DIBORANE

Diborane
(Boroethane, boron hydride, diboron hexahydride)
CAS 19287-45-7

B₂ H₆

Colorless gas
bp -93 °C, mp -165 °C
Rapidly decomposes in water to form hydrogen gas

Repulsive odor detectable at 1.8 to 3.5 ppm

0.96 (air = 1.0)

-90 °C

38 to 52 °C

LC₅₀ inhal (rat) 50 ppm (4 h)

PEL (OSHA) 0.1 ppm

TLV-TWA (ACGIH) 0.1 ppm

Highly toxic, flammable, and reactive gas; contact with air or halogenated compounds results in fires and explosions.

Inhalation of diborane gas results in irritation of the respiratory tract and may result in headache, cough, nausea, difficulty in breathing, chills, fever, and weakness. The odor of diborane cannot be detected below the permissible exposure limit, so this substance is considered to have poor warning properties. Overexposure to diborane can cause damage to the central nervous system, liver, and kidneys. Death can result from pulmonary edema (fluid in the lungs) and/or from lack of oxygen. Exposure to diborane gas has not been found to have significant effects on the skin and mucous membranes, but high concentrations can cause eye irritation, and contact with the liquid can cause burns.

Chronic exposure to low concentrations of diborane may cause headache, lightheadedness, fatigue, weakness in the muscles, and tremors. Repeated exposure may produce chronic respiratory distress, particularly in susceptible individuals. An existing dermatitis may also be worsened by repeated exposure to the liquid. Diborane has not been shown to have carcinogenic or reproductive or developmental effects in humans.

Diborane is a flammable gas that ignites spontaneously in moist air at room temperature and forms explosive mixtures with air from 0.8% up to 88% by volume. Diborane reacts with halogenated hydrocarbons, and fire extinguishing agents such as Halon or carbon tetrachloride are therefore not recommended. Carbon dioxide extinguishers should be used to fight diborane fires. Fires involving diborane sometimes release toxic gases such as boron oxide smoke.

Explodes on contact with fluorine, chlorine, halogenated hydrocarbons (e.g., chloroform and carbon tetrachloride), fuming nitric acid, and nitrogen trifluoride. Diborane is a strong reducing agent that produces hydrogen upon heating or upon reaction with water. Contact with aluminum, lithium, and other active metals forms metal hydrides, which may ignite spontaneously. Diborane is incompatible with oxidizing agents, halogens, and halogenated compounds. Diborane will attack some forms of plastics, rubber, and coatings.

Diborane should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with reactive and explosive compounds described in Chapter 5.G. In particular, diborane should be used only in a fume hood free of ignition sources and should be stored in a cold, dry, well-ventilated area separated from incompatible substances and isolated from sources of sparks and open flames.

In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If this compound is inhaled, move the person to fresh air and seek medical attention at once.

In the event of a leak, remove all ignition sources and ventilate the area of the leak. Respiratory protection and protective clothing may be necessary in the event of a large spill or release in a confined area. If a cylinder is the source of the leak and the leak cannot be stopped, if possible remove the leaking cylinder to a fume hood or a safe place in the open air, and repair the leak or allow the cylinder to empty. If the leak has resulted in a fire, water spray can be used to cool the container and to reduce corrosive vapors, keeping in mind that if flames are extinguished, explosive re-ignition can occur.

Excess diborane and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.