The Apparent Dissociation Constant of Glycine Ethyl Ester.*

According to the classical theory of the dissociation of weak electrolytes, the amino acids show much lower basic and acidic dissociation constants than would be expected from a comparison with other weak acids and bases. In order to explain this anomaly, Adams (1) originally suggested that an ampholyte must necessarily exist almost entirely as an “inner salt.” Bjerrum (2) extended this idea with additional evidence, and adopted the term “Zwitterion” in place of the “inner salt” of Adams. The evidence in favor of this hypothesis has been extended by others, notably Harris (3) and Borsook.’ The attempts to prove the Adams and Bjerrum hypothesis have largely centered on form01 titration methods in which the basic properties of the amino group are reduced. Equally valid as evidence would be a corresponding titration of the amino group after destruction of the acidic properties of the carboxyl groups. This can be accomplished by formation of the ester of the amino acid. Since accurate data on the basic dissociation constants of esters of the amino acids seem to be lacking, this investigation was undertaken to partially remedy this deficiency. Veley (4), using a calorimetric method, reports a value of Kb’ for glycine ethyl ester of 9.7 X 1O-8. Johnston (5), using a catalytic method, states that this value is higher than 2.2 X 10e8.