BORON HYDRIDES Chemische Eigenschaften,Einsatz,Produktion Methoden
Physikalische Eigenschaften
Diborane(6) and tetraborane(10) are colorless gases at ambient temperature and pressure. Diborane has a repulsive odor. Higher boranes up to nine boron atoms are colorless liquids. Decaborane(14) is a colorless crystalline solid. Pentaborane(11) and hexaborane(12) are unstable compounds. The densities and melting and boiling points of selected boron hydrides are shown in the following table:
Boron hydrides are soluble in carbon disulfide, diglyme and ethyl acetate. They react with water.
Verwenden
Boron hydrides are used in rocket propellants. They are ideal water-reactive fuels, liberating high energy when exposed to moist air or traces of water. Two other major applications of these compounds are in preparative chemistry, to produce borohydrides and many organoboranes, and as reducing agents. These substances find limited applications in catalysis. Diborane is a polymerization catalyst for olefins. Some minor applications of these compounds include vulcanization of rubber, corrosion inhibition, dye stripping, mothproofing, and as fluxing agents. Diborane also is used as a doping agent for ρ-type semiconductors.
synthetische
Diborane is prepared by the reaction of sodium borohydride with iodine or boron trifluoride or trichloride in diglyme:
2NaBH
4 + I
2 → B2H6 + 2NaI + H
2
3NaBH
4 + I
2 → 2B2H6 + 3NaBF
4
It also may be prepared by the reaction of sodium borohydride with sulfu-ric acid:
2NaBH
4 + H
2SO
4 → B
2H
6 + 2H
2 + Na
2SO
4
Diborane also can be made by reduction of boron trichloride with either sodium hydride at room temperature in diglyme or with hydrogen over aluminum at 350 to 500°C :
2BClAl
3 + 6H
2 → B2H
6 + 6HCl
Tetraborane too can be prepared from sodium borohydride. The reaction, however, is carried out at a high temperature. The product sodium octahydroborate is treated with hydrochloric acid to yield tetraborane:
2NaBH
4 + I
2 → NaB
2H
8 + 2H
2 + 2NaI
4NaB
2H
8 + 4HCl → 2B
4H
10 + 4NaCl + 8H
2
Higher boranes can be produced from diborane by pyrolysis.
Hazard
Diborane ignites spontaneously in moist air. Its flash point is in the range 38 to 52°C, and it forms explosive mixtures with air over a wide range: the lower and upper flammable limits are 0.8 to 88% by volume in air, respectively. Diborane explodes in contact with chlorine and ignites with fuming nitric acid. All boron hydrides react violently with halogenated extinguishing agents.
Exposure to boron hydride gases or vapors can cause irritation of respiratory passages, acute poisoning of lungs, and pulmonary edema. Ingestion of decaborane can cause spasm, tremor, and convulsion. For decaborane, LD50 oral (mouse) is 41 mg/kg; LD50 skin (mouse) is 740 mg/kg; and LC50 inhalation (40 hr.) (mouse) is 12 ppm.
BORON HYDRIDES Upstream-Materialien And Downstream Produkte
Upstream-Materialien
Downstream Produkte
