Anhydrous hydrobromic acid

Synonyms Hydrobromic acid anhydrous hydrobromic acid... 

Synonyms and trade names anhydrous hydrobromic acid, anhydrous hydrogen bromide, hydrobromic acid... 

SYNS ACIDE BROMHYDRIQUE (FRENCH) ACIDO BROMIDRICO (ITALIAN) ANHYDROUS HYDROBROMIC ACID BROxMOWODOR (POLISH) BROMWASSERSTOFF (GERiMAN) BROOxMWATER-STOF (DUTCH) HYDROBROMIC ACID SOLUTION, >49% hydrobromic acid (UN 1788) pOT) HYDROBROMIC ACID SOLUTION, not >49% hydrobromic acid (UN 1788) pOT) H T)ROGEN BROMIDE (ACGIH.OSHA,-MAK) HYDROGEN BROMIDE, anhydrous (UN 1048) pOT)... 

Among the possible approaches to the preparation of 4-aminoimidazoles is the cyclization of a-cyanoalkyl cyanamidcs (34). When treated with anhydrous hydrobromic acid they give 4(5)-amino-2-bromoimidazoles (35) in a process which bears formal similarities to amidine cyclizations (Scheme 2.2.12). The instabilities of many 4(5)-aminoimidazolcs necessitates their conversion into the more easily handled acetyl derivatives using acetic anhydride [46] (see also Section 3.1.1). Table 2.2.4 lists some examples. 

Although prolonged heating of the pyrroline (192) does not lead to further ring expansion, a second cyclopropylimine rearrangement takes place on heating in the presence of anhydrous hydrobromic acid at 140°C for 10 min, giving after hydrolysis the pyrrolizidinone (193) (equation 128). This sequence opens a route to pyrrolizidines that are of obvious interest in natural product synthesis. 

Finally, the data related to the application of ionic liquids for the cleavage of ethers are also notable. Chloroaluminates [44], anhydrous hydrobromic acid in 1-methylimidazole [45] and concentrated hydrobromic acid in [BMIM][BF4] or p-TsOH/[BMIM][Br] in [BMIM][BF4] [46] have been used to regenerate phenols from the corresponding aryl alkyl ethers. In ionic liquids, in the presence of an efficient proton donor (HBr or TsOH), the bromide anion behaves as a strong nucleophile able to cleave ethers. These latter reactions seem, therefore, to indicate that, as opposed to the situation in the absence of adds, the nudeophihcity of the bromide anion in ionic liquids in the presence of proton donors is higher than in molecular solvents (both pro tic and aprotic). This behavior may be a consequence of a... 

Anhydrous gypsum. See Calcium sulfate Anhydrous hydrobromic acid. See Hydrobromic acid... 

Synonyms Anhydrous hydrobromic acid Hydrobromic acid sol n. Hydrogen bromide Hydrogen bromide anhydrous Classification Inorganic gas... 

Chemical Symbol HBr Synonyms Anhydrous hydrobromic acid CAS Registry Number 10035-10-6 DOT Classification Nonflammable gas DOT Label Nonflammable gas Transport Canada Classification 2.4 UN Number UN 1048... 

II Cleavage reaction with anhydric hydrobromic acid at -78 ... 

Mix 40 g. (51 ml.) of isopropyl alcohol with 460 g. (310 ml.) of constant boiling point hydrobromic acid in a 500 ml. distilling flask, attach a double surface (or long Liebig) condenser and distil slowly (1-2 drops per second) until about half of the liquid has passed over. Separate the lower alkyl bromide layer (70 g.), and redistil the aqueous layer when a further 7 g. of the crude bromide will be obtained (1). Shake the crude bromide in a separatory funnel successively with an equal volume of concentrated hydrochloric acid (2), water, 5 per cent, sodium bicarbonate solution, and water, and dry with anhydrous calcium chloride. Distil from a 100 ml. flask the isopropyl bromide passes over constantly at 59°. The yield is 66 g. 

Allyl Bromide. Introduce into a 1-litre three-necked flask 250 g. (169 ml.) of 48 per cent, hydrobromic acid and then 75 g. (40-5 ml.) of concentrated sulphuric acid in portions, with shaking Anally add 58 g. (68 ml.) of pure allyl alcohol (Section 111,140). Fit the flask with a separatory funnel, a mechanical stirrer and an efficient condenser (preferably of the double surface type) set for downward distillation connect the flask to the condenser by a wide (6-8 mm.) bent tube. Place 75 g. (40 5 ml.) of concentrated sulphuric acid in the separatory funnel, set the stirrer in motion, and allow the acid to flow slowly into the warm solution. The allyl bromide will distil over (< 30 minutes). Wash the distillate with 5 per cent, sodium carbonate solution, followed by water, dry over anhydrous calcium chloride, and distil from a Claisen flask with a fractionating side arm or through a short column. The yield of allyl bromide, b.p. 69-72°, is 112 g. There is a small high-boiling fraction containing propylene dibromide. 

Dibromobutane from 1 4 butanediol). In a 500 ml. threenecked flask fltted with a stirrer, reflux condenser and dropping funnel, place 154 g. (105 ml.) of 48 per cent, hydrobromic acid. Cool the flask in an ice bath. Add slowly, with stirring, 130 g. (71 ml.) of concentrated sulphuric acid. To the resulting ice-cold solution add 30 g. of redistilled 1 4-butanediol dropwise. Leave the reaction mixture to stand for 24 hours heat for 3 hours on a steam bath. The reaction mixture separates into two layers. Separate the lower layer, wash it successively with water, 10 per cent, sodium carbonate solution and water, and then dry with anhydrous magnesium sulphate. Distil and collect the 1 4-dibromo-butane at 83-84°/12 mm. The yield is 55 g. 

Sodium bromide [7647-15-6] NaBr, the most common and available alkali bromide, is a salt of hydrobromic acid (see Bromine compounds). Sodium bromide crystallines from aqueous solution as a 3466-08-5] NaBr-2H20, below 51°C. Above 51°C, it crystallines as the anhydrous compound. 

After this time the excess hydrobromic acid is neutralized with excess sodium carbonate, of which about 100 g. of anhydrous salt is required. To the aqueous solution is then added about 100 g. of anhydrous sodium sulfate until some of the solid does... 

B. a-Hydroxyphenazine (demethylalion). A solution of 4.2 g. (0.02 mole) of a-methoxyphenazine, from A above, in 125 ml. of 55% hydrobromic acid (Note 7) is placed in a 250-ml. round-bottomed flask fitted with a reflux condenser. The flask is immersed in an oil bath, and the solution is heated to 110-120° for 5 hours the evolved gases are absorbed with water in a trap. The reaction mixture is cooled to room temperature, diluted with about 125 ml. of water, almost neutralized with sodium hydro.xide (Note 8), and extracted six times with 30- to 40-ml. portions of ether. The combined ether extracts arc extracted with 25-ml. portions of 10% sodium hydroxide solution (Note 9) until no more purple sodium salt is remox ed from the ether. The aqueous extracts are combined, made acid to litmus with dilute acetic acid, and re-extracted four times with 50-ml. portions of ether. The combined ether extracts are dried over anhydrous sodium sulfate, and the ether is removed by distillation on a steam bath. The residue is recrystallized as follows It is dissolved in the least possible amount of hot alcohol, water... 

Chemical Designations - Synonyms Hydrobromic acid, anhydrous Hydrogen bromide, anhydrous Chemical Formula HBr. 

It is common practice to refer to the molecular species HX and also the pure (anhydrous) compounds as hydrogen halides, and to call their aqueous solutions hydrohalic acids. Both the anhydrous compounds and their aqueous solutions will be considered in this section. HCl and hydrochloric acid are major industrial chemicals and there is also a substantial production of HF and hydrofluoric acid. HBr and hydrobromic acid are made on a much smaller scale and there seems to be little industrial demand for HI and hydriodic acid. It will be convenient to discuss first the preparation and industrial uses of the compounds and then to consider their molecular and bulk physical properties. The chemical reactivity of the anhydrous compounds and their acidic aqueous solutions will then be reviewed, and the section concludes with a discussion of the anhydrous compounds as nonaqueous solvents. 

To 10 g of cyclohexane-1,4-oxide is added 48% aqueous hydrobromic acid (60 g). The phases are mixed thoroughly and allowed to stand at room temperature until the solution separates into two layers (usually 5 days). The mixture is saturated with sodium chloride and extracted twice with 25-ml portions of ether. The ether layer is washed with an equal volume of saturated sodium bicarbonate solution, then with the same amount of water. Finally, the ether solution is dried over anhydrous sodium sulfate, the ether is evaporated, and the residue is allowed to cool, whereupon crystallization should follow. The crude product may be recrystallized from petroleum ether giving material of mp 81-82° (yield, 11 g). 

A solution of 3.1 g of (2-benzoyl-4-chlorophenyl-carbamoylmethyl)carbamic acid benzyl ester in 30 cc of 20% hydrobromic acid in glacial acetic acid was stirred for 45 minutes at room temperature. On addition of 175 cc of anhydrous ether, a gummy solid precipitated. After several minutes the ether solution was decanted. The resultant 5-chloro-2-gly-cylaminobenzophenone was not isolated, but about 155 cc of ether was added to the residue and after chilling in an ice bath, 10% sodium hydroxide was added until the mixture was alkaline. The ether layer was then separated, washed twice with water and dried over sodium sulfate. After filtration, the ether solution was concentrated to dryness in vacuo. The residue was crystallized from benzene to yield 7-chloro-5-phenyl-3H-1,4-benzodiazepin-2(1 H)-one. 

---