Studies of the interaction of methanol with pectin in aqueous solution

Abstract

The interaction of methanol with pectin (degree of esterification 58%) in aqueous solution has been studied by conductivity measurements, circular dichroism, and equilibrium dialysis. Compared to other aliphatic alcohols methanol has a strong precipitating effect on pectin both in water and in 50% sucrose solutions at pH 7·0 and 3·4. The standard Gibbs free energy of methanol transfer from water into pectin solutions of concentration 0·024–0·032 g-equiv. of ester groups (kg of solvent) −1 is 4 kJ mole −1. The interaction of methanol with pectin gives a complex in which each ester group binds one molecule of alcohol. The reaction is assumed to be caused by the formation of a hydrogen bond involving the hydrogen atom of the hydroxyl group of methanol and the unshared electron pair of the carbonyl group. Methanol interacts strongly with pectin compared to other aliphatic alcohols because of its high acidity.