Halides from Alcohols and Phenols by Triphenylphosphine Dihalide

Halides from Alcohols and Phenols by Triphenylphosphine Dihalide 

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 important feature of this reagent is its ability to convert phenols to the corresponding bromides under laboratory conditions. Examples of these conversions are given. 

A 500-ml, three-necked, round-bottom flask is fitted with a mechanical stirrer, a pressure-equalizing addition funnel and a reflux condenser (drying tube). The flask is charged with 100 ml of dry dimethylformamide, 9.2 ml (0.1 mole) of dry -butyl alcohol, and 28 g (0.107 mole) of dry triphenylphosphine. The flask is cooled in a water bath, stirring is begun, and bromine (approx. 16 g, 0.1 mole) is added over about 15 minutes. 

During the addition, the flask temperature is held below 55° by addition of ice to the cooling bath as necessary. The addition of bromine is halted when two drops give a persistent orange color. 

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II. Halides from Alcohols and Phenols by Triphenylphosphine Dihalide... 

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