Rate constants for some reactions of inorganic radicals with inorganic ions. Temperature and solvent dependence

✍ Scribed by S. Padmaja; P. Neta; R. E. Huie

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 455 KB
• Volume: 25
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550250604

✦ Synopsis

Rate constants for several reactions of inorganic radicals with inorganic anions in aqueous and aqueousiacetonitrile solutions have been measured as a function of temperature by laser flash photolysis. The reactions studied were (1) C12'-+ N3-, (2) Br2'-+ N3-, (3) C12'-+ SCN-, (4) Br2'-+ SCN-, (5) SO4'-+ CI-, (6) Sod'-+ C 0 3 2 -, and (7) N; + I -. The rate constants were corrected for ionic strength and ranged from lo6 to lo9 L mol-' s -I . The Arrhenius activation energies varied from 2 to 12 kJ mol-' for the first 4 reactions, were higher for reaction 6, and negative for reaction 5. The pre-exponential factors also varied considerably with log A ranging from 5 to 14. The values of k298 decreased in most cases by more than an order of magnitude upon increasing the acetonitrile (ACN) fraction from 0 to 70%. For most reactions, this decrease in k 2 9 ~ was due to changes in log A with little regularity in the small changes observed in E,. For reaction 7, k298 was practically unchanged due to compensating effects of the changes in E, and log A with ACN mol fraction, giving an isokinetic relationship. An isokinetic relationship was also observed in the case of reaction 6; E, and log A change in parallel while changing ACN mol fraction. Reaction 3 (C12'-+ SCN-) was also studied in waterlt-butanol and water/acetic acid mixtures. Linear correlation was found between log k and the dielectric constant of the medium for water/ACN and waterlt-BuOH but the lines for the two solvent mixtures had different slopes, suggesting specific solvation effects in addition to the primary solvent polarity effects. With water/acetic acid, k decreased and then increased upon addition of acetic acid.