Hydrogen bromide exposure

Bromination-desilylbromination of fS-silyl ketones. The preliminary work on protection of oc,/ -enones by this sequence (8, 196-197) has been perfected in several respects1 and shown to be generally applicable to synthesis of oy8-enones.2 Either bromine or phenyltrimethylammonium tribromide (PTAB, 1,855 2,328 4, 386) can be used. In either case, bromine is introduced mainly at the a-position adjacent to the /1-silyl group. Surprisingly, the undesired a -bromo-/(-silyl ketone is converted to the a-bromo-/)-silyl ketone on exposure to hydrogen bromide at 20°. No other acids can clTccl this conversion. Desilylbromination is generally effected with DBU or F". The sequence is applicable to synthesis of a-methylene ketones (equation I) and lactones. 

Use and exposure Hydrogen bromide is a colorless or faintly yellow-colored, corrosive gas it is highly toxic, with a sharp, unpleasant, irritating odor. It can also be found as a liquid, either as hydrobromic acid (hydrogen bromide dissolved in water) or as a compressed gas under pressure (anhydrous... 

Toxicity and health effects Human exposure to hydrogen bromide causes redness, pain, frostbite, and severe burns and blisters on the skin. Eye contact with the liquid causes redness, pain, severe burns, and possible permanent eye damage. It causes nose and throat irritation, watery eyes, bloody nose, nausea, vomiting, chest pain and/or light-headedness, coughing, shortness of breath, fluid in the lungs or pulmonary edema, unconsciousness, low blood pressure, rapid heartbeat, kidney failure, coma, and death. ... 

Exposure limits OSHA has set a PEL for hydrogen bromide as 3 ppm in an 8-hour period (TWA). Similarly, NIOSH has set a recommended exposure limit (REL) for hydrogen bromide of 3 ppm in working exposure. The ACGIH has set a ceiling of 3 ppm for hydrogen bromide as the working exposure. ... 

Hydrohalogenation of crotonic acid in a crystalline a-cyclodextrin complex gives ( + )-(S)-3-bromobutanoic acid with 58% enantiomeric excess146. Asymmetric reactions catalyzed by cyclodcxtrin have been attempted in solution but all of these reactions afforded the products in low optical yields. Exposure of crystalline cyclodextrin complexes to gaseous hydrogen bromide and hydrogen chloride at 20 °C gives better optical yields. 

PHYSICAL PROPERTIES reddish solid lustrous, ductile, and malleable metal face-centered cubic (fee) structure becomes dull upon exposure to air becomes coated with a green layer of basic carbonate in moist air odorless solid slowly soluble in ammonia water soluble in nitric acid, hot concentrated sulfuric acid, and hydrogen bromide very slightly soluble in hydrochloric acid and ammonium hydroxide insoluble in hot and cold water copper fume is characterized by finely divided black particulates dispersed in air MP (1083°C, 1981°F) BP (2595°C, 4703°F) DN (8.94 g/cm ) SG (8.94) CP (0.092 cal/g/° C solid at 20° C, 0.112 cal/g/°C liquid at 20°C) HV (1150 cal/g) VD (NA) VP (0 mmHg approximately) MOHS HARDNESS (3.0). 

Aluminum bromide, incidentally, shows an interesting type of hydrolysis. With a very little water, such as it absorbs on exposure to moist air, it forms an oxybromide that is insoluble in water, and hydrogen bromide is lost. But if enough water is added at the start, it reacts with considerable evolution of heat to give a clear solution that reacts acid to litmus and probably contains colloidal aluminum hydroxide most of the aluminum, however, is in the form of the very stable hydrated ion Al(OH2)6. The hydrolysis is repressed by the very strong hydration of the cation. A similar hydration occurs when stannic chloride dissolves in water (Experiment 19). 

Difluorodibromomethane (dibromodifluoromethane, Freon 1292 [CAS 75-61-6]) Based on animal tests, vapors irritate the respiratory tract. A CNS depressant. By analogy to other freons, may cause cardiac arrhythmias. In test animals, high-level chronic exposures caused lung, liver, and CNS injury. See also p 209. 100 ppm 2000 ppm Heavy, volatile, colorless liquid vinth an obnoxious, distinctive odor. Vapor pressure is 620 mm Hg at 20 C (68°F). Not combustible. Thermal-breakdown products include hydrogen bromide and hydrogen fluoride. 

Carefully neutralize spills of hydrobromic acid with a suitable agent such as powdered sodium bicarbonate, further dilute with absorbent material, place in an appropriate container, and dispose of properly. Dilution with water before applying the solid adsorbent may be an effective means of reducing exposure to hydrogen bromide vapor. Respiratory protection may be necessary in the event of a large spiU or release in a confined area. 

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