Mesoporous iron phosphate as an active, selective and recyclable catalyst for the synthesis of nopol by Prins condensation.

Article abstract of DOI:10.1039/b313747c

Mesoporous iron phosphate is found to be a highly active and recyclable heterogeneous catalyst for the selective synthesis of nopol by Prins condensation of beta-pinene and paraformaldehyde in acetonitrile at 80 degrees C.

Full text of DOI:10.1039/b313747c

Mesoporous iron phosphate as an active, selective and recyclable catalyst
for the synthesis of nopol by Prins condensation
Unnikrishnan R. Pillai and Endalkachew Sahle-Demessie*
National Risk Management Research Laboratory (NRMRL), Clean Processes Branch, MS 443, United
States-Environmental Protection Agency (US-EPA), Cincinnati, Ohio-45268, USA.
E-mail: Sahle-Demessie.Endalkachew@epa.gov; Fax: 011-513-569-7677
Received (in Corvallis, OR, USA) 29th October 2003, Accepted 6th February 2004
First published as an Advance Article on the web 23rd February 2004
Mesoporous iron phosphate is found to be a highly active and
recyclable heterogeneous catalyst for the selective synthesis of
nopol by Prins condensation of b-pinene and paraformaldehyde
in acetonitrile at 80 °C.
mixing it with 0.05 M sodium acetate in ethanol and stirring at room
temperature for 40 minutes. It was then separated by centrifugation,
washed several times with ethanol and dried at room temperature.
The removal of surfactant was confirmed by an FT IR analysis of
the sample before and after the surfactant removal step.
Mesoporous materials having large internal surface areas and
narrow pore size distributions have attracted considerable attention
ever since the discovery of M41s silica molecular sieves in 1992
due to their wide ranging applications as catalysts, absorbents and
The synthesized catalyst was characterized by X-ray diffraction
analysis using a Siemens D5000 diffractometer with a Cu-Ka
radiation running at 40 KV/30 mA in the 2q range 1° to 70° with a
step size of 0.05°. Single point BET surface area of the catalyst was
determined using N adsorption at 2196 °C (77 K) using a
2
Micromeritics Autochem. II Instrument (Model 2920). A nitrogen
sorption experiment was also carried out using the same instrument
1
2–4
host materials. A variety of mesoporous metal oxides, alumino-
5
,6
7–9
silicates, aluminophosphates and other transition metal oxide
phosphates1
0–14
have been developed and synthesized using several
supermolecular assembly pathways. Iron phosphate has been
reported to be a good catalyst for selective oxidation reactions.1
Mesoporous iron phosphate is expected to have interesting and
novel catalytic properties. Yan et al. have reported the synthesis of
2
at 2196 °C under different N /He pressure ratios to determine the
5,16
type of adsorption.
An X-ray diffractogram of synthesized iron phosphate shows
diffraction peaks at 2q of 2.3–2.4° and no peaks at higher
diffraction angles (Fig. 1). The low-angle diffraction peaks confirm
1
7
mesoporous iron phosphate using a fluoride route.
Terpenes are highly useful materials in the synthesis of a variety
of products such as food additives, pharmaceuticals, agrochemicals
and aromas. Nopol is an optically active bicyclic primary alcohol
used in the agrochemical industry to produce pesticides and also in
the manufacture of soaps, detergents, polishes and other household
products.18 The general method of its production is by Prins
condensation of b-pinene and para-formaldehyde using (i) zinc
chloride as catalyst at 115–120 °C for several hours (57% yield of
nopol), (ii) acetic acid as catalyst at 120 °C which yields nopyl
acetate which is then saponified to nopol and (iii) autoclaving a
mixture of b-pinene and para-formaldehyde at 150–230 °C for
several hours yielding quantitative amounts of nopol.19 All the
above methods form monocyclic isomers and other side products.
Recently Montes de Correa et al. have reported the synthesis of
nopol over Sn-MCM-41 molecular sieves in the presence of toluene
the mesoporous structure of the synthesized iron phosphate sample.
2
4
The synthesized FePO shows a specific surface area of 272 m
2
1
g
. The nitrogen adsorption/desorption pattern shows a type IV
isotherm, again typical of mesoporous materials.
Table 1 shows the results of nopol synthesis† by the Prins
condensation of b-pinene and paraformaldehyde over mesoporous
FePO catalyst. Different experimental parameters such as the
4
effect of solvent, catalyst amount, reaction temperature and
reaction time were studied. It was found that quantitative yields of
nopol could be synthesized using mesoporous iron phosphate
catalyst in the presence of acetonitrile solvent at 80 °C (entry 17).
Control experiments showed no reaction in the absence of the
catalyst (entry 10). Acetonitrile was found to be the most suitable
solvent (entry 1) followed by toluene (entry 2), dichloromethane
(entry 3), dioxane (entry 4), and cyclohexane (entry 5). No
appreciable reaction was observed in methanol solvent (entry 6).
Maximum conversion was observed at 80 °C. A b-pinene–
paraformaldehyde ratio of 1 : 2 is generally used for the reaction.
However, a 1 : 1 ratio was also found to be equally good (entry 9).
A comparison of the activity of the mesoporous material with that
obtained by a conventional precipitation technique showed a lower
activity for the latter (entry 16).
2
0
as a solvent at 90 °C. However, Sn is not often a desirable
constituent due to its toxic nature.
There has been an increasing interest in recent years in
developing environmentally benign and clean technologies, prod-
ucts and processes with economic benefits. The replacement of
harmful volatile organic solvents with less harmful alternative
reaction media and achieving high atom economy are some of the
clean synthetic methodologies. There is also a great demand to
develop highly selective heterogeneous catalyst based technologies
under mild reaction conditions without employing toxic materials.
Herein we report the selective synthesis of nopol over a mesopor-
ous iron phosphate catalyst in the presence of a relatively benign
solvent, acetonitrile, under relatively mild reaction conditions.
Mesoporous iron phosphate was synthesized by a procedure
1
7
similar to that described by Yan et al. A typical synthesis
procedure involves the precipitation of FePO from an aqueous
solution of Fe(NO ·9H O (20 mmol) and Na HPO (50 mmol).
The precipitated FePO was separated by centrifugation and
4
3
)
3
2
2
4
4
washed several times with distilled water. The precipitate was then
suspended in an acidified (HF) solution followed by the addition of
~
1 M solution of sodium dodecyl sulfate (10 mmol) at room
temperature with stirring for 30 minutes. The resultant mixture was
heated to 60 °C and kept for 2.5 h. The mixture was then cooled to
room temperature, centrifuged, washed with water and acetone
when a light yellow solid was obtained which was dried at room
temperature. The surfactant was removed from the catalyst by
4
Fig. 1 XRD pattern of FePO mesoporous catalyst.
8
26
C h e m . C o m m u n . , 2 0 0 4 , 8 2 6 – 8 2 7
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 4

The heterogeneous FePO
reaction mixture by first washing the reaction mixture with acetone
followed by hot water to remove the organics and unreacted
4
catalyst was separated from the
weakly acidic properties which may be responsible for its
activity.
In summary, the present study shows that mesoporous FePO is
4
paraformaldehyde. The recovered FePO
many times with acetone and dried at 110 °C overnight and reused
several times without any loss of activity or product selectivity
4
catalyst was washed
a novel and active catalyst for the selective synthesis of nopol by
Prins condensation of b-pinene and paraformaldehyde in the
presence of a relatively benign solvent, acetonitrile, under rela-
tively milder reaction conditions. The catalyst does not contain any
toxic constituents, emphasizing its environmentally benign nature.
The catalyst is also easily separable from the reaction mixture and
reusable without any loss of activity and selectivity up to five
cycles. This protocol also does not employ any chlorinated or
hydrocarbon based organic solvents.
(Table 2).
The formation of nopol from b-pinene and formaldehyde occurs
through an addition reaction between the two reactants in the
presence of an acid catalyst. It has been known that weak and
medium acid sites are responsible for Prins condensation reac-
tions.21 A comparison of the temperature programmed desorption
of ammonia (TPD) studies on the the synthesized FePO
4
, a
URP is a postgraduate research participant at the National Risk
Management Research Laboratory administered by the Oak Ridge
Institute for Science and Education through an interagency
agreement between the US Department of Energy and the US
Environmental Protection Agency.
magnesia (a basic material) sample and an alumina (weakly acidic
material) sample showed a total ammonia heat of adsorption of
2
1
21
2
24.4 kJ mol for FePO
4
, 215.8 kJ mol for MgO and 225.8
2
1
kJ mol for alumina, thereby suggesting that FePO possesses
4
Table 1 Nopol synthesis by Prins condensation of b-pinene and paraf-
Notes and references
ormaldehyde over FePO
4
†
Synthesis of nopol was conducted in liquid phase in a 100 mL round-
bottomed flask equipped with a reflux condenser and a magnetic stirrer. In
a typical reaction procedure, 5 mmol of b-pinene was mixed with 10 mmol
of paraformaldehyde and 0.10 g catalyst in 10 mL solvent in the R.B. The
mixture was then vigorously stirred at atmospheric pressure for the desired
time period at 80 °C. After the reaction, the mixture was extracted with
acetone and analyzed by a Hewlett-Packard 6890 Gas Chromatograph using
an HP-Innowax polyethylene glycol capillary column (30 m 3 320 mm 3
Tem-
Solvent pera-
Reac-
tion
time
(h)
Catalyst
amount
Entry (g)
Nopol
yield
(%)
amount
(mL)
ture
(°C)
Solvent
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
0.10
Acetonitrile
Toluene
10
10
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
80
30
50
70
80
80
80
80
80
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
4
4
8
12
24
51
35
26
24
20
02
43
30
48
00
08
22
29
55
82
58
100
07
30
45
22
22
57
62
85
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.00
0.01
0
.25 mm) and a quadrupole mass filter equipped HP 5973 mass selective
Dichloromethane 10
detector. Identification of the product was done using the GC-MS as well as
by comparing the retention time of the standard. Quantification of the
products was obtained using a multi-point calibration curve.
Dioxane
Cyclohexane
Methanol
10
10
10
5
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
1
2
3
4
5
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b
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4
ob-
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Table 2 Recyclability of FePO
pinene and paraformaldehyde to nopol in acetonitrile at 80 °C
4
catalyst for the Prins condensation of b-
1
1
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1
1
1
1
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Nopol selectivity (%)
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100
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100
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C h e m . C o m m u n . , 2 0 0 4 , 8 2 6 – 8 2 7
827