Oxyhalogenation of Aromatics over Copper Phthalocyanines Encapsulated in Zeolites

Article abstract of DOI:10.1006/jcat.1997.1749

The oxychlorination and oxybromination, under near-ambient conditions, of benzene, toluene, phenol, aniline, anisole, and resorcinol, using as catalysts the phthalocyanines of Cu, Fe, and Co encapsulated in zeolites X, Y, and L, are reported. Both H₂O₂ and O₂ have been used as oxidants. HCl and alkali chlorides/bromides have been used as sources of halogens. The metal phthalocyanines wherein the aromatic rings are substituted by -Cl or -NO₂ groups are more active. There is a dramatic increase in the turnover frequencies for substrate conversion when the complexes are encapsulated in the cavities of the zeolites X, Y, or L. The oxyhalogenation of both the aromatic nucleus and the alkyl side chains occur. Oxidation of the aromatic ring (to phenols or cresols, for example) does not occur. Alkyl side chains, however, are oxidized by the oxidant H₂O₂ or O₂ to alcohols, ketones, and acids. The performance of these novel catalyst systems as solid oxyhalogenation catalysts in utilizing O₂ and halide ions in the manufacture of halogenated aromatics holds promise in the organic chemicals industry.

Full text of DOI:10.1006/jcat.1997.1749

JOURNAL OF CATALYSIS 170, 244–253 (1997)
ARTICLE NO. CA971749
Oxyhalogenation of Aromatics over Copper Phthalocyanines
Encapsulated in Zeolites
1
Robert Raja and Paul Ratnasamy
National Chemical Laboratory, Pune 411 008, India
Received September 12, 1996; revised May 13, 1997; accepted May 14, 1997
substrates using H2O2 and halide ions present in the ma-
The oxychlorination and oxybromination, under near-ambient rine environment. The biosynthesis of the brominated com-
conditions, of benzene, toluene, phenol, aniline, anisole, and resor- pounds, for example, is likely to be mediated by vanadium
cinol, using as catalysts the phthalocyanines of Cu, Fe, and Co
encapsulated in zeolites X, Y, and L, are reported. Both H2O2 and
O2 have been used as oxidants. HCl and alkali chlorides/bromides
have been used as sources of halogens. The metal phthalocyanines
lization of the halogen instead of only half of the available
wherein the aromatic rings are substituted by –Cl or –NO2 groups
are more active. There is a dramatic increase in the turnover fre-
quencies for substrate conversion when the complexes are encapsu-
lated in the cavities of the zeolites X, Y, or L. The oxyhalogenation of
both the aromatic nucleus and the alkyl side chains occur. Oxidation
bromoperoxidase through electrophilic bromination by ox-
idized bromine species. While oxyhalogenation using in situ
generated halogens has many advantages (like fuller uti-
halogen, easier transport and handling of the aqueous hy-
drogen halides, and dilute H2O2 compared to halogens, etc.)
the major disadvantages of the present day state-of-the-art
processes in the liquid phase are (1) the high cost of H2O2
of the aromatic ring (to phenols or cresols, for example) does not oc- and (2) the disposal of the homogeneous metal catalysts
cur. Alkyl side chains, however, are oxidized by the oxidant H2O2 or used in the processes. The latter poses additional environ-
O2 to alcohols, ketones, and acids. The performance of these novel mental problems. Very recently, a two-stage vapor phase
catalyst systems as solid oxyhalogenation catalysts in utilizing O2
and halide ions in the manufacture of halogenated aromatics holds
process for the conversion of HCl to Cl2 using solid catalysts
has been reported (6). In the first stage, HCl is reacted over
promise in the organic chemicals industry.
�c 1997 Academic Press
copper oxide at 473K producinga copper chloride complex.
In the second stage, the latter is reacted with O2 at 633 K ox-
idizing the copper chloride to copper oxide and Cl2. A solid-
catalyzed, single-step process using H2O2 or preferably
molecular dioxygen as the oxidant for the oxyhalogenation
of aromatic substrates under near-ambient conditions using
halide ions as the source of halogen will be advantageous.
To our knowledge, oxyhalogenation of aromatic substrates
using solid catalysts in the liquid phase at low temperature
and using O2 as the oxidizing agent has not been reported
so far.
1
. INTRODUCTION
The oxidative liberation of halogens from hydrogen
halides or their salts using H2O2 and suitable, homogeneous
catalysts, has been known for more than 70 years (1). The
halogen generated may be used for
2HX + H2O2 → X2 + 2H2O X = Cl, Br, I
halogenating organic substrates (2, 3). Dinesh et al. (3)
The present paper reports the oxychlorination and oxy-
from our group, for example, have recently shown that am- bromination, under ambient conditions, of aromatic com-
monium metavanadate efficiently catalyzes the oxyhalo- pounds (like benzene, toluene, phenol, aniline, resorcinol,
genation of a variety of organic substrates in moderate and anisole) using, as catalysts, the phthalocyanines of tran-
to good yields, using dilute hydrogen peroxide (30% ) as sition metals (like Fe, Co, Cu) encapsulated in zeolites X,
an oxidizing agent, exhibiting remarkable ortho selectivity Y, and L. Both H O and O have been used as oxidants.
2
2
2
with electron-rich aromatics. Similar results had been re- The performance of these novel catalyst systems as solid
ported earlier by Conte et al. (4) and Rosa et al. (5). In oxyhalogenation catalysts is quite promising.
the above studies (3–5) the authors’ main goal was the
development of functional mimics of the haloperoxidase
marine enzymes. These enzymes oxyhalogenate aromatic
2. EXPERIMENTAL
2
.1. Materials
The neat CuCl Pc (where Pc stands for phthalocyanine)
1
To whom correspondence should be addressed. Fax: -91-212-330233.
E-mail: prcat@ncl.ernet.in.
16
complexes were synthesized according to the procedure
244
0
021-9517/97 $25.00
Copyright �c 1997 by Academic Press
All rights of reproduction in any form reserved.

OXYHALOGENATION OF AROMATICS
245
reported by Birchall et al. (7). First, 2.8 mmol of ered by centrifugation (8000 rpm for 2 h) of the hot slurry.
Cu(CH3CO2)2 (0.56 g, BDH) was mixed with 14.0 mmol Chemical analysis of the clear solution (by atomic absorp-
�
2
(
2.8 g, Aldrich) of tetrachlorophthalonitrile in 40 ml of 1- tion spectroscopy) revealed the presence of 1.6 � 10 g of
chloronaphthalene (Aldrich) in a Parr reactor under ni- Cu in 100 g of the clear solution. In most of the encap-
trogen (500 psi). The mixture was heated for 24 h, cooled sulation experiments, the yield of zeolite solid from 100 g
to room temperature, and centrifuged. Then 200 ml of of the solution was 5–7 wt.% . Since the copper content in
petroleum ether was added to the greenish blue filtrate that most of the zeolite catalysts obtained by encapsulation was
was then submerged in an ice bath. The dark greenish blue about 0.1 wt.% . (equivalent to about 0.5 � 10 g of Cu) it
precipitate was recovered by centrifugation. The CuCl16Pc may be concluded that the zeolite synthesis medium con-
complex was recrystallized from sulfuric acid and isolated tained enough dissolved phthalocyanine complex to lead to
in 50.2% yield. CuPc, CoPc, Cu(NO2)4Pc, FeCl16Pc, and the encapsulation levels observed in Table 1. The synthe-
CoCl16Pc complexes were obtained from M/s. Lona Indus- sis of CuCl16Pc, Cu(NO2)4Pc, FeCl16Pc, and CoCl16Pc com-
�
2
tries, Bombay.
plexes encapsulated in zeolite NaX will now be described.
Before we describe the procedure for the encapsula- Aluminium isopropoxide and NaOH (Aldrich) were used
tion of these copper complexes in zeolites, we have to without further purification. In a typical synthesis, the sil-
address the issue of solubility of these complexes in the icate gel was prepared from 4.0 g fumed silica (Sigma);
zeolite synthesis medium. First, 0.6 g of CuCl16Pc (contain- 3.2 g NaOH; 0.30 g CuCl16Pc, Cu(NO2)4Pc, FeCl16Pc, or
�
2
ing 3.5 � 10 g of Cu) was stirred in 100 g of an aqueous CoCl16Pc; and 8.0 ml H2O. Addition of the aluminate solu-
solution of fumed silica and NaOH (pH = 12.8) at room tion (9.0 g Al (iOPr)3, 3.2 g NaOH, 6.0 ml H2O) resulted in
temperature for 24 h, before heating at 363 K for 12 h. a slurry with an intense greenish/blue colour. An additional
This solution was identical to that used during synthesis 36 ml deionized water was added. The gel was then trans-
of zeolites except that the Al source was not added. The ferred to a polypropylene bottle. The mixture with a mo-
latter precaution was taken to avoid the precipitation of lar composition of SiO2 :Al2O3 :Na2O :H2O : CuCl16Pc =
an aluminosilicate solid. At the end of 12 h, 0.34 of the 3 :1 :3.6 :141 :0.015 was aged at room temperature with stir-
�
2
solid CuCl16Pc (equivalent to 1.9 � 10 g of Cu) was recov- ring for 24 h and then heated at 363 K for 15 h. It was then
TABLE 1
Oxyhalogenation of Toluene: Comparison of Catalysts
Products (wt.% )
TOF
�
1
S. no.
Catalyst
(h
)
A
B
C
D
E
F
G
1
2
3
4
5
6
7
8
9
CuPc
CoPc
Cu(NO2)4Pc
CuCl16Pc
CoCl16Pc
FeCl16Pc
0.32
0.14
2.19
8.92
6.96
—
—
100
100
47.0
17.0
13.5
3.8
12.1
19.7
16.1
—
—
—
—
—
—
18.0
2.6
2.2
—
10.3
2.5
3.1
—
—
—
—
—
—
—
—
—
9.7
—
—
21.2
45.0
52.0
63.5
60.0
50.0
48.5
8.3
15.7
11.5
5.7
4.2
8.6
9.2
5.5
10.7
3.3
11.0
3.7
9.1
9.7
9.0
17.5
16.0
—
10.1
13.4
7.31
CuCl2–Na-Y(0.14) (exchanged)
CuCl16Pc–Na-Y (0.32) (impregnated)
CuCl16Pc + Na-Y
42.44
52.25
47.15
(
Phys. mix.; Cu = 0.11 wt.% )
1
1
1
1
1
1
0
1
2
3
4
5
Cu(NO2)4Pc–Na-X (0.14)
CuCl16Pc–Na-X (0.27)
CuCl16Pc–Na-Y (0.11)
CuCl16Pc–K-L (0.10)
CoCl16Pc–Na-X (0.27)
FeCl16Pc–Na-X (0.16)
99.4
161.32
309.3
382.1
106.7
210.28
18.0
46.5
40.4
8.5
45.0
49.5
58.5
31.5
30.3
21.0
9.0
5.0
14.3
17.4
18.7
18.2
8.5
1.5
6.3
9.6
23.5
7.5
15.2
17.0
1.4
2.3
3.5
2.2
—
—
—
—
24.8
18.1
17.3
—
—
—
—
—
—
9.5
Note. Temperature = 338 K; halide, HCl; toluene: H2O2, 3 mole; TOF, turnover frequency; moles of substrate
converted per mole of copper per hour. The TOF and selectivity values are reproducible to about � 10% . A,
benzaldehyde; B, benzyl alcohol; C, orthochlorotoluene; D, parachlorotoluene; E, benzyl halide; F, di- (mainly
ortho- and para-) and trichlorotoluenes; G, benzoic acid. Sample CuCl2–Na-Y (0.14) (exchanged) was prepared
by ion exchanging 0.14 wt.% of copper from aqueous CuCl2 solution into Na-Y. Sample CuCl16Pc–Na-Y (0.32)
(
0
impregnated) was prepared by impregnating Na-Y with a pyridine-acetic acid (glacial) solution of CuCl16Pc to get
.32 wt.% of copper in the final catalyst. Sample (CuCl16Pc + Na-Y) (phys. mix.; Cu = 0.11 wt.% ) was a physical
mixture of 1.017 g Na-Y and 17.5 mg CuCl16Pc.

246
RAJA AND RATNASAMY
allowed to cool to room temperature and was diluted with
copious amounts of deionized water. The solid crystals were
isolated by centrifugation at 8000 rpm for 2 h. The light,
greenish/blue solid was dried at 363 K for 24 h in air and
extracted (soxhlet) first with acetone, then with pyridine,
acetonitrile, and finally again with acetone for 72 h. It was
�
3
finally dried at 363 K under vacuum (10 Torr) for 15 h. The
X-ray diffraction pattern of the material confirmed it to be
the zeolite Na-X. Na-X with varying loadings of CuCl16Pc,
Cu(NO2)4Pc, FeCl16Pc, or CoCl16Pc was prepared similarly.
The synthesis of CuCl16Pc and Cu(NO2)4Pc encapsulated
in Na-Y was also similar to the synthesis procedure de-
scribed above for Na-X. The silica source was sodium sil-
icate (Lona) and aluminium sulfate (Aldrich) was used as
the alumina source. The SiO2/Al2O3 molar ratio was 2.6.
CuCl16Pc was encapsulated in K-L by the following proce-
dure. First, 12.44 g of fumed silica (Aldrich) was stirred in
1
7 ml of distilled, deionised water for 30 min. Then, 0.15 g
of CuCl16Pc was added to the silica-sol and the mixture was
stirred for another 30 min at 333 K. In a separate polypropy-
lene beaker 8.96 g KOH (A.R. Grade, S.D. Fine Chemicals),
FIG. 1. N2 adsorption isotherms at liquid N2 temperature of Na-Y
A), CuCl16Pc–Na-Y (0.32) (impregnated) (B), and CuCl16Pc–Na-Y (0.17)
encapsulated) (C).
(
(
1
.55 g hydrated alumina (Catapal B, Sigma), and 17 ml dis-
tilled, deionized water were stirred for 60 min at 333 K. The
silica solution containing the metal complex was gradually
added to the alumina solution over a period of 45 min. An
additional 10 ml distilled deionized water was added to get a
uniform gel. The contents were stirred for a further 60 min
and then transferred to an autoclave reactor (Parr). The
autoclave was maintained at 414 K, for 4.5 days under stir-
ring (rpm = 300). The SiO2/Al2O3 ratio of the final zeolite L
was 6.8. Zeolites containing impregnated Pc (Table 1, No. 8;
Fig. 1B) were prepared by dissolving the Pc in a pyridine-
acetic acid (glacial) solution and “dry-impregnating” the
zeolite with the solution. The catalysts are designated by the
following notation [(Complex)-(Zeolite) (metal content in
the zeolite, wt.% )]. Thus CuCl16Pc–Na-X (0.27) designates
odically, samples were removed and centrifuged to remove
the solid catalyst. Copper was not detected (by atomic ab-
sorption spectroscopy, Hitachi Model Z-8000) in the color-
less reaction product when using any of the solid catalysts
used in the present study. In the case of oxyhalogenation
reactions using molecular O2 as the oxidant, tertiary butyl
hydroperoxide (TBHP, 70% aqueous solution, Aldrich, eq-
uivalent to 1% by weight of the substrate) was added to the
reaction mixture before air was admitted to the Parr auto-
clave (300 ml). The substrates chosen were toluene, phenol
(
(
A.R. grade, S.D. Fine Chemicals, India), aniline, resorcinol
B.D.H.), anisole, and benzene (Aldrich, USA).
a Na-X zeolite containing 0.27 wt.% copper in the form of
a hexa decachloro copper phthalocyanine complex encap-
2.2.2. Product analysis. The products of the oxyhalo-
sulated, most probably, in the supercages of the faujasite genation reaction were analyzed by gas chromatography
structure.
(Hewlett–Packard, 5880 A), employing a FID detector
and equipped with a capillary column (50 m � 0.25 mm
crosslinked methyl silicone gum). At the end of the reac-
tion, the halogenated aromatics were extracted with diethyl
ether and saturated with sodium hydrogen carbonate prior
to analysis. In some cases, the products were isolated by
column chromatography, after appropriate work-up to es-
tablish yields. The identity of the products was further con-
firmed by GC–MS (Shimadzu QCMC-QP2000A).
2
.2. Procedures
.2.1. Catalytic reactions. In a typical oxyhalogenation
2
reaction, the solid catalyst (0.2 to 0.75 g) was added to
the substrate in a suitable solvent (for example, a 1 : 2 vol-
ume mixture of water : acetonitrile) where the halide source
KX or HX (X = Cl, Br, I) was previously dissolved. When
HCl was used as the halide source the pH of the mixture
was adjusted to 5.0 using phosphate buffer. Aqueous H2O2
2
.3 Catalyst Characterization
(
25 wt.% ) was added after the desired temperature was at-
tained. The catalytic runs were carried out in a three-necked
The copper content and chemical analysis were mea-
flask (100 ml capacity) fitted with a condenser (circulating sured by atomic absorption spectroscopy (Hitachi Model
chilled water) and magnetic stirring. The temperature of Z-8000), EDS (Kevex), and X-ray fluorescence spec-
the reaction vessel was maintained using an oil bath. Peri- troscopy (Rigaku-3070, X-ray spectrometer). Omnisorb

OXYHALOGENATION OF AROMATICS
247
1
00 CX (Coulter Corporation, USA) was used for the mea- ume is still accessible to N2. However, there was a drastic
surement of nitrogen adsorption. Prior to the adsorption reduction in the pore volume in the case of samples con-
measurements, the samples were activated at 373 K for taining the encapsulated copper complex, wherein the ze-
�
6
4
h in high vacuum (1.33 � 10 Pa.) The ESR spectra of olite was synthesized in the presence of the CuCl16Pc com-
the solid catalysts were measured at room and liquid N2 plex (Fig. 1C), providing direct evidence for the presence
temperatures using a Bruker ESR spectrometer (200 D). of the copper complex inside the zeolite cavities and not
X-ray diffractograms of the solid catalysts were recorded on the external surface of the crystals. Similar results were
using a Rigaku D-max III, X-ray diffractometer with a also observed in the case of other encapsulated complexes.
CuK� target. IR and diffuse reflectance UV spectroscopy The structural integrity of the encapsulated complexes was
of the solid catalysts were recorded using a Perkin–Elmer indicated by the XPS, FTIR, and diffuse reflectance UV
1
600 FTIR and a Shimadzu UV-2101 UV–VIS spectropho- spectral data (10–12). However, there was a red shift in
tometer, respectively. The IR spectra of the solid catalysts the UV–VIS electronic spectra of the copper complexes on
were recorded in nujol media (Perkin–Elmer). BaSO4 was encapsulation. Thus, the absorption maxima for CuCl16Pc
used as the reference material for recording the diffuse re- shifted from 665.5 and 374.0 nm to 681.0 and 384.0 nm,
flectance spectra in the 200-to 900-nm region. UV spectra of respectively. These spectra are due to ligand-based elec-
�
liquid samples were measured in the 200- to 400-nm region. tronic (� → � ) transitions. There was no similar spectral
XPS of the solid catalysts were recorded with a VG Scien- shift when the CuCl16Pc complex was merely impregnated
tific ESCA III Mark (II) with MgK� (1253.6 A˚ ) as the ex- into the zeolite (Table 1, S. no. 8). Balkus et al. (13) had
citation source. Scanning electron micrographs of the solid also observed a similar phenomenon in the case of Cobalt
catalysts were recorded on a Leica, Stereoscan-440, Cam- (II) and Copper (II) perfluorophthalocyanines encapsu-
bridge, instrument. The samples were dusted on alumina lated in Na-X zeolites and attributed it to the distortion of
and coated with a thin film of gold to prevent surface charg- the phthalocyanine ligand in the supercage of the zeolite.
ingand to protect the surface materialfrom thermaldamage This hypothesis (applicable to the encapsulated CuCl16Pc
by the electron beam. In all analyses a uniform thickness of in our case) is further supported by computer modeling
about 0.1 mm was maintained. Molecular modeling studies and molecular strain energy minimization calculations (see
were carried out on a Silicon Graphics, Indigo-2 worksta- Experimental). The latter indicate that the geometric en-
tion, using the Insight II software supplied by Biosym, Inc. vironment around the copper is distorted from the square
(
8). The computer models of Pc and Cl14Pc were generated planar symmetry (of the free complex) when encapsulated
and their geometries optimized with respect to their strain in the supercage of the faujasite (Fig. 2). The copper atom
energyusingmolecular mechanicsand energyminimization is now at the bottom of a hydrophobic bowl. The red shift
procedures (9). As a first approximation, it was assumed observed in the UV–VIS spectra provides experimental ev-
that CuPc and CuCl14Pc will have geometric strains similar idence for this molecular distortion. The additional strain
to Pc and Cl14Pc, respectively. This assumption is justified energy required for this distortion (3.6 K cal/mol) is avail-
in view of the small volume occupied by the Cu2 ion in able to the system during the synthesis of the encapsulated
+
the phthalocyanine complex. The interaction potentials of catalyst. Substituted phthalocyanines are known to be quite
2+
Cu and the other atoms of the complex have not, so far, rugged and stable up to about 773 K. Such distortions of the
been reported in literature. symmetry of the complex from square planarity to quasi-
tetrahedral symmetry will admix the dxy orbital with dz
2
orbital, leading to a lower electron density on the metal ion
and thereby enhancing the reactivity of the complex toward
molecular O2 (14) in general and in oxidation reactions in
particular.
3
. RESULTS AND DISCUSSION
3
.1. Catalyst Characterization
The X-ray diffractograms of the catalysts containing the
copper complexes did not reveal any significant difference
from those of the pure zeolites. The encapsulation of the
copper complexes inside the zeolite cavities is indicated by
3
.2. Catalytic Activity
Experimental evidence that the oxyhalogenations inves-
the absence of extraneous material by scanning electron tigated in the present study are indeed catalyzed by the
microscopy. The SEM photographs indicate the presence solid zeolite containing the encapsulated complex is pre-
of well-defined zeolite crystals without any patches of ph- sented in Fig. 3. In one of a set of two identical experi-
thalocyanine complexes overlaid on their external surface. ments, the solid catalyst was removed by filtration at a re-
N2 adsorption data (Fig. 1) confirm the presence of the action time of 4 h (Fig. 3B). While conversion of toluene
copper complex inside the zeolite cavities. When CuCl16Pc to oxyhalogenated products continued in the presence of
was merely impregnated on the external surface of Na-Y the catalyst (Fig. 3A), there was no further conversion of
(
Fig. 1B), there was no significant reduction in the volume toluene when the catalyst was removed from the reaction
of N2 adsorbed, indicating that the large internal pore vol- system (Fig. 3B). This indicates that (1) the solid catalyst

248
RAJA AND RATNASAMY
FIG. 2. Energy minimized structure of CuCl14Pc encapsulated inside the supercage of the faujasite structure red, copper; dark blue, nitrogen;
green, carbon; white, hydrogen; light blue, chlorine.
is essential for the oxyhalogenation reaction to occur—this material is negligible—this conclusion was independently
phenomenon was also observed with the other substrates confirmed by the absence of copper in the filtrate (atomic
used in this study; (2) oxyhalogenations of the substrate absorption spectroscopy);and (3) in the absence ofthe cata-
by dissolved copper complexes leached out from the solid lyst, H2O2 alone is unable to oxyhalogenate the substrate to
any significant extent. In independent experiments carried
out in the absence of the catalyst, the conversion of toluene
under otherwise identical experimental conditions of Fig. 3
was about 1.1 wt.% . When molecular O2 with TBHP as the
initiator was used as the oxidant under the same reaction
conditions, the toluene conversion in the absence of the cat-
alyst wasonly2.1wt.% . The zeolitesalone were also catalyt-
ically inactive in oxyhalogenation. Thus, we may conclude
that the oxyhalogenations reported in the present study are
indeed catalyzed by the metal complexes encapsulated in
the zeolite matrix.
The results of the oxychlorination of toluene, using aque-
ous HCl as the halogenating agent and H2O2 as the oxidant,
at 333 K, over the various copper, cobalt, and iron phthalo-
cyanine complexes, in both the neat and the encapsulated
states, are presented in Table 1. The following points may
be noted:
(
1) The unsubstituted metal phthalocyanines have a low
activity; only oxidation reactions by H2O2 are observed.
Halogenated products are not formed.
(
2) The intrinsic catalytic activities (turnover frequen-
cies, TOF) of the neat copper, cobalt, and iron complexes
are of the same order of magnitude.
FIG. 3. Kinetics of toluene oxybromination in the presence of the
solid catalyst CuCl16Pc–Na-X (0.27) (A) and when the catalyst is removed
(3) When the copper ion is exchanged into the zeolite
from the reaction mixture at 4 h reaction time (B).
without the Pc ligand (CuCl –Na-Y (0.14), No. 7), even
2

OXYHALOGENATION OF AROMATICS
249
though the TOF is relatively higher (TOF = 42.44) than that metal complexes in such mesopores from those encapsu-
of the neat Pc complexes (TOF = 8.92), it is still much lower lated inside the channels/cavities of zeolites or chemisorbed
than that of the encapsulated complexes (TOF = 160–380). on the external surface of the zeolite crystals. The relatively
More importantly, significant differences in selectivity are higher activity of zeolite L (compared to Na-X and Na-Y)
seen: Benzoic acid, which is not formed over the Pc catalysts in oxyhalogenation is not surprising in view of the gener-
is seen among the products; on the other hand, the forma- ation and involvement of molecular halogen during oxy-
tion of mono- and dichlorotoluenes (columns C, D, and F), halogenation reaction (see later). Our earlier studies with
typical products of electrophilic chlorination, is much lower various zeolites had clearly established that zeolite L is the
than over the Pc catalysts.
4) When CuCl16Pc is impregnated on Na-Y (No. 8, molecular halogen (15). While the uniqueness of K-L ze-
CuCl16Pc–Na-Y (0.32) (impregnated), although the TOF olites in catalyzing halogenation reactions using molecular
52.25) is higher than that of the neat complexes, it is still halogen over zeolites is well known (15), further studies
most active zeolite for the halogenation of aromatics using
(
(
lower than that of the encapsulated Pc complexes. More are necessary to delineate the role of the zeolite matrix in
interestingly, the ratio of (dichlorotoluenes + trichloro- K-L, if any, in oxyhalogenation reactions using halide ions.
toluenes)/monochlorotoluenes is higher over the impreg- In addition to the above points, it may be mentioned that
nated catalysts compared to the encapsulated catalysts the central transition metal of the phthalocyanine complex
(
compare catalysts 8 and 12, for example). This difference is the seat of catalytic activity. Cl14Pc or phthalocyanines
in selectivity provides additional evidence for the encapsu- of nontransition metals (like Al) had negligible oxidation
lation of the complexes inside the cavities of the zeolites. or oxyhalogenation activity. While there is a loss of zeolite
5) A physical mixture of CuCl16Pc and Na-Y (catalyst crystallinity and catalytic activity when using HCl or HBr as
, Table 1) behaves in a manner similar to that of catalyst 8 the source of halogen, no significant changes were noticed
(
9
(
CuCl16Pc impregnated on Na-Y).
(at least upto 3 cycles) when alkali halides were substituted
(
6) There is a dramatic increase in the turnover fre- for HCl/HBr.
quency (by more than an order of magnitude) when the
halogenated or nitrated complexes are encapsulated in the
The possibility of benzyl alcohol and benzaldehyde aris-
cavities of zeolites. Further, the TOF increases with site iso- ing from side chain halogenation of toluene followed by
lation of encapsulated complexes. A probable explanation hydrolysis was investigated. Benzyl chloride, under the op-
is that at higher occupancy levels of the supercages of the erating conditions of oxyhalogenation is not converted to
zeolite by the phthalocyanine complexes, the diffusional re- benzyl alcohol/benzaldehyde. The experiment of Table 1,
sistance encountered by the substrate toluene molecules in S. no. 12 was repeated using benzyl chloride instead of
reaching the active sites will be higher, leading to lower toluene as the substrate. The conversion of benzyl chloride
TOF values at higher loading levels of the metal complex. after 24 h was 2.2 wt.% (TOF = 21.6). Benzyl alcohol and
(
7) Both oxidation (of the side chain) and oxyhalogena- benzaldehyde were the only products. Hence, we conclude
tion (of both the aromatic nucleus and the side chain) occur. that most, if not all, of the benzyl alcohol/benzaldehyde in
Oxidation of the aromatic ring to cresols, however, does not our product are formed by the direct oxidation of toluene
occur.
and NOT by chlorination followed by hydrolysis.
(
8) Oxychlorination was more dominant than oxidation
The oxyhalogenation of benzene and toluene over
only when the complexes were encapsulated in K-L zeo- CuCl16Pc–Na-X (0.27) using both H2O2 and O2 as oxi-
lite (No. 13, Table 1). Side-chain oxidation by H2O2 was dants is shown in Tables 2 and 3, respectively. Both hydro-
predominant in the case of Na-X. This is the first report of gen and alkali halides were used as the sources of halide
zeolite L-containing phthalocyanine complexes. While the ions. The absence of di- and trihalogenated products in
high content of parachlorotoluene (23.5% ) in the products Table 2 when using O2 as the oxidant is due to the low
compared to Na-X and Na-Y (6.3 and 9.6% , respectively) levels of conversion of benzene. The dihalobenzenes were
may suggest the location of the complex in a shape selective mainly the ortho and para dihaloproducts with the former
environment, the simultaneous formation of rather large being predominant. Oxidation products of benzene (like
quantities of di- and trichlorotoluenes (24.8% ) is intrigu- phenol) were not observed under the reaction conditions
ing. Perhaps, in the case of zeolite L whose channels are too mentioned in Table 2. Similarly, cresols were absent in the
narrow to accommodate a perchlorophthalocyanine com- products from the toluene experiments indicating that ox-
plex, the latter resides in a mesopore formed during the idation/hydroxylation of the aromatic ring (by H2O2) was
synthesis of the zeolite “around” the metal complex. In- negligible. On the other hand, the oxidation of the methyl
deed, this is a distinct possibility in the synthesis of vari- side chain leading to benzyl alcohol and benzaldehyde was
ous metal complexes encapsulated in other zeolites also. significant. Benzoic acid was not observed at these conver-
We are, at present, developing techniques to distinguish, sion levels. The absence of nuclear hydroxylation products
by various physicochemical and structural measurements, (like phenols and cresols) is interesting since, in the absence

250
RAJA AND RATNASAMY
TABLE 2
TABLE 3
Oxyhalogenation of Benzene over CuCl16Pc–Na-X (0.27)
Oxyhalogenation of Toluene over CuCl16Pc–Na-X (0.27)
Halogenated products
Halogenated products (wt.% )
Conv.
(
wt.% )
Conv.
(% )
Oxidant Initiator Halide
(% )
A
B
C
D
E
Oxidant
Initiator
Halide
Mono-
Di-
Tri-
H2O2
H2O2
H2O2
O2
O2
O2
O2
O2
O2
—
—
—
—
TBHP
—
TBHP
—
TBHP
HCl
KCl
KBr
HCl
HCl
KCl
KCl
KBr
KBr
31.5
19.2
26.6
13.5
15.4
8.2
14.0
11.7
16.8
14.5
20.5 15.0
19.0 18.0 15.5
15.0 27.5
9.5 4.5
35.5 20.5 14.5
30.5 23.0 23.0
30.5 26.5
30.5 26.5
6.5
—
7.0
1.0 78.0
6.0 51.5
4.5 43.0
4.0 49.0
1.5 84.5
5.0 24.5
4.0 19.5
H2O2
H2O2
O2
O2
O2
—
—
—
—
TBHP
TBHP
KCl
KBr
KCl
KBr
KCl
KBr
9.7
11.5
3.2
4.1
5.5
47.5
58
100
100
100
100
37
34
—
—
—
—
15.5
8
—
—
—
—
4.5
—
O2
6.2
9.5 16.0 17.5
5.5 12.5 25.0
Note. Temperature = 338 K; duration = 10 h. Oxidations with O2 (air)
were carried out at 400 psig. Tertiary butyl hydroperoxide (70% in H2O)
was used as the initiator. The concentration of TBHP was 2% of the sub-
strate. The dihalobenzenes were mainly ortho-/para dihalo products. The
molar ratio of H2O2 : substrate was 1 : 3.
Note. Temperature = 338 K; duration = 10 h; Toluene: H2O2 = 3 mole.
Oxidation with O2 (air) was carried out at 300 psig. A, orthohalotoluene;
B, parahalotoluene; C, di- and trihalotoluenes; D, benzyl halide; E, benzyl
alcohol + benzaldehyde. See footnote to Table 2 for other details.
of the halide ions, they are formed in significant quantities
(
11). Apparently the nucleophilic halide ions, when present,
ing that the brominating species is not a radical. The latter
usually leads to significant yields of benzyl bromide (15).
Since the liberation of Br2 from KBr by H2O2 in the pres-
ence of homogeneous and enzyme catalysts is well known,
it was expected that the same situation may prevail in the
present case also. If Br2 is formed from KBr in our system,
coordinate with the copper ions and suppress the forma-
tion of intermediates (like dioxygen complexes) that lead
to nuclear hydroxylation. As was to be expected from the
large pore character of zeolite X, there was no pronounced
shape selectivity favoring parahalotoluenes. In order to in-
vestigate the oxybromination of toluene in more detail, the
kinetics of the reaction using H2O2 as the oxidant was stud-
ied (Fig. 4). Oxidation was the predominant reaction in the
initial stages (curve 3, Fig. 4A). There is an induction period
in the formation of brominated products (curve 2, Fig. 4A).
After the significant onset of the oxybromination reaction
it can be detected spectrophotometrically through its com-
�
plex Br which has an absorption maximum at 267 nm. The
3
tribromide ion is formed according to the equilibrium
Br2 + Br� *) Br3
�
�
(
(
about 4 h), the further formation of oxidation products
like benzyl alcohol and benzaldehyde) ceased and toluene
[Br ]
3
Ke =
�
[
Br2][Br ]
was converted mainly to its brominated products. Among
the brominated products, the bromotoluenes were formed Literature values for Ke vary from 15 to 20 M 1 and
�
at a much faster rate than benzyl bromide (Fig. 4B), suggest- are dependent on reaction conditions (16). We analyzed for
FIG. 4. Kinetic plots for the oxybromination of toluene over CuCl16Pc–Na-X (0.27). (A) Curves 1–3 indicate toluene conversion (1), and formation
of halogenated (2) and oxidation (3) products respectively. (B) Curves 4–6 indicate distribution of monobromotoluenes (4), di + tribromotoluenes (5)
and benzyl bromide (6), respectively.

OXYHALOGENATION OF AROMATICS
251
TABLE 4
TABLE 5
Oxyhalogenation of Phenol over CuCl16Pc–Na-X (0.27)
Oxyhalogenation of Aniline over CuCl16Pc–Na-X (0.27)
Halogenated products
Halogenated products
(
wt.% )
(wt.% )
Conv.
(% )
Conv.
(% )
Oxidant
Initiator
Halide
Mono-
Di-
Tri-
Halide
Mono-
Di-
Tri-
H2O2
H2O2
O2
O2
O2
—
—
—
—
TBHP
KCl
KBr
KCl
KBr
KBr
21.2
24.1
7.9
8.8
18.1
42.0
40.0
64.5
62.5
62.0
32.0
33.5
26.5
33.0
25.0
26.0
26.5
9.0
4.5
13.0
KCl
KBr
9.7
10.3
64.0
63.0
30.0
15.5
6.0
21.5
Note. Temperature = 338 K; duration = 10 h; oxidant, O2 (Air) =
4
00 psig. TBHP was used as the initiator. Orthohaloaniline was the major
monohalogenated product. See footnote to Table 2 for other details.
Note. Temperature = 323 K; duration = 10 h; phenol: H2O2 = 3 mole.
Oxidations with O2 (air) were carried out at 300 psig. For other details see
footnote to Table 2.
nuclear halogenation (like chlorotoluenes) predominated
over those like benzyl chloride arising from chlorination of
the methyl side chain.
�
the presence of Br by measuring the absorption at 267 nm
The oxyhalogenation of phenol, aniline, anisole, and re-
3
spectrophotometrically during the course of oxybromina- sorcinol are shown in Tables 4, 5, 6, and 7, respectively. The
tion of toluene (Fig. 5A). In the presence of catalyst but halogenated derivatives of these aromatics are of significant
�
absence of toluene substantial formation of Br (and hence economic value in the fine chemicals industry. The mono-
3
�
Br ) is detected (curve 1, Fig. 5B). Only a trace amount of halogenated derivatives were ortho/para products with the
Br is detected in the absence of both catalyst and toluene ortho products in slight excess. Metahalogenated products
2
�
3
(
curve 2, Fig. 5B). When toluene is present, the concentra- were not observed. Even though Tables 4–7 present re-
�
tion of Br3 (and hence Br2) is suppressed (curves 3 and sults with KCl and KBr as halogenating agents, similar re-
4
, Fig. 5B), presumably because the Br2 formed is immedi- sults were also obtained with NaCl and NaBr, respectively.
ately consumed in the bromination of toluene and hence no Dinesh et al. (3), reported the oxybromination of phenol
�
free Br2 is available to form Br . Hence, our studies suggest and resorcinol with KBr and H O using ammonium meta-
3
2
2
�
that Br2, formed by oxidation from Br , may be the bromi- vanadate dissolved in acetonitrile–H O as solvent. While
2
nating agent. In agreement with this hypothesis, when Br2 phenol could not be brominated by KBr, resorcinol was
is used to brominate toluene over K-L zeolites, the prod- converted to an extent of about 40% during 20 h of reac-
uct pattern (nuclear vs side-chain bromination) was simi- tion at room temperature (entries 10 and 8 in Table 1 of
lar (15) to that observed in the present study; products of Ref. 3). The major product obtained by the bromination
�
FIG. 5. (A) UV spectrum of Br3 in the reaction mixture during oxybromination of toluene by KBr and H2O2 using CuCl16Pc–Na-X (0.27) as
catalyst. (B) Variation in the intensity of the 267 nm band in the presence of catalyst but absence of toluene (curve 1), in the absence of both catalyst
and toluene (curve 2), in the presence of both catalyst and toluene (curve 3), and in the presence of toluene but absence of catalyst (curve 4).

252
RAJA AND RATNASAMY
TABLE 6
Oxyhalogenation of Anisole over CuCl16Pc–Na-X (0.27)
Halogenated products (wt.% )
Monohalo
Conv.
Oxidant
Halide
(% )
ortho
para
2.4. di
2.4.6. tri
H2O2
O2
O2
KBr
KBr
KCl
13.8
6.7
4.8
27.0
18.0
18.5
21.0
7.5
6.5
13.0
55.0
60.5
39.0
19.5
14.5
Note. Temperature = 338 K; duration = 10 h. TBHP was used as an
initiator in oxidation with O2 (air). For other detailssee footnote to Table 2.
of resorcinol was the 2-bromo derivative. Similar results
are also observed over our solid catalysts with both H2O2
and O2 as oxidizing agents. An advantage in the use of O2
during oxychlorination of resorcinol is the higher selectiv- in the oxybromination of resorcinol using CuCl16Pc
ity for the desired monochloro product (Table 7). Conte et
FIG. 6. The influence of pH on the selectivity for brominated products
–
Na-X (0.27), KBr, and
H2O2 at 333 K.
al. (4) had earlier reported the oxybromination of anisole
with H2O2 and KBr using dissolved NH4VO3 as catalyst.
Parabromoanisole was the major monohalogenated prod-
uct. Our results with the solid catalyst CuCl16Pc–Na-X
enzyme vanadium bromoperoxidase but differs from diox-
ovanadium (V) catalysts which require significantly greater
+
acid concentration (� 0.001 MH ) (5). While the reaction
(
0.27) (Table 6) are different; both the ortho and the para
mechanism of oxyhalogenation catalyzed by enzymes is not
yet clear in all detail, it seems to involve a halogenium ion
derivatives are formed in significant quantities. Perhaps, as
suggested by the authors themselves (4), the two phase,
H2O/CHCl3 solvent system, facilitates the selective forma-
tion of the para derivative. The use of solid catalysts in con-
junction with O2 as the oxidizing agent at low temperatures
is a significant advance in the technology of oxyhalogena-
tion of aromatic compounds.
The influence of pH on the selectivity for halogenated
products in the oxybromination of resorcinol with KBr
and H2O2 is shown in Fig. 6. The pH was adjusted with
a phosphate buffer. The optimal performance of our cata-
lyst system in the pH range 5.0–6.0 is similar to that of the
+ � +
(
X ) or hypohalous acid (HO X ) as an intermediate of
the reaction (17, 18). Bromine, for example, is known to be
in equilibrium with the tribromide ion and hypobromous
acid in aqueous systems, the position of the equilibrium
being
�
Br ,H2O
�
Br2
Br + HOBr
3
dependent on the pH ofthe medium. The observation ofBr2
in our system (Fig. 5A), the ortho–para orientation among
the nuclear halogenated products (Table 3, for example)
and the pH dependence of the conversion (Fig. 6) suggest
that the halogenating agent is an electrophilic species.
TABLE 7
Oxyhalogenation of Resorcinol
4
. CONCLUSIONS
Halogenated products
(
wt.% )
We have developed a novel, solid, catalyst system for
Tri- the oxychlorination and oxybromination of aromatics. The
catalysts comprise of the chloro- or nitrophthalocyanines
Conv.
Catalyst
Oxidant Halide (% ) Mono-
Di-
CuCl14Pc–Na-X
CuCl14Pc–Na-X
CuCl14Pc–Na-X
CuCl14Pc–Na-X
CuCl14Pc–K-L
H2O2
H2O2
O2
O2
O2
KBr
KCl
KCl
KBr
KBr
KBr
31.6
28.5
16.5
18.2
14.9
7.5
54.5
59.0
85.5
100
90.0
100
26.5
30.5
14.5
—
10.0
—
19.0
of Cu, Fe, and Co encapsulated in zeolites. They use H2O2
10.5
or O2 as the oxidants and the halides of hydrogen or alkali
metals as the halogenating agents under ambient or near-
ambient conditions. We envisage their application, espe-
cially in the fine chemicals industry, for the manufacture of
halogenated aromatics in an environmentally clean manner
—
—
—
—
Cu(NO2)4Pc–Na-Y
O2
Note. Temperature = 323 K; duration = 10 h. Oxidations with O2 (air)
were done at 300 psig. No initiator was used. 2-halo resorcinol was the ma- using low value halogenating agents like HCl rather than
jor monohalogenated product. For other details see footnote to Table 2.
more expensive halogens, like Cl2.

OXYHALOGENATION OF AROMATICS
253
ACKNOWLEDGMENTS
7. Birchall, J. M., Hazeldine, R. N., and Morley, O. J., J. Chem. Soc. C,
667 (1970).
2
8
. “Insight II User Guide, Version 2.3.5,” Biosym. Technologies,
SanDiego, 1994.
We thank Dr. R. Vetrivel for the molecular modeling work and the
members of the Catalysis Division for experimental assistance. We also
thank the European Commission (Contract C11-CT93-0361) for partial
financial support. R.R. thanks CSIR for a research fellowship.
9. Ermer, O., Structure Bonding 27, 161 (1976).
1
1
1
0. Raja, R., and Ratnasamy, P., Stud. Surf. Catal. A 101, 181 (1996).
1. Raja, R., and Ratnasamy, P., Stud. Surf. Catal. B 103, 1037 (1996).
2. Raja, R., and Ratnasamy, P., Appl. Catal. A: General 143, l45
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