Polarographic Studies of the Ion-pair Formation and Conjugation Reactions of Acetate and Benzoate Ions in Acetonitrile

An acetate ion (A−) formed a homoconjugated species, A− (HA)2, with 2 molecules of acetic acid (HA) in the presence of a large excess of HA in an acetonitrile solution. In the presence of both acetic acid and LiClO4, one molecule of HA was derived from A− (HA)2 by means of a lithium ion to from an ion-paired species, HA2−Li, as follows: A−(HA)2+Li+2−Li++HA. The equilibrium constant, Kex, was evaluated as 1.1×104 from the shift in the anodic half-wave potential of the acetate ion. As for the benzoate ion (A′−) and HA′, similar reactions occured, and the constant of the exchange reaction was evaluated as 6×103. The effect of the sodium ion and HA (or HA′) on the A− (or A′−) ion was complicated. On the other hand, the presence of [M(A′)2]− (M=Li, Na, K) was proved by the shift of the cathodic wave of the alkali metal.The addition of water caused the apparent stability constant of [Li(A′)2]− to decrease extremely.