Containing Two Unlike Substituents

In the previous chapters the preparation and properties of certain important classes of compounds have been discussed, and the principles which are illustrated in their transformations into one another have been emphasized. These principles are of wide application and can be employed in the preparation of compounds of more complex structure than any met with so far. For example, the method of preparing an alcohol by the treatment of an alkyl halide with water or an alkali, is very general in its application. The reaction consists in the replacement of a halogen atom by a hydroxyl group, and such replacement takes place not only with alkyl halides, but with other compounds which contain halogen. Thus, chloroacetic acid can be transformed into hydroxyacetic acid by water — 

By the application of the synthetic methods which have been described under the various classes of compounds many substances which contain two or more unlike groups may be prepared. These compounds show the properties characteristic of the groups which they contain, but the mutual effect of one group on the activity of another in the same compound, brings about changes which are marked at times. 

Many substances of the greatest importance contain two or more characteristic groups. The alcohol-acids occur in nature as constituents of fruits. The amine-acids and amide-acids occur in fruits and vegetables, and are important products of the decomposition of nitrogenous foods. Ketone-esters are much used in the preparation of other compounds. The ketone-alcohols and aldehyde-alcohols form the important class of substances known as carbohydrates. Only a few of the more important and typical mixed compounds will be considered here. 

Compounds of this class may be prepared by introducing halogen atoms into an acid, or the carboxyl group into halogen derivatives of the hydrocarbons. The former method is ordinarily used. Chloroacetic and bromoacetic acids, for example, may be prepared by the action of chlorine or bromine on acetic acid in the sunlight, or in the presence of a carrier (catalytic agent), such as iodine or sulphur — 

CH3COOH + CI2 = CH2CI.COOH + HCl lodo-acetic acid can not be prepared from acetic acid and iodine. The compound is made by digesting a strong aqueous solution of chloroacetic acid with potassium iodide. 

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