title: A kinetic study of S-nitrosothiol decomposition.
abstract: Under anaerobic conditions S-nitrosothiols 1a-e undergo thermal decomposition by homolytic cleavage of the S-N bond; the reaction leads to nitric oxide and sulfanyl radicals formed in a reversible manner. The rate constants, k(t), have been determined at different temperatures from kinetic measurements performed in refluxing alkane solvents. The tertiary nitrosothiols 1c (k1(69 degrees C) = 13 x 10(-3) min(-1)) and 1d (k1(69 degrees C) = 91 x 10(-3) min(-1)) decomposed faster than the primary nitrosothiols 1a (k1(69 degrees C) = 3.0 x 10(-3) min(-1)) and 1b (k1(69 degrees C) = 6.5 x 10(-3) min(-1)). The activation energies (E# = 20.5-22.8 Kcal mol(-1)) have been calculated from the Arrhenius equation. Under aerobic conditions the decay of S-nitrosothiols 1a-e takes place by an autocatalytic chain-decomposition process catalyzed by N2O3. 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 p-cresol, beta-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.
authors.affiliation: Dipartimento di Chimica Organica A. Mangini, Università di Bologna, Italy. gtossi@ms.fci.unibo.it
authors.forename: Loris
authors.initials: L
authors.lastname: Grossi
authors.forename: Pier Carlo
authors.initials: PC
authors.lastname: Montevecchi
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D002084:Butylated Hydroxytoluene / Q000378:metabolism; D003408:Cresols / Q000378:metabolism; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D026403:S-Nitrosothiols / Q000737:chemistry / Q000378:metabolism*; D020058:Styrene / Q000378:metabolism; D013696:Temperature
chemical_list: D000975:Antioxidants; D003408:Cresols; D026403:S-Nitrosothiols; C032538:4-cresol; D002084:Butylated Hydroxytoluene; D009569:Nitric Oxide; D020058:Styrene; D010100:Oxygen