The reactions of vanillin with octacyanotungstate(V) ions in alkaline solution

In alkaline aqueous media octacyanohmgstate(V) ions are reduced to [W(CN)(8 )](4-) ions by vanillin which is oxidised mainly to bisvanillin. The reacti on proceed in three stages. In the first stage which was studied by stopped -flow technique the initial reaction is first-order in both [W(CN)(8)](3-) and [van(-)] and is catalysed by alkali-metal cations. The rate of reaction increases in the series of alkali metal ions in the order Na+ < K+ < Cs+. The apparent activation parameters, DeltaH(#) are equal to 20.7 +/- 1.4 (Na +) and 14.9 +/- 1.1 (K+) kJ mol(-1) and DeltaS(#) are equal to -174 +/- 20 (Na+) and -188 +/- 25 (K+) J mol(-1) K-1. The mechanism of the first stage is discussed.