What is the function of saturated NaCl and saturated NaHCO3 in Fischer esterification?

1 Answer
Feb 16, 2017

Saturated brine, and saturated sodium carbonate are the standard work-up for an ester synthesis........


For the esterification rxn:

#"ROH + HO(O=)CR'" rightleftharpoons"RO(O=)CR'" +"H"_2"O"#,

as written, this is an equilibrium reaction, and we try to drive the equilibrium to the right. At the end of the reaction, however, there may be some carboxylic acid still present.

The addition of saturated bicarbonate of soda will react with any unreacted acid, i.e.

#"R'CO"_2"H" + "Na"^(+)"HCO"_3^(-) rarr "CO"_2uarr+"R'CO"_2^(-)"Na"^(+)+"H"_2"O"#

The ester will be retained by organic phase; the carboxylate salt will cross to the AQUEOUS phase. Of course, we want the product, the ester, to be wholly contained in the organic phase (which solvent is usually ether, that can be dried over a drying agent, and stripped off under reduced pressure.)