Pentaborane

Description

Pentaborane is a nonmetallic, colorless liquid with a pungent odor. It decomposes at 300°F (148°C), if it has not already ignited, and will ignite spontaneously in air if impure. It is a dangerous fire and explosion risk, with a flammable range of 0.46%–98% in air. Boiling point is 145°F (64°C), flash point is 86°F (30°C), and ignition temperature is 95°F (35°C), which is extremely low. Any object that is 95°F (35°C) or above can be an ignition source. Ignition sources can be ordinary objects on a hot day in the summer, such as the pavement, metal on vehicles, and even the air. In addition to extreme flammability, it is also toxic by ingestion or inhalation and is a strong irritant. TLV is 0.005 ppm in air, and it is immiscible in water. The four-digit UN identification number is 1380. The NFPA 704 designation for pentaborane is health 4, flammability 4, and reactivity 2. The primary uses are as fuel for air-breathing engines and as a propellant.

Description

Pentaborane, a colorless, pyrophoric, low-boiling liquid with a disagreeable odor, was first synthesized from B2H6?in the 1930s by H. I. Schlesinger and A. B. Burg. In the 1950s, it was considered as a rocket fuel by the United States and the Soviet Union. Pentaborane and its boron hydride cousins were the subject of?The Green Flame: Surviving Government Secrecy, a 1991 memoir by Andrew Dequasie.

Chemical properties

Pentaborane is a colorless, volatile liquid. Unpleasant, sweetish odor, like sour milk. The Odor Threshold is 0.8 ppm.

The Uses of Pentaborane

There appears to be no commercial market for pentaborane. In the 1950s it was explored as a potential rocket fuel.

The Uses of Pentaborane

Reducing agent in propellant fuels

Preparation

Pentaborane is obtained by passing diborane through a hot tube. Careful control of temperature, pressure, and flow are required to obtain good yields and avoid further pyrolysis to higher hydrides.

General Description

A clear colorless liquid with a pungent odor like sour milk, and flammable.It is corrosive to natural rubber, some synthetic rubber, some greases, and some lubricants and gives off irritating or toxic fumes (or gases) in a fire. It reacts violently with fire. Pentaboron nonahydride incompatible with strong oxidants such as chromium anhydride, chlorate and potassium permanganate, and other contacts. Vapors toxic both under prolonged exposure to low concentrations and short exposure to high concentrations. Density 0.61 g / cm3. Under prolonged exposure to intense heat the containers may rupture violently and rocket.

Air & Water Reactions

Highly flammable. May ignite spontaneously in air [Merck 11th ed. 1989]. Slowly decomposes in water.

Reactivity Profile

Pentaborane is an extremely reactive reducing agent. Can ignite spontaneously in contact with air and many other materials. Reactions with oxygen are often violently explosive. Reacts with ammonia to form a diammoniate. Is stabilized by the formation of complexes with N, O, P, or S. Is stable in hydrocarbon solvents, but forms shock sensitive solutions in most carbonyl containing solvents.

Health Hazard

May cause death or permanent injury after very short exposure to small quantities.

Fire Hazard

Ignites spontaneously in air. Reacts violently with halogenated extinguishing agents. Boron hydrides present considerable fire and explosion hazard. They undergo explosive reaction with most oxidizing agents, including halogenated hydrocarbons. Fires tend to reignite. On decomposition, Pentaborane emits toxic fumes and can react vigorously with oxidizing materials. Avoid dimethyl sulfoxide, water, most oxidizing agents (including halogenated hydrocarbons). Avoid direct sunlight and sources of ignition, decomposes very slowly at 302. Hazardous polymerization may not occur.

Safety Profile

Poison by inhalation and intraperitoneal routes. Dangerous fire hazard by chemical reaction; spontaneously flammable in air. Dangerous explosion hazard. To fight fire, use special fire-fighting materials; water is not effective; reacts violently with halogenated extinguishing agents. Get instructions from supplier. Explosive reaction with oxygen. Forms shock-sensitive solutions in solvents containing carbonyl, ether, or ester functions; or halogens. Incompatible with dimethyl sulfoxide. Upon decomposition it emits toxic fumes of B. See also BORANES and BORON COMPOUNDS

Potential Exposure

Pentaborane is used in rocket propellants and in gasoline additives.

Shipping

UN1380 Pentaborane, Hazard Class: 4.2; Labels: 4.2-Spontaneously combustible material, 6.1-Poisonous materials. Inhalation Hazard Zone A.

Incompatibilities

Pentaborane is an extremely reactive reducing agent. It can ignite spontaneously in contact with air and many other materials. Reactions with oxygen are often violently explosive. Reacts with ammonia to form a diammoniate. Reacts on contact with water, oxidizers, halogens, including halogenated hydrocarbons. May sel-heat and ignite spontaneously in moist air, decomposes @ 150C. Hydrolyzes slowly with heat in water to form boric acid. Contact with solvents, such as ketones, ethers and esters form shock-sensitive compounds. Pentaborane is stable in hydrocarbon solvents, but forms shock sensitive solutions in most carbonyl containing solvents. Corrosive to natural rubber, some synthetic rubbers and to some lubricants. Avoid dimethyl sulfoxide, direct sunlight and sources of ignition.

Waste Disposal

Incineration with aqueous scrubbing of exhaust gases to remove B2O3 particulates.