Hydrobromic acid: reaction with

A given alcohol is treated with 25 percent excess of aqueous (48 per cent) hydrobromic acid together with sulfuric acid. The mixture is refluxed in order to convert the alcohol as completely as possible into the corresponding bromide, and the latter is then removed from the reaction mixture by distillation. Slight variations from this procedure depend upon the physical and chemical properties of the alcohol used, or of the bromide formed in the reaction. For example, in the preparations of ethyl and allyl bromides, the reaction mixture is not refluxed because of the volatility of the former compound, and because of the chemical reactivity of the latter in the preparation of wo amyl bromide, too large a proportion of sulfuric acid may produce appreciable decomposition while halides of high molecular weight, because of their low volatility, are separated from the reaction mixture mechanically, instead of by distillation. 

The synthesis of tazobactam from 6-APA (Scheme 6.15) proceeded via the 2- -(chloromethyl)penam ester (81 a), which was first prepared by Gottstein and co-workers [47] during the synthesis of 2-/S-(chloromethyl)-2-a-methylpenam-3a-carboxylic acid 1,1-dioxide (29). 6-APA (8) was converted to 6a-bromopenicillanic acid (77) by treatment with sodium nitrite and hydrobromic acid. Oxidation with peracetic acid in the presence of benzophenone hydrazone gave benzhydryl 6a-bromopenicillanate-l-oxide (78) and reduction with zinc and acetic acid gave benzhydryl penicillanate-1-oxide (79). The unsymmetrical azetidinone disulphide (80) was obtained by heating with 2-mercaptobenzothiazole reaction with copper (II) chloride... 

An analogous reaction takes place less readily with hydrobromic acid, but with hydrochloric acid no compound is formed. The difference in reactivity of the halogens and halogen acids as shown in their behavior with ethylene, is, in general, characteristic of these substances. Chlorine is the most active halogen and hydriodic acid is the most active acid. 

Reactions that form water Another type of double-replacement reaction that occurs in an aqueous solution produces water molecules. The water molecules produced in the reaction increase the number of solvent particles. Unlike reactions in which a precipitate forms, no evidence of a chemical reaction is observable because water is colorless, odorless, and already makes up most of the solution. For example, when you mix hydrobromic acid (HBr) with a sodium hydroxide solution (NaOH), as shown in Figure 9.18, a double-replacement reaction occurs and water is formed. The chemical equation for this reaction is shown below. 

The solution of ketone dihydrobromide in 40% HBr was heated to 85 °C and, under mechanical stirring, a solution of 138 g bromine in 275 mL 40% HBr was added over a period of 20 min, during which the temperature was maintained at 85-90° C. The product ( -bromo-e-(2-phenylcinchoninyl)-A-amylamine dihydrobromide) began to crystallize out before all the bromine was added. The mixture was heated to the boiling point and 250 mL 40% HBr was added, but the product did not dissolve. The reaction mixture was then chilled, and the precipitate was collected on a sintered glass funnel. It was washed by suspension in isopropanol to remove hydrobromic acid, then with acetone until the filtrate was colorless, and finally with ether. After drying in vacuo over NaOH, 334.5 g of a... 

The preparation of 2-bromopyridine from 2-amiaopyridine was first reported by Chichibabin and Ryasanjev in 1915/ however, the yield was low/ In 1934, Craig reported a modified method for preparing 2-bromo-pyridine in high yield from 2-amino-pyridine, therefore, this reaction is called Craig 2-bromo-pyridine synthesis. In this reaction, aconcen-trated aqueous solution of sodium nitrite and 2-amino-pyridine was added to a concentrated hydrobromic acid saturated with bromine. It was found that 2 mole of bromine and at least 2.5 mol of sodium nitrite are necessary to obtain an optimal yield of 2-bromo-pyridine. This method has been used to prepare 2-bromo-pyrimidines. ... 

Traugott Sandmeyer (Wettingen, 15 September 1854-Zurich, 9 April 1922) was Victor Meyer s lecture assistant and participated in the discovery of thiophen (see p. 810). He discovered the Sandmeyer reaction for the preparation of halogen derivatives of aromatic hydrocarbons by warming a solution of a diazonium compound with cuprous chloride and hydrochloric acid, or cuprous bromide and hydrobromic acid, or with hydriodic acid or potassium... 

The reactions of fluoro and chlorosulfonic acid, sulfuric, pyrosulfuric, hydrochloric and hydrobromic acids, together with tri-, di- and monochloroacetic acids with anthrone 3 were studied by conductometric and potentiometric techniques, ... 

One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide ... 

By treatment of the alcohol with a mixture of constant boiling point hydrobromic acid and concentrated sulphuric acid the presence of sulphuric acid results, as a rule, in more rapid reaction and improved 3delds. A typical example is ... 

The hydrobromic acid sulphuric acid solution may be prepared by the reduction of bromine with sulphurous acid (Section 11,49, 1) distillation of the reaction product is unnecessary ... 

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. 

Continue the passage of bromine vapour until the solution in A assumes a distinctly yellow colour (2-3 hours) the reaction is then complete. Filter the tribromoaniline on a Buchner funnel, wash it thoroughly with water to remove hydrobromic acid, and suck as dry as possible. Ilecr3 stallise from methylated (or rectified) spirit. The yield is 22 g. m.p. 120°. 

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... 

The last-named reaction provides an excellent method for the preparation of a-substituted glutaric acids the intermediate alkyl (aryl) -2-cyanoethyl-malonate is both hydrolysed and decarboxylated re ily by boiling with an excess of 48 per cent, hydrobromic acid solution. 

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) Sn2 substitution at the allylic alcohol with hydrobromic acid followed by reaction with the requisite secondary amine, or... 

The synthesis of these disubstituied thioureas takes place in three steps. First the alkyl bromide is prepared by the action of hydrobromic acid on the corresponding alcohol (518). Then the dialkylcyanamide is obtained by treatment at 25°C with calcium cyanamide. The yields are of the order of 30 to 60%. Thioureas are obtained in a third step from the cyanamide by reaction at 40 C with HjS in the presence of pyridine. Yields ranged from 57 to 90% (518),... 

Reaction with Halogen Nucleophiles. Hydrochloric acid [7647-01-0] hydrobromic acid [10035-10-6] and hydroiodic acid [10034-85-2] react readily with ethyleneimine (3) to give the corresponding P-halogenoethylamines (20,21). 

Nitric acid gives nitrates and concentrated (48%) hydrobromic acid gives olefins, upon reaction with alkanolamines. 

Other Reactions. Primary amyl alcohols can be halogenated to the corresponding chlorides by reaction with hydrogen chloride in hexamethylphosphoramide (87). Neopentyl chloride [753-89-9] is formed without contamination by rearrangement products. A convenient method for preparing / f/-amyl bromide and iodide involves reaction of / f/-amyl alcohol with hydrobromic or hydroiodic acid in the presence of Li or Ca haUde (88). The metal haUdes increase the yields (85 —95%) and product purity. 

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). 

In the petroleum (qv) industry hydrogen bromide can serve as an alkylation catalyst. It is claimed as a catalyst in the controlled oxidation of aHphatic and ahcycHc hydrocarbons to ketones, acids, and peroxides (7,8). AppHcations of HBr with NH Br (9) or with H2S and HCl (10) as promoters for the dehydrogenation of butene to butadiene have been described, and either HBr or HCl can be used in the vapor-phase ortho methylation of phenol with methanol over alumina (11). Various patents dealing with catalytic activity of HCl also cover the use of HBr. An important reaction of HBr in organic syntheses is the replacement of aHphatic chlorine by bromine in the presence of an aluminum catalyst (12). Small quantities of hydrobromic acid are employed in analytical chemistry. 

Excess of bromine converts each methylpteridine compound into the dibromomethyl derivative which on hydrolysis gives good yields of the corresponding aldehyde. An interesting variation of the reaction conditions was found in the treatment of the C- methylpteridines with POBra, which leads to the same mono- and di-bromomethyl derivatives. 6-Methylpterin reacts with more difficulty and with an excess of bromine in hydrobromic acid forms the... 

Oxaziridines are powerful oxidizing agents. Free halogen is formed from hydrobromic acid (B-67MI50800). Reduction by iodide in acidic media generally yields a carbonyl compound, an amine and two equivalents of iodine from an oxaziridine (1). With 2-alkyl-, 2-acyl and with N-unsubstituted oxaziridines the reaction proceeds practically quantitatively and has been used in characterization. Owing to fast competing reactions, iodide reduction of 2-aryloxaziridines does not proceed quantitatively but may serve as a hint to their presence. 

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. 

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... 

One common kind of reaction involves proton transfer occurring as a rapid equilibrium preceding the rate-determining step, for example, in the reaction of an alcohol with hydrobromic acid to give an alkyl bromide ... 

Chemical Reactivity - Reactivity with Water Moderate reaction with the evolution of heat Reactivity with Common Materials Rapidly absorbs moisture, forming hydrobromic acid. Highly corrosive to most metals, with the evolution of flammable and explosive hydrogen gas Stability During Transport Stable Neutralizing Agents for Acids and Caustics Flush with water and apply powdered limestone, slaked lime, soda ash, or sodium bicarbonate Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

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