9398
J. M. Gnaim, R. A. Sheldon / Tetrahedron Letters 45 (2004) 9397–9399
a
Table 1. Chlorination of phenol with SO
2
Cl
2
in the presence of microporous catalysts
Run No.
Catalyst
Reaction time, h
Yield, mol%
p/o ratio
b
c
Phenol
OCP
PCP
1
2
3
4
5
None
Zn-pillared hectorite
Al-pillared montmorillonite
26
20
91.9
77.9
10.9
4.2
3.0
3.6
5.1
18.5
75.7
83.0
85.3
1.7
5.1
5.7
6.5
8.0
42
22
22
13.4
12.8
10.7
3
+
+
+
Al , Na , K -L zeolite
+
H , Al , Na , K -L zeolite
3+
+
+
4.0
a
Chlorination procedure: to a mixture of phenol (9.4g, 0.10mol), 2,2,4-trimethylpentane (120mL), and the appropriate solid catalyst (10.0g) gently
stirred in a 250mL three-necked round-bottom flask, was added SO Cl
(8.0mL, 0.10mol) dropwise at 25°C. The reaction mixture was st irred at
2
2
this temperature for 20–42h. The solid catalyst was filtered off, volatile solvents were removed under vacuum, and the residue was analyzed by
GLC. The GLC analyses were performed with a Hewlett Packard instrument equipped with a F.I.D. coupled to a Perkin Elmer GP100 recorder.
Yields, given in mol%, determined with 1,2-dichlorobenzene as an internal standard.
OCP: ortho-chlorophenol.
b
c
PCP: para-chlorophenol.
montmorillonite K10, Procter & Gamble clay, laponite
B, surrey powder, fulacolor XW, fulmont premiere, ful-
cat 22A, fulcat 15, or laponite RD clay, resulted in some
catalytic activity. Furthermore, by increasing the
Brønsted acidity of the solid, an increased reaction rate
was achieved. Although, these catalytic systems are
highly specific for monochlorination, relatively poor
regioselectivities were obtained, that is, the para/ortho
ratioswere in the range of 1.0–3.5.
after a 20h reaction. On the other hand, the Al-pillared
montmorillonite, effectively catalyzed the chlorination
of phenol affording a high conversion, ꢀ89% (Table 1,
run 3). Surprisingly, the para/ortho ratio increased dur-
ing the course of the reaction, from 1.8 after 1h to 5.7
after 42h. We can only speculate regarding an explana-
tion for this phenomenon. Possibly, dealumination of
the catalyst by reaction of HCl produced in the system
with the pillaring alumina may afford new aluminum
species, which may enhance the Lewis acidity of the
2
3,24
At the edges of the crystalline clays, the sheet structure is
broken and the crystal is terminated by OH groups. At
high pH, they deprotonate, the edgesbecome negatively
charged, and have a cation exchange capacity. This
interesting property allowed us to introduce mono-, di-,
and trivalent cationsinto the ts ructure of the clay, in
order to enhance itsBrøn st ed and Lewisacidity. Several
catalyst.
Medium pore-size zeolites, such as, H-ZSM-5, TS-1, and
Co-APO-11, and larger pore-size zeolites, such as, Na -
+
+
+
+
+
X, Na -Y, Na -mordenite, and Na , K -L, were tested
in the chlorination of phenol. These catalysts show low
conversions and poor selectivities (para/ortho ratiosof
1.0–2.6) for the para-isomer. The catalytic properties
3
+
3+
2+
+
Al -, Fe -, Cu -, and H -exchanged montmorillonite
2
2
þ
+
clayswere prepared by known techniques,
and tested
of several partially NH -, and H -exchanged zeolites
were also examined. While, the NH -exchanged X, Y,
4
þ
in the chlorination of phenol, affording mixturesof
monochlorophenols with conversions and selectivities
very similar to that of the starting clay mineral (para/
ortho ratios of 1.3–1.8). The poor shape-selectivity
observed with the clays and their analogs, indicates that
the chlorination ismainly occurring on the outer su rface
of the catalyst, rather than inside its interlamellar space.
4
mordenite and L zeolitesgave low es lectivities(
ortho ratiosof 1.1–1.4), the corr pe os nding
exchanged analogs showed relatively improved results
par+a/
H
-
(para/ortho ratiosof 1.3–2.7).
By increasing the amount of the L-type zeolite catalyst,
the selectivity was dramatically improved, yielding a
para/ortho ratio of 5.5. Thisprocesdemanded a rela-
tively large quantity of catalyst. However, we note that
the [catalyst (g)/substrate (mmol)] ratio in our study
(0.1), islower than tho se of previouswork s, for exam-
In order to improve the shape-selective catalysis, a more
highly organized, well-defined, and rigid molecular
pore-size structure is called for. An example of such a
class of materials is the pillared clays, which are micro-
porousmaterialsobtained by propping the i ls icate
sheets of the clay apart with a chemical substance acting
asa molecular prop, and creating a so rt of Ômine shaftÕ
between the layers.
1
5
20
ple, Onaka and Izumi (1.5), Wortle et al. (1.0), Smith
8
1
6
10,18
et al. (1.0), van Dijk et al. (0.9), Smith et al. (0.6–
1
0.7), Smith and Bahzad (0.6), de la Vega et al. (0.3),
Smith et al. (0.3), de la Vega et al.
Masuda (>0.1), and many others, who described the
catalyzed nuclear halogenation of halo- and alkyl-aro-
matic compounds using microporous catalysts.
1
14
1
2
13,19
(0.3), Hojo and
1
7
Asexpected, improved se lectivitieswere achieved for the
para-isomer, using a laboratory synthesized Zn-pillared
hectorite (ꢀ84%, para/ortho ratio of 5.1), and a commer-
cial Al-pillared montmorillonite (ꢀ85%, para/ortho ratio
of 5.7). These results show for the first time, a shape-
selective effect of a solid microporous catalyst on the liq-
uid phase chlorination of phenol (Table 1, runs2 and 3).
To study the effect of the cation type exchanged in the L
zeolite and itscatalytic activity on the chlorination of
phenol, we prepared different partially cation-exchanged
+
+
L zeolites st arting from a commercial Na , K -L zeolite.
The highest para/ortho ratioswere achieved with Al
3
+
,
+
+
+
3+
+
+
However, the Zn-pillared hectorite catalyst was rapidly
deactivated, and only a ꢀ22% conversion was reached
Na , K -L zeolite, and H , Al , Na , K -L zeolite
(6.5 and 8.0, respectively; Table 1, runs4 and 5). Thus,
Gnaim, Jallal M.
