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The effects of changes in the structure of 21 N,Y-disubstituted amides on the extraction of actinide and zirconium nitrates and of nitric acid are given. Successive alkyl substitution on the cu-carbon atom greatly decreases the extraction of quadrivalent actinides and of zirconium, but only moderately decreases the extraction of hexavalent actinides and nitric acid. The extraction mechanisms for the extraction of uranyl nitrate and nitric acid are very similar to the mechanisms of extraction by trialkyl phosphates and dialkyl alkylphosphonates. However, the extraction mechanisms for the quadrivalent species by amides appear to be quite different from the mechanisms with the phosphorus compounds. A connection between the stretching frequency of the carbonyl bond in the amides and their power as extractants is substantiated in a general and qualitative way, but an exception is noted.

It was shown that the rate-controlling step of the oxidation reaction in the system occurs by reaction 1. Succeeding steps are suggested by reactions 2 and 3. Reaction 1 has an activation energy of 12 kcal. The number of hydrogen ions, n, which are involved may be as large as four. The rate of the reaction depends on the fourth power of the concentration of nitric acid. The rate of reaction 2 does not become comparably slow until the concentration of nitrous acid in the aqueous phase is reduced to less than 5 X 10 _ M. Equilibrium data were obtained for the over-all reaction 4. The over-all reaction is slightly endothermic. Equilibrium data are given in Table IV. Depending on the composition of the aqueous phase, the major fraction of the neptunium may be in the hexavalent state at equilibrium.

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