The Effect of Water on Saponification of Organic Esters.

Abstract

SIR : In our recent work involving the analysis of components of woods we required a relatively simple and accurate procedure for the determination of the acetyl content. Owing to the very deep color of our test solutions, the procedure described by blazor and Meisel (6), in which the sample is transesterified with sodium methoxide, was used. The volatile methyl acetate was then distilled into a n alcoholic KOH solution and after saponification of the ester the excess of KOH was back-titrated with HC1. I n this work we used a bulk prepared KOH solution in anhydrous methanol (0.05% HsO) which we usually keep available in the laboratory for several other procedures.Our initial results with the above technique showed serious variations between experiments and consistently lower values than expected. After having checked every stage of the procedure, particularly the distillation, we concluded that the only reason for the variations and low values for the ester content was the incomplete saponification with the KOH solution, and that this in turn was due to absence of water in the reagent.

Titrations in Nonaqueous Solvents

“…The saponification of difficultly saponifiable esters was greatly accelerated by the use of dimethylsulfoxide (DM SO) as the solvent (200). Greive et al (79) stress the importance of the presence of water in the saponification of organic esters. Low and variable results were obtained with an essentially anhydrous alcoholic KOH solution, while good recoveries were obtained with the addition of water.…”