INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Atmospheric Chemistry of 2-Ethyl Hexanal: Photochemistry and Oxidation in presence of NO2.
Autor/es:
JUAN C. FRAIRE; FABIO E. MALANCA *; GUSTAVO A. ARGÜELLO
Lugar:
Mendoza
Reunión:
Congreso; 21st IAPS Winter Conference; 2011
Resumen:
Aldehydes are important atmospheric constituents as
they are emitted by a variety of sources (natural and
anthropogenic). They arise from incomplete fossil fuel combustion, are emitted
by vegetation and are produced during biomass burning as well as atmospheric
oxidation of volatile organic compounds (VOCs). They are important precursors
of radicals and peroxyacyl nitrates (RC(O)OONO2).
The atmospheric degradation of branched-chain aldehydes is controlled by
photolysis and by reaction with OH radicals.In this work we present a kinetic and photochemical study of
2-ethyl hexanal (2-Ethal, C4H9CH(C2H5)C(O)H). it
is a volatile liquid used as solvent and the
main product of the atmospheric degradation of 2-ethyl hexanol (which
is used in the manufacture of plastics, as an additive for
lubricants, surfactants, etc.) . Previous studies of
the oxidation of this aldehyde proposes it as a new reagent to obtain 2-ethyl
hexanoic acid 7-8. According to these industrial scale use, an
increase of it concentration in the atmosphere is expected, and therefore it
is important to know its atmospheric behavior.The rate constant (k) for reaction of 2-Ethal with Cl atoms
was determined through a relative rate method with two reference compounds
(i-pentane and cyclohexane). The mean value obtained (k = (2.74
± 0.73) x10-10 cm3 molecule-1 s-1)
is in agreement with those expected for other long chain aldehydes. The
oxidation mechanism in the presence of NO2 was determined by using
FTIR spectroscopy for the product analysis. The acyl radical forming channel
was the most important in the oxidation mechanism leading to the formation of CO2,
CO, peroxyacetyl, peroxypropionyl, and ethyl nitrate. The mechanism proposed involves
a series of aldehydes: formaldehyde, acetaldehyde and propyonaldehyde, which react to form the nitrates
and peroxynitrates.In order to
determine the quantum yields of the molecule, the UV absorption cross section
was recorded previously over the range 200-350 nm at 298 K. The 254 nm photolysis
mechanism in 700 torr of O2 was determined through FTIR analysis of the
products. Two primary photodissociation channels occur: the formation of
radicals and the dissociation in closed shell molecules. The total quantum
yields (f = 0.51 ± 0.09) agrees
with those reported in bibliography for similar non-linear carbonated chain
aldehydes. The formation of CO, heptane, 3-heptanol and 3-heptanone, as
products of reactions are in accordance with the proposed mechanism.