Diborane exposure

Interest in the photochemistry of boron compounds dates back as far as 1913 when Alfred Stock investigated the effects of light from a mercury vapor lamp on diboran 6) and on tetraboran 10). In the case of diborane(6) he commented UV light will also decompose B2H6. The volume of a sample in a quartz tube increased by 1/6 after 24 hours exposure to a mercury-arc lamp, and a pale yellow crystalline substance appeared. Stock also observed that B4H q decomposition to B2H is not noticeably influenced by sunlight. 

Caution. Diborane(6) and l-methyldiborane(6) inflame explosively on contact with the atmosphere, and methyllithium may inflame on exposure to moist air. 

Caution. Diborane(6) is a highly toxic, extremely flammable gas (bp — 86.5°). Serious explosions have resulted from exposure of diborane(6) to atmospheric oxygen. All apparatus to be used for handling diborane(6) should be checked carefully for leaks. Suitable safety shields should be employed. 

Use and exposure Diborane is a colorless gas at room temperature with a repulsive, sweet odor. It mixes well with air and easily forms explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature and can cause explosions. Diborane is used in rocket propellants and as a reducing agent, a rubber vulcanizer, a catalyst for hydrocarbon polymerization, a flame-speed accelerator, and a doping agent. Diborane is a very toxic and flammable gas used by chemists to make other compounds. It is also used in electronics to impart electrical properties in pure crystals. Industrial workers are exposed to diborane by breathing in its vapors in work areas. - ... 

Exposure limits OSH A has set a limit of 0.1 ppm for diborane in workplace air for an 8-hour workday (TWA). The revised immediately dangerous to life or health (IDLH) concentrations for diborane are set at 15 ppm. ... 

Agency for Toxic Substances and Disease Registry (ATSDR). 2002. Managing hazardous materials incidents. Volume III—Medical management guidelines for acute chemical exposures Diborane (updated 2007). Atlanta, GA U.S. Department of Health and Human Services, Public Health Service. 

The heterocyclic ring of benzoxazoles (156) can be cleaved by exposure to diborane giving borazoles (157 possibly as shown in Scheme 8). Treatment of these products with hydrochloric acid leads to the formation of 2-aminophenols (158). Catalytic hydrogenation of the parent compound (156 R = H) over molybdenum sulfide has a similar end result although, since the conditions of the reaction are quite severe, phenol and 2-toluidine can form as by-products. ... 

Diborane is one of three most toxically efficient boron compounds. Its LD50 is 30 to 90 mg m during a 4-hour exposure [77]. In the course of higher exposure, manifestations of the irritation of the central nervous system, damage to the kidneys, and lung oedema are observed. Concentrations exceeding 2 to 4 ppm [78] can be detected by the smell and a 15-minute exposure to 159 ppm is lethal [79]. 

Animal studies indicate that exposure to diborane results in irritation and possible infection in respiratory passage. In addition to the acute poisoning of the lungs, this gas may cause intoxication of the central nervous system. A 4-hour exposure to 60 ppm may be lethal to mice, resulting in death from pulmonary edema. 

Decaborane is a highly toxic compound by all routes of administration. Its toxicity is somewhat greater than that of diborane. The acute toxic symptoms in humans from inhalation of its vapors could be headache, nausea, vomiting, dizziness, and lightheadedness. In severe poisoning, muscle spasm and convulsion may occur. Symptoms of toxicity may appear 1 or 2 days after exposure, and the recovery is slow. An LC50 value for mice from a 40- hour exposure was 12 ppm. 

The nitroketone (465) was converted to the oxime acetate (466) which was treated with diborane to reduce the imine group followed by hydrogen to reduce the nitro group and give the diamine (467). The diamine condensed with triethyl orthoacetate to yield dazepinil (471) Scheme 5.110.) [628]. An improved route began with o-toluidine (468) which was iV-protected to allow the directed metallation of the methyl group. Treatment with the SchifPs base (469) followed by deprotection and exposure to triethyl orthoacetate gave dazepinil in improved yield [629]. This benzodiazepine has antidepressant properties. 

Toxicology Exposure is by inhalation. Diborane is an irritant (pulmonary system), and the threshold odour detection rotten eggs is 3.3 ppm. 

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. 

OSHA lists an 8-hour Time-Weighted Average-Permissible Exposure Limit (TWA-PEL) of 0.1 ppm (0.1 mg/m ) for diborane. TWA-PEL is the exposure limit that shall not be exceeded by the 8-hour time-weighted average in any 8-hour work shift of a 40-hour workweek [3]. 

Diborane acts primarily as an irritant to the respiratory system. Inhalation causes a heat producing reaction with the moisture in the lungs. Boric acid is produced by hydrolysis [1]. An acute inhalation exposure may lead to respiratory distress-chest tightness, dyspnea, nonproductive cough, and wheezing. Subacute exposure to low concentrations of diborane is more likely to produce central nervous system symptoms such as light-headedness, headache, fatigue, and drowsiness [4]. 

The U.S. Occupational Safety and Health Administration has established an eight-hour time-weighted average exposure limit of 0.1 ppm (0.1 mg/VO ) for diborane which is also the threshold limit value (TLV) adopted by the American Conference of Governmental Industrial Hygienists. [2] and [3]... 

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