Gas-phase and matrix-isolation photochemical studies of diallyl sulfide

YENY A. TOBÓN; BRYAN E. ARANGO HOYOS; SOPHIE SOBANSKA; A. LORENA PICONE; ROSANA M. ROMANO

Villa Carlos Paz

Encuentro; XIII Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2017

In this work the photochemistry of diallyl sulfide (DAS) in presence of molecular oxygen was studied either in gas phase or in matrix isolation conditions at cryogenic temperaturas by means of FTIR spectroscopy. This study is part of a general proyect aimed to the investigation of the photochemistry of organosulfur volatile compounds presenting atmospheric interest. Dially sulfide, CH2=CH-CH2-S-CH2=CH-CH2, is one of the main constituents of garlic. Its presence in the atmosphere was repoted, and attributed to different sources ranging from natural to industrial processes.As might be expected from its UV-visible spectrum in gas-phase, DAS is stable uner UV-visible light (800-200 nm). Gaseous mixtures of DAS and O2 in different proportions were exposed to light from a Hg-Xe lamp, and the evolution of the photoproducts were followed by FTIR spectroscopy. Inittially, acrolein (CH2=CH-C(=O)H) and sulfur dioxide (SO2) were produced. Carbon dioxide (CO2), carbon monoxide (CO) and carbonyl sulfide (OCS) were also detected. Acrolein was an intermediate in the reaction, giving formic acid (HCOOH) at longer irradiation times. When the wavelength of the light was limited to the 450 to 350 nm range, formic acid was not produced, and acrolein, togheter with the other photoproducts, remained as stable products.The photochemical reaction of DAS and O2 was also studied in matrix conditions. The matrix isolation technique combined with FTIR spectroscopy was specially well suited for the study of reactive species, van der Waals complexes, free radiacal and intermediate species. Mixtures of DAS:O2:Ar in different proportions were deposited onto a cold CsI window (~10 K) using the pulsed depositions technique. The high dilution of the reactant mixtures with respect to the inert gas prevents any other mechanisms than bimolecular ones. The integrated intensities of the IR signals were ploted against the irradiation time, and subsequently grouped according to their kinetic behavior. The photochemical mechanisms were proposed, based on the detection of the intermediates and final products.