# 15.4: Preparation of Alcohols

Many of the common laboratory methods for the preparation of alcohols have been discussed in previous post or will be considered later; thus to avoid undue repetition we shall not consider them in detail at this time. Included among these methods are hydration (Section 10-3E) and hydroboration (Section 11-6D), addition of hypohalous acids to alkenes (Section 10-4B), $$S_\text{N}1$$ and $$S_\text{N}2$$ hydrolysis of alkyl halides (Sections 8-4 to 8-7) and of allylic and benzylic halides (Sections 14-3B and 14-3C), addition of Grignard reagents to carbonyl compounds (Section 14-12), and the reduction of carbonyl compounds (Sections 16-4E and 16-5). These methods are summarized in Table 15-2.

Some of the reactions we have mentioned are used for large-scale industrial production. For example, ethanol is made in quantity by the hydration of ethene, using an excess of steam under pressure at temperatures around $$300^\text{o}$$ in the presence of phosphoric acid:

A dilute solution of ethanol is obtained, which can be concentrated by distillation to a constant-boiling point mixture that contains $$95.6\%$$ ethanol by weight. Dehydration of the remaining few percent of water to give “absolute alcohol” is achieved either by chemical means or by distillation with benzene, which results in preferential separation of the water. Ethanol also is made in large quantities by fermentation, but this route is not competitive for industrial uses with the hydration of ethene. Isopropyl alcohol and tert-butyl alcohol also are manufactured by hydration of the corresponding alkenes.

Table 15-2: General Methods of Preparation of Alcohols

The industrial synthesis of methyl alcohol involves hydrogenation of carbon monoxide. Although this reaction has the favorable $$\Delta H^0$$ value of $$-28.4 \: \text{kcal mol}^{-1}$$, it requires high pressures and high temperatures and a suitable catalyst; excellent conversions are achieved using zinc oxide-chromic oxide as a catalyst:

Various methods of synthesis of other alcohols by reduction of carbonyl compounds will be discussed in Section 16-4E.

## Contributors

• John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."