The scrambling most likely occurs between the Si-H
reactants as an alternative reaction pathway competing with
a slow hydrosilylation reaction. This is evidenced by
appearance of scrambled hydrosilanes in the attempted
reaction of methyldiethoxysilane with hindered olefins. It is
worth noting that the related methyldimethoxysilane under-
goes the same unexpected scrambling in similar reactions
using the regular hydrosilylation addition of silane to olefin.
temperature probe, condenser, and nitrogen purge, was added
391 lb [177.7 kg] (1559 mol) of allyl glycidyl ether (AGE),
followed by 151 mL (15 ppm Pt) of 10% CPA catalyst
solution and 0.36 lb [164 g] (470 ppm) of acetic acid
promoter. The reactor contents were heated to 80 °C.
Methyldiethoxysilane (370 lb [168.2 kg], 1255 mol) was then
metered in at such a rate as to keep the reactor temperature
between 80 and 90 °C. After completion of reaction: about
3.5 h of silane addition and a 1 h hold, a majority of the
excess AGE/isomers was stripped to give a crude GC yield
of 86.3% desired hydrosilylation product. GC analysis also
showed 2.53% γ-glycidoxypropyldimethyl(ethoxy)silane and
2.95% γ-glycidoxypropyltriethoxysilane. GC-MS data of
the above mixture again support the structures of the product
and two side-products.
Hydrosilylation of 1 and 2 under Inverse Conditions.
To a 250 mL four-neck round-bottom flask, equipped with
stir bar, thermocouple probe, condenser, addition funnel, and
nitrogen inlet/outlet, were added 67.0 g (0.52 mol) of
methyldiethoxysilane, 78 µL (15 ppm Pt) of 10% CPA
solution (CPA), and 90 µL (650 ppm) of acetic acid. The
mixture was then heated to 85 °C. AGE (70.8 g, 20% excess
at 0.62 mol), which had been charged to the addition funnel,
was then added dropwise to the heated mixture at such a
rate as to keep the pot temperature between 85 and 90 °C.
After AGE addition completion (approximately 80 min), the
reaction was then heated at 85 °C for 30 min. GC analysis
of the crude reaction mixture showed complete conversion
of the methyldiethoxysilane. GC analysis also showed,
besides AGE/isomers, 75.3% of desired product, γ-glyci-
doxypropylmethyldiethoxysilane. Again present, although in
smaller amounts, were the two unexpected scrambled
products γ-glycidoxypropyldimethyl(ethoxy)silane (0.16% by
GC) and γ-glycidoxypropyltriethoxysilane (0.36% by GC).
Hydrosilylation of 1 and 2 under Continuous Condi-
tions. When the hydrosilylation reaction between methyldi-
ethoxysilane and allyl glycidyl ether was run in a continuous
mode (continuous hydrosilylation with recycling9) by co-
feeding allyl glycidyl ether and excess methyldiethoxysilane
to a reactor and recycling the excess methyldiethoxysilane,
both exchanged precursors, Me2(EtO)SiH and (EtO)3SiH,
were observed in the recycle stream. Their combined levels
ranged from approximately 5% to greater than 20% of the
recycled methyldiethoxysilane stream. In addition, the crude
product stream also contained steadily increasing amounts
of exchanged hydrosilylation products, as the reaction time
increased. The level of γ-glycidoxypropyldimethylethoxy-
silane, for example, increased from approximately 0.5% to
more than 2% relative to 70-78% of the expected γ-glyci-
doxypropylmethyldiethoxysilane. GC-MS data of the above
mixture support the structures of the product and two
scrambled side-products.
Experimental Section
Reaction pressures are normally atmospheric. Purification,
as by distillation, is typically run under vacuum. The
processes can be practiced in a variety of equipment ranging
from small laboratory glassware through pilot scale to large
production units. The abbreviations g, mL, mm, mol, ppm,
µL, L, lb, kg, GC, and MS respectively represent gram,
milliliter, millimeter, molar equivalent, parts per million,
microliter, liter, pound, kilogram, gas chromatography, and
mass spectrometry. All temperatures are reported in degrees
Celsius, and all reactions were run in standard laboratory
glassware or pilot scale or production units at atmospheric
pressure under an inert atmosphere of nitrogen, and all parts
and percentages are by weight. Reagents were used without
further purification.
All reactions were monitored by gas chromatography. The
instrument used was a Hewlett-Packard 6890 Series GC.
Product purities also determined by analysis on this GC.
Compound identification was determined by GC-MS analy-
sis. The GC-MS instrument used was a Varian Saturn 2000
GC/MS/MS in conjunction with a Varian 3800 gas chro-
matograph.
Hydrosilylation of Methyldiethoxysilane (1) and Allyl
Glycidyl Ether (2) (Scheme 1). To a 250 mL four-neck
round-bottom flask, equipped with stir bar, thermocouple
probe, condenser, addition funnel, and nitrogen inlet/outlet,
was added 70.8 g (0.62 mol) of allyl glycidyl ether (AGE).
A 20% excess of the raw material was used in the
preparation, as some isomerization of AGE occurs in the
presence of heat and platinum catalyst. A solution of 10%
chloroplatinic acid in ethanol (CPA, 78 µL, 15 ppm Pt)
catalyst and 90 µL (650 ppm) of acetic acid promoter are
added to the AGE in the reaction vessel. The mixture was
then heated to 85 °C. Methyldiethoxysilane (67.0 g, 0.52
mol), which had been charged to the addition funnel, was
then added dropwise to the heated mixture at such a rate as
to keep the pot temperature between 85 and 90 °C. After
silane addition completion (about 80 min), the reaction was
then heated at 85 °C for 30 min. GC Analysis showed,
besides AGE and isomers, 81.1% of desired product,
γ-glycidoxypropylmethyldiethoxysilane. Also present were
two unexpected scrambled products: γ-glycidoxypropyldi-
methyl(ethoxy)silane (1.10% by GC) and γ-glycidoxypro-
pyltriethoxysilane (1.24% by GC). GC-MS data of the
above mixture support the structures of the product and two
scrambled side-products.
Hydrosilylation of (1) with Cyclohexene (8) (Scheme
4). To a 50 mL four-neck round-bottom flask, equipped with
stir bar, thermocouple probe, condenser, addition funnel, and
nitrogen inlet/outlet, was added 5.16 mL (4.19 g, 0.05 mol)
Hydrosilylation of 1 and 2 in a Larger-Scale Reactor.
To a jacketed Hastelloy-C reactor, equipped with agitator,
(8) Filipkowski, M. A.; Petty, H. E.; Schilling, C. L., Jr.; Westmeyer, M. D.
U.S. Patent 6,166,238, 2000.
(9) Schilling, C. L., Jr.; Burns, P. J.; Ritscher, J. S.; Bowman, M. P.; Childress,
T. E.; Powell, M. P.; Graban, E. M. U.S. Patent 6,015,920, 2000.
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Vol. 6, No. 1, 2002 / Organic Process Research & Development