[bharathi]

Recently, I have been working on hydrolysis of an ester to acid and am facing a problem.
Aromatic Compound A (with an ester , R-COOCH3) is dissolved in (methanol+water+NaOH solution, methanol is being used for solution homogeneity) and heated to reflux and maintained at reflux for 3-5 hours. I understand that R-COONa and CH3OH are formed by this basic hydrolysis and this reaction is a one-way reaction(since NaOH is being used) Please correct me if i am wrong with the chemistry.  The mass is then cooled and pH is adjusted to 2.5-3.0 with 20% H2SO4 solution at amibient temperature to form        R-COOH which is isolated by filtration. Analysis of the isolated product shows 40% R-COOCH3 and 60% R-COOH
Can some one help me to understand where the       R-COOH to R-COOCH3 conversion is occuring. Does esterification of R-COOH with the methanol that is already present in the solution occur at ambient temperature. Does diluted (20% H2SO4 )acid catalyse to favour this reaction?

Regds/Bharathi

[Albert]

Yes, dilute H2SO4 catalyses esterification of acids, also because of the volume of methanol you have.

My advice is to try reducing temperature in order to slow down the kinetics of esterification.

[bharathi]

pH adjustment of the R-COONa to form R-COOH is being done for 2-3 hours after which solid ppt is observed and mass is maintained for another one to two hours and filtered.
Do you think 40% of R-COOCH3 formation occurs within so less time (5 hours) at ambient temperature
How can i prove by experimentation that this is occuring
Is there any literature available which suggest that ambient temperature esterification rates are rapid.
Regds/Bharathi

[movies]

Fischer esterification usually requires higher temperatures than that, at least in my experience.

I have had good luck with saponifying esters with LiOH in a 3:1 mixture of THF:water at around 90 degrees C (when the two phases become miscible).  I think LiOH is much better for this reaction than NaOH because Li is a much better Lewis Acid.