Recyclable Pd(OAc)2/ligand/Al(OTf)3 catalyst for the homogeneous methoxycarbonylation and hydrocarboxylation reactions of phenylacetylene

Article abstract of DOI:10.1021/om200603t

The Pd-catalyzed methoxycarbonylation reaction of phenylacetylene was studied making use of various promoters, including aluminum triflate and several other acid-type promoters of this reaction. The influence of the ligand (bidentate-type ligands and monodentate analogues) was found to be determinative of the success of the reaction. The catalyst was found to be recyclable through 10 catalytic runs. The unique results when using BINAP, relating to the selectivity for the branched product and the stability of the catalyst produced, led to a study on the sulfonated analogue thereof, with the intention of performing hydrocarboxylation reactions to directly prepare the carboxylic acid. The product obtained accordingly may be varied between the methyl ester or its carboxylic acid equivalent, depending on the solvent medium and the ligand employed.

Full text of DOI:10.1021/om200603t

ARTICLE
pubs.acs.org/Organometallics
Recyclable Pd(OAc)2/Ligand/Al(OTf)3 Catalyst for the Homogeneous
Methoxycarbonylation and Hydrocarboxylation Reactions of
Phenylacetylene
D. Bradley G. Williams,* Megan L. Shaw, and Tanya Hughes
Research Centre for Synthesis and Catalysis, Department of Chemistry, University of Johannesburg, P.O. Box 524, Auckland Park, 2006,
South Africa
ABSTRACT: The Pd-catalyzed methoxycarbonylation reaction of phenylacetylene
was studied making use of various promoters, including aluminum triflate and
several other acid-type promoters of this reaction. The influence of the ligand
(bidentate-type ligands and monodentate analogues) was found to be determinative
of the success of the reaction. The catalyst was found to be recyclable through 10
catalytic runs. The unique results when using BINAP, relating to the selectivity for
the branched product and the stability of the catalyst produced, led to a study on the sulfonated analogue thereof, with the intention
of performing hydrocarboxylation reactions to directly prepare the carboxylic acid. The product obtained accordingly may be varied
between the methyl ester or its carboxylic acid equivalent, depending on the solvent medium and the ligand employed.
Scheme 1. Methoxycarbonylation Reaction of
Phenylacetylene
’ INTRODUCTION
The carbonylation of alkynes allows for the synthesis of R,β-
unsaturated carboxylic esters or acids in an easy one-step
synthesis (Scheme 1). The reaction occurs much in the same
manner as for alkenes, a reaction that has been quite extensively
studied.1 The reaction requires the presence of a catalyst (usually
Pd), carbon monoxide under pressure, methanol or water, and an
acidic co-promoter. This reaction is of interest since methyl
atropate (methyl 2-phenylacrylate) and its derivatives are poten-
tial precursors of nonsteroidal anti-inflammatories such as ibu-
profen and naproxen.2
While several ligands have been applied to the catalytic
conversion of phenylacetylene into its unsaturated ester deriva-
tives, N-containing phosphine ligands have been shown to
provide good catalysts in terms of stability and activity. Specifi-
cally, 2-pyridyldiphenylphosphine has earned a reputation for
being particularly suited to this transformation.3 Alternative
systems have included iminophosphine-type analogues4 and a
PPh3/pyridine carboxylic acid system.5 Supported catalysts have
also been applied with a fair degree of success.6 When ligands do
not possess the pyridyl moiety, poor results are generally noted.7
As with other alkoxycarbonylation-type chemistry with al-
kenes, the application of alkynes as substrates also calls for an
acidic co-catalyst, typically a Brønsted acid. Recent work in our
laboratories has involved the use of Al(OTf)3 as a co-catalyst in
the methoxycarbonylation of styrene and 1-pentene.8 We
hoped that this robust, recyclable co-catalyst would be useful
in the methoxycarbonylation and hydrocarboxylation react-
ions of phenylacetylene and investigated its application in this
reaction, discovering along the way that PꢀP bidentate ligands
produce excellent catalysts in the presence of this co-promoter.
We also demonstrate that the Pd-based catalyst derived
from BINAP is stable and capable of being recycled a number
of times.
’ RESULTS AND DISCUSSION
Initial reactions using phenylacetylene were carried out under
the conditions we earlier reported,8 making use of Al(OTf)3 as
the co-catalyst in Pd-catalyzed reactions supported by PPh3 as
ligand. The system showed a complete lack of conversion of the
phenylacetylene, a result also noted by others when using mono-
dentate phosphine ligands.9 Several changes to the reaction condi-
tions, while retaining the monodentate ligand, were met with failure.
Previous studies have shown 1,4-bis(diphenylphosphino)butane
(dppb) to be active as a ligand in the methoxycarbonylation reaction
of phenylacetylene.10 We accordingly investigated a few bidentate-
type ligands with varying bite angles (Table 1), including 1,2-
bis(diphenylphosphino)benzene, 2,20-bis(diphenylphosphino)-1,10-
binaphthyl (BINAP), and SiXantphos, in quite long-duration reac-
tions (24 h).
While 1,2-bis(diphenylphosphino)benzene provided no con-
version to the desired product, BINAP- and SiXantphos-based
catalysts afforded 100% conversion of the starting material, but in
reactions in which less than 100% selectivity was shown to the
anticipated ester product. In these cases, a diester byproduct was
isolated (Scheme 2).
Received: July 8, 2011
Published: August 25, 2011
r
2011 American Chemical Society
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Table 1. Methoxycarbonylation Reaction of Phenylacetylene Using Bidentate Ligandsa
a Reaction conditions: 0.045 mmol of Pd(OAc)2, 0.18 mmol of ligand, 0.09 mmol of Al(OTf)3, 2.25 mmol of phenylacetylene, 5.75 mL of MeOH, 35 bar
of CO, 80 ( 2 °C internal temperature, 24 h. b Reference 1. Standardized PꢀMꢀP angles from X-ray structures and calculations. c Conversion of starting
material. d Conversion to ester products (selectivity) as determined by 1H and 13C NMR spectroscopy and quantitative GC-FID analysis. e Secondary
reactions accounted for diminished selectivities (see discussion in the main text).
Scheme 2. Diester Formation by Secondary
Methoxycarbonylation
Table 2. Methoxycarbonylation Reaction of Phenylacetylene
Using Varying Bidentate Ligands at 0.1% Pd Loadinga
Since, in principle, both the linear and branched monoesters
could provide the diester product upon secondary methoxycar-
bonylation (Scheme 2), each of these substances was subjected
to reaction under the conditions detailed in Table 1. It was found
that the reaction leading to the diester product proceeds prefer-
entially via the branched R,β-unsaturated monoester intermedi-
ate (methyl atropate). This became clear as the rate of reaction of
the branched substrate was approximately 5 times faster than that
of the linear analogue (methyl cinnamate), in competitive reac-
tions containing 1:1 mixtures of the two monoesters.
For a greater ability to critically assess the bidentate ligands,
lower catalyst loadings (0.1%) were employed to afford in-
complete conversion of the substrate in a given period of time
(Table 2). In general, all of the ligands tended to favor formation
of the branched ester, varying from moderate selectivity (Table 2,
entries 3ꢀ5) to essentially complete selectivity (Table 2,
entries 2 and 6). The ligands used here possess similar electronic
characteristics, differing mainly in their bite angles. These data
point to a rather determinative effect of the bite angle on the
reactivity of the catalyst as reflected by the yields and upon the
branched/linear selectivity. However, binding of the ring O atom
to the Pd atom in the case of the diphenyl ether- and Xantphos-
derived ligands may also play a role.
a Reaction conditions: Pd:substrate 1:1000; 0.0111 mmol of Pd(OAc)2,
0.0444 mmol of ligand, 0.0222 mmol of Al(OTf)3, 11.1 mmol of
phenylacetylene, 4.7 mL of MeOH, 35 bar of CO, 80 ( 2 °C internal
temperature, 3 h. b Reference 1. Standardized PꢀMꢀP angles from
X-ray structures and calculations. c Isolated yields. d Branched/linear
selectivites are based on 1H and 13C NMR spectroscopy and quantitative
GC-FID analysis. e Formation of Pd black was noted.
catalyst loadings (Table 2, entries 1 and 2), fairly substantial
conversion of the monoester product into the diester analogue
was noted, in reactions performed over 24 h. Shorter reaction
times (Table 3, entry 3) essentially precluded the formation of
this byproduct, which was also not formed at lower catalyst
loadings, presumably because of significant differences in its rate
of formation in comparison to that of the mono ester. A reaction
performed in the absence of Pd catalyst gave essentially no
conversion of the substrate to product (Table 3, entry 8). The
Given the overall excellent results secured with BINAP as
ligand, we further probed this reaction, among others, by varying
the catalyst loading (Table 3). No Pd black was obtained in any of
the runs, indicating the inherent stability of the system. At higher
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Table 3. Methoxycarbonylation Reaction of Phenylacetylene Using BINAP As Ligand at Varying Catalyst Loadingsa
entry
Pd:substrate
conv (%)
productb (%)
diesterb (%)
b:lb
time (h)
TOFc ( ꢁ 102)
1
1:50a
100
100
100
100
99
84
79
98
99
99
67
34
<1
12
48
88
65g
10
19
1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
24
24
3
2
1:500
3
1:500
4
1:1000
0
3
5
1:1000
0
1.5
3
6
1:5000
67
0
11.2
11.3
7
1:10 000
0:10 000d
1:10 000e
1:10 000f
1:10 000f
1:20 000f
34
0
3
8
<1
12
0
3
9
0
>99:1
>99:1
>99:1
>99:1
3
4.0
10
11
12
48
0
3
16.0
88
0
15
15
80
0
10.7
a Reaction conditions: 0.225 mmol of Pd(OAc)2, 0.90 mmol of BINAP, 0.45 mmol of Al(OTf)3, 1.125 mmol of phenylacetylene, 5.9 mL of MeOH,
35 bar of CO, 80 ( 2 °C internal temperature, total volume ca. 6 mL. The amount of catalyst (including Pd(OAc)2, Al(OTf)3, and ligand) was reduced in
later runs. b Conversion to and selectivity for ester products as determined by 1H and 13C NMR spectroscopy and GC-FID analysis. c TOF is the mean
turnover frequency calculated over the duration of the reaction: TOF = mol product/mol Pd/h. d Reaction run in the absence of Pd to test for reactor
memory effect. e Reaction run in the absence of Al(OTf)3. f Reaction run using 8 equiv of Al(OTf)3. g Byproduct formation accounted for 15% of the
starting material converted, evidenced by late peaks in the GC trace indicating uncharacterized higher-boiling materials.
Table 4. Methoxycarbonylation Reaction of Phenylacetylene
Using BINAP As Ligand with Different Co-catalystsa
entry
co-catalyst
productb (%)
b:l
TOFc ( ꢁ 102)
1
2
3
4
5
6
7
Al(OTf)3
La(OTf)3
Hf(OTf)4
p-TsOH
HOTf
34
25
22
19
15
11
3
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
>99:1
11.3
8.3
7.3
6.3
5.0
3.7
1.0
MSA
TFA
a Reaction conditions: Pd:substrate 1:10 000; 0.000 55 mmol of Pd-
(OAc)2, 0.0022 mmol of BINAP, 0.0011 mmol of co-catalyst added,
5.5 mmol of phenylacetylene, 5.3 mL of MeOH, 35 bar of CO, 80 ( 2 °C
internal temperature, 3 h, total volume ca. 6 mL. b Conversion to ester
products as determined by 1H and 13C NMR spectroscopy and GC-FID
analysis. c TOF is the mean turnover frequency calculated over the
duration of the reaction: TOF = mol product/mol Pd/h.
Figure 1. CO uptake curves for BINAP and PyPPh2.
these reactions, indicating a very stable Pd/ligand system. It is also
evident that the acid did not play a role in determining the
selectivity to product in the reaction as the b:l ratio remained the
same throughout.
PyPPh2 is a ligand of choice in Brønsted acid co-catalyzed
methoxycarbonylation reactions of phenylacetylene.11 Un-
fortunately, this ligand is not a simple replacement for the
BINAP ligand that fared so well in the present study.
Optimization0 of the reaction conditions for this ligand,
but using Al(OTf)3 as co-catalyst, afforded a highly active
but relatively unstable catalyst (Figure 1). The catalytic
system provides the ester with good selectivity (Table 5),
possibly by acting as a (hemilabile) bidentate ligand. Despite
much effort, Pd black continued to precipitate from the
reaction mixture in our hands when using Al(OTf)3 as the
co-catalyst, even when applying excess ligand and acid
catalyst, changes that have led to more stable catalysts in
other instances.8 This presumably accounts for the precipi-
tous decline in CO uptake as noted in Figure 1. PyPPh2 is a
monodentate ligand that is held to act in a hemilabile
fashion.12 It may be that the added Al ion coordinates to
the N atom of the pyridyl moiety at some stage of the catalytic
cycle, leading to catalyst destabilization. We accordingly
concentrated our efforts on BINAP-type ligands.
effect of the Al(OTf)3 is neatly demonstrated by entry 9, where
catalyst activity is compromised by the absence of this co-catalyst.
What little activity there was may possibly be ascribed to the
waterꢀgas shift reaction (H2O + CO f H2 + CO2 f H2CO3),
which would generate weak Brønsted acidity. The catalyst
remained stable and active, even at very low loadings, but required
the presence of additional co-catalyst (entries 10ꢀ12) to secure
reasonable catalyst activity. It is clear when comparing the turn-
over frequencies calculated for entries 7 and 9 that the additional
co-catalyst provides a more active catalyst system. At 0.01% Pd,
increased acid (entry 11) as well as increased time (entry 12)
showed that excellent activity was still obtainable even at such
low Pd loadings.
The influence of the co-catalyst was investigated making
use of other triflate salts as well as some Brønsted acids
(Table 4). Here, as previously noted,8 Al(OTf)3 provided the
most active catalyst of the series of co-catalysts employed.
What was also striking is that no Pd black was observed in any of
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ARTICLE
Recycling of the Pd-BINAP catalyst was quite easy (Table 6),
among others, given the high levels of stability of the catalyst
when based on BINAP ligands. Various approaches were fol-
lowed during the recycling, but all included distillation of the
product from the crude mixture. For the experiments detailed
in columns 1ꢀ6, an aqueous extraction of the residue also
removed the Al(OTf)3.13 Columns 1 and 2 show the results of
experiments where the Pd catalyst was recycled as a separate
entity, with fresh co-catalyst, solvent, and substrate added. The
results show retention of the activity of the catalyst but with
attendant loss of selectivity for the branched isomer.
We reasoned that the loss of selectivity may arise due to loss of
ligand through leaching or via oxidation of one or both of the P
atoms on the BINAP and so added 0.1 equiv of ligand per Pd in
each subsequent recycle (columns 3 and 4; the very small
amounts of catalyst employed in these reactions precluded a
spectroscopic conclusion on the matter of the ligand oxidation).
Here, the activity of the catalyst diminishes with each cycle while
selectivity is improved compared to the first set of recycling
experiments. The diminished activity of the catalyst is seemingly
in response to the added ligand and indicates that the putative
loss of ligand may not require the addition of fresh ligand with
each run. Accordingly, we added fresh ligand (again in the amount
of 0.1 equiv per Pd) only after every third cycle (columns 5 and
6), allowing improved catalyst activity and selectivity for product.
Semifinally (columns 7 and 8), the entire catalyst was recycled by
simply distilling off all volatile components from the reaction
vessel and resubmitting the total residue for a further reaction
with fresh substrate and solvent. The overall trend here is similar
to that demonstrated by the results contained in columns 1 and 2.
Importantly, in no case was Pd black detected. Finally, the entire
catalyst was recycled, and additional ligand was added after every
third run, affording good retention of both activity of the catalyst
and selectivity toward the branched ester product.
Given the stability and activity noted with the Pd/BINAP/
Al(OTf)3 system, we investigated the use of sulfonated BINAP
(known as BINAPS (Figure 2), prepared by sulfonation of
BINAP naphthyl rings14) in polar mixed solvent systems contain-
ing water, with the possibility of forming the carboxylic acid
instead of the methyl ester.
Mixed solvent systems were compared, using BINAP as a
benchmark (Table 7, entries 1ꢀ3). Rather interestingly, no
carboxylic acid products were identified, even when making use
of 1:1 or 1:2 MeOH/H2O mixed solvents (entries 2 and 3),
and only the methyl ester products were obtained. This situation
changed when making use of BINAPS, where appreciable
amounts of the carboxylic acid were generated in systems contain-
ing 50% or more of H2O (entries 5ꢀ8). When reaching a ratio of
1:2 MeOH/H2O (entry 7), the ester was no longer detected in
the product mixture. All the while, selectivity for the branched
product (ester or acid) was maintained and the catalyst remained
intact and active (see below). Additionally, the system tolerates
Table 5. Exploring PyPPh2 As Ligand in the Phenylacetylene
Reactiona
entry Pd loading (mol %) ligand equiv acid equiv yield (%) b:l
1
2
3
4
5
0.04
0.02
0.02
0.01
0.01
16
16
32
32
64
8
8
99
57
99
99:1
99:1
99:1
16
16
32
42 (47)b 40:1
81 40:1
a Reaction conditions: identical to those indicated for Table 4, 3 h runs.
Catalyst components were added as indicated in the table. b Yield in
parentheses indicates an equivalent reaction run with 16 equiv of BINAP,
with no Pd black formation.
Figure 2. Sulfonation of BINAP.
Table 6. Recycling Experiments When Using the Pd/BINAP/Al(OTf)3 Catalysta
1b
2
3c
4
5d
6
7e
8
9f
10
b:l
run
yield
b:l
yield
b:l
yield
b:l
yield
b:l
yield
1
2
3
4
5
6
7
8
9
10
100
100
99
98
97
97
96
95
96
94
>99:1
50:1
30:1
30:1
30:1
30:1
30:1
20:1
20:1
20:1
100
88
86
80
78
75
73
70
67
65
>99:1
90:1
90:1
70:1
70:1
70:1
70:1
70:1
60:1
60:1
100
100
100
95
>99:1
99:1
99:1
90:1
90:1
90:1
90:1
90:1
90:1
90:1
100
99
94
94
82
84
73
72
69
66
>99:1
50:1
30:1
30:1
20:1
20:1
20:1
20:1
20:1
20:1
100
100
98
>99:1
>99:1
95:1
95:1
90:1
90:1
90:1
90:1
90:1
90:1
97
94
97
93
93
91
92
90
91
88
90
87
90
a Reaction conditions: Pd:substrate 1:1000; 0.0111 mmol of Pd(OAc)2, 0.044 mmol of ligand, 0.0222 mmol of Al(OTf)3, 11.1 mmol of phenylacetylene,
35 bar of CO, 82 ( 2 °C internal temperature, total volume 12 mL (MeOH used to make up to 12 mL). For recycling, the esters were distilled off and the
Al(OTf)3 was extracted using water. Fresh solvent and substrate were added for each run; ligand and Al(OTf)3 were added as per the footnotes below.
b No added ligand after recycle; added fresh solvent, substrate, and Al(OTf)3. c 0.1 equiv of ligand added after each run in addition to fresh solvent,
substrate, and Al(OTf)3. d 0.1 equiv of ligand added after every third run in addition to fresh solvent, substrate, and Al(OTf)3. e No additional ligand
added; no additional Al(OTf)3 added, only fresh solvent and substrate. f 0.1 equiv of ligand added after every third run in addition to fresh solvent and
substrate; no added Al(OTf)3.
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Table 7. Comparative Study of BINAP and BINAPS with
Varying Solventsa
(TOF = mol product/mol Pd/h) were calculated from the moles of
isolated product.
Recycling. After completion of the reaction, the methanol solvent
was removed under vacuum, and DCM (30 mL) was added to the
residue. The solution was washed with water (3 ꢁ 10 mL), and the
organic phase dried over magnesium sulfate. The solvent was removed
under vacuum, and theresidue dissolved in methanol and used in the next
run. This process allowed recycling of the Pd/ligand part of the catalyst.
In instances where the entire catalyst mixture was recycled (i.e., Pd/
ligand/Al), the residue was used directly after the vacuum distillation step.
Methyl cinnamate: 1H NMR (300 MHz, CDCl3) δH 7.68 (d, 1H, J =
16.3 Hz), 7.50ꢀ7.48 (m, 2H), 7.37ꢀ7.34 (m, 3H), 6.42 (d, 1H, J = 16.3
Hz), 3.78 (s, 3H); 13C NMR (75 MHz, CDCl3) δC 167.3, 144.8, 134.2,
130.2, 128.8, 128.0, 117.7, 51.6.
entry
ligand
solvent
% product
b:l:acidb
1
2
3
4
5
6
7
8
9
BINAP
MeOH
99
95
>99:1:0
>99:1:0
>99:1:0
>99:1:0
70:5:25
30:0:70
0:0:100
0:0:100
0:0:100
BINAP
1 MeOH:1 H2O
1 MeOH:2 H2O
MeOH
BINAP
100
95
BINAPS
BINAPS
BINAPS
BINAPS
BINAPS
BINAPS
1 MeOH:1 H2O
1 MeOH:1.5 H2O
1 MeOH:2 H2O
H2O
100
100
100
100
100
1 H2O:1 DME
1
Methyl atropate: H NMR (300 MHz, CDCl3) δH 7.41ꢀ7.32 (m,
a Reaction conditions: Pd:substrate 1:1000; 0.0111 mmol of Pd(OAc)2,
0.044 mmol of ligand, 0.0222 mmol of Al(OTf)3, 11.1 mmol of
phenylacetylene, 10.8 mL of MeOH, 35 bar of CO, 82 ( 2 °C internal
temperature, total volume ca. 12 mL. b Acid refers to the branched
carboxylic acid (2-phenylacrylic acid).
5H), 6.34 (d, 1H, J = 1.2 Hz), 5.87 (d, 1H, J = 1.2 Hz), 3.80 (s, 3H);
13C NMR (75 MHz, CDCl3) δC 167.2, 141.1, 136.5, 128.1, 128.0, 127.9,
126.7, 52.0.
Dimethyl 2-phenylsuccinate: 1H NMR (300 MHz, CDCl3) δH
7.31ꢀ7.22 (m, 5H), 4.08 (dd, 1H, J = 10.3 and 5.2 Hz), 3.78 (s, 6H),
3.18 (dd, 1H, J = 16.9 and 10.1 Hz), 2.63 (dd, 1H, J = 16.9 and 5.2 Hz);
13C NMR (75 MHz, CDCl3) δC 173.3, 171.8, 144.4, 128.7, 127.9, 127.5,
52.1, 51.7, 46.9, 37.4; CIMS m/z 223 [M + H]+, 191; HRCIMS
calculated for C12H14O4 223.0970, obtained 223.0968.
the use of DME as co-solvent (entry 9), which may be useful for
less soluble substrates.
Disappointingly, initial work performed to recycle the Pd/
BINAPS system has not yet yielded fruitful results and exposes a
potential weakness or limitation of the system. We are currently
pursuing the recycling of this catalyst system.
2-Phenylacrylic acid: Mp 103ꢀ105 °C; 1H NMR (400 MHz,
CDCl3/TMS) δ 12.19 (s, 1H), 7.45ꢀ7.18 (m, 5H), 6.57 (br s, 1H),
6.04 (br s, 1H); 13C NMR (100 MHz, CDCl3/TMS) δ 172.5, 140.6,
136.0, 129.5, 128.6, 128.3, 128.0 (lit.15 13C NMR (100 MHz, CDCl3)
δ 171.9, 140.6, 136.0, 129.2, 128.4, 128.2, 128.0).
’ CONCLUSIONS
The present study shows that the Pd(OAc)2/BINAP/Al-
(OTf)3 combination forms a stable catalyst capable of facilitating
the methoxycarbonylation reaction of phenylacetylene to pro-
vide the branched ester product in high yield and selectivity. This
catalyst can be recycled a number of times, with some small losses
of activity and selectivity through 10 cycles. In the present system,
the Al(OTf)3 co-catalyst leads to the generation of catalysts that
are more highly active than those generated from Brønsted acids
under identical conditions. An advantage of the Al(OTf)3-based
system is its high potential for recycling.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: bwilliams@uj.ac.za. Phone: +2711 559 3431. Fax:
+2711 559 2819.
’ ACKNOWLEDGMENT
We thank Sasol, THRIP, the NRF, and the University of
Johannesburg for financial assistance with this project.
’ EXPERIMENTAL SECTION
’ REFERENCES
Instrumentation. NMR spectra were recorded on a Varian Gemini
2000 300 MHz instrument or on a Bruker Ultrashield 400 MHz
spectrometer. MS data were recorded on a Thermo DFS magnetic sector
instrument, while GC spectra were recorded on a Shimadzu GCMS-
QP2010 instrument fitted with a quadrupole mass detector. A DB1MS
30 m analytical column (i.d.: 0.25 mm, film thickness: 0.25 mm) that
separated the various compounds on the basis of boiling points was used.
For quantitative data, flame ionization detection was employed.
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