Comprehensive kinetic and mechanistic considerations for the gas-phase behaviour of pinane-type compounds

Article abstract of DOI:10.1002/ejoc.200601098

The thermal behaviour of selected pinane-type compounds, α-pinene (1), β-pinene (2), pinane (3) and nopinone (4), has been investigated. The conversion of the bicyclic starting materials to their acyclic and monocyclic isomers as well as the consecutive reactions of the acyclic main isomerisation products are discussed. The conversion of 1-4 in a reaction network is presented and the experimental evidence for the formation of pyrolysis products by a biradical pathway is discussed. In addition to these results a kinetic model describing the isomerisation of the bicyclic compounds to their acyclic and monocyclic isomers is presented. A good correlation between kinetic simulations and experimental data is revealed. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejoc.200601098

FULL PAPER
DOI: 10.1002/ejoc.200601098
Comprehensive Kinetic and Mechanistic Considerations for the Gas-Phase
Behaviour of Pinane-Type Compounds[‡]
Achim Stolle,[a] Bernd Ondruschka,*[a] and Werner Bonrath[b]
Keywords: Terpenoids / Pyrolysis / Reaction mechanisms / Rearrangement / Radical reactions / Kinetic modelling
The thermal behaviour of selected pinane-type compounds,
α-pinene (1), β-pinene (2), pinane (3) and nopinone (4), has
been investigated. The conversion of the bicyclic starting
materials to their acyclic and monocyclic isomers as well as
the consecutive reactions of the acyclic main isomerisation
products are discussed. The conversion of 1–4 in a reaction
network is presented and the experimental evidence for the
formation of pyrolysis products by a biradical pathway is dis-
cussed. In addition to these results a kinetic model describing
the isomerisation of the bicyclic compounds to their acyclic
and monocyclic isomers is presented. A good correlation be-
tween kinetic simulations and experimental data is revealed.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
the transformation of 1 leads to alloocimene (8).[1,7,8,10–12]
Alcohol 6 can be generated from 2-pinanol (5).[13,14] Be-
cause of the functionalisation of the acyclic compounds 6,
7, 12 and 17, they are the starting materials of choice in the
synthesis of fine chemicals.
Introduction
Pinane-type monoterpenes and their oxygen-containing
derivatives play an important role in the synthesis of flav-
ours and fragrances as well as in the production of food
additives (convenience and functional food). Two different
resources can be used in their synthesis: natural-oil-based
compounds (e.g., 2-methyl-2-hepten-6-one) or essential oils
derived directly from plants.[2–5] The compounds extracted
from natural sources have a great advantage over the natu-
ral-oil-based ones as most of them are available in enantio-
meric pure form. No complex enantioselective synthetic
strategies or expensive separation of enantiomers is neces-
sary.
α-Pinene (1) and β-pinene (2) can be conveniently iso-
lated from renewable resources by distillation from crude
sulfate turpentine (CST)[6] and by the extraction of spruce
or pine resins.[4,5] Pinenes 1 and 2 are important starting
materials in the synthesis of linalool (6), which is an impor-
tant intermediate in the synthesis of vitamin E and flavour
compounds. In general the acyclic isomers of pinane-type
monoterpenes are more important in chemical synthesis
than their bicyclic precursors and they are generated from
these compounds by thermal isomerisation. Scheme 1
shows that β-citronellene (17) can be derived from pinane
(3).[7–9] Thermal isomerisation of 2 yields myrcene (12) and
Scheme 1. Thermal decyclisation of pinane-type compounds to
their acyclic isomers. [a] Ocimene (7) isomerises rapidly to the acy-
clic alloocimene (8) (cf. the following text).
Thermal isomerisation can proceed via two different re-
action mechanisms. Depending on the substitution of the
pinane skeleton the rearrangement can take place either
through a reaction involving biradicals (e.g., with 1 and 2)
or through a cycloreversion (e.g., with 5).[1,7,10,15] Kinetic
data for transformations of the bicyclic compounds 1, 2 and
5 to the corresponding acyclic isomers 6, 7 and 12 have
been reported in the literature.[10–14] Table 1 lists the acti-
vation parameters and also data for the experimental set-
tings used in these reactions.
[‡] For a report on the first part of this work, see ref.[1]
[a] Institute of Technical Chemistry and Environmental Chemistry,
University Jena,
Lessingstr. 12, 07743 Jena, Germany
Fax: +49-3641-948402
E-mail: bernd.ondruschka@uni-jena.de
[b] DSM Nutritional Products, R&D Chemical Process Technol-
ogy,
In general, the thermal isomerisation of the discussed
compounds (cf. Table 1) follows first-order kinetics, sup-
porting the proposed reaction mechanisms. However, be-
cause of the different experimental set ups and residence
P. O. Box 3255, 4002 Basel, Switzerland
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
2310
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2310–2317

Gas-Phase Behaviour of Pinane-Type Compounds
FULL PAPER
Table 1. Experimental set ups used to determine the kinetic param- 550 °C, whereas the conversion of 2 occurs at a temperature
eters for the isomerisation of pinane-type compounds.
100 °C lower. The isomerisation of 1 starts at about 300 °C.
Relative to 3 and 4, 1 and 2 seem to be more reactive.
Compound
α-Pinene (1) β-Pinene (2) 2-Pinanol (5)
Acyclic main product ocimene (7)[a] myrcene (12) linalool (6)
Reaction mechanism
Reference
biradical
biradical
cycloreversion
[10,16]
[11,12]
[13–15]
Temperature [°C]
Pressure [mbar]
Residence time [s]
227–257
350–410
27–114
480–600
3.3–56
Ͻ1.3ϫ10–3
2400–27000[b] 0.04–0.48
179
0.06–0.56
EA(transf.) [kJmol–1 [c]
]
204
215/190[d]
[a] Ocimene (7) isomerises rapidly to the acyclic alloocimene (8)
(see later). [b] Reaction time in a 2 L batch reactor. [c] Activation
parameters for the conversion of the bicyclic compounds to iso-
meric compounds. [d] cis-5/trans-5.
times, the reported findings, especially with respect to reac-
tivity, cannot be compared with each other.
Herein we report our investigations of the thermal behav-
iour of bicyclic pinane-type compounds α-pinene (1), β-pi-
nene (2), pinane (3) and nopinone (4) under identical exper-
imental conditions. Based on the composition of the liquid
pyrolysis products, conclusions concerning the reaction
mechanism will be drawn. The kinetics of the degradation
reaction and of the formation of primary pyrolysis products
have been investigated to compare the reactivity and sub-
stituent effects of the compounds studied.
Figure 1. Gas chromatograms (GC-FID) of the liquid pyrolysis
products of α-pinene (1), β-pinene (2), pinane (3) and nopinone (4)
(carrier gas: N2; flow rate: 1.0 L/min; 50 µL starting material; sol-
vent for dissolution of products: trichloromethane for 1, 2 and 3,
ethyl acetate for 4; assigned compounds 7–21 are described in the
text and a complete list of products can be found in the Supporting
Information).
The relationship between the yields of the acyclic iso-
merisation products and the reaction temperature is de-
picted in Figure 3. The yield of each of the acyclic isomers
reaches a maximum at a temperature that is dependent on
the substituents. At temperatures higher then the maximum
yield the fraction of consecutive reaction products (cp)
formed from the acyclic isomers increases, which leads to
an apparent decline in the yield of the acyclic isomer. By
adding the yield of the cp to that of the corresponding iso-
mer yield it is shown that after reaching a maximum, the
changes in yield are minimal (Figure 3). The decrease in
yield at temperatures higher than 550 °C is due to the de-
composition of the thermal isomerisation products. Above
this temperature, besides the liquid products, gaseous prod-
ucts are also formed, but these have not been investigated
in this work. Compared to the acyclic isomers yielded from
Results and Discussion
In order to study the thermal behaviour of 4 and of the
selected monoterpenes 1, 2 and 3 we chose the dilution gas
pyrolysis technique with oxygen-free nitrogen as the carrier
gas, as reported in ref.[1] The advantages of this method are
the short overall reaction time and the high reproducibility
of the results, which are necessary for kinetic investigations.
Furthermore, low consumption of the starting material and
an uncomplicated analysis of the product mixtures gener-
ated are advantageous.
Thermal Behaviour and Reaction Mechanism of α-Pinene,
β-Pinene, Pinane and Nopinone
The thermal behaviour of monoterpenes 1–4 were 1–3, 7-methyl-1,6-octadien-3-one (20) generated from 4 is
studied. Gas chromatograms of the liquid product mixtures thermally more stable. Raising the temperature even higher
obtained from the thermal isomerisation of 1 (400 °C, tri- than 550 °C led to an increase in the concentration of 20.
chloromethane as solvent), 2 (450 °C, trichloromethane), 3 Side-reactions were less important in this reaction than in
(500 °C, trichloromethane) and 4 (500 °C, ethyl acetate) are the reactions of 7, 12 and 17. Beside the main acyclic prod-
depicted in Figure 1. Each investigated compound leads to ucts, monocyclic isomers are also formed during the ther-
one acyclic structural isomer, as determined by FID-GC mal isomerisation of the monoterpenes investigated: limo-
and GC-MS (cf. Figure 1 and Scheme 1). The dependency nene (9) from 1 and 2, cis-/trans-∆8(9)-p-menthene (16)
of the conversion on the reaction temperature is depicted in from 3, 4-isopropenylcyclohexanone (19) from 4 and ψ-lim-
Figure 2. The conversion of the bicyclic starting materials onene (13) can be generated from 2.
increases with temperature and depends on the substituents.
As shown in Figure 3, the acyclic products generated
Figure 2 clearly reveals the differences in the thermal behav- from 1–4 underwent consecutive reactions. Three of the
iour of 1 and 2 compared with 3 and 4. The conversion of four acyclic isomers 12, 17 and 20 underwent a cyclisation
3 and 4 was effected in the temperature range of 450 to reaction to form substituted cyclopentanes.[1,8,17] As shown
Eur. J. Org. Chem. 2007, 2310–2317
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2311

A. Stolle, B. Ondruschka, W. Bonrath
FULL PAPER
Figure 2. Conversion of compounds 1–4 in the thermal isomerisation reaction as a function of reactor temperature (carrier gas: N2; flow
rate: 1.0 L/min).
Figure 3. Yields of the acyclic and consecutive products otained from the pyrolysis of compounds 1–4 (Figure 2) as a function of reactor
temperature (carrier gas: N2; flow rate: 1.0 L/min; monocyclic products are not depicted; cp = consecutive reaction products of acyclic
compounds).
in Scheme 2, for this type of cyclisation process two double formed in an ene-type reaction.[8,17] The number of cyclo-
bonds in the 1- and 6-positions (17 as skeleton) and a hy- pentanes formed depends on the hybridisation of C-3
drogen atom at C-8 are important Through hydrogen mi- (Scheme 2). In the case of sp2 hybridisation (12, 20) four
gration and a concerted cyclisation the cyclopentanes are enantiomers are formed. The two diastereomeric forms 14,
2312
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2310–2317

Gas-Phase Behaviour of Pinane-Type Compounds
FULL PAPER
21 were separated and identified by FID-GC (Figure 1) and
GC-MS. Four diastereomers of type 18 were identified by
analysing the reaction mixture produced from the thermal
isomerisation of 3. The sp3 hybridisation in the case of the
acyclic isomerisation product 17 formed from 3 gave eight
enantiomers (Figure 1, Scheme 2).
Scheme 3. Products formed by the thermal isomerisation of pinane
(3) (carrier gas: N2; flow rate: 1.0 L/min).
17 (Scheme 4).[7,10] Figure 1 and Figure 3 reveal that 7 was
formed in only very low amounts. Through double bond
migration the thermally more stable 8 with a conjugated
double bond system was rapidly formed. Compound 7 as
well as 8 were formed in either cis or trans isomeric forms.
At elevated temperatures 8 isomerised to α-pyronene (10)
Scheme 2. Cyclisation of β-citronellene (17) analogues to the re-
lated cyclopentane derivatives by an ene-type reaction.
The thermal isomerisations of 1–4 proceed via biradical and similarly substituted hydrocarbon 11 (Scheme 4).[10]
intermediates. In all cases, beside the acyclic isomerisation If β-pinene (2) was thermally converted primary pyrolysis
products and their consecutive products, at least one mono- products 9, 12 and 13 would be formed from the biradical
cyclic isomer was identified in the respective reaction mix- intermediates (Scheme 5).[1,7] As in the transformation of 1
tures. The pyrolysis of pinane (3) led to 16, 17 and to iridan- the biradical generated from 2 contains one radical position
8-enes (18), as shown in Scheme 3. The formation of 16 stabilised as an allyl-type radical (Scheme 5). The acyclic
and 17 can be explained by the reactions of the generated main product 12 isomerised at temperatures higher than
biradical (Scheme 3).[7,8] Compound 16 can be formed from 450 °C to form iridane-1(6),8-dienes (14) and 5-ethylidene-
the biradical through a [1,5] hydrogen shift, whereas 17 is 1-methylcycloheptene (15), as shown in Scheme 5.[1,17,18]
formed by homolytic bond cleavage followed by intramolec- The key intermediates in the network of C10H16 hydro-
ular radical recombination. The consecutive reaction of 17 carbons formed from 2 are the biradicals primarily formed
leading to 18 is described in Scheme 2.
and the acyclic unsaturated monoterpene hydrocarbon 12.
Like the transformation of 3, the isomerisation of α-pi- The reaction mechanism that describes both the formation
nene (1) proceeds via biradical intermediates. Because of of 12 and the other products has been reported in ref.[1]
the existing double bond in the reactive part of the molecule
To study the influence of heteroatoms on the reactivity
a biradical is formed with one of the radical positions being and the reaction mechanism for the isomerisation of pi-
a resonance-stabilised allyl-type radical (Scheme 4). Race- nane-type compounds, nopinone (4) was chosen as an oxy-
mic 9 is generated from these by a [1,5] hydrogen shift and gen-containing β-pinene derivative. By formal replacement
the acyclic hydrocarbon 7 is formed in the same way as of the methylene group by oxygen, 4 can be generated from
Scheme 4. Products formed by the thermal isomerisation of α-pinene (1) (carrier gas: N2; flow rate: 1.0 L/min).
Eur. J. Org. Chem. 2007, 2310–2317
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2313

A. Stolle, B. Ondruschka, W. Bonrath
FULL PAPER
spite these facts, the kinetic investigations had to be carried
out in a temperature range in which the conversion of the
bicyclic starting materials increases linearly with rising tem-
perature (cf. Figure 2). The reaction products did not un-
dergo further degradation and the liquid products were
trapped completely within these temperature ranges. First-
order kinetics were chosen for the kinetic model of the iso-
merisation reaction, viz. the formation of biradical interme-
diates was disregarded in the first approximation. Consecu-
tive reactions of the products were neglected and the corre-
sponding parts in the reaction mixture were added to the
respective primary formed product. The parallel first-order
reaction model was chosen to describe the thermal behav-
iour of the compounds investigated. General equations for
the kinetic model used are given in Equation (1), where k =
kB + kC + … and P = B, C, … (Figure 4).
Scheme 5. Thermal isomerisation of β-pinene (2) and nopinone (4)
(carrier gas: N2; flow rate: 1.0 L/min; β-pinene, R = CH2; nopi-
none, R = O).
2 (ozonolysis, oxidation with KMnO4).[1,19–22] The thermal
behaviour of 4 is very similar to that of 2. Formally, the
C=C double bond is replaced by a carbonyl group.[23,24] By
analysing the liquid product mixture obtained from the
thermal isomerisation of 4, almost all the analogous prod-
ucts of 2 were found (Scheme 5), except for those analogous
to 9 and 15. Owing to the fact that besides 20, 19 is also
found in the reaction mixture, the isomerisation of 4 has to
proceed via biradical intermediates. The acyclic main prod-
uct 20 is thermally more stable than 12. Thus, replacement
of the methylene group by oxygen leads to molecules with
a lower reactivity.
(1)
In summary, the thermal isomerisation of the investi-
gated pinane-type compounds leads to at least one acyclic
product (cf. Scheme 3, Scheme 4 and Scheme 5). The
number of consecutive products formed depends on the re-
action mechanism and the substituents on the pinane skel-
eton. The substituents have been shown to have a big influ-
ence on the reactivity of the bicyclic compounds and also
on the tendency for the acyclic isomers to undergo consecu-
tive reactions (e.g., 7). In the case of a biradical reaction
mechanism, at least one monocyclic product, which cannot
be generated from the acyclic isomer, is formed during ther-
mal isomerisation of the bicyclic compounds (e.g., 16 from
3). The acyclic products 12, 17 and 20 underwent ene-type
cyclisation reactions leading to substituted cyclopentanes.
Figure 4. General reaction scheme for the kinetic investigations.
Various rate constants were determined by performing
kinetic pyrolysis experiments at various temperatures. These
data were fitted to calculate the Arrhenius parameters for
the degradation of the investigated compounds and the
products generated from them [Equation (2)]. Table 2 lists
the activation parameters (activation energy EA, frequency
factor A) for the reaction networks investigated.
(2)
With these data the thermal behaviour of each investi-
gated compound under given experimental parameters (re-
Kinetic and Activation Parameters
Variation of the gas velocity in the pyrolysis apparatus actor volume, temperature, residence time, flow rate) was
allowed us to set up various average residence times.[25] simulated and compared with the experimental data. On
Thus it was possible to estimate rate constants for the de- the basis of differences between simulation and experiment
gradation of the investigated monoterpenes. To calculate it is possible to benchmark the performance of the kinetic
the residence times and the rate constants, it had to be en- model. Figure 5 compares simulations of the reaction mix-
sured that no gaseous products were formed and that the ture composition with changing temperature with the ex-
liquid pyrolysis products were completely condensed. De- perimental data for the investigated compounds 1–4.
2314
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2310–2317

Gas-Phase Behaviour of Pinane-Type Compounds
FULL PAPER
Table 2. Activation energies EA and frequency factors A for the of theses compounds can be described by competing paral-
compounds investigated [Equation (2)].
lel reactions very well. It seems that the biradical intermedi-
Compound
EA [kJmol–1]
A [s–1]
ates the reactions proceed through have a minimal effect on
the kinetic model. Hence the biradicals formed from 2, 3
and 4 have very short half-lives: because of this they are
not reaction intermediates but rather transition states.[27,28]
In the case of 1, the discrepancies between simulation and
experiment are larger. However, they are within the calcu-
lated margin of error. Because of the thermal instability of
7, which isomerises rapidly to 8, the model of competing
parallel reactions appears to be extended by the isomeris-
ation of ocimene (7).
A comparison of the activation energies calculated for
the isomerisation of 1 and 2 with the data reported in the
literature (cf. Table 1 and Table 2) revealed that our values
are smaller than those reported in the literature.[10,11] Nev-
ertheless, the smaller activation energy for the thermal iso-
merisation of 1 compared with that of 2 was approved and
is in agreement with the higher reactivity of 1.
α-Pinene (1)[a]
Ocimene (7)
170Ϯ2
178Ϯ2
161Ϯ3
186Ϯ3
188Ϯ3
176Ϯ4
177Ϯ4
168Ϯ9
165Ϯ10
207Ϯ18
166Ϯ7
5.0ϫ1013
1.3ϫ1014
4.1ϫ1012
2.3ϫ1014
2.9ϫ1014
1.8ϫ1012
5.5ϫ1012
4.4ϫ1011
2.4ϫ1011
1.8ϫ1013
3.5ϫ1011
3.4ϫ1011
6.3ϫ1010
Limonene (9)
β-Pinene (2)[b]
Myrcene (12)
ψ-Limonene (13)
Limonene (9)
Pinane (3)[c]
β-Citronellene (17)
∆8(9)-p-Menthene (16)
Nopinone (4)[d]
7-Methyl-1,6-octadien-3-one (20) 170Ϯ16
4-Isopropenylcyclohexanone (19) 161Ϯ10
[a] Temperature range (T) for the determination of the Arrhenius
parameters: 337–412 °C. [b] T = 375–425 °C. [c] T = 450–512 °C.
[d] T = 475–512 °C.
Correlation between simulation and experiment depends
on the substituents and on the temperature (Figure 5). In
general, experimental data and calculated values correlate
very well until the temperature reaches the point of the
curve corresponding to total conversion.[26] Visible discrep-
Conclusions
The thermal behaviour of the pinane-type monoterpenes
ancies are within the error margins of the activation param- α-pinene (1), β-pinene (2), pinane (3) and nopinone (4) has
eters EA and A (Table 2). Notwithstanding, it seems to clear been investigated under similar experimental conditions.
that the thermal behaviour of 2, 3 and 4 is described much The bicyclic compounds clearly differ in their reactivity.
better by the calculated model than that of 1. The differ- Their thermal behaviour is directly influenced by the substi-
ences between model and experiment in the case of 2, 3 and tution of the bicyclic compounds, affecting the reactivity as
4 are marginal, which indicates that the thermal behaviour well as the products found. α-Pinene 1 was the most reactive
Figure 5. Simulated (lines) with experimental (symbols) data for α-pinene (1), β-pinene (2), pinane (3) and nopinone (4) product distribu-
tions at various temperatures (VR: 23 mL; carrier gas: N2; flow rate: 1.0 L/min; filled square: bicyclic starting material; open triangle:
acyclic product and cp; open diamond/asterisk: monocyclic product).
Eur. J. Org. Chem. 2007, 2310–2317
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2315

A. Stolle, B. Ondruschka, W. Bonrath
FULL PAPER
The starting material (50 µL) was introduced on a quartz ladle into
the top part of the pyrolysis apparatus using a glass syringe
(50 µL). The starting material was carried along with the nitrogen
stream into the reactor. Vaporisation of the starting material was
supported by heating the ladle to 200 °C with a hot blast. Pyrolysis
products were collected in a cold trap (liquid nitrogen) and were
dissolved in trichloromethane (1.5 mL) (for 1, 2 and 3) or in ethyl
acetate (1.5 mL) (for 4). The liquid products obtained were ana-
lysed by FID-GC and GC-MS.
compound, followed by 2. The hydrogenated (3) and (oxy-
gen-) modified molecules (4) have similar reactivities, but
are less reactive than 1 and 2.
The thermal isomerisations of the compounds investi-
gated proceed via biradical transition states as acyclic as
well as monocyclic products were identified.[1,7,11,12] Com-
pounds that isomerise via transition states that are reso-
nance-stabilised through the formation of an allyl-type radi-
cal are especially reactive in this type of isomerisation (1
and 2). It is shown in this work that the acyclic main prod-
ucts 12, 17 and 20 undergo ene-type cyclisation reactions
leading to cyclopentane derivatives 14, 18 and 21.
For the first time kinetic models for the thermal isomeris-
ation of 3 and 4 are presented. Owing to the fact that all
reactions were performed in the same apparatus and similar
kinetic models were used, the activation parameters gained
could be compared directly with each other. Comparison of
the kinetic models and experimental data reveals that they
match very well. Because of their short life-times, the birad-
icals formed during the thermal isomerisation reactions are
considered transition states rather than reaction intermedi-
ates.
Synthesis of 6,6-Dimethylbicyclo[3.1.1]heptan-2-one (Nopinone, 4):
Nopinone was synthesised and purified as described in ref.[1] The
purity after column chromatography and removal of the eluent was
determined by FID-GC to be 99% pure nopinone. Yield: 3.5 g
[20]
(60% based on β-pinene after purification); nD
= 1.480. 1H
NMR (CDCl3): δ = 0.85 (s, 3 H), 1.33 (s, 3 H), 1.59 (d, 1 H), 1.96–
2.06 (m, 2 H), 2.24–2.25 (m, 1 H), 2.35–2.38 (dd, 1 H), 2.51–2.58
(m 3 H) ppm. 13C NMR (CDCl3): δ = 21.3, 21.9, 25.3, 25.7, 32.7,
40.2, 41.0, 57.7, 214.8 ppm. IR (ATR): ν = 2949, 2928, 2837
˜
(νaliph. C–H), 1706 (νC=O), 1459 (δC–H) cm–1. MS (EI, 70 eV,
C9H14O): m/z (%) = 139 (0.9) [M + 1]+, 138 (8.6) [M]+, 123 (16.5),
109 (26.3), 95 (40.8), 83 (100), 81 (37.3), 67 (23.1).
Supporting Information (see also the footnote on the first page of
this article): A scheme of the experimental set up used, a list of
important monoterpenes with their IUPAC names, the procedures
for the calculation of the average residence times and the kinetic
simulations.
Based on the work presented herein the thermal behav-
iour of the acyclic compounds will be investigated. The ene-
type cyclisation to the observed cyclopentanes will be ana-
lysed kinetically. The kinetic model presented will be im-
proved with additional data. The palladium- or platinum-
catalysed isomerisation of 7 to 8 is a topic of ongoing re-
search.
Acknowledgments
We gratefully acknowledge Dr. Annegret Stark for her support.
We thank Simon Prickler for synthesising and performing pyrolysis
experiments with nopinone in his laboratory course. We gratefully
acknowledge Antje Tied and Gisela Gottschalt for technical help.
Experimental Section
General Remarks: α-Pinene (1, ca. 98%), β-pinene (2, ca. 99%) and
pinane (3, ca. 98%; trans/cis: 0.103) were purchased from Fluka
and used without further purification. Purity was determined by
capillary gas chromatography. Analyses were carried out with a
6890 Series GC and a 5890 Series II/5972 Series MSD GC from
Agilent Technologies. Products were identified by comparison with
either retention times and/or mass spectra of pure reference com-
pounds. FID-GC: HP 5, 30 mϫ0.32 mmϫ0.25 µm, 5 psi H2; pro-
gram: 35 °C (hold 1 min), 4 K/min up to 80 °C, 4.5 K/min up to
90 °C, 35 K/min up to 280 °C (hold 3 min); injector temperature:
250 °C; detector temperature: 280 °C. GC-MS: HP 5,
30 mϫ0.32 mmϫ0.25 µm, 7 psi He; program: 55 °C (hold 1 min),
5 K/min up to 150 °C, 20 K/min up to 280 °C (hold 5 min); injector
temperature: 280 °C, EI (70 eV). NMR spectra were recorded with
a Bruker Avance 200 MHz system (measurement frequency was
200 MHz for 1H NMR and 50 MHz for 13C NMR) in a 5-mm tube
at room temperature. Measurements were carried out using CDCl3
as solvent. IR spectra were measured with a Perkin-Elmer FT-IR
spectrum 100 series device equipped with a universal ATR sam-
pling accessory.
[1] A. Stolle, C. Brauns, M. Nüchter, B. Ondruschka, W. Bonrath,
M. Findeisen, Eur. J. Org. Chem. 2006, 3317–3325.
[2] K. A. D. Swift, Top. Catal. 2004, 27, 143–155.
[3] N. Ravaiso, F. Zaccheria, M. Guidotti, R. Psaro, Top. Catal.
2004, 27, 157–168.
[4] J. L. F. Monteiro, C. O. Veloso, Top. Catal. 2004, 27, 169–180.
[5] B. Eloers, S. Hawkins (Eds.), Ullmann’s Encyclopedia of Indus-
trial Chemistry, VCH, Weinheim, 1996, vol. A27, p. 267.
[6] CST is a side-product from the pulp and paper industry con-
taining large amounts of α- and β-pinene.
[7] L. Lemée, M. Ratier, J.-G. Duboudin, B. Delmond, Synth.
Commun. 1995, 25, 1313–1318.
[8] R. Rienäcker, Brennstoff-Chemie 1964, 45, 20–23.
[9] W. D. Huntsman, V. C. Solomon, D. Eros, J. Am. Chem. Soc.
1958, 80, 5455–5458.
[10] J. J. Gajewski, I. Kuchuk, C. Hawkins, R. Stine, Tetrahedron
2002, 58, 6943–6950.
[11] H. G. Hunt, J. E. Hawkins, J. Am. Chem. Soc. 1950, 72, 5618–
5620.
[12] J. E. Hawkins, J. W. Vogh, J. Phys. Chem. 1953, 57, 902–905.
[13] I. I. Ilyna, I. L. Simakova, V. A. Semikolenov, Kinet. Catal.
2001, 42, 686–692.
[14] I. I. Ilyna, I. L. Simakova, V. A. Semikolenov, Appl. Catal., A
2001, 211, 91–107.
Pyrolysis: The investigated monoterpenes were pyrolysed in a tem-
perature range of 250 to 700 °C. Dilution gas pyrolysis (DGP) was
carried out in an electrically heated quartz tube of 50 cm length
and with a pyrolysis zone of approximately 20 cm, using the appa-
ratus reported in ref.[1]. In all experiments, oxygen-free nitrogen
with a purity of 99.999% was used as the carrier gas. Residence
times were varied by selecting different carrier gas flow rates (0.25,
0.4, 0.6, 0.8, 1.0 and 1.2 L/min).
[15] V. A. Semikolenov, I. I. Ilyna, I. L. Simakova, J. Mol. Catal. A
2002, 182–183, 383–393.
[16] J. J. Gajewski, L. P. Olson, M. R. Willcott, J. Am. Chem. Soc.
1996, 118, 299–306.
[17] J. de P. Teresa, I. S. Bellido, M. R. Alberdi Albistegui, A.
San Feliciano, M. G. Benito, Anal. Quim. 1978, 74, 305–310.
2316
www.eurjoc.org
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2007, 2310–2317

Gas-Phase Behaviour of Pinane-Type Compounds
FULL PAPER
[18] A. Stolle, Diploma Thesis, University of Jena, 2005.
[19] B. R. Larsen, D. di Bella, M. Glasius, R. Winterhalter, N. R.
Jensen, J. Hjorth, J. Atmos. Chem. 2001, 38, 231–276.
[20] J. Z. Yu, D. R. Cocker, R. J. Griffin, R. C. Flagan, J. H. Sein-
feld, J. Atmos. Chem. 1999, 34, 207–258.
[21] P. L. Joshi, B. G. Hazra, J. Chem. Res. 2000, 38–39.
[22] M. Nüchter, B. Ondruschka, R. Trotzki, J. Prakt. Chem. 2000,
342, 720–724.
ment increased because of decomposition of the products into
smaller molecular fragments. These fragments cannot be con-
densed with the apparatus used and so the mass balance is not
correct. Note that the kinetic model describes only the iso-
merisation of the bicyclic compounds. Decomposition products
are not considered.
[27] A. F. Parsons, An Introduction to Free Radical Chemistry,
Blackwell Science, Oxford, 2000, chapter 5.
[23] C. F. Mayer, J. K. Crandall, J. Org. Chem. 1970, 35, 2688–2690.
[24] J. M. Coxon, R. P. Garland, M. P. Hartshorn, Aust. J. Chem.
1972, 25, 2409–2415.
[25] The calculation procedure is described in the Supporting Infor-
mation.
[28] O. Levenspiel, Chemical Reaction Engineering, 3rd ed., Wiley,
New York, 1999, chapter 2.
Received: December 19, 2006
Published Online: March 20, 2007
[26] At temperatures higher than the temperature corresponding to
total conversion the difference between simulation and experi-
Eur. J. Org. Chem. 2007, 2310–2317
© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
2317