The cross-metathesis of methyl oleate with c/s-2-butene-1,4-diyl diacetate and the influence of protecting groups

Article abstract of DOI:10.3762/bjoc.7.1

Background: α,ω-Difunctional substrates are useful intermediates for polymer synthesis. An attractive, sustainable and selective (but as yet unused) method in the chemical industry is the oleochemical cross-metathesis with preferably symmetric functionalised substrates. The current study explores the cross-metathesis of methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2) starting from renewable resources and quite inexpensive base chemicals. Results: This cross-metathesis reaction was carried out with several phosphine and N-heterocyclic carbene ruthenium catalysts. The reaction conditions were optimised for high conversions in combination with high cross-metathesis selectivity. The influence of protecting groups present in the substrates on the necessary catalyst loading was also investigated. Conclusions: The value-added methyl 11-acetoxyundec-9-enoate (3) and undec-2-enyl acetate (4) are accessed with nearly quantitative oleochemical conversions and high cross-metathesis selectivity under mild reaction conditions. These two cross-metathesis products can be potentially used as functional monomers for diverse sustainable polymers.

Full text of DOI:10.3762/bjoc.7.1

The cross-metathesis of methyl oleate with
cis-2-butene-1,4-diyl diacetate
and the influence of protecting groups
Arno Behr* and Jessica Pérez Gomes
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2011, 7, 1–8.
Chair of Technical Chemistry A, Department of Biochemical and
Chemical Engineering, Technische Universität Dortmund,
Emil-Figge-Str. 66, D-44227 Dortmund, Germany
doi:10.3762/bjoc.7.1
Received: 30 September 2010
Accepted: 01 December 2010
Published: 03 January 2011
Email:
Arno Behr* - behr@bci.tu-dortmund.de
Guest Editor: K. Grela
* Corresponding author
© 2011 Behr and Pérez Gomes; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
cross-metathesis; methyl oleate; monomer; polyester; renewable
resources
Abstract
Background: α,ω-Difunctional substrates are useful intermediates for polymer synthesis. An attractive, sustainable and selective
(but as yet unused) method in the chemical industry is the oleochemical cross-metathesis with preferably symmetric functionalised
substrates. The current study explores the cross-metathesis of methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2) starting
from renewable resources and quite inexpensive base chemicals.
Results: This cross-metathesis reaction was carried out with several phosphine and N-heterocyclic carbene ruthenium catalysts. The
reaction conditions were optimised for high conversions in combination with high cross-metathesis selectivity. The influence of
protecting groups present in the substrates on the necessary catalyst loading was also investigated.
Conclusions: The value-added methyl 11-acetoxyundec-9-enoate (3) and undec-2-enyl acetate (4) are accessed with nearly quanti-
tative oleochemical conversions and high cross-metathesis selectivity under mild reaction conditions. These two cross-metathesis
products can be potentially used as functional monomers for diverse sustainable polymers.
Introduction
In the last decade, olefin metathesis has become a routine and the olefin cross-metathesis has demonstrated its great impor-
competent synthetic method for the formation of carbon–carbon tance in providing access to alkenes bearing a wide range of
double bonds [1-5]. Among investigations of ring opening functional groups [8-11]. Especially, the olefin cross-metathesis
metathesis polymerisation [6] and ring closing metathesis [7], with oleochemicals offers a versatile synthetic approach to
1

Beilstein J. Org. Chem. 2011, 7, 1–8.
prepare value-added substrates starting from renewable raw ma- oleic acid (7) with the unprotected cis-2-butene-1,4-diol (8). By
terials. Due to the cross-metathesis reactions of fatty acid avoiding the use of protecting groups the processing steps to the
derivatives that yield diverse types of α,ω-difunctional polymeric end products would be decisively shortened.
monomers, which can be processed into polymers (polyamides,
polyesters, polyolefins, etc.), partial or even complete substitu- Moreover, the advantage of this cross-metathesis reaction is the
tion of the steadily decreasing petrochemicals by materials from use of the relatively inexpensive substrates 1 and 2. The
renewable resources is warranted [12-14]. So far, cross- acylated substrate 2 can be directly synthesised by the catalytic
metathesis reactions of these raw materials with different cross- reaction of 1,3-butadiene with acetic acid on a large scale. The
metathesis reaction partners (allyl alcohol [15,16], allyl chlo- classical preparative method for 1,4-butanediol is the copper
ride [16], acrylonitrile [17], fumaronitrile [18], acrolein [19], catalysed reaction of acetylene with formaldehyde and subse-
methyl acrylate [20] and diethyl maleate [21]) yielding α,ω- quent hydrogenation of the intermediate [23].
difunctional substrates have been investigated.
Currently, the symmetric acylated substrate 2 is one of the most
In this article, the ruthenium catalysed cross-metathesis of frequently used cross-metathesis substrates in classical
methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2) metathesis research. For instance, the cross-metathesis of 2 with
(Scheme 1) will be described. This synthetic approach gives rise allyl benzene or terminal aliphatic alkenes has often been used
to another group of α,ω-difunctional substrates: The metatheti- in the development of new metathesis catalysts [24-27]. In oleo-
cal conversion studied yields methyl 11-acetoxyundec-9-enoate chemical metathesis research only the tungsten catalysed cross-
(3) and undec-2-enyl acetate (4). The resulting protected metathesis of methyl 10-undecenoate with 2 has been described
α-hydroxy-ω-carboxylic acid derivatives have potential applica- [28]. The highest yield of the resulting cross-metathesis pro-
tions in the preparation of a variety of polymers [22] or lactones duct was 51% after 2 h at 125 °C. With Grubbs 1st generation
[14]. Moreover, undec-2-enyl acetate (4) could be processed catalyst [Ru]-1, the reaction temperature could be lowered to
into polyallylic alcohols under appropriate reaction conditions 45 °C. Quantitative conversions of methyl 10-undecenoate were
[22]. In contrast to many other oleochemical cross-metathesis obtained with a catalyst loading of 5 mol % [Ru]-1 [8].
reactions, both the resulting products can be used in polymer
chemistry. This oleochemical cross-metathesis reaction Results and Discussion
described here was studied under different reaction conditions Scheme 1 outlines the reaction investigated, i.e., the ruthenium
with the aim of optimising oleochemical conversions in combi- catalysed cross-metathesis of methyl oleate (1) with cis-2-
nation with high cross-metathesis selectivities. Additionally, butene-1,4-diyl diacetate (2). The self-metathesis of methyl
several phosphine and N-heterocyclic carbene ruthenium cata- oleate (1), which yields octadec-9-ene (5) and dimethyl
lysts were studied. The optimised reaction conditions were octadec-9-enedioate (6), is the only concurrent metathesis reac-
subsequently investigated in the cross-metathesis reaction of tion which had to be suppressed (Scheme 1). The desired cross-
Scheme 1: Cross-metathesis of methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2) and the self-metathesis of 1.
2

Beilstein J. Org. Chem. 2011, 7, 1–8.
Figure 1: The ruthenium metathesis catalysts used. (SIMes: 1,3-bis-(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene).
metathesis products are the α,ω-diester methyl 11-acetoxyundec (2), the generation of this intermediate cyclic complex is also
-9-enoate (3) and undec-2-enyl acetate (4). Both are thus hindered. In addition, its symmetry only leads to the two desired
derived from a renewable precursor and are interesting products.
substrates for the synthesis of different types of polymers. Sub-
strate 2 can be considered as an important cross-metathesis The catalytic activity of the ruthenium complexes [Ru]-1 to
partner for the metathetical conversion of methyl oleate 1 in [Ru]-8 (Figure 1) using a catalyst loading of 1.0 mol % was
terms of its short chain length. Thus, the chain length of the evaluated in the cross-metathesis of methyl oleate (1) with cis-
cross-metathesis products is appropriate for certain polymer 2-butene-1,4-diyl diacetate (2). The reactions were performed
applications. Therefore, in contrast to polymers prepared from with a fivefold excess of 2 in toluene at 50 °C for 5 h to shift the
short-chain monomers, these polymers have a higher flexibility reaction equilibrium towards the cross-metathesis products 3
and higher stability against hydrolysis [22]. Due to the cis-con- and 4.
figuration of 2, the metathesis reactivity is quite high, although
this is slightly reduced by the two electron-withdrawing func- The differences in metathesis activity of these investigated
tional groups at the β-positions of the double bond. During our metathesis initiators are presented in Table 1. Both conversions
investigations of oleochemical cross-metathesis with diethyl of 1 and yields of the cross-metathesis products 3 and 4 were
maleate, it was found that the trans-isomer is less reactive than determined by gas chromatography with internal standard.
its cis-isomer [21]. The trans-isomer is not able to form the
metallacyclobutane complex to give the desired metathesis As summarised in Table 1, the lowest conversions of 1 (about
products [28]. In the case of trans-2-butene-1,4-diyl diacetate 15%) and yields of each of the desired cross-metathesis prod-
Table 1: Results of metathesis catalyst activities in the cross-metathesis of methyl oleate (1) with 2.a
conversion 1
yield 3
[%]b
yield 4
[%]b
yield 5
[%]b
yield 6
[%]b
entry
catalyst
[%]b
1
2
[Ru]-1
[Ru]-2
14
48
3
4
6
5
29
28
10
10
3
4
[Ru]-3
[Ru]-4
15
42
4
4
6
9
6
24
26
10
5
6
7
8
[Ru]-5c
[Ru]-6c
[Ru]-7c
[Ru]-8c
34
35
90
84
15
16
59
53
14
15
58
52
10
9
11
10
15
16
16
16
areaction conditions: 1.0 mol % cat., m(1) = 0.17 mmol, 0.85 mmol 2, toluene, 5 h, 50 °C, 900 rpm; bdetermined by gas chromatography with internal
standard; caddition of 100 equiv of PhSiCl3 according to [Ru]-5–[Ru]-8.
3

Beilstein J. Org. Chem. 2011, 7, 1–8.
ucts 3 and 4 (about 5%) were achieved using the ruthenium amounted to 16%. Furthermore, the cross-metathesis selectivity
phosphine complexes [Ru]-1 and [Ru]-3 (Table 1, entries 1 and using the ruthenium catalysts [Ru]-7 and [Ru]-8 is decisively
3). Only slight differences in activity were observed between higher compared to the other catalysts used.
the benzylidene catalyst [Ru]-1 and its indenylidene counter-
part [Ru]-3. The self-metathesis of methyl oleate (1) mentioned From the results in Table 2 an increase of conversion of methyl
above could not be suppressed. Other side-reactions were not oleate 1 (from 15 to 94%) and of yield of each of the cross-
observed. No double-bound isomerisation took place. Promising metathesis products 3 and 4 (from 2 to 66%) were obtained with
results were obtained with catalysts bearing N-heterocyclic a catalyst loading of [Ru]-7 in a range of 0.1 and 1.5 mol %.
carbene ligands (Table 1, entries 2 and 4–8) [29]. Up to 48% of Cross-metathesis selectivity was increased by 60% to 67%.
methyl oleate (1) was converted and the yields of the cross- With a catalyst loading of 1.5 mol % of [Ru]-7, a nearly quanti-
metathesis products 3 and 4 of ca. 28% were achievable with tative conversion of unsaturated fatty ester 1 was achievable
ruthenium catalysts [Ru]-2 and [Ru]-4 (Table 1, entries 2 and (Table 2, entry 4). Moreover, the undesired self-metathesis
4). Here, the self-metathesis reaction of 1 is a side-reaction. The products from 1 were obtained in lower amounts (ca. 14% of
yields of 5 and 6 were nearly halved using the second genera- each self-metathesis product 5 and 6). From the results, it can
tion ruthenium catalysts [Ru]-2 and [Ru]-4. The cross- be concluded that a catalyst loading of above 1.0 mol % of the
metathesis selectivity increased considerable. The difunction- ruthenium catalyst [Ru]-7 was necessary for efficient conver-
alised co-substrate 2 was also converted to a greater extent. sion of cis-2-butene-1,4-diyl diacetate (2). Further increasing
Accordingly, these metathesis catalysts illustrate once more the quantity of [Ru]-7 led neither to an essentially higher oleo-
their higher metathesis activity and their higher tolerance chemical conversion nor to higher cross-metathesis yields
towards functional groups [2].
(Table 2, entry 5). The yields of self-metathesis products also
remained constant (about 15%).
Comparable or higher conversions of 1 and cross-metathesis
yields of 3 and 4 (Table 1, entries 5–8) were obtained with The ratio of the two cross-metathesis reaction partners 1 and 2
ruthenium complexes [Ru]-5–[Ru]-8. Due to their bidentate has also a great influence on conversion (Table 3). Besides, it is
Schiff base ligands, they must be chemically activated by the also advantageous to reduce the excess of protected diol 2 in
addition of 100 equiv of phenyltrichlorosilane [30,31]. Within terms of green chemistry and industrial implementation.
this catalyst family it can be concluded that with higher steric
hindrance of the Schiff base ligands higher conversions and Independent of the excess of 2 used, the conversion of methyl
yields were achievable (Table 1, entries 7 and 8). Schiff base oleate (1) was quite high (<96%). The cross-metathesis yields
ligands with a nitro substituent did not lead to a significant reached its maximum at 77% using an eightfold excess of 2
increase or loss of metathesis activity. Consequently, in the (Table 3, entry 4). The yields could be increased by 32% to
oleochemical cross-metathesis reaction [Ru]-7 and [Ru]-8 were 77%. This indicates that the self-metathesis reaction was more
the most active catalysts due to their space-filling isopropyl and more suppressed; the yields of 5 and 6 were decreased by
substituted Schiff base ligands [31]. The cross-metathesis yields 15% to 10%. Further investigations were performed with an
amounted to 59% and methyl oleate (1) was converted up to eightfold excess of 2, because an additional excess of 2 did not
90%. Moreover, the self-metathesis of methyl oleate (1) was have a positive effect on conversions and yields (Table 3, entry
reasonably well suppressed and could be considered as a side- 5). Too high an excess of 2 hindered the conversion of methyl
reaction; the yield of the self-metathesis products 5 and 6 oleate (1).
Table 2: Results of catalytic investigations of cross-metathesis of 1 with 2 with various [Ru]-7 loadings.a
[Ru]-7 loading
conversion 2
yield 3
[%]b
yield 4
[%]b
yield 5
[%]b
yield 6
[%]b
entry
[mol %]b
[%]b
1
2
3
4
5
0.1
0.5
1.0
1.5
2.0
15
32
90
94
96
1
2
7
7
6
6
12
15
15
15
13
16
14
15
59
66
64
58
65
63
areaction conditions: [Ru]-7, m(1) = 0.17 mmol, 0.85 mmol 2, n(PhSiCl3)/n([Ru]-7) = 100/1, toluene, 5 h, 50 °C, 900 rpm; bdetermined by gas chroma-
tography with internal standard.
4

Beilstein J. Org. Chem. 2011, 7, 1–8.
Table 3: Results of catalytic investigations of cross-metathesis of 1 with various amounts of 2.a
conversion 2
yield 3
[%]b
yield 4
[%]b
yield 5
[%]b
yield 6
[%]b
entry
equiv of 2
[%]b
1
2
3
4
5
2
4
96
92
94
96
96
45
54
66
76
77
45
54
65
78
79
25
19
13
10
10
26
18
14
9
5
8
10
10
areaction conditions: 1.5 mol % [Ru]-7, m(1) = 0.17 mmol, n(PhSiCl3)/n([Ru]-7) = 100/1, toluene, 5 h, 50 °C, 900 rpm; bdetermined by gas chromatog-
raphy with internal standard.
The reactions were stopped after fixed reaction times in an rapid self-metathesis at low reaction temperatures (Table 5,
attempt to shorten the necessary reaction time (Table 4). After entry 1). In contrast, the cross-metathesis became more predom-
1 h, 94% of methyl oleate (1) was already converted (Table 4, inant at higher reaction temperatures. This suggests that thermal
entry 1). The highest yields of each cross-metathesis product 3 activation of the cis-2-butene-1,4-diyl diacetate (2) is required.
and 4 were just obtained after 5 h (Table 4, entry 3). With On increasing the reaction temperature from 30 to 50 °C an
longer reaction times, conversions and yields remained increase in the yields of the cross-metathesis products (up to
constant. The reaction equilibrium was shifted towards the 77%) was observed. At the same time the self-metathesis reac-
desired cross-metathesis products 3 and 4, whereas the self- tion of 1 was hindered and only 10% of each of the self-
metathesis reaction of 1 was more and more suppressed and the metathesis products 5 and 6 was produced.
yields of 5 and 6 amounted to around 10%.
Finally, it was desirable to avoid the use of protecting groups.
Thus, the optimised reaction conditions for the cross-metathesis
Table 4: Results of variation of the reaction time of cross-metathesis of
1 with 2.a
of methyl oleate (1) with cis-2-butene-1,4-diyl diacetate (2)
were applied to the cross-metathesis reaction of the corres-
ponding fatty acid 7 with the diol 8. The oleic acid (7) was
reacted with both cis-2-butene-1,4-diyl diacetate (2) and the
diol 8 (Table 6).
time conversion 2 yield 3 yield 4 yield 5 yield 6
entry
[h]
[%]b
[%]b
[%]b
[%]b
[%]b
1
2
3
4
5
1
3
5
7
9
94
94
96
93
93
58
67
78
73
70
61
71
82
78
71
18
13
9
17
14
8
Whilst the conversion of methyl oleate (1) with the protected
diol 2 was nearly quantitative using 1.5 mol % of the ruthe-
nium complex [Ru]-7 at 50 °C within 5 h (Table 6, entry 1),
comparative results in the cross-metathesis of oleic acid (7)
with 2 were only achieved with the use of 3.0 mol % of the
same ruthenium catalyst. Under otherwise similar reactions
conditions, 75% of oleic acid was converted (Table 6, entry 2).
The cross-metathesis yield amounted to 55%. In the complete
10
11
10
10
areaction conditions: 1.5 mol % [Ru]-7, m(1) = 0.17 mmol, 1.36 mmol
2, n(PhSiCl3)/n([Ru]-7) = 100/1, toluene, 50 °C, 900 rpm; bdetermined
by gas chromatography with internal standard.
Moreover, the conversion of methyl oleate (1) appears to be absence of protecting groups, a catalyst loading of 4.0 mol %
temperature-independent (Table 5); conversions were always was necessary to produce similar results (Table 6, entry 3).
higher than 92%. The unsaturated methyl oleate (1) underwent a With regard to technical implementation, it seems to be more
Table 5: Results of variation of the reaction temperature of cross-metathesis of 1 with 2.a
temperature
[°C]
conversion 2
yield 3
[%]b
yield 4
[%]b
yield 5
[%]b
yield 6
[%]b
entry
[%]b
1
2
3
30
40
50
92
94
96
44
55
76
45
53
78
24
20
10
23
19
9
areaction conditions: 1.5 mol % [Ru]-7, m(1) = 0.17 mmol, 1.36 mmol 2, n(PhSiCl3)/n([Ru]-7) = 100/1, toluene, 5 h, 900 rpm; bdetermined by gas
chromatography with internal standard.
5

Beilstein J. Org. Chem. 2011, 7, 1–8.
Table 6: Influence of the protecting groups on the ruthenium catalysed cross-metathesis.a
cross-metathesis
c([Ru]-7)
X(1 or 7)
Y(α,ω-product)
entry
[mol %]
[%]
[%]
substrate
co-substrate
1
2
3
1
7
7
2
2
8
1.5
3.0
4.0
96
75
76
78
55
53
areaction conditions: [Ru]-7, m(1 or 7) = 0.17 mmol, n(1 bzw. 7)/n(2 bzw. 8) = 1/8, n(PhSiCl3)/n([Ru]-7) = 100/1, toluene, 5 h, 50 °C, 900 rpm.
economical to use the protected substrates, since the catalyst with methanol using hypostoichiometric amounts of sodium
loading of the expensive ruthenium complexes is considerably methoxide (30% in methanol). cis-2-Butene-1,4-diyl diacetate
higher.
(2) was prepared by the pyridine catalysed acylation of the diol
8 with acetic anhydride according to [32].
Conclusion
In conclusion, the cross-metathesis of methyl oleate (1) with Analytical equipment and methods
cis-2-butene-1,4-diyl diacetate (2) was feasible with the rela- Analytical thin-layer chromatography (TLC) was performed on
tively low catalyst loading of the Schiff base ruthenium catalyst silica gel TLC-cards (layer thickness 0.20 μm, VWR Interna-
[Ru]-7 to yield two value-added and sustainable intermediates tional). Substrates were visualised with p-anisaldehyde reagent.
in one step. Methyl 11-acetoxyundec-9-enoate (3) and undec-2- Flash chromatography was conducted on silica gel 60
enyl acetate (4) are both very interesting substrates for polymer (40–60 μm, Acros Organics). Nuclear magnetic resonance
synthesis. They could be prepared under mild reaction condi- (NMR) spectra were recorded in deuterated chloroform on a
tions within 5 h. Moreover, this is an advantageous contribu- Bruker AVANCE DRX spectrometer operating at 400 MHz at
tion towards the synthesis of sustainable monomer units 298 K. Chemical shifts (δ) are indicated in parts per million
because a new α,ω-difunctional substrate class starting from a relative to tetramethylsilane as internal standard (TMS,
renewable compound and an inexpensive base chemical was δ = 0.0 ppm). Gas chromatographic (GC) analyses were
prepared.
performed on a Hewlett-Packard HP 6890 apparatus equipped
with a HP5 capillary column (coating: 5% diphenyl-95%-
Various metathesis catalysts were investigated, disclosing that dimethyl-polysiloxane; length 30 m, diameter 0.25 mm, thick-
the Schiff base ruthenium indenylidene catalyst [Ru]-7 bearing ness 0.25 μm) and flame ionisation detection (FID) connected
a N-heterocyclic carbene ligand, which is an already industrial to an autosampler. The oven temperature program was as
implemented metathesis catalyst, led to high conversions and follows: initial temperature 130 °C, hold for 6 min, increase by
yields of the desired cross-metathesis products. Interestingly, 25 °C/min to 320 °C, hold for 4 min. Measurements were
this cross-metathesis could be performed without protecting performed in split–split mode (split ratio 70:1) using nitrogen as
groups, but the catalyst loading had to be adjusted to get similar the carrier gas (linear velocity of 30.0 cm/s at 300 °C). Conver-
oleochemical conversions and cross-metathesis yields.
sions and yields were determined with n-pentadecane as internal
standard and isopropyl alcohol as solvent.
Experimental
Materials
GC–mass spectroscopy (MS) chromatograms were recorded
Sunflower oil with a high oleic content (91.4% oleic acid) was using a Hewlett-Packard HP 6890 instrument with the same
obtained from Emery Oleochemicals. cis-2-Butene-1,4-diol (8) capillary column as specified above and a HP 5973 mass
(97%), solvents and reagents were purchased from Sigma- detector set (70 eV). The oven temperature program, the
Aldrich. Benzylidene ruthenium catalysts [Ru]-1 and [Ru]-2 split–split mode and the specifications of the carrier gas were
were obtained from Sigma-Aldrich and the remaining indenyli- similar to those in the GC-FID method.
dene ruthenium catalysts [Ru]-3–[Ru]-8 were provided by
Cross-metathesis of methyl oleate (1) and
Umicore AG & Co. KG and were used as received.
cis-2-butene-1,4-diyl diacetate (2)
All reactions were performed under an inert atmosphere of A flame-dried Schlenk tube was charged with 0.050 g (0.17
argon using standard Schlenk line techniques. Methyl oleate (1) mmol) methyl oleate (1) and 2–10 equiv cis-2-butene-1,4-diyl
was prepared by transesterifcation of high oleic sunflower oil diacetate (2). The mixture was diluted to 1.250 g with toluene.
6

Beilstein J. Org. Chem. 2011, 7, 1–8.
The solid metathesis catalysts [Ru]-1–[Ru]-8 were added in the 70 eV): m/z (%) = 212 (4) [M+], 170 (5), 152 (3), 141 (4), 124
range of 0.1–2.0 mol % to the reaction mixture. In the case of (12), 110 (8), 96 (19), 82 (26), 67 (25), 54 (31), 43 (100), 39
Schiff base ruthenium catalysts [Ru]-5–[Ru]-8, 100 equiv of (11), 29 (14).
phenyltrichlorosilane (relative to the catalyst) were also added.
The reaction mixture was stirred magnetically at the appro- 9-Octadecene (5)
priate temperature (20–50 °C) for the appropriate time (1–9 h). 1H NMR (500 MHz; CDCl3): δ (ppm) = 0.89 (m, 6H, -CH3),
After completion of the reaction, the mixture was cooled to 1.28 (s, 24H, -CH2-), 2.00 (m, 4H, =CH-CH2-), 5.37 (m, 2H;
ambient temperature. Conversion and yield analyses were =CH-). 13C NMR (125 MHz; CDCl3): δ (ppm) = 13.1, 25.9,
performed by gas chromatography. The metathesis products 26.2, 28.2, 28.5, 28.8, 31.0, 33.4, 129.4. MS (EI, 70 eV): m/z
were isolated after removing toluene in vacuo by flash chroma- (%) = 252 (5) [M+], 154 (1), 139 (2), 125 (10), 111 (29), 97
tography on silica gel with cyclohexane/ethyl acetate (from 10/1 (59), 91 (1), 83 (68), 79 (7), 69 (79), 65 (4).
to 1/2) as eluent, and subsequently characterised by NMR spec-
troscopy.
Dimethyl octadec-9-enedioate (6)
1H NMR (500 MHz; CDCl3): δ (ppm) = 1.27 (m 16H, -CH2-),
1.59 (m, 4H, -C(O)-CH2-CH2-), 1.93 (m, 4H, =CH-CH2-), 2.26
(m, 4H, -C(O)-CH2-), 3.63 (s, 6H, -O-CH3), 5.34 (m, 2H, =CH-
Characterisation of the substrates
Methyl oleate (1)
1H NMR (400 MHz; CDCl3): δ (ppm) = 0.88 (t, 3H, J = 8.0 Hz, ). 13C NMR (125 MHz; CDCl3): δ (ppm) = 24.9, 28.9, 29.4,
-CH3), 1.28 (m, 20H, -CH2-), 1.61 (m, 2H, -C(O)-CH2-CH2-), 29.5, 29.6, 32.5, 34.0, 51.3, 130.2, 174.2. MS (EI, 70 eV): m/z
2.00 (m, 4H, -CH2-CH=), 2.30 (t, 2H, J = 8.0 Hz, -C(O)-CH2-), (%) = 340 (1) [M+], 308 (7), 290 (3), 276 (16), 265 (1), 207 (1),
3.66 (s, 3H, -CH3), 5.34 (m, 2H, -CH=CH-). 13C NMR (100 165 (7), 151 (11), 133 (12), 121 (13), 109 (18), 95 (38), 81 (59),
MHz; CDCl3): δ (ppm) = 14.0, 22.6, 24.9, 27.0, 27.1, 28.9, 74 (44), 67 (58), 55 (100).
29.0, 29.1, 29.2, 29.4, 29.6, 29.7, 31.8, 34.0, 51.3, 129.6, 129.9,
174.2. MS (EI, 70 eV): m/z (%) = 296 (4) [M+], 264 (28), 246 Acknowledgements
(2), 235 (3), 222 (17), 207 (3), 194 (3), 180 (16), 166 (8), 152 This work was financially supported by the German Federal
(10), 137 (14), 123 (24), 110 (29), 97 (54), 83 (55), 74 (65), 69 Ministry of Food, Agriculture and Consumer Protection (repre-
(68), 55 (100), 41 (76), 29 (29).
sented by the Fachagentur Nachwachsende Rohstoffe) and
Emery Oleochemicals GmbH. The authors thank Dr. Alfred
Westfechtel for helpful discussions. Furthermore, the authors
cis-2-Butene-1,4-diyl diacetate (2)
1H NMR (400 MHz; CDCl3): δ (ppm) = 1.96 (s, 6H, -C(O)- would like to thank Umicore AG & Co. KG for the donation of
CH3), 4.57 (d, 4H, J = 4.0 Hz, -O-CH2-), 5.64 (m, 2H, -CH=). several ruthenium metathesis catalysts.
13C-NMR (100 MHz; CDCl3): δ (ppm) = 20.6, 59.7, 127.8,
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