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47
the reactions suffer from lack of chemoselectivity. On the other
hand, limited studies have been reported involving the use of N-
halo compounds in halogenation reactions catalysed by solid acids
[24].
Based on the above considerations, we wish to report here our
results on the reaction of aromatic compounds with the system
TCCA/solid acids.
Fig. 1. Some trihaloisocyanuric acids.
2. Experimental
2.1. Materials and methods
solid was washed with CH2Cl2 (5 mL) in small portions. The result-
ing solution was treated with 10% aqueous Na2S2O3 (5 mL), washed
with water (5 mL) and then dried over anhydrous MgSO4. After fil-
tration and evaporation of the solvent, the residue was analyzed by
GC.
Trichloroisocyanuric acid (Aldrich, 98%), toluene (Carlo Erba,
99%), chlorobenzene (SDS, 99%), nitrobenzene (Merck, 99%) and sol-
vents were used as received. Different commercial zeolites were
tested H-USY (Zeolyst, CBV500), H-BEA (Zeolyst), H-EMT (IS2M,
UHA, Mulhouse), H-MOR (Zeolyst), H-ZSM-5 (Zeolyst CBV30/24)
and H-SAPO-5 (Louvain University, Belgium). Prior to use, these
zeolites were activated at 550 ◦C in static air for 4 h. Non-zeolitic
in MCM-41, SSA = 418 m2/g), SO42−/ZrO2 (SSA = 97 m2/g) [32] and
H3PW12O40 (Aldrich, SSA = 5 m2/g).
The quantification of the Brønsted acid sites present in differ-
ent solid acids was performed according to our home-developed
H/D exchange isotope technique [25–28]. This method is based
on the deuteration of the catalyst by sweeping D2O with nitro-
gen (3 mol%) for 1 h at 200 ◦C. After purging the excess of D2O for
2 h, the D-solid acid catalyst was contacted with water vapor to
perform the back exchange of the Brønsted acid sites. Meanwhile,
partially exchanged water (HxODy) was collected in a cold trap.
this acid solution was then analyzed by 400 MHz 1H and 2H NMR
(CDCl3/CHCl3 mixture used as internal standard). The acid site den-
sity was then calculated based on the H/D ratio determined by NMR
and the weight of HxODy condensed as already reported elsewhere
[25–28].
2.3.2. General procedure for chlorination of chlorobenzene
TCCA (0.6 mmol) was added at room temperature to a well-
stirred suspension of chlorobenzene (1.8 mmol) and the solid acid
(0.54 mmol H+) in the appropriated solvent (10 mL, see Table 3).
After 24 h (reflux or room temperature), the reaction mixture
was cooled, filtered and the solid washed with 1,2-dichloroethane
(5 mL) in small portions. The resulting solution was treated with
10% aq. Na2S2O3 (8 mL), washed with water (8 mL) and then dried
over anhydrous MgSO4. After filtration and evaporation of the sol-
vent, the residue was analyzed by GC.
under flow conditions
The chlorination reaction of nitrobenzene was performed in a
glass flow system with a cylindrical reactor as reported elsewhere
[29]. The gas flow was regulated by means of Brooks 5850E mass
flow controllers and the dry nitrogen flow was set to 100 mL/min
for each experiments. The reaction was carried out by diluting the
catalytic bed (TCCA and H-USY) in an amorphous silica (Grace, USA)
matrix to insure the same height for all catalyst beds. H-USY zeolite
(0.44 mmol H+), TCCA (0.15 mmol) and silica matrix (17 mmol, 1 g)
were blended closely by grinding. The mixture was then transferred
to the cylindrical reactor and the reactor was fixed to the set-up.
The catalytic bed was first dried under dry N2 flow at 150 ◦C for
30 min to desorb the water present in the void volume of the zeolite.
Then, nitrobenzene was supplied in its gaseous state by sweeping a
dry N2 flow through a stripping U-shaped reactor containing liquid
nitrobenzene at room temperature. Hence, this dry nitrogen flow
saturated with nitrobenzene’s vapor pressure was allowed to pass
through the catalytic bed during 5 h. The products were trapped
at −196 ◦C and recovered downstream to the reactor with toluene
(4 mL). After evaporation of the solvent, the residue was analysed
by GC.
Analyses of the reactions were carried out using a GC chro-
matograph with FID using a 30 m (length), 0.25 mm (ID), and
25 m (phase thickness) RTX-5 capillary column and H2 (flow
rate 50 cm/s) as carrier gas (split: 1:10). The chlorinated products
were confirmed by co-injections with the authentic samples and
by GC–MS analyses performed on a Shimadzu GCMS-QP2010S gas
chromatograph with electron impact (70 eV) by using a 30 m DB-5
silica capillary column.
2.2. DFT calculations
All calculations were carried out using the M06-2X functional
and 6-31++G**(C,N,O,H) and ECP(Si,Al,Cl) basis set (see ECP below).
Minima on the potential energy surface were characterised by
absence of the harmonic frequencies of the respective optimized
structures, while the transition state presents a single imaginary
1. All energy differences correspond to enthalpy differences at
298.15 K and 1 atm. The calculations include solvation using the
IEFPCM(H2O) [29]. All calculations were carried out using the
Gaussian 09 package [30].
3. Results and discussion
In our study, we tested the reaction of trichloroisocyanuric
acid with model arenes with different nucleophilic degrees (in
decreasing order of reactivity with an electrophile): toluene,
chlorobenzene, and nitrobenzene. Table 1 presents the several
solid acids of different nature and characteristics (such as micro-
porous zeolites and mesoporous acids) chosen as catalysts for the
reaction. The reactions were typically performed in a round bot-
tom flask under magnetic stirring, using 1 mmol of the aromatic
to 0.3 mol equiv. of H+) of the acid solid and CH2Cl2 or 1,2-
dichloroethane as solvents.
2.3. Chlorination of arenes with TCCA/solid acid
2.3.1. General procedure for chlorination of toluene
TCCA (0.34 mmol) was added at room temperature in small por-
tions to a well-stirred suspension of toluene (1 mmol) and the solid
acid (0.3 mmol H+) in CH2Cl2 (5 mL). After completion of the reac-
tion (determined by GC), the reaction mixture was filtered and the
The results of the reaction of toluene with TCCA using several
solid acids as catalysts are shown in Table 2. One can observe that