REDUCTION OF THORIUM AND PROTOACTINIUM TO THE OXIDATION-STATE-3+ IN TETRAHYDROFURAN SOLUTIONS

The possibility of reduction of thorium to the oxidation state 3+ in r eaction of ThBr4 with TmI2, DyI2, and NdI2 in tetrahydrofuran (THF) so lution was studied by electronic spectroscopy. ThBr4 was not reduced w ith TmI2, as indicated by the unchanged color oi. solution and the f-d absorption bands of Tm2+. In all other cases the color of solution ch anged and the characteristic absorption bands of lanthanides(II) disap peared, which is apparently related to reduction of thorium to oxidati on state 3+ in the presence of Dy2+ and Nd2+. The behavior of protacti nium in the TmI2-TmI3-THF system was studied by cocrystallization. In the presence of Tm2+, microamounts of protactinium cocrystallize with the solid phase of TmI3 solvate, the cocrystallization coefficient bei ng nearly 1. Similar cocrystallization coefficient in this system was obtained for cerium. Thus, in THF in the presence of Tm2+ protactinium is probably reduced to the oxidation state 3+.