Tribromide, boron

TOXIC BY INHALATION, REACTS VIOLENTLY WITH WATER, CAUSES BURNS 

Colorless, fuming liquid with a pungent odor bp, 90°C.  

Reacts violently with water.2 Decomposed by alcohol.1 

Sodium. Mixture with sodium metal explodes on impact.3 

Reacts violently when poured into an excess of water and explosively if water is poured into it. Vessels containing boron tribromide should be cleaned with dry nonpolar solvents, never with water.4,5 

Catalyst in manufacture of diborane, ultrahigh-purity boron, and semiconductors 

Toxicology. Boron tribromide is expected to be an irritant of the eyes, nose, and mucous membranes. 

Boron tribromide reacts violently and explosively with water to yield hydrogen bromide.  

Effects of short-term exposure are expected to be irritation of the eyes, nose, throat, and skin. Pulmonary edema may result from acute respiratory exposure. Contact with skin or the eyes can cause burns. In one case the liquid splashed in the eyes caused no immediate pain but resulted in permanent corneal injury. 

The metathesis outlined in the equation produces [ B]Br3 in unsatisfactory yield unless a large excess of AlBra is used. A ratio of K[( B]F4] AlBra = 1 10 is the most suitable.  

The starting material, K[[ B]F4], is readily prepared by dissolving [ B](OH)a in hydrofluoric acid, and neutralizing the solution with aqueous KOH or K2CO3. Although any pure, freshly sublimed AlBra can be used in the preparation of [ B]Bra, it is advisable to synthesize aluminum bromide shortly before it is used. 

A 500-mL round-bottomed flask is charged with 35.0 g (1.3 mole) of aluminum turnings and a Teflon oated magnetic stirring bar Oength 2.5 cm). The flask 

Part of the aluminum bromide deposits on the cooler parts of the flask, forming colorless crystals. The dropping rate is adjusted so that the AlBr3 vapor does not reach the coil of the reflux condenser. A pressure drop observed towards the end of the reaction can be readily equalized by slowly admitting nitrogen 

After removal of the oil bath, nitrogen gas is admitted through S4 until the pressure has equalized and the flask FI has cooled to room temperature. This flask contains KAIF4, Al, and excess AlBr3. Part of the excess AlBf3 can be recovered by sublimation in a vacuum. The residue may then be removed from the flask by slowly and carefully hydrolyzing its contents over a period of days by adding small quantities of water. This procedure requires an efficient hood. 

Kricheldorf, H. R. a-Aminoacid-N-Carboxy-Anhydride and Related Heterocycles. Springer Berlin, 1987 pp 3-58. Blacklock, T. J. Hirschmann, R. Veber, D. F. The Peptides, Academic New York, 1987 Vol. 9. pp 39-102. 

Juliatiek Roestamadji Shahriar Mobashery Wayne State University, Detroit, MI, USA 

Form Supplied in colorless, fuming liquid a 1.0 M solution in dichloromethane and hexane BBr3-Me2S complex is available as either a white solid or a 1.0 M solution in dichloromethane. 

Handling, Storage, and Precautions BBr3 is highly moisture sensitive and decomposes in air with evolution of HBr. Store under a dry inert atmosphere and transfer by syringe or through a Teflon tube. It reacts violently with protic solvents such as water and alcohols. Ether and THE are not appropriate solvents. 

Removal of Protecting Groups. BBr3 is highly Lewis acidic. It coordinates to ethereal oxygens and promotes C-O bond cleavage to an alkyl bromide and an alkoxyborane that is hydrolyzed to an alcohol during workup (eq 1)  

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The boron so obtained is an amorphous powder. It can be obtained in the crystalline state by reducing the vapour of boron tribromide with hydrogen, either in an electric arc or in contact with an electrically-heated tungsten filament ... 

For adding dopiag impurities duriag vapor-phase growth, a gaseous or easily vaporizable Hquid compound is metered, added to the siUcon source gas stream, and reduced along with the siUcon compound. Typical examples are diborane, 2 phosphine, and boron tribromide, BBr. ... 

Conversion to a more facile, sulfur-derived, leaving group can be achieved by treatment with sodium thiosulfate or salts of thio and dithio acids (75,87). Under anhydrous conditions, boron tribromide converts the 3 -acetoxy group to a bromide whereas trimethyl silyl iodide gives good yields of the 3 -iodide (87,171,172). These 3 -halides are much more reactive, even when the carboxyl group is esterified, and can be displaced readily by cyano and by oxygen nucleophiles (127). 

The reaction is irreversible and can be used to synthesize aUphatic and aromatic esters. In addition, there are no complications involving water removal or azeotrope formation. Boron tribromide can be used ia place of boron trichloride, but the bromide has a stronger tendency to halogenate the alkyl group of the alcohol (26). Boron tritiuoride does not give the ester, but gives either a complex or dehydrated product. 

Boron tribromide [10294-33A], BBr, is used in the manufacture of diborane and in the production of ultra high purity boron (see Boron, ELEMENTAL BoRON COMPOUNDS). Anhydrous aluminum bromide [7727-15-3], AIBr., is used as an acid catalyst in organic syntheses where it is more reactive and more soluble in organic solvents than AlCl. Tballium bromide [7789AOA], TlBr, is claimed as a component in radiographic image conversion panels (39). 

Boron tribromide is reported to be more effective than iodotrimethylsilane for cleaving aryl methyl ethers. ... 

BBr3, CH2CI2, -10°, 1 h -> 25°, 2 h, 80-100% yield. Benzyl carbamates of larger peptides can be cleaved by boron tribromide in trifluoro-acetic acid, since the peptides are more soluble in acid than in methylene chloride. ... 

Benzoyl azide Biphenyl triozonide Boron tribromide Bromine azide Bromine solutions... 

Boron tribromide replaces fluonne with bromine on tertiary or secondary carbons however, trifluoromethyl groups are inert in this reaction [70] (equation 57). 

Fenoldopam (76) is an antihypertensive renal vasodilator apparently operating through the dopamine system. It is conceptually similar to trepipam. Fenoldopam is superior to dopamine itself because of its oral activity and selectivity for dopamine D-1 receptors (D-2 receptors are as.sociated with emesis). It is synthesized by reduction of 3,4-dimethoxyphenylacetonitrile (70) to dimethoxyphenethylamine (71). Attack of diis last on 4-methoxystyrene oxide (72) leads to the product of attack on the epoxide on the less hindered side (73). Ring closure with strong acid leads to substituted benzazepine 74. O-Dealkylation is accomplished with boron tribromide and the catechol moiety is oxidized to the ortho-quinone 75. Treatment with 9NHC1 results in conjugate (1,6) chloride addition and the formation of fenoldopam (76) [20,21]. 

Xn. Demethylation of Aryl Methyl Ethers by Boron Tribromide... 

Boron tribromide reacts with ethers by the sequence shown (22). The boron complex... 

Pyrrolobenzotriazine 43 was obtained by reaction of 42 with nitrous acid. Its demethylation with boron tribromide gave 44, whose oxidation... 

The phenyl ether linkage of butoxy substituted 44 was cleaved with boron tribromide to give a hexaphenol derivative (45) in 60% yield (Scheme 14). The hexaphenol derivative was found to be remarkably soluble in most polar organic solvents, such as ethanol, DMF, DMSO, and dioxane, as well as in aqueous base solution. Condensation with octanoic acid in the presence of DCC and catalytic H+ afforded the inverse ester (46) in high yield. 

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