Kinetics and mechanism of oxidation of hydroxylamine by 12-tungstocobaltate (III) ion in acetate buffer

Abstract

The stoichiometry of the title reaction is expressed by the equation<br><br>

4[Co^IIIU]^5- + 2NH₂OH →<span style="font-size:14.0pt;font-family:HiddenHorzOCR;mso-bidi-font-family:HiddenHorzOCR" lang="EN-US"> 4[Co^IIU]^6- + N₂O + <span style="mso-bidi-font-style:italic">4H⁺<i> </i>+ H₂O<br><br>

The absorbancy of the complex formed between hydroxylamine and [Co^IIIU]^5-and the rate increases with decrease in [<span style="font-size:14.0pt; font-family:" arial","sans-serif";mso-bidi-font-style:italic"="" lang="EN-US">H⁺]. There is an excellent agreement between the rate law derived from the mechanism based on the exclusive reactivity of NH₂OH though another mechanism based on the simultaneous reactivity of NH₂OH and NH₃OH^{<span style="font-size:14.0pt;font-family:" arial","sans-serif";mso-bidi-font-style:="" italic"="" lang="EN-US">+</span>}, which is the dominant species of hydroxylamine in solutions, also leads to a rate law having satisfactory correlation with the results. The high reactivity of NH₂OH is ascribed to the coordination of the nitrogen atom in NH₂OH. The similar coordination by NH₃OH^{<span style="font-size:14.0pt;font-family:" arial","sans-serif";mso-bidi-font-style:="" italic"="" lang="EN-US">+</span>} is improbable because the lone pair is coordinated to the proton. Hence, the formation of a coordinated complex is an essential requirement for the progress of the reaction. The consideration that Co^III atom in 12-tungstocobaltate (III) ion is completely shielded by the tungstate framework, an outer-sphere electron transfer is more probable. <p> </span></span></span>