Synthesis of nopol over MCM-41 catalysts

Article abstract of DOI:10.1039/b206239a

MCM-41 was found to be an active heterogeneous catalyst for the synthesis of nopol by the Prins condensation of β-pinene and paraformaldehyde, but Sn-MCM-41 in which Sn has been grafted on MCM-41 by chemical vapor deposition is far more active and combines high efficiency and recyclability.

Full text of DOI:10.1039/b206239a

Synthesis of nopol over MCM-41 catalysts
Aída Luz Villa de P., Edwin Alarcón and Consuelo Montes de Correa
Departamento de Ingeniería Química, Universidad de Antioquia, Medellín, Colombia.
E-mail: cmontes@catios.ude.edu.co; Fax: (574) 263 8282; Tel: (574) 210 55 37
Received (in Corvallis, OR, USA) 28th June 2002, Accepted 12th August 2002
First published as an Advance Article on the web 11th October 2002
MCM-41 was found to be an active heterogeneous catalyst
for the synthesis of nopol by the Prins condensation of b-
pinene and paraformaldehyde, but Sn-MCM-41 in which Sn
has been grafted on MCM-41 by chemical vapor deposition
is far more active and combines high efficiency and
recyclability.
nopol from b-pinene and paraformaldehyde over MCM-41 and
Sn grafted MCM-41 by CVD (Scheme 1). The latter catalyst
required no solvents or vacuum during its preparation. Fur-
thermore, high yields of nopol were obtained without the use of
chlorinated solvents.
MCM-41 was synthesized according to the procedure
reported by Grun,4 with cethyltrimethylammonium bromide
(CTABr) as template. The molar gel composition was TEOS +
0.15 CTABr + 2.8 NH3 + 141 H2O. The XRD pattern for the as-
synthesized sample exhibits a strong [100] reflection peak with
two small peaks, characteristic of MCM-41 material. After the
organic template was removed by calcination,† the intensity of
the [100] diffraction slightly increased while the peak position
shifted to the low-angle region as previously observed.5 The
BET surface area is 1202 m2 g21 and the pore diameter 1.98 nm.
To obtain Sn grafted MCM-41, 1.0 g of MCM-41 was exposed
to the vapor produced by 1.0 ml SnCl4 (Aldrich) at 100 °C in a
Teflon-lined SS autoclave under autogenous pressure. After
about 8 h the sample was removed from the autoclave,
thoroughly washed with deionized water and calcined to
remove the organic template.† The resulting material, Sn-
MCM-41, exhibited little decrease in the N2 adsorption capacity
and pore diameter. Besides, the MCM-41 structure remained
intact after the Sn deposition. The amount of chlorine present in
Sn-MCM-41 as determined by ionic chromatography was 2.13
mmol g21 and the Sn content obtained by atomic absorption
was 0.51 mmol g21. The tin/chlorine atomic ratio in the fresh
catalyst was found to be 0.24 which is close to that in SnCl4. The
UV-VIS diffuse reflectance spectra of calcined Sn-MCM-41
samples reveal an absorption band at about 208 nm. This band
has been assigned6 to the presence of isolated Sn4+ in tetrahedral
coordination.
Recently, special emphasis has been placed on using natural
renewable raw materials to obtain higher value added products.
In this sense terpenes are widely employed to produce a wide
variety of products such as aromas, food additives, agrochem-
icals and pharmaceuticals. Among terpenes a- and b-pinenes
are the major components of wood turpentine and of numerous
other volatile oils. b-Pinene is a precursor of nopol, an optically
active bicyclic primary alcohol, useful in the agrochemical
industry to produce pesticides. It is also used in the preparation
of soap perfumes, and household products.1 Three general
methods have been used to obtain nopol:2 (1) b-pinene and
paraformaldehyde in acetic acid solution at 120 °C yields nopyl
acetate which is saponified to nopol; (2) heating a mixture of b-
pinene and paraformaldehyde in the presence of a small
quantity of a homogeneous catalyst such as zinc chloride at
115–120 °C for several hours yields about 57% nopol. In both
methods monocyclic isomers and other side products are
formed; (3) autoclaving paraformaldehyde and b-pinene at
150–230°C for several hours yields quantitative amounts of
pure nopol.
In recent years, environmental and economic considerations
have promoted process innovation toward cleaner technologies.
Therefore, there is a great challenge to use heterogeneous
catalysts that can perform under milder reaction conditions, i.e.
lower temperatures, pressures, and which avoid the use of
noxious substances and the generation of toxic waste. Recently,
a MCM-41 anchored quaternary ammonium chloride/SnCl4
catalyst was reported for the Prins condensation of isobutene
and formaldehyde to isoprenol.3 Yields of 90% alcohol were
obtained at 60 °C during 3.5 h. However, catalyst preparation
involved several steps and no report on the activity of the MCM-
41 support was given. Besides, the reaction was carried out in
the presence of a chlorinated solvent. We here report our
preliminary results on the heterogeneous catalytic synthesis of
MCM-41 and Sn-MCM-41 were used to catalyze the Prins
condensation of b-pinene and paraformaldehyde under stirring
at 90 °C in the presence of toluene as solvent. For comparison
Scheme 1 Prins condensation of b-pinene and formaldehyde to nopol.
Table 1 Condensation of b-pinene and formaldehyde to nopol over silica based catalysts and catalyst recyclinga
SnCl4 loading/
mmol (g support)21
Conversion
of b-pinene (%)
Nopol
selectivity (%)
Entry
Catalyst
1
2
3
4
5
6
7
8
Silica gelb
—
—
—
0.51
0.51
0.50
0.50
0.51
37.1
61.3
40
98.9
99.8
99.3
99.6
60
96.1
98.7
98.7
80.5
93.5
93.9
98
MCM-41b
Recycling 1c
Sn-MCM-41
Recycling 1d
Recycling 2d
Recycling 3d
Sn-MCM-41e
65
a Procedure: 0.5 mmol of b-pinene, 1 mmol paraformaldehyde, catalyst containing 12 mmol of Sn and 1 mL of toluene were introduced into a glass reactor
and stirred for 6.5 h at 90°C. b 100 mg catalyst. c Recycling of MCM-41. d Recycling of Sn-MCM-41 after exhaustive washing with acetone at 40 °C and
drying at 100 °C. e Reaction temperature 55 °C, reaction time 2 h.
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CHEM. COMMUN., 2002, 2654–2655
This journal is © The Royal Society of Chemistry 2002

purposes we also tested silica gel (J. T. Baker; average pore
diameter, 15 nm). The catalytic results together with the SnCl4
catalyst loadings in mmol (g support)21 are summarized in
Table 1.
From Table 1 it is clear that MCM-41 and silica gel are active
and selective for nopol production, though MCM-41 is more
active than silica gel. The accessibility of the reactants to the
active sites in the regular and well ordered hexagonal array of
MCM-41 pores allows better diffusion of bulky reactants and
products as compared to silica gel.
However, after reusing MCM-41 its activity decreases and
the catalyst needs to be regenerated by calcination.† In contrast,
Sn-MCM-41 is an excellent catalyst for the Prins condensation
of b-pinene and paraformaldehyde to nopol. It can be reused
after washing with acetone at 40 °C and drying at 100 °C. No
loss of activity was observed after 5 runs. Instead, its selectivity
increases with recycling. We verified that the reaction does not
occur in the absence of catalyst and it is not the result of
homogeneous catalysis by leached elements. The solid catalyst
was filtered out at the reaction temperature, just after 5 min
reaction when b-pinene conversion was only about 5%. This
stopped the reaction with no further conversion being observed
within the next 24 h. Furthermore, as can be observed in Table
1, elemental analysis of Sn in recycled samples confirms that
Sn-MCM-41 is resistant to leaching under the reaction condi-
tions used. The Sn-MCM-41 activity and selectivity to nopol
increase with the reaction temperature from 25 °C up to 90 °C.
As shown in Fig. 1, the reaction is much faster over Sn-MCM-
41 that on MCM-41.
Fig. 1 Conversion of b-pinene vs. time on MCM-41 and Sn-MCM-41.
Reaction conditions: 0.5 mmol of b-pinene, 1 mmol paraformaldehyde, 100
mg catalyst, 90 °C.
condensation of b-pinene with paraformaldehyde in the pres-
ence of toluene. Thus, efficient Sn(IV) sites can be created by a
simplified CVD method and the highly selective and recyclable
catalyst does not need a chlorinated solvent.
The authors gratefully acknowledge COLCIENCIAS-BID
and Universidad de Antioquia for sponsoring this work through
the project 1115-05-040-99.
Notes and references
† Calcination was performed by heating the dried solid at 1 °C min21 to 550
°C and holding this temperature for 5 h.
The present results confirm the previous finding3 that Sn(IV
)
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cations immobilized on MCM-41 material using SnCl4 pre-
cursor are efficient catalytic sites for Prins condensation not
only of simple unsaturated olefins but also of a complex
molecule containing double bonds, such as nopol. Preliminary
characterization results suggest that CVD of SnCl4 lead to a
uniform distribution of the volatile complex throughout the
mesoporous structure of MCM-41 without cluster formation.
The new Sn-MCM-41 catalyst is an efficient, selective and
recyclable catalyst to for the production of nopol by the Prins
CHEM. COMMUN., 2002, 2654–2655
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