Hydrobromic acid Additions

Addition of concentrated sulphuric acid to a solid bromide produces hydrobromic acid, but also some bromine (brown vapour). 

In the preparation of bromo compounds by the Sandmeyer reaction, the amine is generally diazotised in sulphuric acid solution (or in hydrobromic acid solution), and the resulting aryldiazonium sulphate (or bromide) is treated with a solution of cuprous bromide in excess of hydrobromic acid the addition... 

In a 1 or 1-5 htre round-bottomed flask prepare a solution of 53-5 g. of o-toluidine in 170 ml. of 48 per cent, hydrobromic acid, cool to 5° by immersion in a bath of ice and salt. Diazotise by the gradual addition of a solution of 36 -5 g. of sodium nitrite in 50 ml. of water stopper the flask after each addition and shake until all red fumes are absorbed. Keep the temperature between 5° and 10°. When the diazotisation is complete, add 2 g. of copper powder or copper bronze, attach a reflux condenser to the flask, and heat very cautiously on a water bath. Immediately evolution of gas occurs, cool the flask in crushed ice unless the... 

The basic premise for making bromosafrole has been to mix sa-frole with Hydrobromic Acid (a.k.a. hydrogen bromide, HBr). That s it. The HBr does what is called a Markovnikov addition reaction whereby the HBr sees the allyl double bond of safrole and preferentially attaches its hydrogen to the gamma carbon and its bromine to the middle beta carbon (don t ask). 

A considerable amount of hydrobromic acid is consumed in the manufacture of inorganic bromides, as well as in the synthesis of alkyl bromides from alcohols. The acid can also be used to hydrobrominate olefins (qv). The addition can take place by an ionic mechanism, usually in a polar solvent, according to Markownikoff s rule to yield a secondary alkyl bromide. Under the influence of a free-radical catalyst, in aprotic, nonpolar solvents, dry hydrogen bromide reacts with an a-olefin to produce a primary alkyl bromide as the predominant product. Primary alkyl bromides are useful in synthesizing other compounds and are 40—60 times as reactive as the corresponding chlorides (6). 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

Ethylene bromohydrin has been prepared by the reaction between ethylene glycol and hydrobromic acid and phosphorus tribromide. It has also been prepared by the direct addition of hypobromous acid to ethylene, and by the reaction between ethylene and dilute bromine water. With ethylene oxide now available at a reasonable price, the method described is probably the best because of the high yields and the convenience of reaction. 

The chief difference between the two groups of n/3 and j3y Linsaturatcd acids lies in the behaviour of the additive compounds which they form with hydrobromic acid and bromine. 

Amino-5-bromoselenazole is mentioned in a patent without further details. It is stated to be a starting material for pharmaceutical products. In analogy to the corresponding thiazole compounds, it is stated to be prepared by heating 2-aminoselenazole in aqueous hydrobromic acid under reflux and slow addition of an equivalent amount of bromine. 

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. 

Thebaine is dissolved in aqueous formic acid and treated with 30% HjO neutralization with aqueous ammonia gives 14-hydroxycodeinone. It is hydrogenated to give oxycodone. 90 ml of concentrated hydrobromic acid are heated to 90°C. 9 grams of 14-hydroxydi-hydrocodeinone (oxycodone) are then added under stirring and the mixture is quickly heated to 116°C and kept at this temperature under reflux condenser for 20 minutes, with continued stirring. The resulting brown solution Is diluted with about 90 ml of water and chilled with ice. Aqueous 10% sodium hydroxide solution is now added to alkaline reaction and the liquid is extracted 3 times with 100 cc portions of chloroform. The layers are separated and the aqueous phase is fiitered and acidified by the addition of concentrated aqueous hydrochloric acid, treated with charcoal and filtered. 

A 0.1375 M solution of potassium hydroxide is used to titrate 35.00 mL of0.257 M hydrobromic acid. (Assume that volumes are additive.)... 

Benzofurazan (benz-1,2,5-oxadiazole) reacted with bromine by addition to give a4,5,6,7-tetrabromo adduct. Bromine in hydrobromic acid solution 4-brominated both 5-methyl- and 5-bromo-benzofurazans (74JHC8I3). When 4,7-dinitrobenzofurazan was treated with ammonium chloride in refluxing acetic acid, nucleophilic displacement gave rise to the 4-chloro-7-nitro derivative (83URP1004375). Naphtho[l, 2-c]furazans (42) are mainly 4-halogenated, but there is minor substitution in the 8-position (73CHE1331). 

Explain what happens to (a) the pH of a solution of phosphoric acid after the addition of solid sodium dihydrogen phosphate (b) the percentage deprotonation of HCN in a hydrocyanic acid solution after the addition of hydrobromic acid (c) the concentration of H ions when pyridinium chloride is added to an aqueous solution of the base pyridine. 

The mixed aliphatic - aromatic ethers are somewhat more reactive in addition to cleavage by strong hydriodic acid and also by constant b.p. hydrobromic acid in acetic acid solution into phenols and alkyl halides, they may be bromi-nated, nitrated and converted into sulphonamides (Section IV,106,2). 

As illustrated in Figure 12, the reaction mixture contains mono-, di-, and tri-brominated glycols, hydrobromic acid, and water. The mixture is extremely corrosive, and the reactor is operated at a temperature just above the freezing point of the product. The key to successfully sampling this mixture was the use of a corrosion-resistant tantalum sampling system. In addition, the sample line was continuously flushed with reactor solvent except during sampling. 

Mediated by Tin. In 1983, Nokami et al. observed an acceleration of the reaction rate during the allylation of carbonyl compounds with diallyltin dibromide in ether through the addition of water to the reaction mixture.74 In one case, by the use of a 1 1 mixture of ether/water as solvent, benzaldehyde was allylated in 75% yield in 1.5 h, while the same reaction gave only less than 50% yield in a variety of other organic solvents such as ether, benzene, or ethyl acetate, even after a reaction time of 10 h. The reaction was equally successful with a combination of allyl bromide, tin metal, and a catalytic amount of hydrobromic acid. In the latter case, the addition of metallic aluminum powder or foil to the reaction mixture dramatically improved the yield of the product. The use of allyl chloride for such a reaction,... 

A mixture of 127.5 g. (1 mole) of a good commercial grade of o-chloroaniline and 300 ml. (2.5 moles) of 48% hydrobromic acid (Note 1) in a 2-1. flask set in an ice bath is cooled to 0° by the addition of ice. A solution of 70 g. (1 mole) of sodium nitrite in 125 ml. of water is added rapidly, with stirring, the temperature being kept below 10° by the addition of small pieces of ice. When only about 5 ml. of the sodium nitrite solution remains, further additions are made cautiously until an excess of nitrous acid remains after the last addition (Note 2). 

The excess of bromine is converted into hydrobromic acid by means of formic acid and, finally, after addition of potassium iodide, the iodine liberated is titrated with thiosulphate. 

Bromomethylation of arenes using 1,3,5-trioxane and hydrobromic acid is catalysed by the addition of a phase-transfer catalyst. Yields in excess of 90% are attained using (tetradecyl)trimethylammonium bromide under relatively mild conditions for a range of arenes [55]. Tetra-n-butylammonium bromide is ineffective, suggesting the catalytic effect may be micellar. 

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