Organic compounds -- part of the class 532-570 series – Organic compounds – Boron containing
Reexamination Certificate
2002-05-23
2004-01-20
Vollano, Jean F. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Boron containing
Reexamination Certificate
active
06680411
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a carborane supercluster and a method of producing the same. More particularly, the invention relates to a carborane supercluster containing boron-rich carborane (if carborane is given as the molecular formula C
2
B
10
H
12
, the boron content is approximately 75% by weight) with high thermodynamic and chemical stability as its unit constituent (i.e., a cluster molecule), and a method of producing the same.
2. Description of the Related Art
Carborane is generally a compound consisting of boron hydride into which carbon atoms are introduced which has a hollow-cage-shaped structure. Boron hydride (i.e., hydride of boron) is usually termed “borane”, because of its similarity to “alkane” (i.e., saturated hydrocarbons).
A well-known borane is decaborane (
14
) expressed by a chemical formula B
10
H
14
, which is comparatively stable and industrially important. Decaborane (
14
) has a skeletal structure of boron (B) atoms, as shown in FIG.
1
(
a
). The skeletal boron structure of FIG.
1
(
a
), which is cage-shaped, constitutes a regular icosahedron formed by 12 boron atoms located at its respective vertexes and at the same time, the two adjacent boron atoms are removed therefrom. The molecular structure of decaborane (
14
) is that the remaining ten boron atoms of the skeletal structure are respectively terminated by hydrogen (H) atoms, where the two adjacent boron atoms including opened sites are bridged by hydrogen atoms at four positions.
o-Carborane (i.e., ortho-carborane, 1,2-dicarba-closo-dodecaborane), which is expressed by a chemical formula C
2
B
10
H
12
, is known as one of typical carboranes. o-Carborane has a similar molecular structure to the above-described molecular structure of decaborane (
14
), as shown in FIG.
1
(
b
). Specifically, the four bridging hydrogen atoms are removed from the above-described molecular structure of decaborane (
14
) and then, two carbon atoms are respectively inserted to the two opened sites thereof, thereby completing the regular icosahedron. Moreover, the two carbon atoms and the ten boron atoms, which are respectively located at the 12 vertexes of the icosahedron, are respectively terminated by hydrogen atoms. Thus, the molecular structure of o-carborane is formed.
Actually, o-carborane is synthesized from decaborane (
14
). Specifically, if decaborane (
14
) is reacted with acetylene under the existence of a Lewis base such as acetonitrile and alkylamines, o-carborane is produced. o-Carborane has two isomers, m-carborane (i.e., meta-carborane, 1,7-dicarba-closo-dodecaborane) and p-carborane (i.e., para-carborane, 1,12-dicarba-closo-dodecaborane), according to the relative position of the two carbon atoms. m-Carborane has a molecular structure shown in FIG.
1
(
c
), where one boron atom is located between the two carbon atoms. p-Carborane has a molecular structure shown in FIG.
1
(
d
), where the two carbon atoms are located symmetrically with respect to the center of the regular icosahedron.
If o-carborane is heated at 425° C. in an inert atmosphere, it is irreversibly isomerized to m-carborane. If o-carborane is heated at 700° C. in an inert atmosphere, it is irreversibly isomerized to 75% of m-carborane and 25% of p-carborane.
In general, a geometrically-closed, cage-shaped borane cluster (which is expressed by a chemical formula B
n
H
n
, where n is a positive integer) has (n+1) bonding molecular orbitals in its cage-shaped skeletal structure. Thus, to close electronically the shell of the borane cluster, 2(n+1) electrons are necessary to fill these orbitals.
Regarding boron, a boron atom has three valence electrons, where one of the valence electrons is used for forming the B—H bond. Therefore, the remaining two electrons are available to the formation of the skeletal structure. For example, with dodecaborane expressed as B
12
H
12
(n=12), which is neutral and which has a skeletal structure of a regular icosahedron, 26 (=2(12+1)) electrons are necessary to fill the molecular orbitals to thereby close electronically the shell. Since dodecaborane contains 12 boron atoms 24 (=2×12) electrons are available to the formation of the skeletal structure. This means that two electrons are deficient. Accordingly, the shell of dodecaborane (B
12
H
12
) is unable to be closed electronically and thus, dodecaborane is instable.
Unlike this, with carborane (C
2
B
10
H
12
), where the two boron atoms of dodecaborane (B
12
H
12
) are respectively replaced with two carbon atoms, each of these carbon atoms provides three electrons available to the formation of the skeletal structure. This is because a carbon atom has four valence electrons while one valence electron is used for forming the C—H bond. Therefore, carborane contains 26 (=2×10+3×2) electrons available to the formation of the skeletal structure. This means that the bonding orbitals of carborane are filled and thus, its shell is closed electronically. Moreover, the molecular structure of carborane is geometrically closed. Due to the synergism of the geometrically-closed molecular structure and the electronically-closed shell, carborane is expected very stable.
In the following explanation of this specification, the word “carborane” means a specific boron hydride expressed by C
2
B
10
H
12
for the sake of simplification.
Boranes, which are used as the starting source material for synthesizing a desired material, are generally instable. In contrast, the carborane (C
2
B
10
H
12
) is chemically stable against reagents such as oxidizing agents, strong acids (heated, concentrated sulfuric acid and nitric acid), and alcohols. Moreover, the carborane (C
2
B
10
H
12
) is not deteriorated at high temperatures, which is simply isomerized even at 700° C. as described previously. This means that the carborane (C
2
B
10
H
12
) is very stable not only chemically but also thermally.
To utilize the chemical and thermal stability of the carborane, conventionally, the carborane has been introduced into a macromolecule as a function group to thereby improve the characteristic of the macromolecule. These carborane-introduced macromolecules have been used for heat- and chemical-resistant piping materials, gaskets, membranes, and covering materials.
Furthermore, to make use of the excellent insulation properties of the carborane-introduced macromolecules, insulating/insulated gloves and insulating/insulated clothes have been developed and at the same time, various trials to use the macromolecules as the integrated-circuit insulator have been made. To utilize the rigidity or inflexibility of the carborane molecules, application as constituent elements of liquid crystals has been studied as well.
Moreover, since the boron content of the carborane is approximately 75 wt %, applications that use the properties of boron (which is a trivalent element containing three valence electrons) have been developed. Boron is usually used as a dopant for introducing holes into silicon (which is a tetravalent element containing four valence electrons). Similar to this, to produce a p-type semiconductor, there has been a trial to deposit the carborane on a silicon substrate by a CVD (Chemical Vapor Deposition) process.
Boron has two stable isotopes,
10
B (19.8%) and
11
B (80.2%). The isotope
10
B has a very large cross-section (3.840×10
−∞
m
2
) with respect to thermal neutron capture and therefore, it has been used as a neutron capture agent. High-energy particles generated through the nuclear reaction
10
B+n=
4
He+
7
Li+2.79 MeV (n: neutron, MeV: 10
6
electron volts) have a property that breaks all substances existing in their flying range. An application of this property to medical care is “boron-neutron capture therapy”, where a derivative of the carborane is administrated to a sufferer from a tumor to thereby enter an invaded organ and then, a neutron beam is irradiated to the tumor cells to necrotize the same.
Additionally
Hiura Hidefumi
Kanayama Toshihiko
Agency of Industrial Science and Technology
Vollano Jean F.
Young & Thompson
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