A Kinetic Study of S-Nitrosothiol Decomposition

✍ Scribed by Loris Grossi; Pier Carlo Montevecchi

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 150 KB
• Volume: 8
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/1521-3765(20020118)8:2<380::aid-chem380>3.0.co;2-p

✦ Synopsis

Under anaerobic conditions S-nitrosothiols 1 a ± e undergo thermal decomposition by homolytic cleavage of the SÀN bond; the reaction leads to nitric oxide and sulfanyl radicals formed in a reversible manner. The rate constants, k 1 , have been determined at different temperatures from kinetic measurements performed in refluxing alkane solvents. The tertiary nitrosothiols 1 c (k 1(69 8C) 13 Â 10 À3 min À1 ) and 1 d (k 1(69 8C) 91 Â 10 À3 min À1 ) decomposed faster than the primary nitrosothiols 1 a

and 1 b (k 1(698C) 6.5 Â 10 À3 min À1 ). The activation energies (E # 20.5 ± 22.8 Kcal mol À1 ) have been calculated from the Arrhenius equation. Under aerobic conditions the decay of S-nitrosothiols 1 a ± e takes place by an autocatalytic chain-decomposition process catalyzed by N 2 O 3 . The latter is formed by reaction of dioxygen with endogenous and/or exogenous nitric oxide. The autocatalytic decomposition is strongly inhibited by removing the endogenous nitric oxide or by the presence of antioxidants, such as pcresol, b-styrene, and BHT. The rate of the chain reaction is independent of the RSNO concentration and decreases with increasing bulkiness of the alkyl group; this shows that steric effects are crucial in the propagation step.