ON THE MECHANISM OF THE ESTERIFICATION OF A BETA-HYDROXY ALKYLAMIDE WITH A CARBOXYLIC-ACID

Beta-Hydroxy alkylamide reacts with carboxylic acid to form an ester m uch faster than with a normal alcohol. Many suggestions have been made to describe the mechanism of this reaction, but none of them have bee n proved. It is clear that this reaction cannot be seen as a normal es terification since it cannot be catalysed by acids or bases. We have p repared model compounds, for which calibration curves have been obtain ed by means of UV spectroscopy. A technique was developed for separati ng the starting materials and the expected reaction products by means of HPLC. In this way, quantitative and qualitative information about t he reaction mixtures could be obtained as a function of time. This met hod revealed the existence of an intermediate oxazolinium cation. The formation of this compound plays a key role in the esterification. Apa rt from the expected ester and the intermediate, various other reactio n products were determined. All the reaction products could be obtaine d in a pure state with the aid of preparative HPLC. The structures of the compounds were studied using H-1 NMR spectrometry. A reaction mech anism has been put forward to explain the experimental data.