SOME REACTIONS OF THE PERBROMATE ION IN AQUEOUS-SOLUTION

The reaction of the perbromate ion with a number of two-equivalent reductants have been studied in aqueous solution at an ionic strength of approximately one. Reaction rates increase in the order N3 -< ClO2 -~ SeO3 2-~ NO2 -< P(III) « S(IV) < As(III) < Sb(III). The perbromate-sulfur (IV) reaction obeys the rate law -d[BrO4 -]/dt = ks[BrO4 -] [SO3 2 -] in solutions more basic than pH 4.5. At 25 °C, ks= 5.8 X 10-3L/mol•. The perbromate-arsenic(III) reaction obeys the rate law -d[BrO4 s]/dt = [(k1,[H+] + k2K1+ k3K1/[H+])/(KI+ [H+])][BrO4 -][As(III)]. At 39.7 °C, k1= 5.6 X 10-4L/ mol•, k2= 1.96 X 10-2L/mol•: = 1.16 X 10-13s-1, and K1= 1.6 X 10-9M. This rate law can be interpreted in terms of increasing reactivity of the species H3AsO3, H2AsO3 -, and HAsO3 2 -toward perbromate. In strong base, the perbromate-an-timony(III) reaction obeys theratelaw -d[BrO4 -]/dt = ksb[BrO4 -][Sb(III)], where ksb= 0.47 L/mol• at 25 °C. Activation parameters were determined for the sulfur(IV), arsenic(III), and antimony(III) reactions, and the dependences of the S(IV) and As(III) reactions on total salt concentration were elucidated. The results of isotopic tracer studies show that in its reactions with S(IV) and As(III) the perbromate ion transfers one of its oxygen atoms to the reductant. Oxygen exchange between 0.14 M KBrO4and water proceeded to less than 7% of completion in the course of 19 days at 94 °C, in solutions ranging from 0.06 M acid to 0.02 M base. The implications of all of these results are discussed. © 1979, American Chemical Society. All rights reserved.