Note: Descriptions are shown in the official language in which they were submitted.
i~32
- 1 - RD 16,653
SILYL CARBAMATES AND THEIR USE IN THE
PREPARATION OF BIS(AMINOALKYL)DISILOXANES
This invention relates to the novel silyl
carbamates, a method for their preparation and a method
for converting them to symmetrical bis(aminoalkyl)-
disiloxanes.
Bis(aminoalkyl)disiloxanes are useful in many
applications including the preparation of polyimides,
especially polyetherimides such as those prepared by
reaction of diamines with such dianhydrides as 2,2-bis[4-
(3,4-dicarboxyphenoxy)phenyl]propane dianhydride ("bis-
phenol A dianhydride"). A particularly valuable
bis(aminoalkyl)disiloxane used for this purpose is
1,9-diamino-4,4,6,6-tetra-methyl-5-oxa-4,6-disilanonane,
also known as bis(3-aminopropyl)tetramethyldisiloxane and
bis(~ -aminopropyl)tetramethyldisiloxane. Commercial
utilization of these compounds, however, has been
inhibited by the lack of convenient methods for their
preparation on a large scale. Previous methods for
their preparation have involved a large number of complex
and expensive reactions and/or processing steps.
Canadian Application Serial No. 498,350,
filed December 20, 1985, Webb et al, describes a method
for the preparation of bis(aminoalkyl)disiloxanes from
acyclic olefinic silazanes by hydrosilation followed by
hydrolysis. The productions, however, are frequently
mixtures of isomers. For example, the substantially pure
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- 2 - RD 16,653
monosilazane 2-methyl-2-sila-3-aza-5-hexene can be
converted to substantially pure l,9-diamino-4,4,6,6-
tetramethyl-5-oxa-4,6-disilanonane; but the monosilazane
is ordinarily obtained in admixture with the disilazane
2-methyl-3-dimethylsilyl-2-sila-3-aza-5-hexene, and
hydrosilation-hydrolysis of such mixtures yields a
mixture of l,9-diamino-4,4,6,6-tetramethyl-5-oxa-4,6-di-
silanonane with its isomers l,~-diamino-2,3,3,5,5-penta-
methyl-4-oxa-3,5-disilaoctane (which is unsymmetrical) and
1,7-diamino-2,3,3,5,5-6-hexamethyl-4-oxa-3,5-disilaheptane.
Therefore, there is still an interest in developing
methods for preparing substantially isomer-free symmetrical
bis(aminoalkyl)disiloxanes.
A principal object of the present invention,
therefore, is to provide a new method for the preparation
of symmetrical bis(aminoalkyl)disiloxanes.
A further object is to prepare said bis(amino-
alkyl)disiloxanes substantially free from isomers thereof.
A further object is to provide a preparative
method which is convenient and relatively inexpensive.
A still further object is to provide novel
chemical intermediates which are useful in said method,
and a method for their preparation.
Other objects will in part be obvious and will in
part appear hereinafter.
In one of its aspects, the present invention is
directed to silyl carbamates having formula I in the
drawings, wherein Rl is a Cl 4 primary or secondary alkyl
radical, phenyl or substituted phenyl; each R is inde-
pendently hydrogen, a Cl 4 primary or secondary alkyl
radical, phenyl or substituted phenyl; and m is from 1
to about 20.
As is apparent from formula I, the silyl
carbamates of this invention are characterized by the
presence of a terminal olefinic bond in the organic
group attached to nitrogen. The Rl values therein may
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~32
- 3 - RD 16,653
be phenyl radicals; substituted phenyl radicals such as
tolyl, chlorophenyl, carbomethoxyphenyl or cyanophenyl;
or (preferably) Cl 4 primary or secondary alkyl radicals
such as methyl, ethyl, l-propyl, 2-propyl, l-butyl,
2-butyl and 2-methyl-1-propyl. Methyl and ethyl radicals,
especially methyl, are particularly preferred.
The R values are usually all hydrogen. Any
of them may, however, be phenyl, substituted phenyl or
Cl 4 primary or secondary alkyl radicals such as those
described hereinabove with respect to R , with the same
preferences. It should be noted that the present
invention contemplates the use of compounds wherein all
R values are the same, as well as compounds wherein they
are all different. This includes compounds in which m is
up to about 20 and all of the R2 substituents on the
resulting alkylene radical are different. The value of
m is usually 1 or 2 and preferably 1.
The silyl carbamates of this invention may
be prepared by carbonating a silazane composition
comprising at least one of (1) a monosilazane of formula
II and (2) a mixture of a disilazane of formula III and
an amine of formula IV; that is, by reacting said
composition with carbon dioxide. The silazane composition
may be prepared by known methods such as the reaction of
an olefinic amine of formula IV with a chlorosilane of
the formula (Rl)2SiHCl in the presence of an acid
acceptor such as excess olefinic amine, as disclosed,
for example, in Example 12 of U.S. Patent 3,642,~54, issued
February 15, 1972 to Kozjukov et al. Suitable olefinic
amines include allylamine (which is preferred),
methallylamine and 3-butenylamine. The preferred chloro-
silane is dimethylchlorosilane.
The product of the olefinic amine-chlorosilane
reaction is the monosilazane of formula II, the
corresponding disilazane of formula III, or a mixture
thereof, depending on various factors such as the molar
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_ 4 - RD 16,653
ratio of the reactants. While no part of the present
invention is dependent on any particular theory of reaction,
it is believed that the monosilazane undergoes a dis-
proportionation reaction upon standing, yielding the
5 disilazane and the olefinic amine in equimolar amounts.
The disproportionation reaction is apparently an
equilibrium reaction, and an important feature of the
present invention is the fact that it is immaterial
whether or not said reaction takes place. This
circumstance is described more fully hereinafter.
Carbonation may be accomplished by passing
carbon dioxide into the silazane composition at a
temperature of about 25-125 C . Elevated temperatures,
usually at least about 50C, are usually required for
15 carbonating disilazanes; monosilazanes may frequently
be carbonated at room temperature. If a monosilazane-
disilazane mixture is used, the exothermic monosilazane-
carbon dioxide reaction may increase the temperature
sufficiently to initiate disilazane carbonation. In
general, temperatures up to about 100C are preferred.
It is generally advantageous to employ a solvent
for the silazane composition. Typical solvents are
aliphatic hydrocarbons such as n-hexane and petroleum
naphtha, aromatic hydrocarbons such as toluene and xylene,
ethers such as tetrahydrofuran and dioxane, and aprotic
polar solvents such as dimethyl sulfoxide.
The carbonation of trialkylsilazanes to the
corresponding silyl carbamates is known in the art.
Reference is made, for example, to Japanese Kokai
79/119418 ; Zoeckler et al., J. Org. Chem., 48, 2539-2543
(1983); and Breederveld, Rec.`trav. chim., 81, 276-278
(1962). However, these publications relate only to the
carbonation of silazanes containing three methyl groups
attached to silicon. Moreover, the Breederveld method
iS applicable only to dialkylamino compounds and the
other two require catalysts such as transition metal
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- 5 - RD 16,653
chlorides, ruthenium carbonyl or rhodium carbonyl.
According to the present invention, on the other hand,
carbonation of compounds containing only two hydrocarbon
substituents on silicon and one on nitrogen is easily
accomplished in the absence of catalysts. It is
generally mildly exothermic and proceeds with facility
at the above-described temperatures.
It is also within the scope of the invention to
carbonate a mixture of the monosilazane with the
corresponding disilazane and olefinic amine, the latter
two compounds generally being present in approximately
equimolar amounts. Again disclaiming basis on any
reaction theory, it is believed that an intermediate
species is an ammonium carbamate of formula V which can
in turn react (through the carbamate anion) either with
monosilazane to form silyl carbamate and olefinic amine,
or with disilazane to form silyl carbamate, monosilazane
and olefinic amine with the monosilazane in turn reacting
with more carbon dioxide. The overall result is that
any free olefinic amine plays a catalytic role in the
carbonation sequence. In any event, the desired
symmetrical bis(aminoalkyl)disiloxane is the only final
product obtained irrespective of the presence of
disilazane and olefinic amine in the silazane composition.
The preparation of the silyl carbamates of
this invention is illustrated by the following examples.
All parts are by weight.
; Exa'mpl'e'l
A silazane composition was prepared by the
30 reaction of dimethylchlorosilane with allylamine to
produce 2-methyl-2-sila-3-aza-5-hexene. Upon storage,
disproportionation occurred and the product actually
used contained 50 mole percent of the monosilazane and
25 mole percent each of allylamine and 2-methyl-2-sila-
35 3-dimethylsilyl-3-aza-5-hexene.
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- 6 - RD 16,653
A solution of 40 parts of the silazane composi-
tion in 40 parts of toluene was heated to 80-85C, with
stirring, as carbon dioxide was passed in under the surface.
A positive pressure of about 1-3 inches of toluene was
maintained; under these conditions, there was no net
escape of gas from the reaction vessel. An exothermic
reaction occurred, after which the temperature was
raised to 110C. The reaction was monitored by vapor
phase chromatography and mass spectroscopy, which showed
the formation of the desired dimethylsilyl allylcarbamate.
Carbon dioxide addition was discontinued when no further
reactants were detected.
Example 2
The procedure of Example 1 was repeated, using
a silazane composition comprising about 74~ 2-methyl-2-
sila-3-aza-5-hexene and about 18% 2-methyl-2-sila-3-
dimethylsilyl-3-aza-5-hexene. A substantially identical
product was obtained.
Example'3
The procedure of Example 1 was repeated,
f~' using substantially pure, freshly prepared 2-methyl-2-
,~ ~ sila-3-aza-5-hexene. A substantially identical product
was obtained.
Exa'mple'4
A mixture of equimolar proportions of
2-methyl-2-sila-3-dimethylsilyl-3-aza-5-hexene and
allylamine was charged to a carefully dried round-
bottomed flask fitted with a thermometer, sintered
~ glass tube for gas introduction and condenser,
f,','' ~ 30~ maintained under dry conditions. A tube sealed ~n the
'',~ top of the condenser passed into a cylinder of toluene
- to provide back pressure.
h~ The mixture was heated to 50C and dry carbon
dioxide was bubbled in at a rate which just balanced the
back pressure so that all the carbon dioxide was absorbed.
An exothermic reaction occurred which caused the
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- 7 - RD 16,653
temperature of the reaction mixture to increase to 80C.
When absorption of carbon dioxide had ceased, the mixture
was analyzed by gas chromatography and was found to
comprise dimethylsilyl allylcarbamate of high purity.
The silyl carbamates of this invention are
useful as intermediates in the preparation of symmetrical
bis(aminoalkyl)disiloxanes. Accordingly, another
aspect of the present invention is a method for preparing
a symmetrical bis(aminoalkyl)disiloxane of formula VI,
wherein Rl, ~2 and m are as previously defined, which
comprises (A) contacting a silyl carbamate of formula I
with a hydrosilation catalyst to form an intermediate,
and (B) hydrolyzing said intermediate.
Hydrosilation catalysts useful in step A are
those known in the art. They are typically platinum
catalysts in which the platinum may be present in
elemental or chemically combined (i.e., divalent or
tetravalent) form. Illustrative hydrosilation catalysts
are platinum supported on substantially inert substrates
such as carbon, aluminum or silica gel; platinum compounds
such as PtC14, Na2PtC14, K2PtC14, H2PtC16, PtC12(CH3CN)2
and alkylplatinum halides; and siloxyorganosulfur-
platinum or aluminoxyorganosulfur-platinum compositions
of the type disclosed in U.S. Patent 4,503,160, issued
March 5, 1985 to Williams, Jr.
In many instances, the hydrosilation catalyst
is preferably formed by the reaction of a platinum
compound with at least one olefinic siloxane, as
disclosed in the following U.S. patents:
3,419,593, issued December 31, 1968 to Edwards et al,
3,715,334, issued February 6, 1973 to Karstedt,
3,775,452, issued November 27, 1973 to Karstedt,
3,814,730, issued June 4, 1974 to Karstedt, and
4,288,345, issued September 8, 1981 to Ashby et al.
Particularly useful as the reaction products of
platinum compounds, especially chloroplatinic acid and
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- 8 - RD 16,653
hydrates thereof, with 3,3,5,5-tetramethyl-3,5-disila-
4-4Oxa-1,6-heptadiene. The amount of hydrosilation
catalyst used is usually such as to provide an amount
of platinum equal to about 10-400 ppm. (by weight) based
on the olefinic amine.
Step A may be conveniently conducted by heating
the mixture of the silyl carbamate and hydrosilation
catalyst at a temperature in the range of about 75-125C,
preferably in a substantially inert organic solvent such
as those list hereinabove.
The molecular structure of the intermediate
formed in step A is not known with certainty. It
appears to be polymeric. Relating specifically to the
hydrosilation product of dimethylsilylallyl carbamate,
there is evidence that it comprises structural units
having formula VII. However, the molecular structure
of the ntermediate is not a limiting feature of the
invention.
In step B, the intermediate formed in step A
is hydrolyzed. Hydrolysis may be conveniently and
simply effected by merely adding water to the
intermediate, which is most often maintained in solution
in the solvent previously used. The reaction is
` exothermic and is accompanied by the evolution of carbon
dioxide. It is usually preferred to add the water
gradually at a temperature within the range o~ about
80-110C.
- In general, an excess of water is employed,
typically about a 25-100% excess. When all the water
has been added, the mixture may be heated to a temperature
' within the range of about 75-100C to drive the reaction
to completion. The desired symmetrical bis(aminoalkyl)-
disiloxane may then be recovered by conventional methods
such as distillation or crystallization.
It is sometimes found that the symmetrical
bis(aminoalkyl)disiloxane product obtained by the method
of this invention contains minor but substantial amounts
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- 9 - RD 16,653
of higher bis(aminoalkyl)siloxanes, such as the
trisiloxane and tetrasiloxane. The presence of such
higher siloxanes is generally not detrimental to the
known utilities of the bis(aminoalkyl)disiloxanes. This
is particularly true when the product is to be used in
the preparation of polyimides, since a preliminary
step in said preparation is frequently the equilibration
of the diamine with such materials as octamethylcyclo-
tetrasiloxane to increase the number of siloxane units
therein. -`
The method of this invention for the
preparation of symmetrical bis(aminoalkyl)disiloxanes
is illustrated by the following examples.
EXample 5
The silyl carbamate solution of Example 1
wa~ combined with 1 ml. of a hydrosilation catalyst
prepared from chloroplatinic acid and 3,3,5,5-tetra-
methyl-3,5-di-sila-4-oxa-1,6-heptadiene by the method
disclosed in Example 10 of the aforementioned U.S.
Patent 3,814,730, said catalyst containing 5% platinum.
The resulting solution contained platinum in the amount
of 200 ppm. based on silyl carbamate. The mixture was
heated slowly, with stirring, whereupon an exothermic
reaction occurred and the temperature rose about 20C.
25 ~ When the exotherm had subsided, the mixture was heated
- under reflux for 8 hours. Analysis then showed that all
the silyl carbamate had reacted.
The mixture was cooled and a 50% stoichio-
- metric excess of water was added dropwise, with stirring,
~ whereupon an exothermic reaction occurred. The rate of
water~addition was regulated so as to maintain a reaction ~ -
temperature of about 50C. When the exotherm had
subsided, the mixture was heated unaer reflux for 15 hours.
The toluene and solvent were then removed by distillation
35~ and the product was distilled; the desired l,9-diamino-
4,4,6,6-tetramethyl-S-oxa-4,6-disilanonane was recovered
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- 10 - RD 16,653
at 100C/1 torr. The yield was 84% of theoretical, and
the product contained about 20% trisiloxane and about
5% tetrasiloxane.
Example 6
The procedure of Example 5 was repeated, using
as a starting material the silyl carbamate composition of
Example 2. The yield of 1,9-diamino-4,4,6,6-tetra-
methyl-5-oxa-4,6-disilanonane was 82%, and the product
contained about 20% trisiloxane and about 5% tetra-
siloxane.
Example 7
The procedure of Example 6 was repeated, using
the silyl carbamate composition of Example 5. Similar
results were obtained.
Example 8
The silyl carbamate solution of Example 1
was combined with platinum tetrachloride to provide
200 ppm. of platinum based on silyl carbamate. The
mixture was heated slowly, with stirring, whereupon an
exothermic reaction occurred and the temperature rose
about 20C. When the exotherm had subsided, the mixture
was heated under reflux until analysis showed that all
the silyl carbamate had reacted.
The mixture was maintained at 100C as a
50~ stoichiometric excess of water was added dropwise,
with stirring. The mixture was heated at 100C for
one hour after water addition was complete. The toluene
and solvent were then removed by distillation and the
product was distilled; the desired l,9-diamino-4,4,6,6-
tetramethyl-5-oxa-4,6-disilanonane was recovered at
100C/1 torr. The yield was 84.5% of theoretical, and
the product contained about 14.6% trisiloxane and
1.6% tetrasiloxane.
Examples 9-12
The procedure of Example 8 was repeated, using
the silyl carbamate composition of Examplr 4 and various
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- 11 - RD 16,653
platinum-containing catalysts in substantially equivalent
amounts. The relative parameters and results are given
in the following table.
Hydrosilation
5Exam~le Catalyst time, hrs.$ product
..
9 Pt(1% on carbon) 8 68
Ptcl2(cH3cH)2 62
11 2 t 6 6 2 4 67
12 Same as Example 5 8 76
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