Note: Descriptions are shown in the official language in which they were submitted.
9486
104~)3~6
Thi5 invention relates in general to the synthesis
of decaborane(l4). In one aspect, the invention is
; directed to the preparation of decaborane(l4) in an
efficient,multistep process from readily available
starting materials. In a further aspect, this invention
relates to the preparation of the intermediate BllHl4-
ion which can be conveniently oxidized to decaborane(l4)~
In a still further aspect the invention is directed to a
process for the preparation of decaborane(l4) from
10 sodium borohydride and boron trlfluoride diethyletherate.
Prior to the present invention decaborane(14)
:, ,
was prepared by the controlled thermolysis of diborane~6)
or mixtures of diborane(6) tetraborane(10~ and various
diluent gases, such as hydrogen. However, in the prior ?
; art processes, including static systems, hot tube systems
l and liquid-containing systems, only complex, hazardous
:.,
mixtures were obtained. Even though yields of BloH14
were reasonably good by some of these methods, technical
difficulties experienced precluded efficient scale-up and '
20 most were not practical for laboratory use. Decaborane(14)
has also been prepared in very small quantities by the
, thermal decomposition of decaborane(l6) in the presence
~, of I2. The decaborane(l6) was prepared from pentaborane(9).
Thus, prior to the present invention, it was not possible
to prepare decaborane(l4) efficiently and in relatively
high yields which would be suitable for commercial operations
without the need for elaborate equipment and the use of
potentially hazardous chemicals.
~,
; - 2 -
.~" .. , . ,. .. . . . ~
9486
1040386
Accordingly, one or more of the following
objects will be achicved by the practice of the present
invention. It is an object of this invention to provide
a process for the synthesis of decaborane(14). A
further object is to provide a multi-step process which
is efficient and employs readily available starting
materials. Another object of the invention is to
provide a process for the preparation of decaborane(14)
which avoids the use of hazardous and expensive starting
materials. A still further object of this invention is
to provide a process for the preparation of the BllHl4-
ion. Another object i8 to provide a process for the
preparation of the BllH14- ion from several different
starting materials. A further object of this invention
i9 to prepare the BllH14- ion from the B3H8- ion.
;
These and other objects will readily become apparent
, to those skilled in the art in the light of the teachings
;,ii~ set forth.
~, In its broad aspect, this invention is directed
to a process for the synthesis of decaborane(l4). One
r: embodiment of the invention is also directed to the
~~l preparation of decaborane(l4) from different starting
!
materials, such as lower alkylammonium octahydrotri-
borates.
. .j .
~' In the first embodiment decaborane(14) is
prepared by a process which comprises the steps of:
(a) contacting in an inert atmosphere
. . .
9486
~ 0 40 38 6
(i) a metal borohydride of the
formula:
MBH4
wherein M represents a monovalent
ion and is a member selected from the
group consisting of sodium, potassium,
rubidium, cesium, and lithium, with
(ii) a boron trifluoride-containing
compound to provide the tetradecahydro-
undecaborate(-l) ion, the metal borohydride
and the borontrifluoride-containing compound
being employed in a mole ratlo of from
about 5:6 to abou~ 6 respectively.
(b) contacting the tetradecahydroundecaborate(-l)
ion with an oxidizing a~ent having an electrode
potential (E) of at least about +0.6 volts, and
(c) thereafter recovering the decaborane(l4).
The process of this invention provides a
convenient and safe method for the synthesis of decaborane(l4)
from readily available starting materials. As indicated
above, in the first step of the process a metal borohydride
is contacted with a compound containing boron trifluoride
.,
itself. m e process is conducted in an inert atmosphere
and within the temperature range and conditions hereinafter
indicated.
; In this first step the borohydride a~d boron tri-
fluoride-containing compound react to provide the tetra-
decahydroundecaborate(-l) ion in accordance with the
- 4 -
.. , ........... ..
9486
104!~)386
following general equation wherein sodium borohydride and
boron trifluoride diethyletherate are typical reactants:
NaBH4 + BF3 0(C2Hs)2 ~~~~ NaBllH14
The synthesis of the BllH14- ion by the reaction
of metal borohydrides with decaborane(14) has been
reported in the literature. For example, V.D.
Aftandilian, et al., disclose in Inorganic Chemistry
Vol. 1, No. 4, pages 734-737 (1962) the reaction of
metal borohydrides with ethereal decaborane at 90C.
; 10 to give M BllH14 . Similarly, H.C. Miller et al.
have reported in Inorganic Chemistry, Vol. 3, No. 10,
;; pages 1456-1462 (1964) that the preparation of polyhedral
borane 9 tructures such as BllH14- has been achieved in
two basic reactions.
.,
In the first step of this process it has
been found that the mole ratio of metal barohydride to
boron trifluoride-containing compound is critical if
optimum results are to be obtained. It has been
found that the ratio of borohydride to the boron
trifluoride compound employed be preferably 5 to 6.
Ratios of 5 to ~6 can also be employed but are less
preferred.
f:
Y - 5 -
9486
104t~386
As indicated above, a variety of metal boro-
hydride compounds can be employed. Similarly, the boron
trifluoride-containing compound can be boron trifluoride
itself or a boron trifluoride di~lkyletherate ~uch as
those wherein the alkyl group can contain 1-4 carbon
atoms. The alkyl groups need not be of the same chain
length in the same molecule.
It is also desirable to conduct the reaction
in a solvent. For example, ethe~s boiling at or
above 100C. at the reaction pressure are suitable:
dimethyl ether of diethylene glycol; diethyl "Cellosolve",
diethyl "Carbitol", and dimethoxy-1,3-butane are
illustrative. Obviously, ethers boiling below 100C.
at atmospheric pressure could be used if the reaction
were conducted at superatmosphereic pressure but no
obvious advantage is obtained by so doing. The amount
of solvent is not narrowly critical but must be present
in sufficient quantity to permit adequate mixing of the
' reactants.
;1 2~ The reaction is conducted at a temperature of
ll from about 100 to about 120C~
:~l As hereinbefore indicated, the second step of
~ the process of this invention is the oxidation of the
. . . ..
BllH14- ion to decaborane(l4). Oxidation can be
; effected by a variety of methods.
:,
- 6 -
... .
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. ~ . . . .
9486
104~)386
Although the electrochemical oxidation of
BllH14- ion to decaborane has not been reported in the
literature, it has been found that chemical oxidation in
solution does produce the desired decaborane(14). The
highest yields were obtained when the oxidizing agent was
used in excess of that required by the proposed equation.
The excess was presumably required due to competition of
BllH14
BllHl4 + 3H2O > BloH14 + B(OH)3
ion, BloH14 or other species for oxidizing agent, In
the course of the reaction BloH14 was extracted into a
benzene layer which could be used directly in further
reactions requiring BloH14 as a starting material.
Clearly one of the most interesting of these i8 in the
preparation of dicarba-closo-dodecaborane(12).
In practice, it has been observed that a
wide variety of compounds can be employed to effect
the chemical oxidation of the BllH14- ion. It has
also been found that for optimum results the oxidizing
agents should have an electrode potential (E) of
at least + 0.6 volts and preferably at least + 1.0
volts.
,,
.
-- 7 --
~ .
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. ..
. ~ ..
:. . .
9486
1~)4~386
Illustrative oxidizing agents which can be
employed include, among others, potassium permanganate,
potassium dichromate, hydrogen peroxide, peracetic acid,
perbenzoic acid, and the like. Other oxidizing agent~
which could be used include:
Ag+2 /H+
AU+3 /H+
Ce+4 /H
CeOH+3 /H+
HC 10 /H+
C103 /H~
C104 /H
Co+3
Cr /H
Fe(phenanthroline)3 /H+
I03 /H
MnO 2 /H
NiO2 /H+
Np+4
02/H+
' " PbO2/H+
.. ' PbO2/S04 /H+
: Pu+4
~2 Pu+5
Ru04
:` Ti+3
U+5
V (OH)+
: - 8 -
:. ;;
9486
104~386
In practice it has been found that the oxidation
step employed in this invention must be carried out under
an inert atmosphere. A wide variety of inert atmospheres
can be employed, the only requirement being that they
do not adversely affect either the reactants or the
decaborane(l4) produced. Illustrative inert gases
which can be employed include, among others, nitrogen,
the noble gases, such as argon, and the like, methane,
ethane, and the like.
It has àlso been observed that the reaction
temperature during the oxidation step is preferably
from about -10C. to about 50C., and more preferably
from about 5C. to about 50C.
The reaction time is not necessarily critical.
The product is, however, subject to slow hydrolysis in
the aqueous reaction mixture and thus it is preferred
to complete the oxidation and separations within a
reasonable time. In some instances, the use of drying
agent may be desirable to remove water. Most any dessicant
can be employed as long as it is non-reactive. Illustra-
tive dessicants include, solid dessicants, such as
magnesium sulfate, copper sulfate, anhydrous silica
gel, molecular sieves and the like. In addition gaseous
dessicants, such as phosgene, can also be employed.
Although azeotropic distillation is satisfactory due to
hydrolysis it is less preferred.
_ g _
9486
104~386
A variety of inert solvents can be employed
for`extraction of the decaborane(l4). Preferably, the
solvent is an aromatic hydrocarbon stable in the
presence of the particular oxidizing agent used,
melting below 5C. and boiling below 160C. Illustrative
solvents are benzene, toluene, and the like.
Less preferred solvents which can also be
employed are aliphatic hydrocarbons, (C4 or
higher) which boil below 160C., aliphatic ethers, and
the like.
In a further embodiment, this invention is
directed to a process for ~he preparation of tetradeca-
hydroundecaborate(-l) ion from starting materials other
than the metal borohydrides.
In the course of studying the reaction of NaBH4
with BF3 O(C2H5)2 to produce B3H8- ion it was found
that on continued addition of BF3 O(C2H5)2 beyond the
stoichiometric amount necessary for completion of the
; reaction that the concentration of B3H8- ion in the
; 20 reaction mixture decreased. As the concentration of B3H8-
ion decreased, a simultaneous production of BllH14- ion
occurred. At approximately 160% of the BF3 O(C2H5)2
required to complete the reaction, the concentration of
B3H8- ion was essentially zero and with the exception of
` BllH14 ion only traces of other boron-containing species
; were present. Inasmuch as the B3H8- ion is believed to
be formed as an intermediate in the reaction of
the metal borohydrides with boron trifluoride
. - 10 - .
...... ~.
:: .
. . ,
9486
1~)4~)386
-containing compounds, it was found that the octahydro-
triborate could be substituted as a reactant for the
metal borohydride in the preparation of decaborane(14).
In this embodiment the process comprises the step of:
(a) contacting in an inert atmosphere
(i) an octahydrotriborate of the formula:
MB3H8
wherein M represents a monovalent ion and
is selected from the group consisting
:'1
of sodium, potassium,rubidium, cesium
and lithium, and lower alkylammonium
ions, with
~ (ii) a boron trifluoride-containing
¦ compound selected from the group
I consisting of boron trifluoride and
l boron trifluoride dialkyletherate to
ii provide the tetradecahydroundecaborate(-l)
,. I
;l~ ion,the octahydrotriborate and the
~,
boron trifluoride-containing compound
being employed in a mole ratio of from
about 1:1 toabout 1:~ 1 respectively.
,. l
(b) contacting the tetradecahydroundecaborate-
(-1) ion with an oxidizing agent having an . -
. electrode potential (E) of at least about
. .
+ 0.6 volts, and
(c) thereafter recovering the decaborane(l4).
. For the first step of the process of this
~ embodiment, the reaction is conducted in a solvent
: I and at a temperature ofl lfrom about 100C. to about 1~0C.
9486
104~386
Both in this embodiment and the previous
embo~diment wherein a metal borohydride is employed,
the addition of the boron trifluoride compound is
critical at least to the extent that if it is added
too rapidly B2H6 is evolved from the reaction mixture
and the yield of BllH14 is reduced. Thus the reactant8 -
are employed in the indicated mole ratios but by the
gradual addition of the boron trifluoride compound
to either the borohydride or the octahydrotriborate.
The reaction is preferably conducted in a
solvent as indicated in the first embodiment of this
invention.
As indicated, a variety of octahydrotriborates
can be employed as the starting material. In addition
to the monovalent metals set forth above, the lower
alkylammonium octahydrotriborates can be employed.
Preferred compositions are those within the nitrogen
atom contains four alkyl groups of from 1 to 4 carbon
atoms and need not necessarily be the same throughout
the molecule.
The second step, or oxidation of the B11~14
ion to decaborane(14) employs the same conditions as
previously indicated in the first embodiment.
Decaborane(14) prepared by the process of this
;. invention is a useful precursor to various boranes
including carboranes. The carboranes themselves are
useful for the synthesis of carborane-siloxane polymers
and elastomeric gum stocks which have attractive appli-
cations as sealants and the like. The carborane derivatives
-la-
.~ .
9486
104~386
are also useful as rocket propellant additives.
The following examples are illustrative:
EXAMPLE I
Synthesis of Decaborane(14) usin~
Potassium Perman~anate
A 2000 milliliter, three neck, round bottom
flask was employed for this experiment. The flask was
fitted with a dry-ice trap and an ether trap attached
to one of the necks. A mechanical stirrer was also
connected thru the center neck and the remaining neck
was connected to a metering pump which led to a reservoir
of boron trifluoride diethyletherate. Means also were
provided for temperature measurements in the flask
as well as the introduction of nitrogen. Commercial
;
grade sodium borohydride andboron trifluoride diethylether-
ate (98 per cent) were employed. Diglyme was heated over
sodium and benzophenone until a dark blue color was
obtained and then distilled at 67C. at a pressure
of 13 mm/ Hg. The flask was charged with 500 ml of
diglyme and 60 g (1.59 mol) of NaBH4. The trap was
cooled with Dry ice/2-propanol, the mixture was heated
to 105C. and boron trifluoride diethyletherate (250ml, 2.04
mol) was added at the rate of approximately 40 ml/hr.
When addition was complete the viscous, yellow mixture
was allowed to cool to room temperature. The contents
of the flask were filtered in air using a medium frit.
; The solids were washed with two, 50 ml portions of dry
diglyme. The combined diglyme solutions were stripped to
- 13 -
. ~
,
9486
104~)386
a yellow semi-solid using a rotary evaporator and
mechanical pump at approximately 57C. The semi-solid
was taken up in ~00 ml of water and added to a cooled
solution of 100 ml of water, 100 ml of conc. H2SO4
and 946 ml of benzene ccntained in a 5~000 ml, 3 neck
flask which had been equipped with a N2 inlet, mechanical
stirrer and dropping funnel. The ~ask and contents were
cooled to 10C. in an ice bath and a solution of 53.3g
(O.34 mol) of KMnO4 in 1600 ml of water and 160 ml of
H2SO4 was added over approximately 40 min. The contents
of the flask were poured into a separatory funnel and the
benzene layer separated and washed with 700 ml of water.
; The benzene solution was dried over MgS04, filtered and
,. j
stripped to a yellow oil. The oil was placed into a
sublimer, evacuated and heated to 50C. with the cold-
-finger cooled with ice. After the residual benzene and
diglyme had passed, decaborane(l4), collected on the cold
finger. Yiel~j9.13g (0.075 mol, mp. 97.5-98C.). The
infrared, llB nmr and mass spectra were identical to
authentic samples.
.' '.
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, .
- 14 -
. ~.;.. , ~,
9486
r
lU4~386
EXAMPLE 2
Synthesis of Decaborane(14) Using Sodium
Dichromate Without Removal of Sodium Tetrafluoroborate
.~ .
: In a manner similar to that employed in
Example 1. The flask was charged with 500 ml of
diglyme and 60.0g (1.59 mol) of NaBH4. The trap was
cooled with Dry-ice/2-propanol, while the flask and
; contents were heated with stirring to 105C. and
,,; BF3~0(C2H5)2 (250 ml, 2.04 mol) was added over a
: 6 hour period. When the addition was complete the
~":
viscous yellow mixture was allowed to cool to room
temperature. The trap contained 124g of ethyl ether.
The additional apparatus and trap apparatus were removed
and a 10 inch Vigreaux column topped with an alembic
~`; still head was added. The pressure was reduced to
approximately 50 mm/Hg and stirred for 0.5 hours. The
.:
~' flask was heated using a steam bath and the solvent
was distilled. After approximately 400 ml of solvent
had been removed the pressure was reduced to approximately
"
0.1 mm/Hg and an additional 40 ml of solvent was removed.
;~1 20 The flask was cooled in an ice bath and a cooled solution
,,,
' of 200 ml of water and 200 ml of conc. H2S04 was slowly
added. ~enzene, 500 ml, was added followed by the
~;,l slow addition of 118.5g(0.4mol) Na2Cr2O7 2H20 in 60 ml of
water (approximately 105 ml total) in 1.0 hours. The tempera-
ture of the contents of the flask rose to 30C. When ;~
the addition was complete the organic layer was separated
.i,,
.: .
~l - 15 _
....
i
9486
104~386
and the aqueous layer was washed with 400 ml of benzene.
The combined benzene layers were dried over MgS04 and
. filtered. The dried benzene solution (930 ml total)
was analyzed and found to be 0.07 molar (7.99g,
0.65 mol,) ln ~lOH14'
. '.
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- 16 -
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9486
~1~)4~3386
EXAMPLE 3
nthesis of (C2H5)4NBllH14
from (C2Hs)4NB3H~
The apparatus employed in this experiment was a
1000 ml. 3 neck flask similar to that employed in the
previous examples with the exception that the acetone
trap wascmitted. The off-gases were passed through a
trap which contained 200ml of triethylamine and thence
through a wet-test meter. The flask was charged with 18.0g
(0.105 mol) of (C2H5~4N B3H8 and 500 ml of diglyme and
heated to 105C. Over a period of 2.37 hours 15.0 ml
(0.120 mol) of BF3 O(C2Hs)2 was added and 0.248 mols of
gas were evolved. The triethylamine was stripped on a
rotary evaporator to an oil which was identified by the
infrared spectrum as (C2Hs)3N BH3, (2.48g, 0.022 mol).
The contents of the flask were cooled to room temperature
and filtered with a medium frit. The solids (16.6g,
0.077 mol) of ~2H5)4N BF4 were washed with two, 50ml
portions of diglyme. The combined diglyme fractions were
stripped at reduced pressure using a rotary evaporator
` to a yellow oil. The oil was triturated in ethyl ether
and filtered. The solids were dissolved in acetone and
water was added to the hot solution until cloudiness
appeared. The hot solution was filtered and water was
added. The solution was allowed to cool and maintained
' at 10C. overnight. me crystals were filtered and dried
in vacuo. The yield was 3.55 g (0.013 mol) of (C2H5)4N
BllH14. A second crop (0.75 g, 0.003 mol) was obtained
from the liquor.
- 17 -
9486
104C~386
EXAMPLE 4 -
SyntheSis of (C2H5)4NBllH14
from B~HR~ion Prepared in situ
; Into a 2000 ml, 3 neck flask which was equipped
` with a N2 inlet and a mechanical stirrer was placed
500 ml of diglyme and 60.0 g. (1.59 mol) of NaBH4.
The off-gases were passed through an acetone bubbler
to destroy any evolved B2H6. A thermometer was placed
;; in the acetone. A temperature rise of greater than 5C.
; ~o indicated that the rate of addition of BF3 0(C2H5)2 was
.: ,
too rapid. The contents of the flask were heated to
105 ~ 2C.. The trap was filled with Dry-ice and
2-propanol, and BF3-0(C2H5)2 was added at 40 ml/hr
(250 ml, 2.04 mol). After the addition was complete
(6 hr) the flask and contents were allowed to cool to
room temperature. Theether trap contained 121.1 g
(1.64 mol) of ethyl ether. The contents of the flask
were filtered in air using a medium frit. The solids
(141.6 g, 1.29 mol, NaBF4) were washed twice with 50 ml
;ij ,,
; 20 of dry diglyme. The combined diglyme solution was
.,
' evaporated to an oil using a rotary evaporator (1 mm.Hg,
67C.). The oil was taken up in 500 ml of water and
... ....
added in one portion to a solution of 100 g (0.475 mol)
of(C2H5)4NBr in 200 ml of water. The mixture was
allowed to stand 15 min. and filtered. The filter
cake was dissolved in 300 ml of acetone (sllght degassing)
, . . . .
~ - 18 -
; ,;j,
,. ...
~, ,
9486
16~4V386
and heated to reflux. Water was added until slight
clo~diness appeared and the solution was allowed to
cool slowly to room temperature then cooled to 10C.
overnight. The pale yellow crystals were filtered and
dried in vacuo to yield 25.7 g (0.098 mol,~
o (C2H5)4N BllH14. The liquid was evaporated
to about one-half the original volume and water
added to cloudiness. The solution was cooled as above
; and the yellow crystals filtered. The crystals were
washed with ethyl ether to remove the yellow color to
yield 5.1 g (0.019 mol) of tan crystals. The pale
yellow and tan materials were indi~tinguishable by llB
nmr and lr spectro8copy. The llB nmr 8pectra were
.
- 19 -
': ~
, . .. .
9486
16~14~386
Although the invention has been illustrated
by the preceeding examples it is not to be construed
as belng limited to the materials employed therein
but rather, the invention relates to the generic area
as hereinbefore disclosed. Various modifications and
embodiments thereof, can be made without departing from
the spirit and scope thereof.
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- 20 -
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