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

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.

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

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.

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

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.

Pentaborane is used in rocket propellants and in gasoline additives.

If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit.

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

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.

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.

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

Reducing agent in propellant fuels

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

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.