The Kinetics of the Reaction Which Takes Place between Iodoacetic Acid and Glycine

1. The kinetics of the reaction which takes place between glycine and iodoacetic acid was studied by means of the polarographic method. 2. On the basis of kinetic equations, evidence was obtained that (a) The reaction proceeds in two steps in which the hydrogens of the amino group are consecutively replaced by the acetyl radicals, the velocity constants being in the ratio 2:1. (b) Only the anionic form of glycine is able to react since the velocity constants at any pH are proportional to the concentration of glycine anion. (c) The reaction is of the ionic type, showing a positive salt catalysis, which, according to Brönsted's hypothesis, involves the primary and the secondary salt effects. 3. The fact that only the glycine anion is able to react was explained as being due to the existence of an unbonded pair of electrons on the nitrogen in the NH(2) group. The NH(3) (+) group, however, in which these electrons are shared by H(+), must, therefore, be inactive.