Hydrohalic acids reaction with alcohols

A halogenating system related to the preceding case is formed by the reaction of triphenylphosphine with molecular bromine or chlorine. The system is not as sensitive to moisture as the phosphine-carbon tetrahalide system (see preceding section), but it suffers from the disadvantage that hydrohalic acids are produced as the reaction proceeds. Nevertheless, sensitive compounds can be successfully halogenated by the system, as exemplified by the preparation of cinnamyl bromide from the alcohol. 

An in-depth study of the industrially important hydrolysis of titanium alkoxides has been carried out by Bradley.234,235 A number of intermediate complexes were isolated and characterized. The alcohol exchange reaction has been discussed previously. The addition of hydrohalous acids to alkoxides is clearly related to the reverse reaction, the addition of alcohols to metal halides. In general, the products of these two reactions will be the same (equation 59). Hence, complete substitution will occur to give metal halides that are known to form only alcoholates with alcohols (equations 60 and 61),31,236... 

Since the first synthesis of organogermanium nitrogen derivatives it was found that the Ge—N bonds display high reactivity, especially an easy protolysis with water, alcohols, phenols, carboxylic acids, hydrohalic acids, SH-, NH-, PH- and CH-acids, etc36,37,77,346,347. All these reactions were initiated by electrophilic attack of the reactant proton on the nitrogen atom76,468,469. 

Summary Sn2 Reactions OfTosylate Esters 478 11-6 Reduction of Alcohols 478 11-7 Reactions of Alcohols with Hydrohalic Acids 479... 

Predict the products of the reactions of alcohols with oxidants, hydrohalic acids, dehydrating agents, and alkali metals. 

Tosylation of an alcohol, followed by displacement of the tosylate by a halide ion, converts an alcohol to an alkyl halide. This is not the most common method for converting alcohols to alkyl halides, however, because simple, one-step reactions are available. A common method is to treat the alcohol with a hydrohalic acid, either HBr, HC1, or HI. 

Limitations on the Use of Hydrohalic Acids with Alcohols The reactions of alcohols with hydrohalic acids do not always give good yields of the expected alkyl halides. Four principal limitations restrict the generality of this technique. 

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