Exchange reactions between neptunium ions

The exchange reaction between Np(VI) and Np(V) has been investigated using the isotopic method ( Np) and an extraction separation (Np(VI) with tri-butylphosphate or thenoyltrifluoroacetone in toluene) Cohen et al. have found, for the exchange in perchlorate media, a rate law 

IONS OF SAME METAL IN DIFFERENT OXIDATION STATES 

Cohen et al and Sullivan et al , in further articles, report some data obtained under higher ionic strength conditions and have suggested that depends on [H in the manner  

In deuterated solvent the rate of exchange was found to be lower than in aqueous media the ratio k H20) k D20) was found to be dependent on the acid concentration. Sullivan et al. have suggested a hydrogen atom transfer process and a water bridging process 

Cohen et al have studied the effect of the addition of both chloride and nitrate ions (up to 3 Mat = 3.0 M) on this exchange. Whereas nitrate ion was found to have vertually no effect on the exchange rate, chloride ion had an accelerating influence. For exchange in the presence of chloride ions rate data was found to be fitted by an expression 

---

A kinetic study has been made of the oxidation of ascorbic acid (H A) by neptunium(vi). The rate law is of the form — d[NpVi]/dr=A 2[H2A] [Np i] with no evidence for a hydrogen-ion dependence over the range 0.05 < [H+] < l.OOM. In aqueous media Np i exists as the [O—Np—0] + ion with between four and six equatorial water molecules. A comparison with the reactions with aquo-ions, e.g. or where inner-sphere reactivity is established and with [Fe(phen)3] + indicates that the preferred pathway is outer sphere. The exchange rate for [(5-nitrophen)gFe] +/ + and the redox potential are both greater than for the Np VNp " couple and these features are considered- the reason for the rate of the present reaction being 40 times slower than that of the iron system. 

---