A green and sustainable method for the oxidation of 1,3-dihydrobenzo[c] thiophenes to sulfones using metalloporphyrin complexes

Article abstract of DOI:10.1016/j.catcom.2014.06.032

Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[c]thiophenes to sulfones in good to high yields using H ₂O₂ in the presence of catalytic amounts of porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The presence of electron-donating or electron-withdrawing groups, in the benzene ring of 1,3-dihydrobenzo[c]thiophene, is well tolerated.

Full text of DOI:10.1016/j.catcom.2014.06.032

A
green and sustainable method for the oxidation of 1,3-
dihydrobenzo[c]thiophenes to sulfones using metalloporphyrin complexes
Gustavo da Silva, So´nia M.G. Pires, Vera L.M. Silva, Ma´rio M.Q. Simo˜es,
M. Grac¸a P.M.S. Neves, Susana L.H. Rebelo, Artur M.S. Silva, Jose´ A.S.
Cavaleiro
PII:
DOI:
Reference:
S1566-7367(14)00265-9
doi: 10.1016/j.catcom.2014.06.032
CATCOM 3966
To appear in:
Catalysis Communications
Received date:
Revised date:
Accepted date:
14 June 2014
25 June 2014
26 June 2014
Please cite this article as: Gustavo da Silva, S´onia M.G. Pires, Vera L.M. Silva,
M´ario M.Q. Sim˜oes, M. Grac¸a P.M.S. Neves, Susana L.H. Rebelo, Artur M.S. Silva,
Jos´e A.S. Cavaleiro, A green and sustainable method for the oxidation of 1,3-
dihydrobenzo[c]thiophenes to sulfones using metalloporphyrin complexes, Catalysis Com-
munications (2014), doi: 10.1016/j.catcom.2014.06.032
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ACCEPTED MANUSCRIPT
A GREEN AND SUSTAINABLE METHOD FOR THE OXIDATION OF
1,3-DIHYDROBENZO[C]THIOPHENES
TO
SULFONES
USING
METALLOPORPHYRIN COMPLEXES
Gustavo da Silva,a,# Sónia M. G. Pires,a,# Vera L. M. Silva,a,* Mário M. Q. Simões,a,*
M. Graça P. M. S. Neves,a,* Susana L. H. Rebelo,b Artur M. S. Silva,a José A. S
Cavaleiroa
aQOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
bREQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto,
Rua do Campo Alegre, 4169-007 Porto, Portugal
#these two authors contributed equally to this work
*Corresponding authors to whom correspondence should be addressed
Phone: +351 234 370 200; Fax: +351 234 370 084; e-mail address: verasilva@ua.pt (V.L.M. Silva)
Phone: +351 234 370 713; Fax: +351 234 370 084; e-mail address: msimoes@ua.pt (M.M.Q. Simões)
Phone: +351 234 370 710; Fax: +351 234 370 084; e-mail address: gneves@ua.pt (M.G.P.M.S. Neves)
Abstract
Two efficient methods are reported for the oxidation of 1,3-dihydrobenzo[c]thiophenes
to sulfones in good to high yields using H2O2 in the presence of catalytic amounts of
porphyrin-based catalysts in ethanol or acetonitrile as solvents at room temperature. The
presence of electron-donating or electron-withdrawing groups, in the benzene ring of
1,3-dihydrobenzo[c]thiophene, is well tolerated.
Keywords: Thiophenes; Oxidation; Catalysis; Metalloporphyrins; Hydrogen peroxide;
Sulfones
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1. Introduction
1,3-Dihydrobenzo[c]thiophene 2,2-dioxides, also named sulfones, are well-known
cyclic diene precursors in Diels-Alder cycloaddition reactions [1,2]. These compounds
are stable intermediates for the generation of ortho-benzoquinodimethanes (o-xylylenes)
or benzocyclobutenes, which can be trapped in situ by several dienophiles, yielding the
corresponding cycloadducts [2]. Ortho-benzoquinodimethanes are particularly useful in
organic synthesis as transient and highly reactive dienes, generated via chelotropic loss
(thermal extrusion) of sulfur dioxide [2]. These compounds have a wide variety of
applications, namely in the synthesis of several natural products and heterocyclic
compounds [3]. In our group, they have been used in Diels-Alder cycloaddition
reactions with several dienophiles such as porphyrin [4,5], fullerene [6], pyrazole [7],
chromone [8-10], chalcone [11], and quinolone [12] derivatives. Therefore, the
development of new, sustainable methods to perform the oxidation of
1,3-dihydrobenzo[c]thiophenes to the corresponding sulfones is of great interest.
Several methods involving different oxidation agents have already been reported to
obtain sulfones from the adequate dihydrobenzo[c]thiophenes. However, these methods
usually require the use of stoichiometric amounts of hazardous oxidants, such as m-
chloroperbenzoic acid (MCPBA) and solvents (e.g. chloroform, methylene chloride),
which generate a large amount of dangerous wastes. The research and application of
“Green Chemistry” principles has led to the development of other methods such as the
use of hydrogen peroxide (in non-chlorinated solvents), as eco-friendlier alternative
oxidation systems, both environmentally and economically desirable [13,14]. Among
the catalysts proposed for the oxidation of sulfides, thiophene and benzothiophenes with
hydrogen peroxide are those based on water-soluble metallophthalocyanines [15],
polyoxometalates [16-18], WOx/ZrO2 [19,20], titanium-containing molecular sieves
[21], vanadium silicates [22],V2O5/TiO2, V2O5/Al2O3 [23-25], supported PdCr2O3,
MnOx, and Co-Mo/Al2O3 [26], and the manganese(IV) complex salt [L2Mn2O3](PF6)2
(L=1,4,7-trimethyl-1,4,7-triazacyclononane) [27]. Acetic acid [16,17,27], acetonitrile
[15,18,19,21,22,25,26], or other polar solvents [19,25] were added to the reaction
mixture to enhance the catalytic activity. Oxidation of benzothiophene by hydrogen
peroxide in the presence of crown ethers with or without a metal catalyst has been
studied as well [28,29]. Recently, we have reported the excellent performance of
metalloporphyrins as catalysts in the oxidation of sulfides and recalcitrant
benzothiophenes and dibenzothiophenes with hydrogen peroxide [30,31]. Those results
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and the fact that only a few reports considered the use of iron(III) and manganese(III)
porphyrin catalytic systems in the oxidation of organosulfur derivatives [32], prompted
us to study for the first time the sulfoxidation of
a
series of
1,3-dihydrobenzo[c]thiophenes with hydrogen peroxide catalysed in the presence of
manganese(III) and iron(III) porphyrin complexes, aiming to develop a facile and eco-
friendly approach for important diene precursor sulfones.
2. Experimental
2.1. Materials and instrumentation
All solvents and reagents were used as received without further purification. Hydrogen
peroxide (30% w/w aqueous solution) and ammonium acetate were purchased from
Sigma-Aldrich. The 1H NMR spectra were recorded on a Bruker Avance 300 at 300.13
MHz, using CDCl3 as solvent and TMS as internal reference. The GC-FID analyses
were performed on a Varian 3900 chromatograph using helium as the carrier gas (30
cm/s) and a fused silica capillary DB-5 type column (30 m x 0.25 mm i.d., 0.25 m film
thickness). The GC-MS analyses were performed on an Agilent 6890N chromatograph
connected to an Agilent 5973 mass quadrupole selective detector operating with an
electron impact mode at 70 eV, using helium as the carrier gas (35 cm/s) and a fused
silica capillary DB-1 type column (30 m x 0.25 mm i.d., 0.15 m film thickness).
2.2. Substrate and catalyst synthesis
The
selected
metalloporphyrin
catalysts,
and
chloro[5,10,15,20-tetrakis(2,6-
chloro[5,10,15,20-tetrakis(4-
dichlorophenyl)porphyrinate]manganese(III)
dimethylamino-2,3,5,6-tetrafluorophenyl)porphyrinate]iron(III), that will be referred as
catalysts (I) and (II), respectively (Figure 1), were synthesized according to well-
established procedures in our laboratory [33,34]. The 1,3-dihydrobenzo[c]thiophenes 1-
4 (Table 1) were obtained using well established procedures [9,13]. In particular, the
experimental procedures for the preparation of thiophenes 2 and 4 as well as the
corresponding NMR data are presented in supplementary information (please see ESI).
2.3. Catalytic studies
In the general procedure for the catalytic assays with the substrates 1-4, the substrate
[0.3 mmol for the Substrate/Catalyst (S/C) molar ratio of 300; 0.9 mmol for the S/C
molar ratio of 900; 1.8 mmol for the S/C molar ratio of 1800], the internal standard
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(chlorobenzene, 0.3 mmol) and the catalyst (1.0 x10-3 mmol) were dissolved in the
appropriate solvent (acetonitrile in the case of manganese catalyst I and ethanol for the
iron catalyst II). Only in the experiments involving the manganese porphyrin a co-
catalyst was added to the reaction mixture, namely ammonium acetate (0.12 mmol).
The reaction mixture was kept under magnetic stirring, in the absence of light, and at
controlled temperature between 22-25 ºC. Finally, the oxidant [30% (w/w) H2O2
aqueous solution diluted 1:10 in the same solvent of the reaction] was progressively
added in aliquots corresponding to half of the substrate amount (0.15 mmol each).
3. Results and discussion
The commonly used synthetic procedure to oxidize the 1,3-dihydrobenzo[c]thiophenes
to the corresponding 1,3-dihydrobenzo[c]thiophene 2,2-dioxides or sulfones requires a
mixture of oxone and aluminium oxide in refluxing chloroform for 4-6 h which, besides
being time consuming, is not an environmentally safe strategy at all. Alternatively, in
some cases the oxidation can be performed using m-chloroperbenzoic acid (2.2 equiv)
in dichloromethane at room temperature, which are both hazardous oxidant and solvent,
respectively. Recently, we have demonstrated the success of metalloporphyrin/H2O2
catalytic systems in the sulfoxidation of benzo- and dibenzothiophenes [30,31].
Encouraged by our previous results we decided to apply a similar approach to the
oxidation of 1,3-dihydrobenzo[c]thiophene derivatives 1-4. Herein we present the
results of the catalytic tests with substrates 1-4 using two well-known and very efficient
metalloporphyrins: catalysts (I) and (II) (Scheme 1). The results are summarized in
Table 1. Both catalytic systems [catalyst I/H2O2 and catalyst II/H2O2] proved to be very
efficient, affording excellent conversion values. In fact, for all the substrates, and using
a substrate/catalyst (S/C) molar ratio of 300, it was possible to achieve conversions of
99.9 % with both catalysts (I) and (II). However, the iron complex (II) appears to be
more efficient as it allows shorter reaction times, under similar reaction conditions.
At the end of the catalysed reactions, all the substrates (1-4) are partially or fully
converted into the corresponding dioxide products (5-8), as represented in Scheme 1. In
fact, these results were observed for all the assays performed with catalyst (I), for which
1
the GC-MS and H NMR analyses of the isolated products confirmed the structure of
sulfones 5-8. In the case of substrate 3, and for the experiments involving catalyst (II),
the formation of sulfone 7 was initially detected. However, it was verified that under
4

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these conditions the sulfone is not stable, affording several non-identified compounds
with lower retention time than the starting thiophene 3.
In general, when comparing the presently disclosed methodology to obtain 1,3-
dihydrobenzo[c]thiophene 2,2-dioxides (sulfones) with the already established ones,
besides overcoming the principal environmental issues (chlorinated solvents are no
longer required, reactions are performed at room temperature and H2O2 is used as
oxidant) this new methodology is also faster. The procedures followed in the
metalloporphyrin catalysed reactions reveal some differences, depending on the metal
present in the macrocycle core. These differences are attributed to distinct catalytic
species involved for manganese or iron complexes, and are related with the solvent used
in the reaction and the presence or the absence of a co-catalyst. For all the assays with
catalyst (I) an aprotic solvent (acetonitrile) and a co-catalyst (ammonium acetate) are
used, while whenever the iron catalyst (II) is employed the solvent needs to be protic
(ethanol) and the reactions are performed in the absence of a co-catalyst [35].
Considering the above-mentioned differences, in general the use of catalyst (II), besides
being more efficient, also allows the establishment of a greener procedure. Moreover, in
this case, the sulfone easily precipitates in the reaction medium (ethanol), as
exemplified in figure 2, thus contributing to a simpler and efficient purification process.
Thinking on the possibility of applying this sustainable procedure to a larger scale
conditions, additional scale-up experiments were performed in the presence of the iron
catalyst (II). Therefore, using substrate 1 as a model reaction, its oxidation was studied
using higher quantities of substrate but maintaining the same amount of catalyst (S/C
molar ratios of 900 and 1800). Thus, as can be observed in Table 1, the excellent
efficiency, namely the selectivity for sulfone 5 (100%) at conversions of 99.9% is
maintained for the S/C molar ratio of 900. For the S/C molar ratio of 1800, the results
merit also to be highlighted, since with a conversion of 91% the sulfoxide is now the
main product (selectivity of 82%). So, depending on the S/C molar ratio, it is possible to
favour efficiently the formation of the sulfone or the sulfoxide products.
4. Conclusions
The use of metalloporphyrin catalysts in the sulfoxidation of 1,3-
dihydrobenzo[c]thiophenes using hydrogen peroxide, as oxidant, proved to be a highly
efficient and environmentally friendly approach. For all the substrates tested excellent
5

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conversions (99.9%) were observed, generally affording the correspondent dioxide
products, which were isolated and characterized.
Despite both catalysts (I and II) remain highly efficient, in general the iron complex (II)
proved to be more active in the oxidations and allows also the use of a more sustainable
synthetic procedure. The solvent used in the reactions with complex (II) is ethanol, no
co-catalyst is necessary, and the products precipitate in the reaction medium facilitating
its isolation.
Acknowledgments
We would like to thank Fundação para a Ciência e a Tecnologia (FCT, Portugal), the
European Union, QREN, FEDER, COMPETE, for funding the Organic Chemistry
Research Unit (QOPNA) (PEst-C/QUI/UI0062/2013) and the Portuguese National
NMR Network. V.L.M. Silva thanks the project New Strategies Applied to
Neuropathological Disorders (CENTRO-07-ST24-FEDER-002034), co-funded by
QREN, Mais Centro-Programa Operacional Regional do Centro, and EU, FEDER for
her Assistant Researcher position. S.L.H. Rebelo thanks NORTE-07-0124-FEDER-
000067-Nanochemistry for her Post Doctoral Grant. S.M.G. Pires thanks FCT for her
PhD Grant (SFRH/BD/64354/2009) and G. Silva also thanks the project QREN
(FCOMP-01-0124-FEDER-010840, PTDC/QUI-QUI/102454/2008).
6

ACCEPTED MANUSCRIPT
A GREEN AND SUSTAINABLE METHOD FOR THE OXIDATION OF
1,3-DIHYDROBENZO[C]THIOPHENES
USING
METALLOPORPHYRIN
COMPLEXES
Gustavo da Silva,a,# Sónia M. G. Pires,a,# Vera L. M. Silva,a,* Mário M. Q. Simões,a,*
M. Graça P. M. S. Neves,a,* Susana L. H. Rebelo,b Artur M. S. Silva,a José A. S
Cavaleiroa
aQOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
bREQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto,
Rua do Campo Alegre, 4169-007 Porto, Portugal.
Ar
Cl
M= Mn(III)
M= Fe(III)
I) Ar=
Cl
M
N
N
N
N
Cl
F
Ar
Ar
F
F
II) Ar=
N
F
Ar
Figure 1- Structure of the catalysts used in the study
Figure 2- Illustration of the sulfone precipitation at the end of reaction if performed in ethanol
7

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Scheme 1- General sulfoxidation of 1,3-dihydrobenzo[c]thiophenes using hydrogen peroxide in
the presence of porphyrin catalysts
8

ACCEPTED MANUSCRIPT
A GREEN AND SUSTAINABLE METHOD FOR THE OXIDATION OF
1,3-DIHYDROBENZO[C]THIOPHENES
TO
SULFONES
USING
METALLOPORPHYRIN COMPLEXES
Table 1. Results obtained in the oxidation of substrates (1-4) with H2O2 catalysed by
the metalloporphyrins (I and II)a
Product selectivity (%)
S/C
Conversion
(%)
Time
(min)
Substrates
Catalyst
molar ratio
S=O
SO2
300
300
99.9
99.9
99.9
90.9
-
-
100
100
100
12
120
90
I
II
II
II
900
-
90
(1)
(2)
1800
88
90#
300
300
99.9
99.9
-
-
100
100
120
60
I
II
300
300
99.9
85.0
18
*
82
*
90§
30
I
II
(3)
(4)
300
300
99.9
99.9
-
-
100
100
120
90
I
II
(a)The substrate (0.3 mmol for the S/C molar ratio of 300; 0.9 mmol for the S/C molar ratio of 900; 1.8
mmol for the S/C molar ratio of 1800) was dissolved in 2.0 mL of the appropriate solvent (CH3CN for
catalyst I and ethanol for catalyst II) and kept under magnetic stirring at 22-25 ºC in the presence of the
catalyst (I or II, 1.0 x 10-3 mmol). The oxidant, diluted 1:10 in the same solvent of the reaction, was
progressively added at regular intervals of 15 min in small aliquots, each corresponding to a half-substrate
#
amount. The conversion and selectivity values are the result of at least two essays. Under these
§
conditions the conversion and selectivity values were in the range of ±2.5%. Under these conditions the
selectivity values were in the range of ±1%. *The 85% of conversion after 30 min of reaction were
determined by GC-MS. Under these conditions, the sulfoxide and the sulfone undergo further oxidation
affording several non-identified compounds.
9

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GRAPHICAL ABSTRACT
A GREEN AND SUSTAINABLE METHOD FOR THE OXIDATION OF
1,3-DIHYDROBENZO[C]THIOPHENES
TO
SULFONES
USING
METALLOPORPHYRIN COMPLEXES
Gustavo da Silva,a,# Sónia M. G. Pires,a,# Vera L. M. Silva,a,* Mário M. Q. Simões,a,*
M. Graça P. M. S. Neves,a,* Susana L. H. Rebelo,b Artur M. S. Silva,a José A. S
Cavaleiroa
aQOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
bREQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto,
Rua do Campo Alegre, 4169-007 Porto, Portugal.
H2O2
Cl
Ar
N
N
Ar
Fe
Ar
N
N
R1
R2
Ar
R1
R3
O
R3
S
S
O
Ethanol
r. t.
R2
10

ACCEPTED MANUSCRIPT
A GREEN AND SUSTAINABLE METHOD FOR THE OXIDATION OF
1,3-DIHYDROBENZO[C]THIOPHENES
USING
METALLOPORPHYRIN
COMPLEXES
Gustavo da Silva,a,# Sónia M. G. Pires,a,# Vera L. M. Silva,a,* Mário M. Q. Simões,a,*
M. Graça P. M. S. Neves,a,* Susana L. H. Rebelo,b Artur M. S. Silva,a José A. S
Cavaleiroa
aQOPNA, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal
bREQUIMTE, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade do Porto,
Rua do Campo Alegre, 4169-007 Porto, Portugal.
Highlights
A green and sustainable approach for the oxidation of 1,3-dihydrobenzo[c]thiophenes.
Metalloporphyrins and hydrogen peroxide proved to be a highly efficient at r.t..
Excellent conversions (99.9%) were observed, affording the correspondent sulfones.
For the iron(III) porphyrin the products precipitate directly in the reaction medium.
11

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References
[1] T. Thiemann, D. J. Walton, A. O. Brett, J. Iniesta, F. Marken, Y.-Q. Li, Arkivoc (ix)
(2009) 96-113.
[2] J. L. Segura, N. Martin, Chem. Rev. 99 (1999) 3199-3246.
[3] D. C. Dittmer, A. M. S. Silva, A. C. Tomé, 1,3-Dihydrobenzo[c]thiophene 2,2-
Dioxide. In: e-ROS Encyclopedia of Reagents for Organic Synthesis. John Wiley &
Sons (2009).
[4] A. C. Tomé, P. S. S. Lacerda, M. G. P. M. S. Neves, J. A. S. Cavaleiro, Chem.
Commun. (1997) 1199-1200.
[5] A. C. Tomé, P. S. S. Lacerda, A. M. G. Silva, M. G. P. M. S. Neves, J. A. S.
Cavaleiro, J. Porphyrins Phthalocyanines 4 (2000) 532-537.
[6] A. C. Tomé, R. F. Enes, J. P. C. Tomé, J. Rocha, M. G. P. M S. Neves, J. A. S.
Cavaleiro, J. Elguero, Tetrahedron 54 (1998) 11141-11150.
[7] V. L. M. Silva, A. M. S. Silva, D. C. G. A. Pinto, J. A. S. Cavaleiro, J. Elguero, Eur.
J. Org. Chem. (2004) 4348-4356.
[8] A. Sandulache, A. M. S. Silva, J. A. S. Cavaleiro, Tetrahedron 58 (2002) 105-114.
[9] A. Sandulache, A. M. S. Silva, J. A. S. Cavaleiro, Monatsh. Chem. 134 (2003) 551-
563.
[10] D. T. Patoilo, A. M. S. Silva, D. C. G. A. Pinto, A. C. Tomé, J. A. S. Cavaleiro, J.
Het. Chem. 44 (2007) 1345-1350.
[11] C. M. Brito, D. C. G. A. Pinto, A. M. S. Silva, A. M. G. Silva, A. C. Tomé, J. A. S.
Cavaleiro, Eur. J. Org. Chem. (2006) 2558-2569.
[12] R. S. G. Seixas, A. M. S. Silva, D. C. G. A. Pinto, J. A. S. Cavaleiro, Synlett 20
(2008) 3193-3197.
[13] M. P. Cava, A. A. Deana, J. Am. Chem. Soc. 81 (1959) 4266-4268.
[14] J. A. Oliver, P. A. Ongley, Chem. Ind. (London) (1965) 1024-1024.
[15] N. D’Alessandro, L. Tonucci, M. Bonetti, M. Di Deo, M. Bressan, A. Morvillo,
New J. Chem. 27 (2003) 989-993.
[16] K. Yazu, T. Furuya, K. Miki, K. Ukegawa, Chem. Lett. 32 (2003) 920-921.
[17] C. Komintarachat, W. Trakarnpruk, Ind. Eng. Chem. Res. 45 (2006) 1853-1856.
[18] K. Yazu, T. Furuya, K. Miki, J. Jpn. Petrol. Inst. 46 (2003) 379-382.
[19] L. F. Ramirez-Verduzco, E. Torres-Garcia, R. Gomez-Quintana, V. Gonzalez-
Pena, F. Murrieta-Guevara, Catal. Today 98 (2004) 289-294.
12

ACCEPTED MANUSCRIPT
[20] F. Figueras, J. Palomeque, S. Loridant, C. Feche, N. Essayem, G. Gelbard, J. Catal.
226 (2004) 25-31.
[21] V. Hulea, F. Fajula, J. Bousquet, J. Catal. 198 (2001) 179-186.
[22] Y. Shiraishi, T. Naito, T. Hirai, Ind. Eng. Chem. Res. 42 (2003) 6034-6039.
[23] L. C. Caero, E. Hernandez, F. Pedraza, F. Murrieta, Catal. Today 107-108 (2005)
564-569.
[24] L. C. Caero, F. Jorge, A. Navarro, A. Gutierrez-Alejandre, Catal. Today, 116
(2006) 562-568.
[25] H. G. Bernal, L. C. Caero, Int. J. Chem. Reactor Eng. 3 (2005)
URL:http://www.bepress.com/ijcre/Vol3/A28.
[26] B. Zapata, F. Pedraza, M. A. Valenzuela, Catal. Today 106 (2005) 219-221.
[27] G. B. Shul’pin, G. Süss-Fink, L. S. Shul’pina, J. Mol. Catal. A: Chem. 170 (2001)
17-34.
[28] A. V. Anisimov, A. V. Tarakanova, F. V. Tkhai, Petroleum Chemistry 47 (2007)
225-225.
[29] A. V. Tarakanova, M. Kh. Baishev, E. V. Rakhmanov, S. V. Kardashev, and A. V.
Anisimov, Theor. Found. Chem. Eng. 44 (2010) 540-544.
[30] S. M. G. Pires, M. M. Q. Simões, I. C. M. S. Santos, S. L. H. Rebelo, M. M.
Pereira, M. G. P. M. S. Neves, J. A. S. Cavaleiro, Appl. Catal. A-Gen. 439-440 (2012)
51-56.
[31] S. M. G. ires, M. M. . Sim es, I. C. M. S. Santos, S. L. H. Rebelo, F. A. A. Paz,
M. G. P. M. S. Neves, J. A. S. Cavaleiro, Appl. Catal. B-Environ. 160-161 (2014) 80-
88.
[32] H. Srour, P. Le Maux, S. Chevance, G. Simonneaux, Coord. Chem. Rev. 257
(2013) 3030-3050 and references cited herein.
[33] R. De Paula, M. A. F. Faustino, D. C. G. A. Pinto, M. G. P. M. S. Neves, J. A. S.
Cavaleiro, J. Heterocycl. Chem. 45 (2008) 453-459.
[34] A. D. Adler, F. R. Longo, F. Kampas, J. Kim, J. Inorg. Nucl. Chem. 32 (1970)
2443-2445.
[35] S. L. H. Rebelo, M. M. Pereira, M. M. Q. Simões, M. G. P. M. S. Neves, J. A. S.
Cavaleiro, J. Catal. 234 (2005) 76-87.
13