Kinetics of copper(II)-catalyzed oxidation of S(IV) by atmospheric oxygen in ammonia buffered solutions

✍ Scribed by Anil Kumar Sharma; Abhilasha Singh; R. K. Mehta; Sudhanshu Sharma; S. P. Bansal; K. S. Gupta

• Publisher: John Wiley and Sons
• Year: 2011
• Tongue: English
• Weight: 443 KB
• Volume: 43
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20550

✦ Synopsis

Abstract

To understand the chemistry of Cu(II)–NH~3~–S(IV)–O~2~ system, the kinetics of the oxidation of sulfur(IV) catalyzed by amminecopper(II) complexes has been studied in the ammonia‐buffered solutions. Sulfur(IV) is oxidized to sulfate. The complexes, Cu(NH~3~)^2+^, Cu(NH~3~)~2~^2+^, and Cu(NH~3~)^2+^~3~ appear to be equally reactive and Cu(NH~3~)~4~^2+^ appears to be unreactive. The kinetics obey the rate law:

equation image

where α~1~ and γ~1~ are the rate constants for O~2~‐dependent and O~2~‐independent pathways, respectively, for Cu(NH~3~)^2+^, Cu(NH~3~)^2+^~2~, and Cu(N H~3~)~3~^2+^ complexes, which appear to be equally reactive. The values of α~1~ and γ~1~ were found to be (1.32 ± 0.21) × 10^6^ L^2^ mol^−2^ s^−1^ (1.74 ± 0.40) × 10^9^ L^3^ mol^−3^ s^−1^respectively at 30°C. The reaction rate is not influenced by the presence of ethanol—a free radical scavenger, so a nonradical mechanism has been proposed. The results of this study are useful in understanding the atmospheric chemistry of aqueous phase autoxidation of dissolved sulfur dioxide in copper(II)–ammonia–sulfur(IV)–oxygen system at high pH. © 2011 Wiley Peiodicals, Inc. Int J Chem Kinet 43: 379–392, 2011