Preparation and Properties of Amides

Introduction. The general methods for the preparation of amides are (1) ammonolysis of esters, acyl halides, and anhydrides (2) the dehydration of the ammonium salts of carboxylic acids  

CHaCOOCsHs + NHs —CHsC0NH2 + C2H6OH CH3COCI + 2 NHs —CHsC0NH2 + NH4CI (CH3C0)20 + NHs — CHsCONHs + CHsCOOH 

The ammonolysis of acyl chlorides is commonly employed whenever the preparation of an amide is desired for the identification of a carboxylic acid. The acyl chloride is prepared and treated with aqueous ammonia, or, if the amide is very soluble in water, with ammonia in benzene. In the latter case the ammonium chloride is filtered off, and the amide obtained by evaporation of the benzene with powdered ammonium carbonate. The preparation of amides from carboxylic acids is based upon the formation of an equilibrium mixture when the ammonium salts of the acid are heated  

Removal of water by distillation shifts the equilibrium point to favor formation of the amide. For preparation of the amide by this method the ammonium salt of the carboxylic acid is prepared and dehydrated, melted, allowed to cool, and then pulverized. The powdered material is placed in a distilling flask and heated. Another method is to add solid ammonium carbonate to the carboxylic acid, and distill directly. 

The crude acetamide may be recrystallized from a mixture of three parts of benzene to one part of ethyl acetate, or from an alcohol-ether mixture. Dissolve 0.5 g of acetamide in 1 ml of methanol by warming cool, and add 6-7 ml of ether. Cork tube, and cool. If crystals do not separate within a few minutes, even on stirring, add a minute crystal of pure acetamide and allow to stand. Filter the crystals with suction and wash with ether. Place on a paper disc or watch glass and dry in a dessicator. Determine the melting point. 

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Table 20 Preparations and Properties of Amide and Peptide Complexes of Cobalt(ffl)...

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