Reaction of a superoxochromium(III) ion with nitrogen monoxide: Kinetics and mechanism

The kinetics of the rapid reaction between CraqOO2+ and NO were determined by laser flash photolysis of CraqNO2+ in O-2-saturated acidic aqueous solutions, k = 7 x 10(8) M-1 s(-1) at 25degreesC. The reaction produces an intermediate, believed to be NO2, Which was scavenged with ([14]aneN(4))Ni2+. With limiting NO, the CraqOO2+/NO reaction has a 1:1 stoichiometry and produces both free NO3- and a chromium nitrato complex, CraqONO22+. In the presence of excess NO, the stoichiometry changes to [NO]/[CraqOO2+] = 3:1, and the reaction produces close to 3 mol of nitrite/mol of CraqOO2+. An intermediate, identified as a nitritochromium(III) ion, CraqONO2+, is a precursor to a portion of free NO2- In the proposed mechanism, the initially produced peroxynitrito complex, CraqOONO2+, undergoes O-O bond homolysis followed by some known and some novel chemistry of CraqO2+ and NO2. The reaction between CraqO2+ and NO generates CraqONO2+, k > 10(4) M-1 s(-1). CraqOO2+ reacts with NO2 with k = 2.3 x 10(8) M-1 s(-1).