Hipsher, Harold F

Kaye, Samuel

Tannenbaum, Stanley

English

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THE SYNTHESIS OF BUTYLSILANES BY A LARGE-SCALE REDUCTION 
WITH LITHIUM AL UMINUM HYDRIDE 
By Samuel Kaye, Stanley Tannenbaum 
and Harold F. Hipsher 
Lewis Flight Propulsion Laboratory 
Cleveland, Ohio 
CLASSIFICATION CHAiGED TO 
U CLASSIFIED ' 
UTHOkITY CkO LEY CBA.GE 01753 
DATE 12-11-53 T.C.P. 
CLASSIFIED DOCUMENT 
ThIs material contalnS Information affecting the National Defense of the United States within the meaning 
of the espionage laws, Title 18, U.S. c., Sees. 793 and 794, the transmission or revelaUoQ of which in any 
manner to an unauthorIZed person Is prohibited by law. 
NATIONAL ADVISORY COMMITTEE 
FOR AERONAUTICS 
WASHINGTON 
July 22, 1953 
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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS 
RESEARCH MEMORANJJJM 
THE SYNTHESIS OF BUTYLSILANES BY A LARGE-SCALE REDUCTION WITH 
LITHTIJM ALUMINUM HYDRIDE 
By Samuel Kaye, Stanley Tannenbaum, and Harold F. Hipsher 
SUMMARY 
Eighty pounds of butylsilanes required for test purposes was synthe-
sized by reducing butyltrichlorosilane with lithium aluminum hydride in 
dioxane solution. This was safely and successfully accomplished by 
operating in steel equipment under an atmosphere of oil-pumped nitrogen 
to minimize the hazards involved in conducting this operation on a large 
scale. The apparatus and procedure used to carry out the necessary 
manipulations are described in this report. 
INTRODUCTION 
As part of a series of investigations at the NACA Lewis laboratory 
on flame speeds, ignition, and other burning characteristics of high-
energy fuels, several alkylsilanes were prepared in laboratory quanti-
ties and their chemical and physical properties reported {ref. 1). The 
results of preliminary combustion studies suggested that further studies 
in a large-scale combustor might yield information useful for the evalua-
tion of these compounds as fuels or fuel components for jet aircraft. 
This necessitated the preparation of large quantities of butylsilanes. 
Although these compounds had been prepared previously on a small 
scale (ref. 2), no information was available on any large-scale prepara-
tion. The laboratory synthesis reported previously proceeds according 
to the reaction 
The same reaction was used in the research reported herein, but the 
scale-up of this synthesis to the quantity of product desired magnified 
several difficulties and hazards associated with this reaction and 
required a careful refinement of technique, which is reported in this 
paper. 
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The finely ground lithium aluminum hydride required for the synthe -
s i s is subject to deterioration by reaction with oxygen and moisture in 
the atmosphere. Under some conditions it is pyrophoric i n a ir . A second 
difficulty was introduced by the possible toxicity of butyltrichloro-
silane and its ease of hydrolysis i n moist air to evolve acid fumes . 
Finally, t he products, butylsilanes, are themselves reducing agents and 
could be oxidized by air, especially at elevated temper atures, or by 
water i n t he pr esence of hydroxyl ion (ref. 3, p . 6) : 
I 1 I 
-Si-H + ~2-- - Si - OH 
I 2 I 
I OH- I 
- Si-H + H20 ---Si-OH + H2 
I I 
These problems were solved by covering materials in the reactor 
with an inert atmosphere of nitrogen and by manipulating lithium alumi-
num hydride and making necessary transfers of material in systems sealed 
from the atmosphere. The techniques used for the manipulations are 
described. The largest single batch of product prepared yielded an 
estimated 27 pounds of mixed butylsilanes. 
APPARATUS 
Preliminary experiments were run in the 5- gallon reactor shown in 
figure 1, but the main portions of the product were prepared in the 
50- gallon reactor (fig . 2(a)) . A diagram showing t he l ayout for the 
50 - gallon reactor is shown in figure 2(b) . The small reactor was made 
of stainless steel and was j acketed for steam or hot or cold water . The 
dished top was fitted with a stainless - steel stirrer and b affle plate. 
Solvents and butyltrichlorosilanes were added to the reactor by gravity 
from a double - valved addition tank provided with a nitrogen purge line. 
The r ate of addition could be determined visually by means of a sight 
glass between the tank and the reactor. 
The t ank for the addition of lithium aluminum hydride slurry was 
placed on a fitting between the reactor and the glass-lined reflux con-
denser attached to the reactor. This t ank was double - valved, made of 
Inconel, and provided with a fitting for blanketing the slurry with 
nitro gen . To avoid plugged openings due to caking, gate valves were 
used. If plugging did occur, pressurized nitrogen sufficed to force 
the slurry through the large opening. A sight valve below the condenser 
afforded a means for checking the rate of reflux. Additional informa-
tion on the course of the reaction was obtained from three thermocouple 
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stations located in the water jacket, in the reactor next to the stirrer, 
and in the condenser reflux line. Atmospheric air and moisture were 
kept out of the system by means of a check valve in the condenser vent. 
For safety purposes, the spent residues from the reaction were discharged 
through a double-valved line into a portable container which was likewise 
fitted with a nitrogen purge line. The product receivers were double-
I 
valved 4~gallon tanks fitted with a nitrogen inlet and outlet. 
The 50-gallon reactor was constructed similarly except for the 
following details. The butyltrichlorosilane was fed by gravity into a 
nitrogen purged reservoir tank fitted with a sight gage and a sight 
glass. The solvents for the reaction were pumped directly from a 
55-gallon drum into the reactor by a rotary pump through aT-fitting 
which held a nitrogen purge line. 
The powder-addition tank used to add lithium aluminum hydride to 
the large reactor is shown in figure 3. It consisted of a stainless-
steel tank to which the nut of a 2~ inch union was welded. The face of 
the pear-shaped valve was spherically ground to close on the seat of 
the pipe union. The valve was manipulated by means of a rod which 
extended through the container and was sealed from the outside atmosphere 
by an a-ring. Several scrapers were welded to the rod above and below 
the valve. These served to break up any caked material which formed in 
the tank. A pipe at the bottom of the container held a nipple through 
which nitrogen flowed to purge the system while the tank was being 
attached to the reactor. 
The horizontal copper-tube-bundle condenser on this reactor pro-
vided for complete vapor condensation. It was connected to the reactor 
by a 2~-inch line and was vented to the atmosphere through a check 
valve. Condensed vapors were recycled through a liquid check valve to 
the reactor when the take-off valve in the condensate line was closed. 
A 2-pound-per-square-inch-pressure relief valve on a T between the reactor 
and the condenser handled possible surges in the reaction. This valve 
discharged through the roof to a storage tank which was purged by the 
stream of nitrogen passing through the system. 
The residues from the reaction were carefully alcoholized and pumped 
into a container from which they were poured into a sand box and quenched 
with a large volume of water. 
The dry box illustrated in figure 4 was used to protect the lithium 
aluminum hydride from atmospheric moisture and oxygen during handling 
and grinding. It waS equipped with six pairs o£ rubber gloves sealed to 
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openings in the sides of the box. The atmosphere within the box was 
kept sufficiently dry and air free by flushing continuously with a 
stream of oil-pumped nitrogen which entered through a perforated header 
encircling the dry box about 3/4 inch from the bottom. 
The lithium aluminum hydride was crushed to pebble size in a mortar, 
then powdered by means of a food blender. The housing for the motor in 
the base of the blender was enclosed in a metal casing and pressurized 
with nitrogen in order to minimize the possibility of a spark acting as 
a source of ignition. This motor and the dry box itself were indi-
vidually grounded to the aluminum floor on which the equipment rested. 
The column used to fractionally distill the combined crude products 
at atmospheric pressure had a pot capacity of 200 gallons. It was com-
posed of a stainless-steel tube 4 inches in diameter and 100 feet tall 
packed with 3/8-inch Raschig rings. The construction of this column was 
similar to that described for the 30-foot column in reference 4. 
MATERIALS 
Lithium aluminum hydride. - Lithium aluminum hydride, LiAlH4J com-
mercially obtained, was furnished as small cakes, which were broken and 
then pulverized to a fine powder before use. This operation caused the 
evolution of ether absorbed on the salt. 
Dioxane. - The dioxane was purchased in 55-gallon drums and purified 
by percolation through a 10-foot column of activated alumina. The puri-
fied dioxane gave no reaction with lithium aluminum hydride, thus indi-
cating the absence of water, aldehydes, and peroxides. 
Butyltrichlorosilane. - The butyltrichlorosilane was purchased from 
a commercial source and was reported to be a mixture of 50 percent normal 
butyltrichlorosilane and 50 percent of mixed iso- and secondary butyltri-
chlorosilanes. When 117 pounds from a drum of discolored reactant was 
distilled under nitrogen in a 3O-foot column rated at about 100 theo-
retical plates, 21.4 pounds (18.3 percent) boiled at 280.40 to 288.50 F, 
and 20.4 pounds (17.4 percent) boiled at 288.50 to 296.60 F. A third 
fraction of 69.8 pounds (59.6 percent) boiling at 296.60 F was shown to 
be the n-butyl isomer by independent synthesis from silicon tetrachloride 
and n-butylmagnesiumchloride. A head fraction of about 2 pounds and a 
residUe of about 3 pounds of material were discarded. A second drum con-
tained water-white material and was used directly without distillation. 
Nitrogen. - Oil-pumped nitrogen was used directly from tanks with-
out further treatment. 
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PROCEDURE 
The general procedure used in all the runs in the 50-gallon reactor 
is illustrated by the following typical preparation: The reactor was 
cleaned and rinsed with acetone, and the system was then dried with air. 
The air was replaced with an inert atmosphere of nitrogen by purging the 
system overnight. 
The addition tank and 12.35 pounds (0.326 Ib-moles) of lithium 
aluminum hydride were sealed into the dry box together with the equipment 
necessary for pulverizing the hydride and sealing off the .addition tank. 
The dry box was purged of air and flushed continuously with nitrogen 
while the lithium aluminum hydride which had been crushed to pebble size 
was ground to a fine powder in a food blender. The finely ground lithium 
aluminum hydride was then sealed into the dry-powder-addition tank. This 
piece of apparatus could then be safely removed from the dry box. 
Meanwhile, 30 gallons of dioxane was pumped into the reactor and 
stirring was begun. The addition tank was attached to the reactor while 
a stream of nitrogen flushed the opening. The valve of the addition 
tank was lifted and turned slowly until,all the lithium aluminum hydride 
had been added to the dioxane. The tank was then quickly removed and 
replaced with a sealing flange. The temperature of the dioxane slurry 
was raised to 1310 F prior to adding the butyltrichlorosilane in a slow 
stream over a period of 2 hours until 64.90 pounds (0.34 Ib-moles) had 
been added. The mixture was refluxed for an additional l~ hours before 
take-off was begun. 
The product was stripped from the reaction mixture slowly at first. 
Most of the butylsilanes came over in the first 3 gallons of stripped 
material. A total of 255 pounds of crude material was collected for 
fractional distillation. After the crude product was stripped from the 
reactor, 9 gallons of methanol was carefully added to the reactor with 
stirring. The alcoholized residue was allowed to remain in the reactor 
several hours before the fluid slurry was drawn off and deactivated in 
a sand box. 
The combined quantity of distillate collected from all the runs 
amounted to 413 pounds. This was charged into a 100-foot distilling 
column. 
At the beginning of the distillation, a large volume of gas was 
observed issuing from the vent; therefore, two dry-ice traps were attached 
to this opening. The material collected in these traps was distilled 
separately in a small column of about 100 theoretical plates. The head 
fraction of this forerun was hydrogen sulfide H2S, which was identified 
by the lead acetate and cadmium chloride tests. The source of the H2S 
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is believed to be the sulfur coating on some of the rubber stoppers used 
to close the flasks in which lithium aluminum hydride - dioxane slurry was 
prepared for the small reactor. A second source could have been the dis-
tillation column itself. All copper lines were found to have been reduced 
to a brilliantly pure copper color at the end of the distillation. 
Another fraction (140 to 42.80 F) was believed to consist of butane 
and isobutane. Unfortunately, this material was lost by evaporation 
before it could be weighed or analyzed. The rest of the material col-
lected in the traps was n-butylsilane and isobutylsilane, . which had been 
entrained in the gases and nitrogen purging stream. The remainder of the 
material distilled in a normal fashion. 
RESULTS 
The total over-all yield of final purified product amounted to 
80.5 pounds. This was equivalent to a total over-all yield of 82 per-
cent based on the butyltrichlorosilane and does not include handling 
and distillation losses. The yields obtained as shown by separate puri-
fication of products synthesized in the smaller reactor can run as high 
as 91 percent of butylsilane. 
The materials obtained in the fractional distillation of the products 
are summarized in the following table: 
Fraction Boiling point, Amount, Remarks 
OF lb 
I 111. 2-116. 6 3.5 Heads 
II 116.6-118.4 29.5 Low-boiling branched isomers 
III 118.4-131.0 4.5 Intermediate 
IV 131.0-132.8 38.0 High-boiling ~-butyl isomer 
V 
-----------
3.0 Vent trappings 
VI 132.8-140.0 2.0 Tails 
The ratio ~f normal to mixed iso- and secondary butylsilanes in the 
product is about 4:3. The structure of the normal isomer was confirmed 
by an independent synthesis from pure materials. 
CONCLUDING REMARKS 
Butylsilanes may be synthesized from butyltrichlorosilanes and 
lithium aluminum hydride with yields greater than 80 percent in pilot-
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plant size equipment. This may safely be accomplished by conducting all 
operations under an atmosphere of oil-pumped nitrogen and in double-
valved sealed containers. 
Lewis Flight Propulsion Laboratory 
National Advisory Committee for Aeronautics 
Cleveland, Ohio, May 14, 1953 
REFERENCES 
1. Tannenbaum, Stanley, Kaye, Samuel, and Lewenz, George F.: Synthesis 
and Properties of Some Alkylsilanes. (To be published in Jour. 
Am. Chern. Soc.~ 
2. Finholt, A. E., Bond, A. C., Jr., Wilzbach, K. E., and Schlesinger, 
H. I.: The Preparation and Some Properties of Hydrides of Elements 
of the Fourth Group of the Periodic System and of their Organic 
Derivatives. Jour. Am. Chern. Soc., vol. 69, no. 11, Nov. 1947, 
pp. 2692-2696 • 
3. Rochow, Eugene G.: An Introduction to the Chemistry of the Silicones • 
Second ed., John Wiley & Sons, Inc., 1951. 
4. Reynolds, Thaine W., and Sugimura, George H.: Evaluation of Packed 
Distillation Columns. I - Atmospheric Pressure. NACA TN 2342, 
1951. 
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Figure 1. - Fi ve-ga Hon reactor. 
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(a) Operational setup. 
Figure 2 . - Fifty-gallon reactor. 
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Check valve 
Condenser 
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Halide addition tank 
Vapor 
2-Pound 
relief valve 
thermOCOU7
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Spent 
residues 
(b) Schematic diagram. 
Powder-addition tank 
Dioxane 
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Reactor thermocouple 
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Figure 2. - Concluded. Fifty-gallon reactor. 
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Figure 3 . - Powder-addition tank for lithium aluminum hydride. 
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Figure 4. - Dry box. 
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The Synthesis of Butylsilanes by a Large-scale Reduction with Lithium Aluminum Hydride

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