Reactions aided by azeotropic distillation

3 Reactions Aided by Azeotropic Distillation In many organic reactions, the starting materials are nearly as stable thermodynamically as the products to obtain a good yield, it is necessary to force the equilibrium to the right by removing one of the products (not necessarily the desired one). This technique has already been illustrated in Sec. 1.8.1 by a Dieck-mann condensation, forced to completion by removal of ethanol via the ethanol-xylene azeotrope. 

The commonest reaction in which an azeotropic technique is useful involves the acid-catalyzed conversion of an acid to an ester. For such reactions, a simple Dean-Stark trap [Figs, l-l(s) and 1-14] will usually suffice for removal of the water. More difficult esterifications have been successfully. effected using more sophisticated equipment. For example, in the preparation of methyl pyruvate,f the position of the 

Another situation involving azeotropic distillation, in which the lower layer must be returned to the reaction flask, is illustrated by the following example. 

An efficient preparation of catechol from guaiacol involves refluxing the ether with hydrobromic acid for an extended period f 

In order to have the reaction proceed at a useful rate, concentrated hydrobromic acid (48%) is required. As the reaction proceeds, the concentration 

---