Sensitized photoxygenation of piroxicam in neat solvents and solvent mixtures

Manakin: DSpace XMLUI Project v2

Sensitized photoxygenation of piroxicam in neat solvents and solvent mixtures

Cómo citar
Cómo citar

Sensitized photoxygenation of piroxicam in neat solvents and solvent mixtures

.
Copiar
Título: Sensitized photoxygenation of piroxicam in neat solvents and solvent mixtures
Autor: Lemp Miranda, Else Mónica; Zanocco Loyola, Antonio Luis; Günther Sapunar, Germán
Resumen: Detection of O-2((1)Delta(g)) phosphorescence emission, lambda(max) = 1270 nm, following laser excitation and steady state methods were employed to determine the total rate constant, k(T), for the reaction between the non-steroidal anti-inflammatory drug piroxicam (PRX) and singlet oxygen in several solvents. Values of k(T) ranged from 0.048+/-0.003 X 10(6) M-1 s(-1) in chloroform to 71.2+/-2.2x10(6) M-1 s(-1) in N,N-dimethylformamide. The chemical reaction rate constant, k(R), was determined by using thermal decomposition of 1,4-dimethylnaphthalene endoperoxide as the singlet oxygen source. In acetonitrile, the k(R) value is equal to 5.0+/-0.4x 10(6) M-1 s(-1), very close to the kT value. This result indicates that, in this solvent, the chemical reaction corresponds to the main reaction path. Dependence of total rate constant on the solvent parameters,pi* and beta can be explained in terms of a reaction mechanism that involves the formation of a perepoxide intermediate. Rearrangement of the perepoxide to dioxetane followed by ring cleavage and transacylation accounts for the formation of N-methylsaccharine and N-(2-pyridyl)oxamic acid, the main reaction products. Data obtained in dioxane-water (pH 4) mixtures with neutral enolic and zwitterionic tautomers of piroxicam in equilibrium show that the zwitterionic tautomer reacts with singlet oxygen faster than the enolic tautomer.
URI: http://www.captura.uchile.cl/handle/2250/13064
Fecha: 2001-12-31
Cita del item: JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 65 (2-3): 165-170


Archivos vinculados

Formato: Nombre: Tamaño: Descripción: Ver
PDF
LEMP_2001.pdf
6.079Mb
Abrir / Descargar

Este ítem aparece en la(s) siguiente(s) colección(ones)