Hydrobromic acid addition reaction product

This would be equivalent to the contention that the earth is flat because nobody had gathered evidence against this philosophically satisfactory shape. There are, indeed, some pieces of evidence against our first attempt to explain this seemingly simple reaction. The first is the consumption of one full mole of bromine in the reaction. The second is the absence of hydrobromic acid among the products of the first step. These facts can only be accommodated by addition of molecular bromine across the double bond of I to give a trans diaxial dibromo derivative (V). In actual fact, a compound featuring no vinyl protons after treatment with bromine in DMF was observed. 

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,... 

Later, Linda and Marino84, 90, 180 were able to compare the relative reactivities of all four fundamental systems (furan, thiophene, selenophene, and pyrrole) toward bromination by molecular bromine in acetic acid. Unfortunately, the comparison could not be made on the unsubstituted rings for the following reasons first, the rates of substitution for furan and pyrrole were too high to be followed by standard kinetic techniques second, furan and pyrrole undergo ring fission and/or polymerization under the influence of the hydrobromic acid formed in the reaction finally, furan tends to give addition as well as substitution products in the reaction with bromine.1818. 

Cyclopropane-1,1-dicarboxylic acid (30a) reacted with hydrobromic acid to (2-bro-moethyl)malonic acid (31a) . In a similar reaction, ethyl 1-acetylcyclopropane-l-carboxylate (31b) ( C enriched) was converted to 5-bromopentan-2-one upon treatment with hydrobromic acid and decarboxylation." In 2-benzoyl-3-phenylcyclopropane-1,1-dicarboxylic acid (31c), two different activating functions are present and can influence the addition of hydrogen bromide. In fact, products arising from the cleavage of either bond that link the phenyl-substituted carbon were isolated. Both primary products had lost hydrogen bromide and carbon dioxide. 

Addition of thiocyanogen to r/.v-cyclooctcne affords trans-1,2-dithiocyanocyc o-octane (12), which is converted quantitatively into the imino dithiocarbonate (13) by refluxing for 2 hrs. with 47% hydrobromic acid, followed by neutralization with sodium carbonate. The tra/w-thiocarbonate (14) is produced from this imine by reaction with hydrogen sulfide in ethanol and converted into /rarcs-cyclooctene (15) by heating with triisooctyl phosphite at 135° (41 hrs.), using the entrainment technique to remove product as formed. 

A noteworthy difference is observed in the condensation of thiosemicarbazide with aromatic a-halocarbonyl compounds in comparison to aliphatic a-halocarbonyl compounds. It has been found26 that the reaction of phenacyl bromide with thiosemicarbazide furnishes 5-phenyl-1,3,4-thiadiazin-2-amine together with a small amount of 5-phenylthiazolc-2-hydrazine, Similarly, the reactions of thiosemicarbazide with 2-bromo-l,2-diphenylethan-l-one,7 8,41 2-bro-mo-l-phenylpropan-l-one,10,41 and 2-bromo-l-phenylbutan-l-one 10,41 in ethanolic solution give 1,3,4-thiadizines. However, the main products are the thiazole-2-hydrazine derivatives (cf. Houben-Weyl, Vol. E8b, p 72ff). The addition of an equimolar amount of 48% hydro-bromic acid results in the exclusive formation of the 1,3,4-thiadiazines 2 a, c, and d. When the condensations of thiosemicarbazide with 2-bromo-l,2-diphenylethan-l-one, 2-bromo-1-phenylpropan-l-one or 2-bromo-l-phenylbutan-l-one are performed in ethanol at room temperature, the S-(oxoalkyl)-isothiosemicarbazide hydrobromides are formed as open-chain intermediates and also undergo cyclization in ethanol upon addition of an equimolar amount of 48% hydrobromic acid to furnish 2 a, c, and d. 

The hydrobromic acid-acetic acid method works well using 33-48% of hydrobromic acid in acetic acid (which can be purchased) with phenol as a bromine scavenger. Phenol is not necessary. The reaction can be carried out at room temperature for an extended period of time, under reflux, refluxed in a sealed tube for an extended period of time, or in a sealed tube at 120°C. Isolation of the product is easier than with the use of concentrated sulfuric acid. Usually, the addition of a large amount of an organic solvent such as ether causes the product to separate as the hydrobromide salt. 

The fact that methyl alcohol is much more readily converted into methyl iodide by hydriodic acid than into methyl chloride by hydrochloric acid, is evidence that the reactions involved are probably not of the same nature as those of neutralization in inorganic chemistry. It is probable that the reaction between the alcohol and the halogen acid involves the formation of an intermediate addition-product, which subsequently decomposes into water and the alkyl halide. That such addition-products can exist is shown by the fact that when methyl alcohol is treated with liquid hydrobromic acid, a compound having the composition CHaOH.HBr is formed. 

Thus, as shown in Scheme 14.7, the reaction of ethyl formate with ethyl acetate in ether in the presence of sodium metal yielded ethyl sodium formyl acetate. Then, the addition product of ethyl bromide with thiourea was treated with aqueous base and the ethyl sodium formyl acetate was added so that, after standing for a number of hours, acidification with acetic acid yielded 2-ethylmercapto-6-oxypyrimidine. Treatment of the latter with phosphorus pentachloride yielded the corresponding 2-ethylmercapto-6-chloropyrimidine subsequent alcoholic ammonolysis generated 2-ethylmercapto-6-aminopyrimidine and boiling aqueous hydrobromic acid resulted in the production of 6-amino-2-oxypyrimidine (cytosine). 

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