Hydrobromic acid substitution reaction product

The prominent role of alkyl halides in formation of carbon-carbon bonds by nucleophilic substitution was evident in Chapter 1. The most common precursors for alkyl halides are the corresponding alcohols, and a variety of procedures have been developed for this transformation. The choice of an appropriate reagent is usually dictated by the sensitivity of the alcohol and any other functional groups present in the molecule. Unsubstituted primary alcohols can be converted to bromides with hot concentrated hydrobromic acid.4 Alkyl chlorides can be prepared by reaction of primary alcohols with hydrochloric acid-zinc chloride.5 These reactions proceed by an SN2 mechanism, and elimination and rearrangements are not a problem for primary alcohols. Reactions with tertiary alcohols proceed by an SN1 mechanism so these reactions are preparatively useful only when the carbocation intermediate is unlikely to give rise to rearranged product.6 Because of the harsh conditions, these procedures are only applicable to very acid-stable molecules. 

Conflicting results have been reported for the reaction of the manno epoxide with hydrochloric acid in acetone. Mukheijee and Srivastava100 claimed that approximately equal amounts of the normal and abnormal products are formed, whereas Newth and Homer 10 reported that 3-substitution (ratio 92 8) mainly occurs, as would be expected. Although the former workers claimed similar results for hydrobromic acid, their anomalous results need re-investigation. 

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. 

Discussion When a bromide is treated with concentrated sulphuric acid, hydrobromic acid and an acid sulphate are formed, as would be expected but then a further reaction takes place. Just as hydrochloric acid can be oxidized by a sufficiently strong oxidizing agent, as was shown in Experiment 23, so hydrobromic acid also may be oxidized. But this latter compound is more readily oxidized than hydrochloric acid and even sulphuric acid, which does not react with hydrochloric acid, serves to bring about this oxidation. Hence the hydrobromic acid expected from the double decomposition of a bromide and sulphuric acid will contain bromine and the reduction products of the sulphuric acid. Pure hydrobromic acid may be prepared by the substitution of phosphoric for sulphuric acid or by some entirely different method, such as the reaction between phosphorus pentabromide and water. 

Sorbic Acid, C5H7.COOH, is an example of acids of this class, very few of which are known. It is present in the unripe berries of the mountain-ash. The structure of the acid has been proved by its synthesis and its reactions to be that represented by the formula CH3 CH =CH.CH =CH.COOH. It adds four atoms of bromine or two molecules of hydrobromic acid, and is thereby converted into substitution-products of caproic acid, which is a member of the series of saturated acids. 

The azide-alkyne click reactions are useful to attach a number of polar FGs including various azobenzene moieties to the pendants of poly(l-phenyl-5-chloro-l-pentyne), (Eq. (7)) [90]. Nucleophilic substitutions of the same starting polymer result in the formation of an imidazole-functionalized, disubstituted acetylene polymer, (Eq. (8)) [91]. The degree of incorporation of the imidazole moiety is about 65%, and the product polymer exhibits good solubility in ethanol. Hydrolysis reaction of poly[l-(/w-methoxycarbonylphenyl)-l-octyne] yields a carboxy-functionalized disubstituted acetylene polymer poly[l-(/w-carboxyphenyl)-l-octyne], (Eq. 9) [92]. Hydrazine-catalyzed deprotection of poly[l-phenyl-ll-Af-benzimide-l-undecyne] affords the corresponding polyamine, which can be further ionized with hydrobromic acid to give a polyelectrolyte ammonium salt, (Eq. (10)) [93]. 

Differentiation between Phenols and Acids.—Although the above solubility differentiation for these two classes of compounds possesses a certain value when applied in the light of the limitations, a more valuable method of differentiation is available because of the fact that the phenol gi-oup increases enormously the velocity of bromine substitution in the benzene ring. The sign of reaction in carbon tetrachloride is the evolution of copious amounts of hydrobromic acid. When the test is conducted with a dilute aqueous solution of a phenol, the sign of reaction is the formation of a sparingly soluble bromine substitution product. OH... 

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