Mechanism of 1-Acetyl-2-methoxynaphthalene Isomerisation over a HBEA Zeolite

Article abstract of DOI:10.1006/jcat.1999.2762

Over HBEA, liquid phase acetylation of 2-methoxynaphthalene (2-MN) by acetic anhydride leads directly to 1-acetyl-2-methoxy-naphthalene (I), to 2-acetyl-6-methoxynaphthalene (II), and to a small amount of 1-acetyl-7-methoxynaphthalene (III). At a long contact time, isomer I undergoes deacylation into 2-MN and isomerisation into II and III. Isomerisation of I is much faster in the presence of 2-MN than in its absence, which suggests that this reaction occurs through an intermolecular transacylation mechanism. The transformation of isomer I with a deuterated methoxy group (OCD₃) in the presence of 2-MN shows that isomer II results only from this mechanism whereas an intramolecular mechanism participates also in the formation of isomer III.

Full text of DOI:10.1006/jcat.1999.2762

Journal of Catalysis 190, 433–438 (2000)
doi:10.1006/jcat.1999.2762, available online at http://www.idealibrary.com on
Mechanism of 1-Acetyl-2-methoxynaphthalene Isomerisation
over a HBEA Zeolite
�
�
,1
E. Fromentin, J.-M. Coustard,† and M. Guisnet
�
Facult e´ des Sciences Fondamentales et Appliqu e´ es, UMR CNRS 6503 and 6514†, Universit e´ de Poitiers, 40 avenue du Recteur Pineau,
8
6022 Poitiers Cedex, France
Received August 6, 1999; revised November 10, 1999; accepted November 12, 1999
This paper deals with the liquid phase preparation of
Over HBEA, liquid phase acetylation of 2-methoxynaphthalene 2-acetyl-6-methoxynaphthalene (II) which is a precursor
2-MN) by acetic anhydride leads directly to 1-acetyl-2-methoxy- of (S)-Naproxen, an important anti-inflammatory drug.
(
naphthalene (I), to 2-acetyl-6-methoxynaphthalene (II), and to a
small amount of 1-acetyl-7-methoxynaphthalene (III). At a long
contact time, isomer I undergoes deacylation into 2-MN and iso-
merisation into II and III. Isomerisation of I is much faster in the
presence of 2-MN than in its absence, which suggests that this reac-
tion occurs through an intermolecular transacylation mechanism.
The transformation of isomer I with a deuterated methoxy group
Acetylation of 2-methoxynaphthalene (2-MN) was inves-
tigated over solid catalysts by various authors (17–20).
Harvey and M a¨ der (17) studied the acetylation of 2-MN
with acetic anhydride over large pore zeolites. They showed
that 1-acetyl-2-methoxynaphthalene (I) and 2-acetyl-6-
methoxynaphthalene (II) were initially formed, isomer I
undergoing deacylation afterward. Thanks to this deacyla-
tion, isomer II was selectively synthesised at 100 C by use
of a large amount of HBEA catalysts. However, at this tem-
perature, the production of isomer I, which is too bulky to
(
OCD3) in the presence of 2-MN shows that isomer II results only
from this mechanism whereas an intramolecular mechanism par-
ticipates also in the formation of isomer III.
Key Words: 1-acetyl-2-methoxynaphthalene isomerisation; mec-
�
�c 2000 Academic Press
hanisms, intramolecular and intermolecular; acetylation; HBEA enter the pores of a HBEA zeolite, could only occur on the
zeolite.
external surface (18), which is generally very large with this
zeolite.
In this paper we confirm that acetylation of 2-MN over
HBEA leads directly to I and II. Moreover, small amounts
of 1-acetyl-7-methoxynaphthalene (III) are also formed.
This direct acetylation is followed not only by deacylation
of I but also by its isomerisation into II and III. This latter
reaction is demonstrated to occur mainly through an inter-
molecular transacylation mechanism, part of III resulting
however from an intramolecular process.
INTRODUCTION
Arylketones, which are intermediates in the synthesis of
various fragrances and pharmaceuticals, are generally pre-
pared by acylation catalysed by Lewis acids such as AlCl3
(
1–3). As the arylketone forms a stable 1 : 1 molar adduct
with the catalyst, more than stoichiometric amounts of
Lewis acids are required. The adduct is usually hydrolysed
with water and consequently a large amount of inorganic
�
METHODS
by-product, more than 4 mol of Cl /mol of ketone, are gen-
erated when acylchlorides are used as acylating reagents.
This is why the development of alternative acylation pro-
cesses using other acylating agents such as carboxylic acids
or acid anhydrides, and noncorrosive solid and reusable
catalysts, is particularly active. The possibility of using ze-
olites as catalysts for acylation of various aromatics is well
demonstrated (2–20). Furthermore, a commercial process
of acetylation of anisole and of veratrole with acetic anhy-
dride (selectively in the para position) was recently devel-
oped by Rh oˆ ne Poulenc (7, 8).
The reactions were carried out in the liquid phase in
a batch reactor over a HBEA zeolite (total and frame-
work Si/Al ratios of 11 and 15, respectively) provided by
PQ Zeolites and previously calcinated overnight under air
�
flow at 500 C. The total pore volume of the zeolite was
3
� 1
3
0
g
.694 cm g , the total micropore volume of 0.269 cm
�
1
3
� 1
including 0.167 cm g for the structural micropores
3
� 1
and the mesopore volume of 0.525 cm g . These meso-
pores are due to intercrystalline voids resulting from the
agglomeration of the very small crystallites of HBEA: a
TEM micrograph shows that the sample presents crystals
smaller than 20 nm. The concentrations of Br o¨ nsted and
1
To whom correspondence should be addressed. Fax: 05.49.45.37.79.
�
E-mail: michel.guisnet@campus.univ-poitiers.fr.
Lewis acid sites able to retain pyridine adsorbed at 150 C
433
0021-9517/00 $35.00
Copyright �c 2000 by Academic Press
All rights of reproduction in any form reserved.

4
34
FROMENTIN, COUSTARD, AND GUISNET
20
20
� 1
were found to be equal to 3.1 � 10 and 2.3 � 10 sites g
21, 22).
Time zero of the reaction was taken as the time of intro-
(
duction of the zeolite in the reactant mixture heated at the
reaction temperature. Small samples of the reaction mix-
3
ture (0.1 cm ) were taken at various times and analysed by
GC on a 25-m capillary CP Sil 8 CB column. Identification
of the products was carried out by using reference samples
or by mass spectrometry.
The synthesis of nondeuterated 1-acetyl-2-methoxy-
naphthalene (isomer I) was performed according to Ref.
(
23) by reacting 1-acetyl-2-hydroxynaphthalene (1 equiv)
with Me2SO4 (1 equiv) in the presence of K2CO3 (1 equiv)
using acetone as a solvent (54 equiv) under stirring at
room temperature for 24 h. The product is recovered and
recrystallised in petroleum ether (yield of 83% ). Isomer
I deuterated on the methoxy group was prepared through
the same reaction by using deuterated Me2SO4 instead of
nondeuterated Me2SO4. Due to a primary isotopic effect,
FIG. 1. Influence of reaction time (from 1 min to 1 h) on the conver-
sion of 2-methoxynaphthalene (2-MN) at 120 and 155 C. X2-MN/Xmax is the
ratio between the actual conversion and the maximum possible conversion
0.2) with the initial acetic anhydride/2-MN ratio.
�
(
5
days (instead of 1) are necessary for the reaction (yield
after 10–30 min. This quasi-plateau is due to the fact
that acetic anhydride is completely converted both by
acetylation of 2-MN and by hydrolysis during the first 10–
of 80% ; 99% of [D3] species).
3
0 min of reaction time. It may be noted that acetic acid
RESULTS AND DISCUSSION
was found to be inactive as an acylating reagent (4).
1
. Preliminary Results
Acetylation of 2-methoxynaphthalene (2-MN) with
Whatever the temperature, I, II, and III isomersappear as
primary products. Initially, isomer I is largely predominant,
particularly at low temperatures (Table 1). This favourable
substitution of 2-MN at the 1-position could be expected,
thisposition beingthe most activated one (Scheme 1). How-
ever, isomer I disappears afterward at the benefit of II and
III, (Fig. 2). The higher the reaction temperature, the faster
acetic anhydride was first carried out in a batch reactor
under the following conditions: 500 mg of HBEA, 35 mmol
of 2-MN, 7 mmol of acetic anhydride, 39 mmol of nitroben-
zene, which corresponds to a total volume of 10 cm , and
temperatures of 90, 120, and 155 C.
Whatever the temperature, the reaction products are
mainly three isomers indicated as I (1-acetyl-2-methoxy-
naphthalene), II (2-acetyl-6-methoxynaphthalene), and III
3
�
�
this disappearance; thus, after 8 h at 155 C, isomer I has
�
completely disappeared, whereas at 90 C it remains largely
predominant after 25 h (Table 1). Figure 2 shows that this
isomerisation is slower than the direct acetylation of 2-MN
into I and even into II. Therefore, the initial formation of II
cannot be due to a rapid isomerisation of the predominant
(
1-acetyl-7-methoxynaphthalene) resulting from acetyla-
tion of 2-methoxynaphthalene, acetic acid resulting from
this reaction but also from hydrolysis of acetic anhydride
and cracking of the acylation products. The other isomers,
and particularly the one which corresponds to the slightly
activated 3-position of 2-MN (Scheme 1), are observed
only in trace amounts: the sum of their concentrations
is always less than one-third of the concentration of
isomer III. Figure 1 shows that while initially 2-MN is
rapidly transformed, the conversion is nearly constant
TABLE 1
Distribution (%) of Acetylmethoxynaphthalene Isomers
as a Function of Reaction Temperature
Temperature
Reaction time (h)
I
II
III
�
0a
1
5
0a
1
5
9
0 C
88.3
80.8
73.7
8.6
16.2
23.7
3.1
3.0
2.6
2
2
�
1
1
20 C
77
63.9
35.9
20.6
33.3
58.4
2.4
2.8
5.7
�
0a
1
8
55 C
74.5
34.0
0
23.5
59
85.7
2.0
7.0
14.3
a
SCHEME 1
Estimated by extrapolation at zero conversion.

1
-ACETYL-2-METHOXYNAPHTHALENE ISOMERISATION
435
2
-MN acetylation with acetic anhydride. Under these con-
ditions, the isomerisation of I is very slow: only 4% of II
and III can be obtained after 40 h whereas during acety-
lation with acetic anhydride, 50% of these isomers were
formed during the same time, half of this production oc-
curring after the total disappearance of acetic anhydride. A
possible origin of this very low rate of isomerisation could
be the absence of 2-MN in the reactant. Indeed, this com-
pound which is present in large amounts during acetylation
could participate through transacylation in an intermolec-
ular mechanism of isomerisation (reaction 1).
�
FIG. 2. Acetylation of 2-methoxynaphthalene at 120 C. Yields into
acetylmethoxynaphthalene isomers I, II, and III versus reaction time.
It should however be noted that a small amount of 2-MN is
rapidly formed by deacylation of I (14% after 40 h).
product of 2-MN acetylation (I), hence results truly from
acetylation of 2-MN with acetic anhydride.
2
. Influence of 2-MN on the Rate of Isomerisation of I
Whereas isomer I can be completely transformed at
�
1
55 C (after 8 h of reaction), this transformation is not only
To confirm the participation of 2-MN in isomerisation,
due to isomerisation into II and III but also to deacylation.
This deacylation is well-known to occur easily with ketones
hindered in the ortho position in the presence of acidic solu-
tions (24). It is practically negligible at lower temperatures:
at 155 C, there is a decrease in the apparent conversion
of 2-MN whereas it is not the case at lower temperatures
the transformations of I in the presence and in the absence
of 2-MN were compared under identical conditions of
concentrations of I and of nitrobenzene. Indeed, polar
solvents, such as nitrobenzene, can compete with reactants
for adsorption on the acidic sites (25–27). The following
conditions were chosen: 4 mmol of isomer I, 9.7 mmol
of nitrobenzene, and either 20 mmol of 2-MN (A) or of
�
(
Fig. 3). This is why afterward all the reactions were carried
�
out at 120 C.
1
-methylnaphthalene (B) (we have checked that 1-methyl-
The transformation of I was investigated under the fol-
lowing conditions: 500 mg of HBEA, 20 mmol of I, and
naphthalene underwent no reaction), which corresponds
3
in both cases to a total volume of 5 cm . Figure 4 shows
9
.7 mmol of nitrobenzene, which corresponds to a total vol-
that isomerisation is much faster in the presence of 2-MN
than in its absence. The positive effect of 2-MN is more
pronounced for the formation of isomer II (Fig. 4a) than
for that of III (Fig. 4b): the rate of formation of II is 10
times higher, that of III is 5 times higher.
3
ume of 5 cm , i.e., with a concentration of isomer I 14 times
higher than the maximum concentration obtained during
From these experiments it can be concluded that the
formation of isomer II occurs essentially through an in-
termolecular mechanism (reaction 1). This mechanism is
probably the only one which is involved in this formation.
Indeed, the slow formation of II which is observed in con-
ditions B could be due to the small amount of 2-MN rapidly
formed through deacylation of isomer I. On the other hand,
the less pronounced effect of 2-MN on the formation of iso-
mer III suggests a small participation of an intramolecular
mechanism in its formation. Figure 4a shows that the non-
sterically-hindered ketone II undergoes deacylation but,
however, more slowly than isomer I.
3
. Confirmation of the Isomerisation Mechanisms
by Use of Deuterated Isomer I
FIG. 3. Influence of reaction time (from 1 min to 25 or 8 h) on the con-
�
version of 2-methoxynaphthalene (2-MN) at 120 and 155 C. X2-MN/Xmax
is the ratio between the actual conversion and the maximum possible con-
version (0.2) with the initial acetic anhydride/2-MN ratio.
To confirm the isomerisation mechanisms, the trans-
formation of isomer I with a deuterated methoxy group

4
36
FROMENTIN, COUSTARD, AND GUISNET
(
OCD3) in the presence of 2-MN was investigated under
conditions A, the products being analysed by mass spec-
trometry after various reaction times. Only species with
OCD3 or OCH3 groups were found in 2-MN and isomers
I, II, and III, i.e., no single exchange of deuterium atoms
occurs during isomerisation. Both formations of II and III
were slightly slower from deuterated isomer I than from
the nondeuterated one (very small secondary isotopic ef-
fect).
Figure 5 shows the change with reaction time in the per-
centage of deuterated species in isomers I (a), in isomers II
and III (b), and in 2-MN (c). A considerable change in the
isotopic composition of the reactants is observed in the first
minute of reaction: the percentage of deuterated species of
isomer I passes from practically 99% to approximately 70%
whereas the percentage of deuterated species of 2-MN in-
creases from 0 to 30% . Afterward, the change is much less
pronounced, in particular, for 2-MN. The isotopic compo-
sition of isomers II and III depends only slightly on the re-
action time: approximately 15% of the deuterated species
in isomer II and 25% in isomer III.
The small amount of deuterated species in isomers II
and III indicates that at least a large part of isomerisa-
tion does not occur through an intramolecular process
FIG. 5. Isomerisation of deuterated 1-acetyl-2-methoxynaphthalene
�
(
I) at 120 C. Percentage of deuterated species in I (a), II and III (b), and
2-MN (c) versus reaction time.
(
reaction 2)
�
FIG. 4. Isomerisation of 1-acetyl-2-methoxynaphthalene (I) at 120 C.
Yields in isomers II (a) and (III) (b) versus reaction time in the presence
or in the absence of 2-methoxynaphthalene.
but involves most likely transacylation reactions
(reaction 3).

1
-ACETYL-2-METHOXYNAPHTHALENE ISOMERISATION
437
SCHEME 2. Formation of the �-complex from 1-acetyl-2-methoxy-
naphthalene on zeolite.
On the other hand, the deuterated species of isomers II isomer I and deuterated 2-MN molecules (reaction 6).
and III do not result necessarily from reaction 2. Indeed,
this reaction cannot explain the simultaneous formation of
nondeuterated species in isomer I and of deuterated species
in 2-MN. This formation, which occurs very quickly, can
be explained by an intermolecular process involving both
compounds I and 2-MN (reaction 4), i.e., by a transacylation
process similar to the one proposed for the formation of the
nondeuterated isomers II and III.
The initial rate of formation of nondeuterated isomer I
(
measured after 1 min) was found to be 20 times greater
than the rate of production of isomers II and III, indicating
that reaction 4 is really much faster than reactions 3 and 6.
Therefore, it can be considered that most of the deuterated
species found in isomers II and III result from reaction 6,
i.e., that isomerisation of I into II and III occurs mainly
through an intermolecular mechanism.
The non deuterated isomer I can only result from reac-
tion 4. Indeed, in agreement with the literature (19), we
have found that reaction 5, which could lead to this com-
pound,
However the greater percentage of deuterated species in
isomer III than in isomer II suggests that an intramolecular
process (reaction 2) is involved with reaction 3 in the for-
mation of III. This participation of reaction 2 was proposed
above to explain the lower effect of 2-MN on the rate of
formation of isomer III compared to isomer II (Fig. 4).
The mechanism of isomerisation of deuterated I into
nondeuterated I can be explained as follows. The attack
of a proton from the zeolite at the position bearing the acyl
group (IPSO position (29)) leads to a positively charged
was impossible for thermodynamic reasons (28). On the �-complex that is partially stabilised by the methoxy group
other hand, deuterated 2-MN can be formed through reac- and the adjacent aromatic ring (Scheme 2).
tion 4 and also through deacylation of deuterated isomers I,
This complex can also be stabilised by a 2-methoxy-
II, and III. Therefore, if reaction 4 is faster than reaction 3, a naphthalene molecule: indeed, the electron-rich aromatic
large part of the deuterated species found in isomers II and ring of 2-methoxynaphthalene can form some kind of
III should result from transacylation between deuterated charge transfer adduct with the �-complex with both
SCHEME 3. Formation of 1-acetyl-2-methoxynaphthalene from [D3]-1-acetyl-2-methoxynaphthalene.

4
38
FROMENTIN, COUSTARD, AND GUISNET
SCHEME 4. Intramolecular formation of [D3]-1-acetyl-7-methoxynaphthalene from [D3]-1-acyl-2-methoxynaphthalene.
molecules having their aromatic ring plans roughly parallel
to each other (Scheme 3). In this conformation, acyl
transfer from the deuterated �-complex to the nondeuter-
ated 2-MN may occur easily because of entropic factors:
7. Spagnol, M., Gilbert, L., Jacquot, R., Guillot, H., Tirel, P. J., and
Le Govic, A. M., in “Heterogeneous Catalysis and Fine Chemicals
IV” (H. U. Blaser, A. Baiker, and R. Prins, Eds.), Studies Surface
Science Catalysis, Vol. 108, p. 92. Elsevier, Amsterdam, 1996.
8
9
. Spagnol, M., Gilbert, L., and Alby, D., Ind. Chem. Libr. 8, 29 (1996).
. Rohan, D., Canaff, C., Fromentin, E., and Guisnet, M., J. Catal. 177,
296 (1998).
(
favorable conformation) and of energetic (both reactants
and products have nearly the same formation energies).
The intermolecular acyl transfer occurs preferably on
the most reactive C1 carbon of 2-methoxynaphthalene
to form deuterated 2-MN and the C1 �-complex of non-
deuterated 1-acetyl-2-methoxynaphthalene (I). This last
10. Harvey, G., Vogt, A., Kouwenhoven, H. W., and Prins, R., in “Proceed-
ings from the 9th International Zeolite Conference, Montreal, 1992”
(
R. van Ballmoos, J. B. Higgins, and M. M. J. Treachy, Eds.), p. 383.
Butterworth/Heineman, Stoneham, MA, 1993.
11. Freese, U., Heinrich, F., and Roessner, F., Catal. Today 49, 237 (1999).
�
-complex may then lose a proton to afford nondeuterated 12. Neves, I., Jayat, F., Magnoux, P., Perot, G., Ribeiro, F. R.,
Gubelmann, M., and Guisnet, M., J. Mol. Catal. 93, 169 (1994).
3. Guisnet, M., Lukyanov, D. B., Jayat, F., Magnoux, P., and Neves, I.,
Ind. Eng. Chem. Res. 34, 1624 (1995).
4. Subba Rao, Y. V., Kulkarni, S. J., Subrahmanyam, M., and Rama Rao,
A. V., Appl. Catal. A Gen. 133, L1 (1995).
I (Scheme 3). This intermolecular acyl transfer may also
occur in the other activated positions, leading to isomers
II and III.
1
1
On the other hand, the formation of the minor isomer
III was shown to occur partly through an intramolecular 15. Hoefnagel, A. J., and van Bekkum, H., Appl. Catal. A Gen. 97, 87
(
1993).
process. This intramolecular process may be proposed as
resulting from an acyl shift between carbons 1 and 8 of the
1
6. Gunnewegh, E. A., Downing, R. S., and van Bekkum, H., in “Zeo-
lites: A Refined Tool for Designing Catalytic Sites” (L. Bonneviot and
S. Kaliaguine, Eds.), Studies Surface Science Catalysis, Vol. 97, p. 447.
Elsevier, Amsterdam, 1995.
�
-complex resulting from IPSO protonation on the C1 car-
bon. The �-complex obtained leads by proton elimination
to the deuterated III isomer (Scheme 4). A cyclic transition 17. Harvey, G., and M a¨ der, G., Collect. Czech. Chem. Commun. 57, 862
(
1992).
state can be postulated.
1
8. Harvey, G., Binder, G., and Prins, R., in “Catalysis by Microporous
Materials” (H. K. Beyer, H. G. Karge, I. Kiricsi, and J. B. Nagy, Eds.),
Studies Surface Science Catalysis, Vol. 94, p. 397. Elsevier,
Amsterdam, 1995.
The same mechanism could explain a transformation of
III into II. However, as only a small amount of III is ob-
tained, this secondary transformation plays, most likely, a
limited role in the production of II, as furthermore con- 19. Gunnewegh, E. A., Gopie, S. S., and van Bekkum, H., J. Mol. Catal.
A Chem. 106, 151 (1996).
0. Choudary, B. M., Sateesh, M., Kantam, M. L., and Ram Prasad, K. V.,
Appl. Catal. A Gen. 171, 155 (1998).
1. Coutanceau, C., Da Silva, J. M., Alvarez, M. F., Ribeiro, F. R., and
Guisnet, M., J. Chim. Phys. 94, 765 (1997).
22. Guisnet, M., Ayrault, P., Coutanceau, C., Alvarez, M. F., and Datka,
J., J. Chem. Soc. Faraday Trans. 93, 1661 (1997).
firmed by the primary formation of II. On the other hand,
2
2
a direct acyl shift between the carbons 1 and 6 of the
-complex is most unlikely because of the large distance
�
between these carbons, which explains that intramolecular
isomerisation of I into II, if it exists, is very limited.
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1