Carborane temperature

Nonicosahedral carboranes can be prepared from the icosahedral species by similar degradation procedures or by reactions between boranes such as B H q and B H with acetylenes. The degradative reactions for intermediate C2B H 2 species (n = 6-9) have been described in detail (119). The small closo-Qr Yi 2 species (n = 3-5 are obtained by the direct thermal reaction (500—600°C) of B H using acetylene in a continuous-flow system. The combined yields approach 70% and the product distribution is around 5 5 1 of 2,4-C2B3H2 [20693-69-0] to l,6-C2B Hg [20693-67-8] to 1,5-C2B3H3 [20693-66-7] (120). A similar reaction (eq. 60) employing base catalysts, such as 2 6-dimethylpyridine at ambient temperature gives nido-2 >-(Z, ... 

Although c/oso-carboranes are stable to high temperatures and to most common reagents, M. F. Hawthorne showed (1964) that they can... 

While the Olin efforts on the production of high-temperature polymers were centered mainly on FeCl3-catalyzed condensation reactions, subsequent efforts from Union Carbide, Inc. utilized an aminosilane route and a ureidosilane route (Fig. 3) to synthesize carboranylenesiloxane polymers of high molecular weights. Using the former route, the polymer was produced by a condensation reaction between a carborane-disilanol and bis(dimethylamino)dimethylsilane, during which an expulsion of a... 

Ando and co-workers have reported the synthesis of a silyl-carborane hybrid diethynylbenzene-silylene polymer (108) (Fig. 66) possessing high thermal stability.136 The polymer contained Si and —C=C— group in the main chain and m-carborane and vinyl groups in the side chain. The 5% weight-loss temperature of the cured polymer in air was over 1000°C as determined by thermogravimetric analysis. 

A polycondensation reaction of 4,4 -dihydroxybiphenyl, sebacic, and m-carboranedicarboxylic acids was reported to produce a carborane-containing polymer (142) (Fig. 78) that led to the production of a new columnar phase at elevated temperatures.157 This new phase was formed in addition to the crystalline and liquid crystalline smectic phases typically formed from only 4,4 -dihydroxybiphenyl and sebacic acids. 

Figure 4 Weight loss vs. temperature for poly( -carborane-siloxane)s in air.

The final class of polymers containing carboranyl units to be mentioned here is the polyphosphazenes. These polymers comprise a backbone of alternating phosphorous and nitrogen atoms with a high degree of torsional mobility that accounts for their low glass-transition temperatures (-60°C to -80°C). The introduction of phenyl-carboranyl units into a polyphosphazene polymer results in a substantial improvement in their overall thermal stability. This is believed to be due to the steric hindrance offered by the phenyl-carborane functionality that inhibits coil formation, thereby retarding the preferred thermodynamic pathway of cyclic compound formation (see scheme 12). 

In the literature, there are reports of carborane units bearing energetic groups, including nitro- and nitro-phenyl. The treatment of o-carborane with 100% nitric acid at room temperature is reported36 to yield a B-hydroxyl and a B-nitrato-o-carborane (see scheme 13). 

The solution is cooled to room temperature and is washed with a few milliliters of benzene into a single-necked flask. The solvent is removed with a rotary evaporator connected to a water aspirator vacuum gentle heat is supplied from a steam bath. The residue is cooled to room temperature before air is admitted. About 200 ml. of hexane is added and stirred with the residue to extract most of the carborane. The brownish tar which remains undissolved is allowed to settle and the solution is decanted. A second extraction of the tar with 40 ml. of hexane converts the residue to a solid which is removed by filtration. The solid is washed on the filter with an additional 40 ml. of hexane. The combined hexane extracts are filtered and then washed in a separatory funnel with four 100-ml. portions of a chilled aqueous 10% sodium hydroxide solution, followed by four 100-ml. portions of water. After the yellow hexane solution has been dried over anhydrous magnesium sulfate and filtered, the solvent is removed by use of a rotary evaporator connected to a water aspirator. The carborane is washed with a small amount of pentane into a 300-ml. single-necked flask which is attached to an alembic column as pictured in Fig. 13. 

The distilling flask, collection flask, and column are continuously evacuated with a high-vacuum system. When the bulk of the pentane and residual hexane have distilled away, the temperature of a silicone oil bath surrounding the distillation flask is raised from room temperature to 125° over about a one-hour period. When the distillation rate diminishes appreciably, the temperature is slowly raised to 150° and maintained there until no more liquid is obtained. The distillation flask is cooled to room temperature before air is admitted to the system. The distilled product weighs 86.5 g. (89% yield checkers report 89 %t) and melts at 32 to 32.5°. In this state of purity, (bromomethyl)-carborane is suitable for most uses, but it may be further purified by crystallization from pentane or methanol. For example, crystals obtained by chilling a solution of 86.5 g. of the car-... 

After the addition of methyl iodide, the solution is heated to the reflux temperature for an additional 3 hours. The reaction mixture is allowed to cool to room temperature and it is slowly added with stirring to about 400 ml. of chilled dilute (IN) hydrochloric acid. The mixture is placed in a separatory funnel, and the carborane is extracted first with 250 ml. of diethyl ether... 

The reaction is carried out in a 500-ml. three-necked flask equipped with a reflux condenser, mechanical stirrer, heating mantle, and nitrogen inlet. The equipment is similar to that pictured in Fig. 11, except that an addition funnel is not required. In the reaction flask 20 g. (0.36 mol, 100% excess) of potassium hydroxide is dissolved in 300 ml. of absolute ethanol. The spare neck is closed with a ground-glass stopper, and the solution is stirred until it reaches room temperature. Addition of the carborane to the warm basic solution may result in an initial vigorous reaction. To this solution is added 30.0 g. (0.175 mol) of solid dimethylcarborane. The solution is stirred for one hour at room temperature and is then heated at the reflux temperature for 14 hours or until hydrogen evolution has stopped. 

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