On the acid behaviour of the alcoholic group of serine

The behaviour of l-serine in strongly alkaline solution was studied at 25°C and in 3.00 mol/l NaClO4, as a constant ionic medium, to obtain quantitative information about the eventual dissociation of its alcoholic group. A spectrophotometric method was employed to measure the free concentration of hydrogen ions. Two indicators, methyl thymol blue and eriochrome blue type R, were used. Their values as protonation constants and absorbance coefficients were determined in advance. The method here proposed has been validated beforehand by applying it to d-mannite and glycerine and by comparing results so obtained with those previously provided by literature. The investigation showed weak acid properties of the –OH of serine and its dissociation constant was determined. Polynuclear species or further dissociation were not observed.