Hofmann reaction experimental conditions

The Curtius, Hofmann (see p. 267), and Schmidt (see p. 307) reactions are in that order decreasingly mild, decreasingly flexible, and increasingly expeditious. The last-named quality varies somewhat with the available starting material, whether the free acid or the ester. The Curtius reaction lends itself to the preparation of isocyanates, sym-and 08-ureas, amides, urethans, and amines at will, and provides a wide choice of experimental conditions. For synthetic purposes the Hofmann reaction can be used only to prepare sym-ureas, urethans, and amines directly, and halting the reaction at a desired intermediate is often not possible. The variety of experimental conditions is narrower and more limited. The Schmidt reaction on carboxylic acids or derivatives has been applied as a preparative method only to the production of amines although urethans and isocyanates have been prepared occasionally by this reaction, it can hardly be considered a preparative method for them. Amides can be prepared by the Schmidt reaction only from ketones. The choice of experimental conditions employable in the Schmidt reaction is narrow. 

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