Preparation of Butyl Chlorides

The reaction reaches equilibrium rapidly if the hydroxyl group is attached to a reactive radical, as in tertiary alcohols. In such cases, excess of the halogen acid is shaken with the alcohol, and the mono-halogen compound is separated. With primary and secondary alcohols, equilibrium is reached more slowly, and a catalyst (such as zinc chloride in the case of hydrochloric acid, and sulfuric acid in the case of hydrobromic acid) is used. On account of its cost, hy-driodic acid is not used, but iodine and phosphorus, which react as follows  

The preparation of iodides by this method requires special precautions, if extensive side reactions are to be avoided. The direct action of bromine and chlorine on saturated open-chain hydrocarbons in the presence of catalysts results in the formation of isomeric monohalides, and in the laboratory the separation of these is difficult. In industry, however, this method is practicable. 

The direct halogenation of aromatic hydrocarbons in the laboratory is feasible. Chlorination or bromination of benzene gives one monohalogen, CoHisX, and by proper control of temperature and concentration of the halogen, the formation of dihalogen com-poimds, C6H4X2, can be kept at a minimum  

The halogenation is usually performed in the presence of catalysts. A great variety of so-called halogen-carriers can be used. Iron, phosphorus or its halides, and sulfur and its halides are among the most common. 

Butyl chlorides. As stated in the preceding paragraphs, tertiary alcohols react rapidly with halogen acids. If excess of hydrochloric acid is used, the tertiary halide is formed at room temperatures. n-Butyl and sec-butyl alcohols require heating with a mixture of concentrated hydrochloric acid and fused zinc chloride in order to yield appreciable amounts of the normal and secondary chlorides. It should be noted that the ease of formation of the halide corresponds to the ease of hydrolysis. This should be expected if we consider the following equation  

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