Kinetics evidence for a complex between peroxynitrous acid and titanium(IV).

Area of Science:

• Inorganic Chemistry
• Reaction Kinetics
• Coordination Chemistry

Background:

• Peroxynitrous acid (ONOOH) is a reactive species implicated in various chemical and biological processes.
• Metal-oxo complexes, such as titanium(IV) oxide (TiO(2+)), play roles in catalysis and materials science.
• Understanding the interaction between reactive nitrogen species and metal ions is crucial for mechanistic studies.

Purpose of the Study:

• To investigate the reaction mechanism between TiO(2+) and ONOOH in acidic media.
• To identify and characterize intermediate complexes formed during the reaction.
• To determine the kinetic parameters governing the complex formation and rearrangement.

Main Methods:

• Spectrophotometric analysis to monitor reaction progress and identify species.
• Kinetic studies in 0.9 M sulfuric acid to determine rate constants.
• Analysis of reaction intermediates and final products.

Main Results:

• Direct observation of a previously uncharacterized HOONO-metal complex.
• The reaction proceeds through an end-on complex, followed by rearrangement to a side-on complex.
• Rate constants for complex formation (k = 3.0 x 10^2 M^-1 s^-1) and rearrangement (k ≈ 20 s^-1) were determined.
• Excess ONOOH significantly slows the rearrangement (k ≈ 0.1 s^-1), suggesting steric hindrance.
• The final product exhibits an absorption spectrum consistent with TiO(2)(2+), with likely loss of NO+.

Conclusions:

• The reaction between TiO(2+) and ONOOH involves the formation and rearrangement of HOONO-metal complexes.
• The observed kinetics and product distribution provide insights into the reactivity of peroxynitrous acid with metal ions.
• This study elucidates a novel reaction pathway and intermediate species in titanium-peroxynitrite chemistry.