KINETICS AND MECHANISM OF THE REDUCTION OF NEPTUNIUM(VI) BY METHYLSALICYLIC ACIDS

The kinetics of the reduction of NpO22+ by three methylsalicylic acids (MSA) have been studied with the techniques of solvent extraction and spectrophotometry. The rate constants were found to decrease in the sequence 5-MSA > 3-MSA > 4-MSA. The general rate equation is -d[NpO22+]/dt = k[NpO22+]-[MSA][H+]-1. The activation parameters for these reactions were determined and the values were found to vary in the order: DELTA-H-not-equal 4-MSA > 3-MSA approximately 5-MSA; DELTA-S-not-equal 4-MSA > 3-MSA greater-than-or-equal-to 5-MSA. The rate constant sequence for NpO22+ reduction by various phenolic compounds correlates with the electronic effect of substitution groups on the basicity of the phenolic oxygen.