reaction
ꢀH1
ꢀH2
−12.0
+51.5
+77.6
+235.9
–
−76.1
−194.2
+278.6
a
Performed at the B3LYP/6-311++G**//B3LYP/6-31++G** level.

180
G.F. Mendonc¸ a et al. / Applied Catalysis A: General 401 (2011) 176–181
Fig. 3. 13C NMR spectra of TCCA in 98% H2SO4.
4. Conclusions
In summary, we have shown that trichloroisocyanuric acid can
be protonated by 98% H2SO4 and DFT calculations, along with 13
C
NMR data, suggest the formation of a monoprotonated superelec-
trophilic species. This species can efficiently transfer electrophilic
Cl+ to even very weak nucleophiles, such as m-dinitrobenzene.
Fig. 2. Geometries for TICA and its protonated forms at B3LYP/6-31++G** level.
Acknowledgements
strates required higher temperatures. Under these conditions, even
1,3-dinitrobenzene, a highly deactivated substrate for electrophilic
substitution, reacted to produce 5-chloro-1,3-dinitrobenzene in
50% isolated yield.
We thank CNPq and FAPERJ for financial support.
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