Meta selectivity in the Friedel-Crafts reaction induced by a faujasite-type zeolite

Full text of DOI:10.1021/jo005716r

2
874
J . Org. Chem. 2001, 66, 2874-2876
Meta Selectivity in th e F r ied el-Cr a fts
Rea ction In d u ced by a F a u ja site-Typ e
Zeolite
novel approach, we therefore tried to use a heterogeneous
catalyst for this reaction (Scheme 1).
Instead of aluminum chloride, a faujasite-type zeolite
8
can be used as a thermal catalyst for this reaction. This
Hendrikus W. G. van Herwijnen and Udo H. Brinker*
zeolite contains supercages of 12 Å that can be accessed
through windows of 7.5 Å diameter. Thus, the pores and
cavities are large enough for benzyl chloride to be in-
Institut f u¨ r Organische Chemie, Universit a¨ t Wien,
W a¨ hringer Strasse 38, A-1090 Wien, Austria
9
cluded. The benzyl chloride molecules are believed to be
udo.brinker@univie.ac.at
partly “shielded” by the zeolite framework and are there-
fore not as freely accessible as in solution. Thus, it was
hoped that the ability to polymerize should be reduced.
Indeed, compared with the solvent reaction, consider-
ably less polymer is formed within NaY. After 2 h, only
Received November 2, 2000
Zeolites comprise a broad range of both natural and
synthetic microporous, crystalline aluminosilicates that
are constructed from corner-sharing SiO4/2 and AlO4/2
1
7% was not converted into polymer in the retarded
1
tetrahedra. They have a substantial potential as shape-
solvent reaction (Table, entry 2), whereas 73% could be
isolated from the zeolite (Table, entry 4). Benzylbenzyl
chloride (1) was obtained in yields of 12%. In addition,
selective catalysts. Within their micropores, only mol-
ecules of proper shape and dimension can undergo
reactions. The reaction pathways can be completely
different from those in solution, even for highly reactive
5
3% of unreacted benzyl chloride and 2% of trimers were
recovered from the zeolite. When the reaction time was
prolonged, more benzyl chloride was converted into 1,
increasing the yield remarkably to 33% (Table, entry 6).
Although, with the exception of entry 6, polymer
formation exceeds that of the dimer, these preliminary
results show that zeolites seem destined to become the
medium of choice for coupling reactions that normally
lead to uncontrollable polymerization.
2
intermediates such as carbenes. Pentasil zeolites, such
as ZSM-5, with their three-dimensional framework of
one-dimensional channels, have often been used to obtain
linear” products. For example, para selectivity was
“
observed when ethyl benzene was alkylated within this
3
zeolite. Furthermore, the para isomerization from o- and
m-xylene catalyzed by pentasil zeolites is a major indus-
trial process.4
Without doubt, the most interesting aspect revealed
by these experiments is the peculiar isomer ratio of the
dimers formed. This study presents an example whereby
the “banana-shaped” space created by a cage-window-
cage arrangement favors formation of the “bent” meta
product, even though electronic effects favor the ortho
Faujasite-type zeolites do not have linear pores, but
their cavities are arranged in a tetrahedral pattern.
Nevertheless, some examples of a high para selectivity
in substitution reactions catalyzed by a faujasite exist.5
It is well-known that when a conventional Lewis acid,
like AlCl
3
, is added to benzyl chloride, a polymeric resin
6
and para isomers. The CH Cl pendant in benzyl chloride
is rapidly formed. Indeed, upon addition of AlCl
3
at room
2
has a slight electron-withdrawing inductive effect, which
temperature, neat benzyl chloride immediately polymer-
izes (see Table, entry 1). However, if the dimer 1-(chloro-
methyl)-x-(phenylmethyl)benzene (x ) 2, 3, 4) (benzyl-
benzyl chloride) (1) is sought instead of the polymer, one
must employ a multistep reaction starting from another
compound. But if the Friedel-Crafts reaction from benzyl
chloride with a homogeneous catalyst is preferred, one
should retard the polymerization process to obtain the
primary product. Thus, the solution must be dilute and
the reaction performed at a lower temperature. This
deactivates not only the ortho/para positions, but also,
though to a smaller extent, the meta position. This
deactivation is opposed in the ortho/para positions, but
not in the meta position, by an activating mesomeric
effect. In the case of benzyl chloride, this leads to a
deactivating effect, which is most pronounced in the meta
positions, weaker in the ortho positions and insignificant
in the para position.10 This agrees with the isomer ratio
obtained from the solvent reaction (Table, entry 2). In
the zeolite-catalyzed reactions, however, the meta isomer
is always highly favored (Table, entries 4-8).
7
reaction was conducted 70 years ago. The authors
obtained the dimer in no more than 2% isolated yield,
while our yield was about 8% (see Table, entry 2). In a
Since the meta isomer is generally the thermodynami-
cally most stable isomer,11 one could suspect that the
preference for this isomer is due to thermodynamic
*
To whom correspondence should be addressed. Tel: +43-1-4277
2121; Fax: +43-1-4277 52140.
1) Meier, W. M.; Olson, D. H.; Baerlocher, Ch. Atlas of Zeolite
Structure Types, 4th ed.; Elsevier: London, 1996. Zeolites 1996, 17,
5
(
(8) For the photochemical behavior of BnCl within NaY see: Alvaro,
M.; Corma, A.; Garcia, H.; Miranda, M. A.; Primo, J . J . Chem. Soc.,
Chem. Commun. 1993, 1041-1042. Among other products, 1 was also
formed. The number of isomers of 1 as well as their ratio, however,
were not reported.
1
-230.
(
2) (a) Kupfer, R.; Poliks, M. D.; Brinker, U. H. J . Am. Chem. Soc.
1
994, 116, 7393-7398. (b) Brinker, U. H.; Rosenberg, M. G. In
Advances in Carbene Chemistry; Brinker, U. H., Ed.; J AI: Stamford,
1
998; Vol. 2, pp 29-44.
(9) Approximately 2 mmol of BnCl were taken up by 1 g of activated
zeolite. This corresponds to 3 molecules of BnCl per supercage! This
large number can be explained by assuming that there is one molecule
of BnCl in the center of each supercage, and one in every window
accessing the supercages.
(
3) Kim, J .-H.; Yamagishi, K.; Namba, S.; Yashima, T. J . Chem. Soc.,
Chem. Commun. 1990, 1793-1794.
(
4) H o¨ lderich, W.; Gallei, E. Chem.-Ing.-Tech. 1984, 56, 908-915.
(
5) (a) Chiche, B.; Finiels, A.; Gauthier, C.; Geneste, P.; Graille, J .;
Pioch, D. J . Org. Chem. 1986, 51, 2128-2130. (b) Smith, K.; Bahzad,
(10) Ingold, C. K.; Shaw, F. R. J . Chem. Soc. 1949, 575-581.
(11) (a) McCauley, D. A.; Lien, A. P. J . Am. Chem. Soc. 1952, 74,
6246-6250. (b) Olah, G. A.; Tolgyesi, W. S.; Dear, R. E. A. J . Org.
Chem. 1962, 27, 3441-3449. (c) Olah, G. A.; Tolgyesi, W. S.; Dear, R.
E. A. J . Org. Chem. 1962, 27, 3449-3455. (d) Olah, G. A.; Tolgyesi,
W. S.; Dear, R. E. A. J . Org. Chem. 1962, 27, 3455-3464. (e) Olah, G.
A.; Meyer, M. W. J . Org. Chem. 1962, 27, 3464-3469.
D. Chem. Commun. (Cambridge) 1996, 467-468.
(
6) (a) Friedel, C.; Crafts, J . M. Bull. Soc. Chim. Fr. 1885, 43, 53.
(
b) Montaudo, G.; Passerini, R.; Bottino, F.; Finocchiaro, P. Ann. Chim.
(
Rome), 1967, 57, 905-926.
(
7) Wertyporoch, E.; Farnik, A. J ustus Liebigs Ann. Chem. 1931,
4
91, 265-273.
1
0.1021/jo005716r CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/29/2001

Notes
J . Org. Chem., Vol. 66, No. 8, 2001 2875
Sch em e 1. Dir ection s of Rea ction P a th w a ys
reasons. Strong Lewis acids catalyze the isomerization
of alkyl benzenes, so that the thermodynamic equilibrium
can be reached. However, there are three convincing
arguments against this hypothesis:
Sch em e 2. In d ep en d en t Syn th esis of
-(Ch lor om eth yl)-x-(p h en ylm eth yl)ben zen e (1)
1
First, when the reaction time is extended and if
isomerization were to take place, one would expect that
the share of the thermodynamically most stable isomer
would increase. The isomer ratio, however, remained
unchanged within the experimental error (Table, com-
pare entry 4 with 5 and entry 7 with 8). These results
also rule out the possibility that the meta isomer is the
slowest to be converted into polymer, because also in this
case, the isomer ratio would change with time. In
solution, however, different polymerization rates for 1
were found.6b
Second, the usual strategy to find the thermodynamic
equilibrium is to perform the reaction at higher temper-
atures, so that activation energy barriers become less
important. Thus, at temperatures that are high enough
to reach the thermodynamic equilibrium, the main
isomer obtained is the thermodynamically favored one.
Raising the reaction temperature from room temperature
to 35 °C did not affect the isomer ratio (Table, compare
entry 4 with entry 7 and entry 5 with entry 8) within
the margins of error. Because of complete polymerization
it was not possible to study the isomer ratio of the
reaction in solution at higher temperatures (Table, entry
chloride.13 The ortho isomer of 3 was converted to o-4 with
over a Pd/C catalyst14 because Wolff-Kishner condi-
H
2
tions yielded 4-phenyl-1(2H)-phthalazinone as the main
product.15
In summary, the Friedel-Crafts reaction of benzyl
chloride is a convincing example for the benefits of a
zeolite acid catalyst over a conventional homogeneous
Lewis acid catalyst. The faujasite-type zeolite consider-
ably reduces the usual head-to-tail reaction leading to
polymer. Moreover, its shape-selectivity causes the pre-
dominant formation of the meta dimer, which under
conventional conditions, is difficult to obtain.
3
). Of course, this is not unexpected, since the thermo-
dynamically most stable product is in fact the polymer!
Third, and most convincing, when neat o- or p-benzyl-
benzyl chloride (1) was included within NaY polymeri-
zation continues. Important is, however, that no isomer-
ization takes place. Even after 20 h no other isomers
could be extracted. Next to 1, secondary products [mainly
1
-(hydroxymethyl)-x-(phenylmethyl)benzene
(benzyl-
benzyl alcohol) (5)] were isolated. However, these were
exclusively products with the same constitution as the
included 1.
Exp er im en ta l Section
The 1H and 13C NMR spectra were recorded on a Bruker
Thus, under the reaction conditions applied, no thermo-
dynamic equilibrium is established. The reaction within
the zeolite is kinetically controlled, and the preference
for the formation of the meta isomer is therefore expected
to be due to a molding effect of the zeolite.
To identify the isomers of benzylbenzyl chloride (1)
without doubt, they were synthesized independently from
commercially available benzoyl benzoic acids (3) (Scheme
Avance DPX 250 MHz spectrometer at 300 K. Deuteriochloro-
form was used in all cases. UV spectra were measured on a
Perkin-Elmer Lambda 7 spectrometer.
1
. Cla ssica l Or ga n ic Syn th esis: F r ied el-Cr a fts Syn th e-
sis of 1-(Ch lor om eth yl)-x-(p h en ylm eth yl)ben zen e (1). A
solution of 2 (9.0 mL, 9.1 g, 72 mmol) in nitrobenzene (33 mL)
3
was cooled to -8 °C. AlCl (0.15 g, 1.1 mmol) was added, and
the resulting mixture was stirred for 2 h. The reaction was
quenched by the addition of water (30 mL). The organic phase
was separated from the aq phase and washed with CH Cl . The
2 2
combined organic layers were evaporated under reduced pres-
2
). The reaction sequence included a reductive Wolff-
12
Kishner removal of the ketone to benzylbenzoic acid (4),
reduction with LAH to the corresponding benzylbenzyl
alcohols (5),12,13 and a substitution reaction with thionyl
(14) Horning, E. C.; Reisner, D. B. J . Am. Chem. Soc. 1949, 71,
1
036-1037.
(15) J ohnson, R. E.; Hane, J . T.; Schlegel, D. C.; Perni, R. B.;
(
(
12) Brasen, W. R.; Hauser, C. R. J . Am. Chem. Soc. 1955, 77, 4158.
13) Speeter, M. E. U.S. Patent 2 759 934, 1956; Chem. Abstr. 1957,
Herrmann, J . L., J r.; Opalka, C. J .; Carabateas, P. M.; Ackerman, J .
H.; Swestock, J .; Birsner, N. C.; Tatlock, J . H. J . Org. Chem. 1991, 56,
5218-5221.
5
1, 2044b.

2
876 J . Org. Chem., Vol. 66, No. 8, 2001
Ta ble 1. P r od u cts Obta in ed in th e F r ied el-Cr a fts Rea ction of Ben zyl Ch lor id ea
Notes
c
trimerd (%)
e
f
entry
reaction conditionsb
T (°C)
time (h)
BnCl (%)
0
dimer (%)
0
ratio o:m:p
other (%)
solid (%)
1
2
3
AlCl3,
no solvent
RT
0.1
2
-
0
0
0
0
100
83
g
AlCl3,
C6H5NO2
AlCl3,
C6H5NO2
NaY
NaY
NaY
NaY
NaY
-8
8
0
8
0
35:25:40
-
1
0
RT
2
100
4
5
6
7
8
RT
RT
RT
35j
35j
2h
53
25
45
16
4
12
29
33
24
23
20:60:20
25:65:10
30:60:10
25:65:10
25:65:10
2
9
9
8
3
5
1
1
6
0
27
36
12
46
70
h
24
24
2
24
i
h
h
h
a
b
Conversions and isomer ratios were determined by GC; average of at least 3 experiments. See Experimental Section for details.
Reaction time starts as soon as the BnCl solution is added to the catalyst. d Identified by GC MS. e Mainly benzyl alcohol and dibenzyl
c
ether. f Amount of BnCl converted to polymer in the AlCl3-catalyzed reactions and the amount that could not be extracted in the zeolite-
catalyzed reactions. 0.15 g of AlCl3 added to 9 mL of BnCl. h Extraction times not included. Scaled up by a factor of 10. j Reaction
g
i
temperatures of 35 °C were obtained by keeping the zeolite in refluxing pentane.
sure. Afterward, unreacted 2, and the nitrobenzene, were
removed using vacuum distillation. The resulting brown residue
(m, 1 H); 13C NMR CH
: δ 38.4, 62.9 CH: δ 126.1, 126.7, 127.8,
2
128.2, 128.4, 128.6, 130.4, C: δ 138.4, 138.8, 140.4; m-5: Yield:
1
was extracted with Et
2
O. The extract was weighed and analyzed
0.13 g (0.66 mmol; 56%) colorless oil. H NMR δ 2.83 (s, br, 1
1
3
by GC MS and GC FID. Yield: 8% (not isolated).
H), 4.04 (s, 2 H), 4.62 (s, 2 H), 7.15-7.45 (m, 9 H); C NMR
Syn t h esis of 1-(Ch lor om et h yl)-x-(p h en ylm et h yl)b en -
zen e (1). The three isomers were synthesized in three steps from
the corresponding x-benzoylbenzoic acids (3), which are com-
mercially available from Aldrich.
o-Ben zylben zoic Acid (4). The reduction of o-3 (3.0 g, 13
mmol) was performed in acetic acid (4.5 mL) with 0.3 g of Pd/C
2
CH : δ 41.7, 64.8, CH: δ 124.6, 126.0, 127.4, 128.0, 128.3, 128.5,
128.8, C: δ 140.9, 141.1, 141.2; p-5: Yield: 0.11 g (0.56 mmol;
47%) white crystals. mp 41 °C (lit.16 42 °C); H NMR δ 3.05 (s,
1
1
3
br, 1 H), 4.05 (s, 2 H), 4.67 (s, 2 H), 7.20-7.45 (m, 9 H);
NMR CH : δ 41.6, 64.9, CH: δ 126.0, 127.2, 128.4, 128.8, 129.0,
C: δ 138.5, 140.5, 141.0.
-(Ch lor om eth yl)-x-(p h en ylm eth yl)ben zen e (1). For 4 h,
(0.42 g, 2.1 mmol) was refluxed in 1.1 mL (15 mmol) of SOCl
and one drop of pyridine. The excess SOCl was evaporated and
the crude product cleaned by filtering through silica gel with
Et O/petroleum ether (5:95) eluent. o-1: Yield: 0.38 g (1.8 mmol;
C
2
catalysts at 65 °C and under 1 bar of H
reaction was complete. The catalyst was filtered off and washed
with 25 mL of a hot Na CO solution. Concentrated HCl was
2
gas. After 44 h, the
1
5
2
2
3
2
slowly dropped into the filtrate and the product precipitated.
The product was washed with water and dried overnight over
2
CaCl
2
. Yield: 2.1 g (9.9 mmol; 76%). mp 114 °C (lit.16 115 °C);
1
8
7
1
4%), colorless oil. H NMR δ 4.20 (s, 2 H), 4.59 (s, 2 H), 7.14-
13
1
H NMR δ 4.45 (s, 2 H), 7.1-7.35 (m, 7 H), 7.55 (t, 1 H), 8.05 (d,
.43 (m, 9 H); C NMR CH
2
: δ 38.3, 44.4, CH: δ 126.3, 127.0,
1
3
1
1
2
H), 9.80 (s, br, 1 H); C NMR CH : δ 39.6, CH: δ 125.9, 126.3,
28.5, 128.7, 129.3, 130.4, 130.9, C: δ 135.7, 139.6, 140.0; m-1:
28.3, 129.0, 131.4, 131.6, 132.6, C: δ 140.8, 143.0.
1
Yield: 0.39 g (1.8 mmol; 86%) colorless oil. H NMR δ 4.03 (s, 2
m - or p-Ben zylben zoic Acid (4). To a suspension of 3 (1.0
13
2
H), 4.59 (s, 2 H), 7.13-7.40 (m, 9 H); C NMR CH : δ 41.8,
g, 4.4 mmol) and 0.7 g of finely powdered NaOH in triethylene
glycol (30 mL) was added 0.7 mL of aq hydrazine. The mixture
was heated for 8 h at 110 °C and then for 10 h at 210 °C. The
solution was cooled, and water was added until there was only
one phase. The solution was washed twice with Et O. Concen-
2
trated HCl was dropped slowly to the water phase while stirring,
and white crystals precipitated. The product was filtered off and
4
6.2, CH: δ 126.2, 126.4, 128.5, 128.85, 128.92, 129.0, 129.1, C:
δ 137.6, 140.6, 141.7; p-1: Yield: 0.34 g (1.6 mmol; 76%) colorless
1
oil. H NMR δ 4.02 (s, 2 H), 4.60 (s, 2 H), 7.18-7.38 (m, 9 H);
13
2
C NMR CH : δ 41.6, 46.1, CH: δ 126.2, 128.5, 128.7, 128.9,
1
29.3, C: δ 135.3, 141.5.
2
. Gen er a l P r oced u r e: Zeolite-Med ia ted Or ga n ic Syn -
th esis of 1. Zeolite NaY (2.4 g of LZ-Y52, obtained from Aldrich)
was activated for 2 h in an evaporating dish at 200 °C in a muffle
furnace (lost approximately 24 wt % of lattice water). After the
activating period, the hot zeolite was immediately transferred
into a dry flask filled with argon, and the flask was sealed. As
soon as the zeolite reached room temperature, the loading
solution of 870 mg of 2 in 150 mL of pentane (dried over
molecular sieves prior to use) was added. The suspension was
magnetically stirred during the reaction time. A drying tube
1
7
dried. m-4: Yield: 0.74 g (3.5 mmol; 80%). mp 102-104 °C (lit.
1
1
02-104 °C); H NMR δ 4.09 (s, 2 H), 7.2-7.5 (m, 7 H), 8.0-8.1
13
(m, 2 H); C NMR CH
2
: δ 41.7, CH: δ 126.4, 128.59, 128.62,
1
28.7, 128.9, 130.6, 134.4 C: 129.5, 140.3, 141.7, 172.1; p-4:
1
8
1
Yield: 0.76 g (3.6 mmol; 82%). mp 159 °C (lit. 159 °C). H NMR
1
3
δ 4.05 (s, 2H), 7.20-7.40 (m, 7H), 8.05 (d, 2H); C NMR CH
δ 42.0, CH: δ 126.4, 128.6, 129.0, 129.1, 130.5, C: 127.2, 139.9,
47.6, 172.0.
-(Hydr oxym eth yl)-x-(ph en ylm eth yl)ben zen e (5). A warm
solution of 4 (0.25 g, 1.2 mmol) in 7 mL of Et O was added
dropwise to a stirred suspension of 0.05 g LAH in 2 mL of anhyd
Et O. After refluxing for 1 h, 1 mL of water was added to destroy
the excess of LAH. The ether layer was diluted to 10 mL and
washed twice with 1 mL of a 10% H SO solution. The combined
2
:
1
1
2
containing anhyd CaCl was mounted on the flask to keep out
2
moisture. The guest uptake within the zeolite was monitored
by UV analysis of aliquots from the supernatant solution. The
2
-1
-1
signal of 2 (ꢀ260 nm ) 202 M cm ) decreased as more guest was
taken up by the zeolite. The uptake was found to be rapid: 90%
of the maximum loading was reached within only 5 min and
complete uptake within 15 min. Abundant 2 remaining within
pentane did not react. After the reaction time, the zeolite was
filtered through a glass sinter (Por. 4) and washed several times
with pentane. The zeolite was continuously extracted for 18 h
2
4
acidic aq phases were washed with 5 mL of ether. The organic
phases were combined and washed twice with 2 mL of a 10%
Na
ether. All organic phases were combined and dried overnight
over anhyd MgSO . Evaporation of the solvent afforded 5. o-5:
2 3
CO solution. The basic aq phase was washed with 5 mL of
4
2 2
with hot CH Cl using a Soxhlet apparatus. The solution
obtained was evaporated under reduced pressure and the
recovered material weighed and analyzed (see Table 1).
1
Yield: 0.18 g (0.91 mmol; 76%) colorless oil. H NMR δ 2.04 (s,
br, 1 H), 4.13 (s, 2 H), 4.67 (s, 2 H), 7.15-7.40 (m, 8 H), 7.4-7.5
(
16) Budzikiewicz, H.; Rullk o¨ tter, J .; Schiebel, H. M. Org. Mass
Ack n ow led gm en t. The authors thank R. A. Wagner
for GC MS measurements and helpful discussions.
Spectrom. 1972, 6, 251-264.
(
17) Berg, U.; Åstr o¨ m, N. Acta Chem. Scand. 1995, 49, 599-608.
(18) Singh, A.; Andrews, L. J .; Keefer, R. M. J . Am. Chem. Soc. 1962,
8
4, 1179-1185.
J O005716R