| Abstract: | Reactions of trifluoroacetic acid with poly(vinyl alcohol) and various model alcohols were investigated by observing the fluorine and the proton magnetic resonance spectra of the reaction mixtures. At equilibrium the degree of conversion to ester under given conditions decreased in the order isopropanol, pentane-2,4-diol, heptane-2,4,6-triol and poly(vinyl alcohol). Therefore the equilibrium constant for esterfication of a hydroxyl group is depressed by the presence of neighboring hydroxyl groups. It was observed that the steric structures of the models and polymers also affect the equilibrium position of the reaction and this is mainly ascribable to the fact that meso (isotactic) molecules react more slowly with the acid than do racemic (syndiotactic) molecules. In acid-catalyzed acetylation of the model alcohols with acetic acid no similar dependence on the steric configuration was found. Therefore trifluoroacetylation seems to be specific in this respect. |
