Application of the dropping-mercury electrode to the investigation of the polyhydroxy acids and lactones
Journal of Research of the National Institute of Standards and Technology
ABSTFACT The polarographic method is used in a study of the polyhydroxymonocarboxylic acids, their lactones, lactides, and other condensation products. With a tetraethylammonium chloride environment, polarographic waves are obtained which show the behavior of the hydroxy acids and their lactones with respect to electrolytic reduction and the products which they form in dilute aqueous solution. Freshly prepared solutions of the aldonic acids give the ordinary hydrogen wave but do not give waves
... do not give waves which correspond to the reduction of the carboxyl group. When a solution containing an aldonic acid is allowed to stand, the wave due to the hydrogen ion decreases and a wave caused by the gamma lactone appears. In the presence of oxygen a wave, apparently caused by some substance produced by the interaction of the sugar acid, mercury, and oxygen, forms at about -1.1 v. The formation of this wave is accompanied by a corresponding decrease in the hydrogen wave. Freshly prepared solutions of the delta lactones of the aldonic acids give waves at about -2.3 v, with respect to a mercury anode, which appear to be due to the reduction of the lactones. The heights of these waves decrease with time until, after several hours, they disappear. The absence of an appreciable delta lactone wave in a 0.01 M aqueous solution of an aldonic acid shows that the position of the equilibrium between the free acid and the delta lactone is far toward the free acid. The gamma lactones of the aldonic acids give polarographic waves at potentials slightly higher than the delta lactones. When a solution containing a gamma lactone is allowed to stand, the height of the gamma lactone wave decreases while a wave corresponding to the reduction of the hydrogen ion appears. The inflection points for the gamma lactone waves vary only slightly with the configuration of the groups comprising the lactone structure. This small variation in the inflection points shows a regularity which indicates that the stereomeric positions of the hydroxyl groups are of importance. When the hydroxyl of carbon 2 and the residual carbon group attached to carbon 4 are in the cis position, the reduction potential seems to be higher than it is when these groups are in the tran8 position.