Reduction of iodate-ion by phosphine catalyzed by molybdenum (6)

The kinetics and mechanism of catalytic reduction of iodine (5) by phosphine have been studied. In the experiments the system NaIO3-HClO4-NaX-K2-MoO4-H2O has been used. Reduction of iodine (5) by phosphine is observed only with the concentration of Csub(H3O+)(>=)1x10-4 molexl-1. Introduction of molubdenum (6) at Csub(H3O+)<1x10-4 molex-1 exerts no influence on the rate of the process. With Csub(H3O+)(>=)1x10-4 molexl-1 molybdenum already at the concentration of approximately 10-7 mole l-1 increases the reaction rate. Proceeding from the kinetic data obtained, a mechanism of catalytic reduction of the iodate ion by phosphine in the presence of a metallocomplex catalyst of molybdenum (6) is suggested. It has been established that catalysis with molybdenum (6) resides in the formation of the intermediate complex MoO3OH(IO3)X3-, where X-=I-, Br-, which undergoes redox-transformation with isolation of the free halogen. The catalyst Mo (6) does not change the valence state