What is the function of saturated NaCl and saturated NaHCO3 in Fischer esterification?
Answer:
Fischer esterifications liberate H20 during the reaction. The glassware setup involves a Dean-Stark trap. If you do not what a Dean-Stark apparatus is then check this out http://en.wikipedia.org/wiki/dean-stark_... This setup helps drive the reaction to the right (ie. force the reaction to completion since it is an equilibrium process). Many times these reactions are run without solvent but most of the time a solvent such as toluene is used. As this mixture refluxes during the reaction a mixture of solvent (toluene) and H2O is collected in the Dean-Stark trap (an azeotropic distillation). The H2O is therefore removed from the reaction which helps drive the reaction to completion. As more H2O collects in the Dean-Stark trap two layers will form in the trap. The top layer will be the toluene but it will have some H2O in it so if you add some saturated NaCl it will help to completely remove any H2O dissolved in the toluene. Once the reaction is finished there may be some unreacted acid (your starting material) left so during the workup if you wash it with saturated NaHCO3 the remaining acid will be removed. Next wash the solution with H2O and finally again with saturated NaCl. After this dry the mixture with MgSO4 or Na2SO4 and concentrate it then you will have the final product. So in summary the saturated NaCl helps remove any H2O from your reaction and the saturated NaHCO3 removes any inreacted acid. I know this was long but I thought explaining the Dean-Stark apparatus would help. Good luck.
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