Zeolites efficiently promote the cyclization of nonactivated unsaturated alcohols

Article abstract of DOI:10.1002/chem.201001593

Excellent cyclization: Zeolites H-BEA, H-MFI, H-FAU, and H-STF were found to be efficient, selective, and reusable catalysts in the cyclization of cis-4-decenol, affording the corresponding tetrahydrofuran with excellent yields to provide a new synthetic route to alkylfurans. Bronsted and Lewis acid sites in the zeolites under study are probably the active sites, because both of them catalyze this reaction.

Full text of DOI:10.1002/chem.201001593

COMMUNICATION
DOI: 10.1002/chem.201001593
Zeolites Efficiently Promote the Cyclization of Nonactivated
Unsaturated Alcohols
[c]
[a]
Elena Pꢀrez-Mayoral,[a, b] InÞs Matos,[a, c] Isabel Fonseca, and Jirˇꢁ Cejka*
ˇ
Tetrahydrofurans are an important class of five-membered
oxygen heterocycles often present in a great variety of natu-
ral products[1] and as synthetic compounds exhibit biological
activity.[2] Among their industrial applications they are
widely used in cosmetic formulations, perfumes and fla-
vors.[3] As examples, mucoxin is a natural product with high
potential as specific antitumor agent against breast carcino-
ma.[4] Furans 1a, 1b and 1c are known as flavors[5] and show
insecticidal activity[6] (Scheme 1).
recently applied to the synthesis of muxocin.[4] In the Green
Chemistry context, Coulombel et al.[8] recently reviewed the
use of trifluoromethane sulfonates, as Lewis superacids and
environmental-friendly catalysts, for intramolecular cycliza-
tion of alcohols of nonactivated olefins, for example, TfOH,
AlACHUTGTNERNNUG(TfO)3 and SnACHTNUGTRENNUNG
heterogeneous catalysts such as hetero
N
ACHTUNGTRENNUNG
uids as solvents,[9] metal(IV) phosphates[10] and Amberlyst
H-15[11] have been reported up-to-now, not including zeolites
as robust catalysts with modulable acidity, useful for produc-
tion of Fine Chemicals.[12] TS-1 has been used for the prepa-
ration of furans by epoxidation/cyclization of unsaturated al-
cohols in the presence of H2O2.[13]
In this communication, we report on the intramolecular
cyclization of cis-4-decenol (2), selected as model unsaturat-
ed alcohol, efficiently catalyzed by several zeolites. Zeolites
offer the possibility of tailoring the appropriate size and
connectivity of their pores and adjusting the concentration
and strength of their active acid sites.[14] Based on our expe-
rience, we selected H-BEA, H-MFI, H-FAU, and H-STF as
catalysts but not H-MOR, which was completely inactive.
Commercial clay, montmorillonite K-10, was used for com-
parison with zeolites in this study.
Scheme 1. Tetrahydrofurans with biological activity.
The simplest synthetic strategies to prepare cyclic ethers
consists of the intramolecular cyclization of suitable unsatu-
rated alcohols or by dehydration of 1,4-diols.[7] Both reac-
tions take place in the presence of Brønsted acids often
used in excess amounts. An alternative to the ring closure of
unsaturated alcohols is the intramolecular oximercuration
Table 1 shows textural and chemical parameters including
type and concentrations of acid sites of zeolites. These zeo-
lites were tested in the cyclization of cis-4-decenol (2) as
shown in Scheme 2.
The cyclization of 2 in nitroethane as solvent at 358 K was
catalyzed by the zeolites of our choice, affording compound
3 with yields in the range of 78–95% (Table 2). In general,
zeolites with 3D and 1D channel structure promote effi-
ciently the cyclization of hydroxyl group to nonactivated C=
C double bond yielding compound 3 with excellent yields.
Furthermore, the reaction takes place with almost total se-
lectivity, yield of pyran 4 being lower than 5% in all cases.
The ring closure provides the corresponding five-membered
ring following the Markovnikovꢀs rule, as expected. In a
blank experiment it was shown that no cyclization of 2 was
observed in the absence of catalyst.
ˇ
[a] Dr. E. Pꢁrez-Mayoral, Dr. I. Matos, Prof. J. Cejka
´
Department of Synthesis and Catalysis, J. Heyrovsky Institute of
Physical Chemistry, Academy of Sciences of the Czech Republic
ˇ
v.v.i., Dolejskova 3, 182 23 Prague 8 (Czech Republic)
Fax : (+420)28658-2307
E-mail: jiri.cejka@jh-inst.cas.cz
[b] Dr. E. Pꢁrez-Mayoral
Departamento de Quꢂmica Inorgꢃnica y Quꢂmica Tꢁcnica
Facultad de Ciencias, UNED, Paseo Senda del Rey 9,
28040 Madrid (Spain)
[c] Dr. I. Matos, Dr. I. Fonseca
REQUIMTE, FCT-UNL, Lisboa (Portugal)
Chem. Eur. J. 2010, 16, 12079 – 12082
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12079

Table 1. Structural and textural parameters of zeolites under study.
lonite K-10 takes place more
rapidly than using zeolites for
short reaction times, this clay is
inactivated with increasing re-
action time. This circumstance
was not observed when using
H-BEA and H-MFI zeolites as
catalysts yielding the furan 3 in
quantitative yield after 2 h.
[b]
[c]
[d]
Catalyst
Origin
Channel
structure
Si/Al
SBET
A
Channel diam-
eter [nm]
cLC
[mmolgÀ1
cBC
[mmolgÀ1
Coke[e]
[wt%]
ratio[a]
[m2 gÀ1
]
R
]
N
]
ACHTUNGTRENNUNG
H-BEA
Zeolyst
3D
12.5
674
0.64ꢅ0.70
0.55ꢅ0.55
0.51ꢅ0.56
0.74
0.54ꢅ0.57
0.65ꢅ0.70
0.26ꢅ0.57
0.40
0.32
–
H-MFI
H-FAU
H-STF
H-MOR
Zeolyst
Zeolyst
Chevron
Zeolyst
3D
3D
1D
2D
15
15
38.5
10
395
769
475
393
0.13
0.18
0.10
0.25
0.25
0.12
0.23
0.27
1.29
2.67
–
5.64
Concentration of Lewis or
Brønsted acid sites differs for
zeolites under study (Table 1)
[a] Determined by ICP-MS. [b] SBET, BET surface area. [c] cLC =concentration of Lewis acid sites. [d] cBC =con-
centration of Brønsted acid sites, both of them determined by FTIR using pyridine as probe molecule.[15b]
[e] Determined by a combustion analyzer EA 2000 (Analytikjena).
Scheme 2. Intramolecular cyclization of cis-4-decenol (2).
Table 2. Conversions for the cyclization of cis-4-decenol (2) over zeolites
and montmorillonite K-10 at 358 K.
Catalyst
t [h]
Yield 3 [%]
H-BEA
H-MFI
H-FAU
H-STF
1.5
2
4
4
1.5
95
90
89
78
65
montmorillonite K-10
With these results in mind, we confirmed that the cycliza-
tion proceeds under milder reaction conditions than those
reported for AlACHTUNGTRENNUNG(TfO)3 (374 K in nitromethane) affording
compound 3 with quantitative yield during 90 min when
using H-BEA. It is important to note that in none cases the
corresponding dehydration product from 2 was isolated. H-
BEA resulted in the most active catalyst. Figure 1 depicts
the kinetic profiles for the reaction in each case. As shown
in Figure 1A, the yield of compound 3 over H-MFI was
slightly lower than for H-BEA at the shortest reaction times
while this trend was inverted from the first 30 min of the re-
action. H-FAU and H-STF were less efficient catalysts as
compared with H-BEA and H-MFI. After 60 or 90 min, it
can be clearly seen (Figure 1A) that the conversion order is
H-BEA > H-MFI > H-FAU > H-STF. No activity of H-
MOR in cyclization of the alcohol 2, even at 373 K, was due
to the highest acid strength of H-MOR and only one-type of
accessible channels in comparison with other zeolite cata-
lysts inducing fast deactivation due to coke formation (cf.
Table 1 for other zeolites). Cyclization of 2 catalyzed by
montmorillonite K-10, under the same experimental condi-
tions, yielded furan 3 in 65% during 90 min. It was observed
a slight evolution of the cyclization reaction from the short-
est reaction times. Thus, compound 3 was obtained in 58%
of yield in only 15 min while reaction times longer than
90 min did not produce increased yield of 3. The results sug-
gest that although the cyclization catalyzed by montmoril-
Figure 1. Kinetic profiles for the cyclization of cis-4-decenol (2) catalyzed
by A) H-BEA (12.5), H-MFI (15), H-FAU (15) and H-STF (38.5) at
358 K (catalyst amount 300 mg). B) H-BEA (12.5). Influence of the cata-
lyst amount.
but both of them could contribute to their catalytic activity
in the cyclization of 2 as reported.[8,11] In more detail, H-
BEA and H-MFI exhibited the highest conversions; H-BEA
being the most active zeolite showing the highest concentra-
tion of Lewis acid sites. This feature strongly suggests that
the cyclization is predominantly promoted by the Lewis acid
sites in zeolites. It is in accordance with the lower catalytic
performance observed for H-FAU and H-STF. Although H-
STF exhibited the lowest conversion of cis-4-decenol, this
zeolite was rather active considering its 1D 10-ring channel
system and low concentration of Lewis acid sites. This fact
could be attributed to its special channel morphology with
18-ring STF cages as described for p-xylene alkylation.[15]
Brønsted acid sites may also contribute to the catalytic ac-
tivity of zeolites; thus, H-MFI with predominantly Brønsted
acid sites is highly active. In contrast, having H-MOR as in-
active catalyst in this cyclization reaction, one can assume
that strong Brønsted acid sites are not sufficient to catalyze
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Zeolites
COMMUNICATION
this reaction even though the size of H-MOR channels is
larger than of H-MFI or H-STF.
Despite different channel sizes and dimensionality, zeo-
lites H-BEA, H-MFI, H-FAU and H-STF catalyze cycliza-
tion of unsaturated alcohols with high conversions. It could
be mostly due to the fact that 2-hexyltetrahydrofuran can fit
into the channel structure of 10-ring zeolites without any
severe steric restrictions. Simultaneously, size of the chan-
nels prevents the formation of more bulky products, which
could block the channel system and decrease the rate of the
reaction.
In addition, Figure 1B depicts the influence of the catalyst
amount used in the cyclization reaction. This study was per-
formed at 358 K when using the most active catalyst, H-
BEA. As shown, the increased catalyst amount from 100 to
300 mg, in all cases, produced slightly increased conversions
clearly detected after 60 or 90 min of the reaction becoming
quantitative within less than 2 h. Lower amount of the cata-
lyst (50 mg) yielded the compound 3 in 60% after 2 h.
Remarkably, the cyclization takes also place at lower re-
action temperatures; as example, the yield of 3, at 337 K
were 92% (6 h) and 99% (24 h) catalyzed by H-BEA and
H-MFI, respectively. In both cases the different catalytic be-
havior was notably observed maintaining the activity order.
Obviously, when operating at higher temperatures the con-
versions were considerably increased and the reaction times
reduced (Figure 2). At the highest temperatures no signifi-
cant differences were found between H-BEA and H-MFI.
However, yields of 3 when catalyzed by zeolite H-BEA at
337 or 313 K were 20% while almost negligible conversion
was obtained over H-MFI. The differences in the conversion
over zeolites H-BEA and H-MFI at low reaction tempera-
tures can be explained either in terms of lower activation
barrier for Lewis acid catalyzed reaction or by a slower dif-
fusivity of reactants/products in 10-ring channel system of
zeolite H-MFI.
Figure 2. Temperature effect in the cyclization of cis-4-decenol (2) cata-
lyzed by A) H-BEA and B) H-MFI.
Experimental Section
The surface areas and void volumes of the zeolites under study were de-
termined from adsorption isotherms of nitrogen at 77 K applying the
BET method using a static volumetric apparatus Micromeritics, ASAP
2020 (Table 1). Type and concentration of acid sites was determined by
FTIR using pyridine as probe molecule with a FTIR Nicolet 6700.
NMR spectra were recorded with a Varian Mercury 300 spectrometer. 1H
chemical shifts (d) in CDCl3 are given from internal tetramethylsilane.
MS spectra were with recorded with a GS/MS ThermoElectron. The re-
actions were followed by GC, Agilent 6850 using mesitylene as internal
standard. All the reagents and solvents were obtained from Aldrich.
Typical procedure: To a solution of cis-4-decenol (2) (2 mmol) in nitro-
ethane (4 mL), at a given reaction temperature, the catalyst (300 mg) was
added and the reaction mixture was stirred during the time shown in
Table 2. Catalysts were activated at 723 K using a ramp of 283 KminÀ1
during 90 min.
Recyclability of studied zeolites should be stressed; partic-
ularly H-BEA can be reused for the preparation of com-
pound 3 while maintaining its catalytic activity during at
least three consecutive cycles.
For the reutilization studies, catalyst was filtered from the reaction crude,
washed with CH2Cl2 for three times and dried at 333 K during 1 h.
In summary, in this communication we report on efficient
zeolite catalysts to synthesize 2-hexyltetrahydrofuran (3)
with almost total conversion and excellent selectivity. The
yield of by-product pyran 4 was in all reactions lower than
5%. H-BEA and H-MFI zeolites were the best catalysts for
the cyclization of cis-4-decenol (2). Probably, the reaction is
catalyzed by both Brønsted and Lewis acid sites in these
zeolites. Pore size and dimensionality in zeolites under study
influence their catalytic activity. In the case of H-STF, lower
conversion values to 3 are probably due to its special cage
structure. Zeolites reported here were found reusable, effec-
tive and selective even more than the other heterogeneous
catalysts reported earlier. This methodology finds its appli-
cation in the synthesis of oxygen heterocycles with industrial
importance.[6,16]
Acknowledgements
ˇ
J.C. thanks the Ministry of Industry and Trade of the Czech Republic
(FT-TA5/005) for financial support of this research. I.M. thanks Funda-
c¼o para CiÞncia e Tecnologia for grant SFRH/BPD/34659/2007.
Keywords: alcohols · cyclization · ethers · heterogeneous
catalysis · zeolites
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Received: June 7, 2010
Published online: September 14, 2010
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