Transition-Metal Catalyzed Autoxidation of cis- and trans-Pinane to a Mixture of Diastereoisomeric Pinanols

Article abstract of DOI:10.1021/jf960472q

Autoxidations of the pinanes, obtained after hydrogenation of naturally occurring Pinus elliottii oil, were performed with or without solvent, using the catalytic system Co(OAc)₂/Mn(OAc)₂/NH₄Br in a 9:1:5 molar ratio, and dioxygen as the oxidant. The best selectivity for the pinanols was 71% (cis:trans ratio, 3:1) with 17% conversion. Autoxidations were also carried out in the absence of catalyst. The hydroperoxides formed with 17% conversion were decomposed with Na₂SO₃ and PPh₃, resulting in 62% pinanols (cis:trans ratio, 5:1). The pyrolysis of the pinanols at 600°C and a contact time of 1.15 × 10^-2 s/mol yielded 54% of linalool. The side products were mainly due to an "ene" reaction, giving diastereoisomeric 1,2-dimethyl-3-isopropenylcyclopentanols.

Full text of DOI:10.1021/jf960472q

J. Agric. Food Chem. 1997, 45, 1361
−1364
1361
Tr a n sition -Meta l Ca ta lyzed Au toxid a tion of cis- a n d tr a n s-P in a n e to
a Mixtu r e of Dia ster eoisom er ic P in a n ols
Ricardo Sercheli, Alfredo L. B. Ferreira, Lu´cia H. B. Baptistella, and Ulf Schuchardt*
Instituto de Qu´ımica, Universidade Estadual de Campinas, CEP 13083-970, C.P. 6154,
Campinas, Sa˜o Paulo, Brazil
Autoxidations of the pinanes, obtained after hydrogenation of naturally occurring Pinus elliottii
oil, were performed with or without solvent, using the catalytic system Co(OAc)2/Mn(OAc)2/NH4Br
in a 9:1:5 molar ratio, and dioxygen as the oxidant. The best selectivity for the pinanols was 71%
(cis:trans ratio, 3:1) with 17% conversion. Autoxidations were also carried out in the absence of
catalyst. The hydroperoxides formed with 17% conversion were decomposed with Na2SO3 and PPh3,
resulting in 62% pinanols (cis:trans ratio, 5:1). The pyrolysis of the pinanols at 600 °C and a contact
time of 1.15 × 10-2 s/mol yielded 54% of linalool. The side products were mainly due to an “ene”
reaction, giving diastereoisomeric 1,2-dimethyl-3-isopropenylcyclopentanols.
Keyw or d s: Catalytic oxidation; pinane; pinanol; pyrolysis; linalool
INTRODUCTION
The acyclic linalool is an important alcohol being used
as a feedstock for the manufacture of vitamin E and
flowery-fresh-based fragrances. It is also used in flea
shampoos and insecticidal sprays for house plants (Tsao
and Coats, 1995). Currently, several large-scale pro-
cesses have been developed for the synthesis of linalool
starting with 2-methyl-2-hepten-6-one. Linalool can be
easily obtained after ketone ethynylation with acetylene,
followed by a selective hydrogenation (Pasedach et al.,
1967). The synthesis from essential oils is also possible,
and pinenes are among the preferred starting materials.
Linalool can be obtained from pinene extracts by
hydrogenation, followed by oxidation to the respective
hydroperoxides which are reduced in a stoichiometric
process (Fisher et al., 1953; Schmidt and Fisher, 1954).
The alcohols formed are then pyrolyzed to linalool. The
liquid-phase autoxidation of cis- (1a ) and trans-pinane
(1b) has already been studied, and the main products
are pinane-2-hydroperoxides (2), derived from the oxi-
dation of the tertiary carbon in position 2 (Brose et al.,
1992) (Figure 1). When the autoxidation is carried out
in the presence of catalytic amounts of azobisisobuty-
ronitrile (AIBN), followed by a stoichiometric reduction
with Na2SO3, cis- (3a ) and trans-pinanol (3b) are
obtained with a selectivity of up to 95%, using only 1a
as the substrate (Filliatre and Lalande, 1968). On the
other hand, in the absence of AIBN, 3a and 3b are
obtained with a selectivity of up to 85%, using Na2SO3
as the reducing agent and 1a as the substrate (Brose
et al., 1992). When the decomposition is carried out in
the presence of sodium methylate to remove acids as
they are formed, 50% of 3a and 3b are obtained among
the products (Schmidt and Fisher, 1959).
The reports describing the autoxidation of pinanes are
always related to the use of only 1a or 1b as the
substrate. Therefore, no studies have been reported on
the oxidation of mixtures of pinanes. We wish to report
here our results on the catalytic oxidation of hydroge-
nated Pinus elliottii oil, which contains 1a and 1b as
F igu r e 1. Formulas of the principal products.
main components, with molecular oxygen. This proce-
dure replaces the oxidation and reduction steps by only
one catalytic step, using Co(OAc)2/Mn(OAc)2 as catalyst,
directly producing the alcohols 3a and 3b. The mixture
of oxidation products is then conveniently pyrolyzed to
linalool (4) (Ohloff and Klein, 1962).
* Corresponding author (fax +55 19 239 38 05; e-mail
ulf@iqm.unicamp.br).
S0021-8561(96)00472-4 CCC: $14.00
© 1997 American Chemical Society

1362 J. Agric. Food Chem., Vol. 45, No. 4, 1997
Sercheli et al.
Ta ble 1. Non ca ta lytic Oxid a tion s of cis- a n d
tr a n s-P in a n e
EXPERIMENTAL PROCEDURES
Ma ter ia ls. P. elliottii oil was obtained from Eucatex
Qu´ımica; R-pinene, linalool, and Pd/C were purchased from
Aldrich Chemical Co. (Milwaukee, WI). Cobalt and manga-
nese acetates were purchased from Alfa Products (Ward Hill,
MA) and Fluka (Buchs, Switzerland). Chlorobenzene, dichlo-
roethane, ammonium bromide, triphenylphosphine, sodium
sulfite, and magnesium sulfate were purchased from Merck
(Darmstadt, Germany).
P r ep a r a tion of P in a n es. The pinanes were prepared by
hydrogenation of 15 mL of P. elliottii oil (94% R- and â-pinene)
in 10 mL of diethyl ether at room temperature in a 100 mL
autoclave, using an H2 pressure of 50 bar and 0.4 g of 5% Pd/C
as catalyst. The conversion was quantitative, producing cis-
and trans-pinane in a 4:1 ratio.
P r ep a r a tion of P in a n e Hyd r op er oxid es. The oxidation
reactions were performed in a 125 mL three-necked flask
equipped with a reflux condenser, a thermometer, and a gas
inlet tube with a glass frit. The flask was filled with 12.4 g of
cis- and trans-pinane, magnetically stirred, and thermostated
at 80 to 125 °C. Oxygen was then introduced into the system
under different flow rates. The reaction was stopped at
approximately 17% conversion, which was determined by
iodometric titration during the course of the reaction. At
higher conversions the selectivity for pinane hydroperoxides
was significantly reduced.
temperature (°C)
reaction time (h)
conversion of pinanes (%)
product distribution (%)b
cis-pinanol (3a )
80
16.5
14
80
100
8
125
3.5
27
16.5
3.5
17a
49
8
2
1
4
4
7
27
52
10
1
6
4
4
9
26
46
7
22
6
trans-pinanol (3b)
isopinocamphone (5)
pinocamphone (6)
isopinocampheol (7)
R-terpineol (8)
2
5
5
3
4
3-methylnopinone (9)
others
3
27
44
a
Conversion of pinanes after reduction with P(C6H5)3. b Product
distribution after reduction with Na2SO3 (12.4 g of pinanes, 85
mL min-1 O2 flow).
Red u ction of P in a n e Oxid a tes w ith Sod iu m Su lfite.
A 125 mL three-necked flask, equipped with a reflux condenser
and a dropping funnel, was filled with 60 mL of a 1.27 mol
L-1 aqueous solution of Na2SO3. The solution was heated to
60 °C, and 12 mL of pinane oxidates (previously weighed) was
added under magnetic stirring over 4 h. The organic layer
was separated, and the aqueous layer was extracted twice with
20 mL of diethyl ether. The organic extracts were combined
and dried with MgSO4, and the solvent was evaporated under
reduced pressure.
Red u ction of P in a n e Oxid a tes w ith Tr ip h en yl P h os-
p h in e. Into a 125 mL flask were introduced 50 mL of a
solution of 0.09 M PPh3 in dichloroethane and 3.7 g of the
pinane oxidate. The mixture was magnetically stirred at room
temperature for 5 h. The solvent was evaporated under
reduced pressure, and the product mixture was directly
analyzed.
F igu r e 2. Intermediates for cis- and trans-pinanol.
Ta ble 2. P r od u ct Distr ibu tion a fter Ca ta lytic Oxid a tion s
of cis- a n d tr a n s-P in a n e in Ch lor oben zen e (5.5 g of
P in a n es, 16.5 h , 80 °C)
oxygen flow (mL min-1
)
40
85
85
substrate/catalyst molar ratio
conversion of pinanes (%)
product distribution (%)
cis-pinanol (3a )
10:1
17
10:1
27
50:1
21a
54
17
4
32
17
6
5
11
2
trans-pinanol (3b)
isopinocamphone (5)
pinocamphone (6)
isopinocampheol (7)
R-terpineol (8)
6
3
3
3
8
68
3-methylnopinone (9)
others
8
34
19
Ca ta lytic Oxid a tion of P in a n es. In a 125 mL three-
necked flask, equipped with a reflux condenser, thermometer
and a gas inlet tube with a glass frit, 25 mL of chlorobenzene
and 5.5 g of cis- and trans-pinane were added to 10 mol % of
the catalyst [0.9 g of Co(OAc)2/0.1 g of Mn(OAc)2/0.2 g of NH4-
Br]. Some oxidations were carried out with 12.4 g of cis- and
trans-pinane and 2 mol % of the catalyst. The reactions were
performed under magnetic stirring and different oxygen flow
rates (40-85 mL min-1) for 16.5 h. The reaction mixture was
filtered through neutral alumina, diluted with 25 mL of water,
and then extracted three times with 20 mL of diethyl ether.
The organic extracts were combined and dried with MgSO4,
and the solvent was evaporated under reduced pressure.
P yr olysis of P in a n ols. The unconverted pinanes were
separated from the pinane oxidates by distillation under
reduced pressure. The pinanol-containing oxidation mixture
was pyrolyzed, using the apparatus described by Ohloff and
Klein (1962), under an argon flow rate of 200 mL min-1 at
approximately 1 mbar. Under these conditions the contact
time of the pinane oxidates with the hot part of the reactor
a
Reaction carried out without solvent, using 12.4 g of pinanes.
methylsilicone (HP Ultra 1), coupled to a HP 5970B mass
detector operating at 70 eV. The temperature was pro-
grammed at 3 °C min-1 from 40 to 100 °C. The mass espectra
were compared with those of a Wiley NBS database showing
similarity indices always higher than 90%.
RESULTS AND DISCUSSION
The P. elliottii oil, containing 94% R- and â-pinene,
was hydrogenated at room temperature and 50 bar of
hydrogen, giving a complete conversion of the pinenes
to 1a and 1b (4:1 molar ratio). The oxidation reactions
were first carried out in the absence of a catalyst and
solvent, at temperatures in the range 80-125 °C. The
hydroperoxides formed in these reactions were decom-
posed with Na2SO3 or PPh3. The best selectivity for
pinanols (Table 1) was found at 80 °C and 17% conver-
sion, using PPh3 as the reducing agent. Under these
conditions, a 62% yield of 3a and 3b (5:1) was obtained,
as well as some byproducts derived from the oxidation
of secondary carbons. Conversions higher than 17% and
reaction temperatures above 100 °C decrease the selec-
tivity for pinanol. At 125 °C and 27% conversion, only
28% of pinanols were obtained as the desired products
easily overoxidize to other products under these condi-
tions. Brose et al. (1992) found similar results and
was 0.0115 s mol-1
.
Ga s Ch r om a togr a p h y (GC)/Ma ss Sp ectr om etr y (MS).
The products were semiquantified by area normalization, using
a Siemens SICHROMAT 1 gas chromatograph, equipped with
a 30 m × 0.2 mm × 0.33 µm capillary column of crosslinked
5% phenylmethylsilicone (HP Ultra 2), coupled to a flame
ionization detector. The temperature was programmed at 3
°C min-1 from 40 to 100 °C. The pinanes, pinanols, and
linalool were identified by comparison of their retention times
with those of authentic samples. The other products were
identified using an HP 5890 gas chromatograph equipped with
a 25 m × 0.2 mm × 0.33 µm capillary column of crosslinked

Autoxidation of cis- and trans-Pinane
J. Agric. Food Chem., Vol. 45, No. 4, 1997 1363
Ta ble 3. Ma ss Sp ectr a l Da ta a n d Reten tion Tim es for th e Vola tiles An a lyzed in th e Ca ta lytic Au toxid a tion of P in a n es
peak
no.
retention
time (min)
compound
m/ z (relative abundance in %)
1
2
3
4
5
6
7
8
9
7.4
7.8
9.2
â-pinene
93 (100); 79 (30); 41 (30); 92 (25); 77 (19); 91 (15); 121 (12); 136 (10); 94 (5)
93 (100); 92 (42); 91 (41); 77 (31); 41 (28); 79 (27); 121 (11); 94 (8)
R-pinene
trans-pinane
cis-pinane
not identified
trans-pinanol
cis-pinanol
isopinocamphone
pinocamphone
not identified
not identified
verbenone
55 (100); 41 (99); 95 (77); 67 (71); 82 (57); 81 (55); 83 (45); 69 (44); 138 (2)
55 (100); 41 (97); 95 (77); 67 (71); 81 (57); 82 (54); 69 (46); 83 (42); 138 (2)
69 (100); 43 (89); 83 (89); 41 (68); 84 (58); 55 (40); 97 (37); 67 (19); 71 (17)
43 (100); 99 (57); 41 (53); 71 (46); 93 (42); 81 (37); 55 (36); 83 (23); 69 (20); 121 (18); 67 (17)
43 (100); 99 (66); 71 (48); 41 (45); 93 (40); 55 (33); 81 (30); 83 (24); 69 (20); 121 (17); 67 (14)
55 (100); 83 (90); 41 (80); 69 (66); 81 (22); 95 (18); 152 (8)
55 (100); 41 (82); 69 (76); 83 (65); 95 (62); 43 (32); 67 (23); 81 (19); 152 (8)
43 (100); 85 (93); 41 (79); 55 (53); 95 (47); 67 (38); 79 (37); 83 (33)
83 (100); 55 (77); 41 (59); 95 (57); 57 (39); 109 (28); 43 (26); 137 (9); 152 (9)
107 (100); 91 (71); 135 (66); 41 (57); 80 (50); 79 (49); 150 (43); 43 (33); 67 (28)
9.7
14.5
16.1
17.1
18.0
18.6
19.4
20.2
20.5
10
11
12
oxygen content of the reaction mixture (Sawyer, 1991).
The best results were obtained with an oxygen flow of
40 mL min-1, which assures a sufficient oxygen supply.
On the other hand, if under the same conditions the
oxygen flow is reduced to 15 mL min-1, we found
ocimene (11) as the main product (60% selectivity)
formed by substrate rearrangement.
The reaction mixture, containing approximately 70%
3a and 3b, was pyrolyzed in a quartz reactor at 600 °C,
with a contact time of 0.0115 s mol-1. Linalool (4) was
obtained with 54% selectivity at conversions of up to
60%. Coxon et al. (1972) reported a selectivity for 4 of
only 44%, but observed the same byproducts as obtained
by us. The byproducts are mainly due to an “ene”
reaction of 4, giving diastereoisomeric 1,2-dimethyl-3-
isopropenylcyclopentanols. Reduction of the contact
time should further increase the selectivity of the
F igu r e 3. Gas chromatogram of the catalytic oxidation of
pinanes.
pyrolysis reaction.
The catalytic oxidation of hydrogenated naturally
occurring P. elliottii oil produces a mixture of diastereo-
isomeric pinanols in good yields, which can be easily
converted to linalool. The overall selectivity for linalool
from P. elliottii oil is 38% and does not involve the use
of expensive reagents. As the catalytic oxidation elimi-
nates the reduction step of the hydroperoxide and does
not require reagents in stoichiometric amounts, it
suggests an interesting alternative for the industrial
production of linalool.
reported that the fragmentation of the 2-pinanyl radical
becomes more important than its combination with
molecular oxygen in this temperature range. On the
other hand, under a low oxygen flow (15 mL min-1) no
oxidation products were found. Limonene (10) was the
main product, showing that the availability of oxygen
is important for the formation of 3a and 3b.
Compound 3a rather than 3b is the favored oxidation
product, i.e., the attack of molecular oxygen at the
2-pinanyl radical occurs trans to the gem-dimethyl
group. This preference is expected, since the gem-
dimethyl group hinders the approach of the oxygen
molecule from the same side. Furthermore, we suggest
that the intermediate leading to 3a is lower in energy
than that leading to 3b. The higher energy of the latter
is related to its boat conformation, while the intermedi-
ate leading to 3a prefers the chair conformation (Figure
2).
LITERATURE CITED
Brose, T.; Pritzkow, W.; Thomas, G. Studies on the oxidation
of cis- and trans-pinane with molecular oxygen. J . Prakt.
Chem. 1992, 334, 403-409.
Coxon, J . M.; Garland, R. P.; Hartshorn, M. P. The pyrolysis
of pinanes. Aust J . Chem. 1972, 25, 353-360.
Filliatre, C.; Lalande, R. Autoxydation des cis et trans pinanes.
Bull. Soc. Chim. Fr. 1968, 4141-4145.
Catalytic oxidation produced a higher percentage of
pinanols (Table 2), in addition to some byproducts
derived from the oxidation of secondary carbons. The
best results were obtained for a substrate/catalyst molar
ratio of 10:1 using chlorobenzene as solvent. At 80 °C
and 17% conversion, a selectivity for 3a and 3b (3:1) of
71% was obtained. The volatiles identified from the
catalytic oxidation reaction are listed in Table 3 (a
typical chromatogram is shown in Figure 3). The higher
percentage of 3b, formed in the catalytic process, may
be explained by an easier attack of the molecular oxygen
at the same side as the gem-dimethyl group, due to the
interaction of the transition metal with the 2-pinanyl
radical. Chlorobenzene was used as the solvent, not
only to solubilize the catalyst but also to increase the
Fisher, G. S.; Stinson, J . S.; Goldblatt, L. A. Peroxides from
turpentine. II. Pinane hydroperoxide. J . Am. Chem. Soc.
1953, 75, 3675-3678.
Ohloff, G.; Klein, E. Die absolute Konfiguration des Linalools
durch Verknu¨pfung mit dem Pinansystem. Tetrahedron
1962, 18, 37-42.
Pasedach, H.; Hoffmann, W.; Himmele, W. BASF, Pat. DE-
AS 1 643 710, 1967.
Sawyer, D. Oxygen Chemistry; Oxford University Press: New
York, 1991; p 21.
Schmidt, G. A.; Fisher, G. S. Terpene hydroperoxides. IV. The
thermal decomposition of pinane hydroperoxide. I. J . Am.
Chem. Soc. 1954, 76, 5426-5430.
Schmidt, G. A.; Fisher, G. S. The decompositon of pinane
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1364 J. Agric. Food Chem., Vol. 45, No. 4, 1997
Sercheli et al.
Tsao, R.; Coats, J . R. Starting from nature to make better
insecticides. CHEMTECH 1995, J uly, 23-28.
PADCT, and CNPq. Fellowships from CAPES and CNPq are
acknowledged.
J F960472Q
Received for review J une 28, 1996. Revised manuscript
received J anuary 16, 1997. Accepted J anuary 17, 1997.X This
work was financed by the Brazilian agencies FAPESP, FINEP-
X Abstract published in Advance ACS Abstracts, March
1, 1997.