Platinum-Catalysed Hydrosilylation of Unsaturated Fatty Acid Esters

Article abstract of DOI:10.1002/1615-4169(200212)344:10<1142::AID-ADSC1142>3.0.CO;2-P

Different Pt(IV), Pt(II) and Pt(0) catalysts were screened for the hydrosilylation of fatty acid esters containing terminal as well as internal double bonds. The reaction of terminally unsaturated fatty acid esters proceeded smoothly with short reaction t

Full text of DOI:10.1002/1615-4169(200212)344:10<1142::AID-ADSC1142>3.0.CO;2-P

FULL PAPERS
Platinum-Catalysed Hydrosilylation of Unsaturated Fatty Acid
Esters
Arno Behr,* Franz Naendrup, Dietmar Obst
University of Dortmund, Chair of Process Development, Emil-Figge-Str. 66, 44221 Dortmund, Germany
Phone: ( ‡ 49)-231-755-2310, Fax: ( ‡ 49)-231-755-2311, e-mail: behr@ct.uni-dortmund.de
Received: June 20, 2002; Accepted: September 13, 2002
Abstract: Different Pt(IV), Pt(II) and Pt(0) catalysts leate, a conjugation of the two internal double bonds
were screened for the hydrosilylation of fatty acid before the hydrosilylation was observed. The reaction
esters containing terminal as well as internal double was carried out in substance as well as in solvent
bonds. The reaction of terminally unsaturated fatty systems permitting a catalyst recycling and reuse. In
acid esters proceeded smoothly with short reaction these systems, however, hydrogenation and double
times for nearly all examined catalysts, whereas bond isomerisation were found as side reactions.
Pt(IV) species and Pt(II) or Pt(0) species with labile
ligands were sufficiently active in the reaction of Keywords: biphasic catalysis; homogeneous catalysis;
internally unsaturated compounds. For methyl lino- hydrosilylation; oleochemicals; platinum
Introduction
triethoxysilanylundecanoic acid methyl ester
(Scheme 1). The results are given in Table 1.
3
Many hydrosilylation reactions are carried out using
homogeneous transition metal catalysts, especially
platinum compounds such as H2PtCl6 in 2-propanol
solution (Speier×s catalyst[1]) or the Pt(0)-divinyltetra-
methyldisiloxane complex (Karstedt catalyst[2]). The
hydrosilylation of unsaturated fatty esters leads to a
number of substances with potentially interesting
physical and chemical properties, such as low surface
tension, hydrophobic and antifoam behaviour.
In 1974, Saghian and Gertner presented the first results
of the hydrosilylation of unsaturated fatty acid esters
usingtheSpeiercatalyst.[3] A publicationofDelpech etal.
in 2001 focused on the regioselectivity of this reaction.[4]
Our group has recently reported about the hydrosilyla-
tion of unsaturated fatty acid esters using H2PtCl6 in
single-phase and biphasic reaction systems.[5,6]
In this article, we presentthe results of the screening of
different Pt(0), Pt(II), and Pt(IV) compounds for the
hydrosilylation of fatty acid esters containing terminal
as well as internal double bonds.
Scheme 1.
Table 1. Hydrosilylation of methyl undec-10-enoate 1 with
triethoxysilane 2 (Tˆ 40 8C, t ˆ 10 min, 1 mol % catalyst,
ester/silane ratio 1:1).
Catalyst
Fatty acid ester
Product
conversion [%][a]
yield [%][a]
H2PtCl6
PtCl4
PtCl2
Pt on carbon
K2PtCl4
94
51
93
38
0
88
50
79
21
0
Results and Discussion
Karstedt
H2Pt(OH)6
78
1
99
10
51
77
0
70
10
50
[b]
H2Pt(OH)6
[c]
Hydrosilylation of Terminally Unsaturated Fatty Acid
Esters
Pt(acac)2
[d]
Pt(cod)Cl2
[a]
Determined by GC analysis.
4 h reaction time.
(acac): 2,4-pentanedionate.
(cod): 1,5-cyclooctadiene.
[b]
[c]
[d]
At first, we checked the hydrosilylation activity of Pt
compounds for the reaction of methyl undec-10-enoate
1 with triethoxysilane 2 in a single phase to 11-
1142
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Adv. Synth. Catal. 2002, 344, No. 10

Platinum-Catalysed Hydrosilylation of Unsaturated Fatty Acid Esters
FULL PAPERS
Using H2PtCl6, PtCl2 or the Karstedt catalyst, product hydrogen source might be the silane. The GC-mass
yields of 77 up to 88% are obtained in spite of the short spectra of the reaction mixtures gave hints for the
reaction time of only 10 min. PtCl4 as catalyst gives a occurrence of disilanes, however, attempts to isolate
lower yield due to its low solubility in the reaction those compounds were not successful. With the Pt(IV)
system. The catalysts with oxygen-containing ligands catalysts H2PtCl6, PtCl4, and H2Pt(OH)6, as well as with
[H2Pt(OH)6 and Pt(acac)2] gave only small amounts of Pt(cod)Cl2, moderate to good yields of 60 up to 84% were
the product 3 under the chosen conditions. The reason obtained, where PtCl4 works best. Using the Karstedt
for this might be a relatively long induction period that is catalyst, only 46% product formation is observed. The
necessary for the formation of the catalytically active reason for this might be a decomposition of the catalyst
compound. Prolongation of the reaction time leads to with the formation of platinum colloids during the
much better results [70% yield for H2Pt(OH)6 after 4 h]. reaction, which is shown by the dark brown colour of
The heterogeneous catalyst Pt on activated carbon the reactionmixture. Theuse ofPt(acac)2 led toa product
showed only a moderate hydrosilylation activity. After formation of only 33% after 4 h, whereas further 18% of
filtration and reuse, the catalyst had no activity at all, conjugated methyl linoleate were formed without sub-
showing that the metal catalyst was ™leaching∫ from the sequenthydrosilylation. Incontrast to the hydrosilylation
carbon surface. K2PtCl4 was very sparingly soluble in the of methyl undec-10-enoate 1, PtCl2 and Pt on carbon
reaction system and showed no catalytic activity in the showed no hydrosilylation activity at all for the internally
hydrosilylation of 1.
unsaturated methyl linoleate 4. Pt(IV) species or Pt(II)
species with labile ligands such as (cod) or, to some
extent, (acac) as well as the Karstedt catalyst can be used
to perform the hydrosilylation of 4.
The results mentioned before led us to a closer
examination of the double bond conjugation during the
Hydrosilylation of Internally Unsaturated Fatty Acid
Esters
We also examined the hydrosilylation of methyl formation of 6. Performing the reaction again with
linoleate 4 (Scheme 2). 1 mol % H2PtCl6 as catalyst, we obtained the yield
The reaction time was prolonged from 10 min (as for versus time plot that is given in Figure 1.
methyl undec-10-enoate) to 4 h to achieve acceptable
It is shown that the formation of 6 is a consecutive
ester conversions. We found that best product yields reaction of double bond conjugation and hydrosilylation
were achieved with a two-fold molar excess of the of the conjugated double bond. Furthermore, a slight
hydrosilane. As hydrosilane, we chose chlorodimethyl- decomposition of 6 to high-boiling products is observed
silane 5, because the hydrosilylation of 4 with trieth- at reaction times above 45 min. This decomposition
oxysilane 2 using hexachloroplatinic acid as catalyst did occurs due to the reactive Si-Cl bond in the product.
not proceed under our conditions. We obtained mixtures
of isomers of dimethylchlorosilanyl-octadecenoic acid
methyl ester 6 as products and found that the remaining Hydrosilylation versus Hydrogenation in Solvent
double bond in 6 was in the a-position to the silanyl- Systems
substituted carbon atom, indicating a double-bond
migration. Interestingly, no double bond migration Recently, we proposed the use of temperature-depend-
was observed without addition of the silane to the ent solvent systems for the recycling of homogeneous
reaction mixture. Our results are given in Table 2.
In all cases, oligomerisation of the fatty acid ester to
Table 2. Hydrosilylation of methyl linoleate 4 with chlorodi-
high boiling products occurred. Furthermore, hydro-
methylsilane 5 (Tˆ 40 8C, t ˆ 4 h, 1 mol % catalyst, ester/
genation of the double bonds was observed. The
silane ratio 1:1.8).
Catalyst
Fatty acid
ester conversion
[%][a]
Product
yield
[%][a]
H2PtCl6
PtCl4
PtCl2
Pt on carbon
K2PtCl4
Karstedt
H2Pt(OH)6
Pt(acac)2
Pt(cod)Cl2
93
92
11
17
28
98
91
58
94
70
84
0
0
0
46
60
33
67
[a]
Scheme 2.
Determined by GC analysis.
Adv. Synth. Catal. 2002, 344, 1142 1145
1143

Arno Behr et al.
FULL PAPERS
Figure 1. Yield versus time plot of the hydrosilylation of
methyl linoleate 4 with chlorodimethylsilane 5. : methyl
Figure 3. Yield versus time plot of the hydrosilylation of
methyl undec-10-enoate 1 with triethoxysilane 2 in the
solvent system cyclohexane/toluene/propylene carbonate.
Conditions: 40 8C, equimolar amounts of 1 and 2, 1 mol %
&
~
*
linoleate 4, : conjugated methyl linoleate, : product 6.
1 mol % H2PtCl6, further conditions as given in Table 2.
&
^
Pt as Karstedt solution. : methyl undec-10-enoate 1,
:
:
~
*
isomerised methyl undecenoates, : methyl undecanoate,
hydrosilylation product 3.
The hydrosilylation of methyl undec-10-enoate 1 with
triethoxysilane 2 was further examined in a temper-
ature-dependent solvent system of cyclohexane, toluene
and propylene carbonate in equal parts by weight (see
Figure 2).
We found that the use of H2PtCl6 as catalyst led mainly
to hydrogenation of 1 in the first run, but after
separation and recycle of the catalyst phase, mainly
hydrosilylation of 1 occurred. As a further side reaction,
the double bond isomerisation of methyl undec-10-
enoate was observed. In the first run, the catalyst
showed an induction period of about 4 minutes, which
was not observed in the second run.
The Karstedt catalyst solution was also examined in
the same solvent system (Figure 3).
The reaction was complete even after 1 min at 40 8C,
with 76% hydrosilylation product formed. This shows
that the Karstedt solution already contains the catalyti-
cally active species that has to be preformed when
H2PtCl6 is used. Unfortunately, our further investiga-
tions showed that the Karstedt solution decomposes at
temperatures above 70 8C forming a dark brown
solution with a significantly reduced activity. There-
fore, it is only suitable for reactions at or slightly above
room temperature.
Figure 2. Yield versus time plot of the hydrosilylation of
methyl undec-10-enoate 1 with triethoxysilane 2 in the
solvent system cyclohexane/toluene/propylene carbonate.
Conditions: 40 8C, equimolar amounts of 1 and 2, 1 mol %
^
H2PtCl6 (above: first use, below: second use). : methyl
Conclusion
&
~
undec-10-enoate 1, : isomerised methyl undecenoates,
:
*
methyl undecanoate, : hydrosilylation product 3.
For the hydrosilylation of the terminally unsaturated
methyl undec-10-enoate, a broad range of Pt(IV), Pt(II)
catalysts.[7] Special multicomponent solvent systems and Pt(0) compounds can be used under mild conditions
allow a single-phase reaction process at reaction giving moderate to good yields of up to 88% after
temperature combined with an easy catalyst separation 10 minutes. For catalysts with oxygen-containing li-
by the two-phase technique at room temperature.
gands, prolonged reaction times are necessary due to
1144
Adv. Synth. Catal. 2002, 344, 1142 1145

Platinum-Catalysed Hydrosilylation of Unsaturated Fatty Acid Esters
FULL PAPERS
cyclohexane and 8 mL propylene carbonate were added. A
biphasic mixture formed, and the upper cyclohexane phase was
analysed by GC as already reported in ref.[5]
Hydrosilylation of methyl linoleate 4: 4.74 g (10.0 mmol)
methyl linoleate and 1.70 g (18.0 mmol) chlorodimethylsilane
were combined under argon and heated to 40 8C. After
addition of 0.1 mmol of the catalyst, the reaction mixture was
stirred 4 h at 40 8C. The work-up procedure was the same as
described for the hydrosilylation of 1.
an induction period for the formation of the catalytically
active compound.
The hydrosilylation of methyl linoleate, a fatty acid
ester with two internal double bonds, proceeded only
with Pt(IV) species, Pt(II) species with labile ligands, or
with the Karstedt solution with a yield of 33 up to 84%
after 4 h reaction time. A conjugation of the double
bonds was observed as first step of the reaction.
The activity of H2PtCl6 and the Karstedt solution in
the hydrosilylation of methyl undec-10-enoate was also
examined in solvent systems where the catalyst was
separated and recycled. H2PtCl6 showed a significant
The products were characterised by NMR and GC/MS
methods as already described.[5].
induction period and good hydrogenation activity in the Hydrosilylation in Solvent Systems
first run, whereas in the second run, the hydrosilylation
1.98 g (10.0 mmol) methyl undec-10-enoate and 1.64 g
predominated without a noticeable induction period.
Using the Karstedt solution, mainly hydrosilylation
occurred, and the reaction was completed even after
only 1 min.
Our results indicate that the catalytically active
species is formed by silane addition to the Pt complex,
which agrees with the widely accepted ChalkÀHarrod
mechanism.[8]
(10.0 mmol) triethoxysilane were dissolved in 10 mL cyclo-
hexane and 10 mL toluene. To this mixture, a solution of
0.01 mmol catalyst in 20 mL propylene carbonate was added
under argon. The mixture was stirred for 1 h at 40 8C. Samples
were taken from the reaction mixture using a syringe. After
cooling down to room temperature and phase separation, the
upper phase was analysed by GC.
Acknowledgements
Experimental Section
The authors wish to thank Degussa Metals Catalysts Cerdec
(now a division of OMG group) for the donation of the catalysts,
Wacker Chemie for the donation of the silanes, and Cognis
Deutschland GmbH for the donation of methyl linoleate and for
financial support.
Materials
H2PtCl6 ¥ 6 H2O (40% Pt), H2Pt(OH)6 (64% Pt), K2PtCl4
(46.65% Pt), PtCl4 (57% Pt), PtCl2 (73% Pt), Pt(acac)2
(49.6% Pt), Pt(cod)Cl2 (52% Pt), Karstedt solution [Pt(0)-
1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex, 19.2% Pt]
and Pt on carbon (5% Pt) were obtained from Degussa Metals
Catalysts Cerdec (now a division of OMG group). H2PtCl6 ¥
6 H2O was dried under vacuum (2 h, 200 8C) before use.
Methyl linoleate was obtained from Cognis Deutschland
GmbH (Edenor SbO5 ME, methyl linoleate content 62%).
Undec-10-enoic acid was purchased from Acros and quanti-
tatively esterified using catalytic amounts of thionyl chloride.
Triethoxysilane (99%) and chlorodimethylsilane (99%) were
obtained from Wacker Chemie. Cyclohexane, toluene and
propylene carbonate were purchased from Fluka and Acros
and dried over molecular sieve. All reactions were carried out
under an inert argon atmosphere.
References
[1] J. L. Speier, J. A. Webster, G. H. Barnes, J. Am. Chem.
Soc. 1957, 79, 974 979.
[2] B. D. Karstedt (General Electric), U. S. Patent 3,775,452,
1973.
[3] N. Saghian, D. Gertner, J. Am. Oil Chem. Soc. 1974, 51,
363 367.
¡
¡
[4] F. Delpech, S. Asgatay, A. Castel, P. Riviere, M. Riviere-
Baudet, A. Amin-Alami, J. Manriquez, Appl. Organomet.
Chem. 2001, 15, 626 634.
[5] A. Behr, F. Naendrup, D. Obst, Eur. J. Lipid Sci. Technol.
2002, 104, 161 166.
[6] A. Behr, N. Toslu, Chem. Eng. Technol. 2000, 23, 122
125.
[7] A. Behr, C. F‰ngewisch, Chem. Eng. Technol. 2002, 25,
143 147.
[8] A. J. Chalk, J. F. Harrod, J. Am. Chem. Soc. 1965, 87, 16
21.
Hydrosilylations without Solvent
Hydrosilylation of methyl undec-10-enoate 1: 1.98 g
(10.0 mmol) methyl undec-10-enoate and 1.64 g (10.0 mmol)
triethoxysilane were heated to 40 8C under argon. After
addition of 0.1 mmol of the catalyst, the reaction mixture was
stirred for 10 min at 40 8C. To stop the reaction, 8 mL
Adv. Synth. Catal. 2002, 344, 1142 1145
1145