FTIR spectroscopic study of the OH-induced oxidation of two linear acetates: ethyl and n-propyl acetates

Abstract

OH-induced oxidation mechanisms of ethyl and n-propyl acetates have been investigated at room temperature (298 ^5 K) and atmospheric pressure by photolysing mixtures with FTIR CH 3 ONO/acetate/NO spectroscopy as analytical device. The main oxidation products and their yields were as follows : from ethyl acetate, acetic acid (0.75 ^0.13), acetoxyacetaldehyde (0.15 ^0.05), acetic anhydride (0.02 ^0.01), formic acetic anhydride (0.02 ^0.01) and peroxyacetyl nitrate (PAN) ; from n-propyl acetate, acetoxyacetaldehyde (0.22 ^0.06), formic acetic anhydride (0.28 ^0.03), acetic acid (0.15 ^0.02), acetaldehyde (0.35 ^0.10), peroxypropionyl nitrate (PPN) and probably acetoxypropionaldehyde (0.30 ^0.10). From these data, oxidation schemes of these two acetates were elucidated. This study reveals in particular the speciÐc reactivity of acetates by conÐrming the novel a-ester rearrangement proposed recently by Tuazon et al. (J. Phys. Chem. A, 1998, 102, 2316 and then by showing that oxygenated alkoxyl radicals may not follow the same rules of reactivity as other alkoxyl radicals. This last observation shows the necessity for further experiments to understand the inÑuence of the oxygenated function on alkoxyl reactivity.

The atmospheric oxidation of ethyl formate and ethyl acetate over a range of temperatures and oxygen partial pressures

“…Despite the inherent uncertainty in the measured rate coefÞcient ratio, it is apparent that the α-ester rearrangement will dominate the chemistry of CH 3 C(O)OCH(O • )CH 3 at 298 K, occurring about 24 times more rapidly than its reaction with O 2 in air at 1 atm. This result conÞrms earlier laboratory and theoretical Þndings [5,11,13]. Tuazon et al [5], in their initial discovery of the α-ester process, found a 96 ± 8% yield of AA and a less than 5% yield of AAn in the OH-initiated oxidation of ethyl acetate in air at 1 atm and 298 K, entirely consistent with the 96%:4% ratio predicted by our rate coefÞcient ratio.…”

“…However, there is evidence to suggest that the observed FAn is not obtained from reaction (11). First, the appearance proÞle ( Fig.…”

“…Tuazon et al [5], in their initial discovery of the α-ester process, found a 96 ± 8% yield of AA and a less than 5% yield of AAn in the OH-initiated oxidation of ethyl acetate in air at 1 atm and 298 K, entirely consistent with the 96%:4% ratio predicted by our rate coefÞcient ratio. In a similar OH-initiated experiment, Picquet-Varrault et al [11] also found a high ratio of AA (75 ± 13%) to AAn (2 ± 1%) but also reported the formation of measurable (15 ± 5% yield) amounts of acetoxyacetaldehyde, CH 3 C(O)OCH 2 CHO. More general conclusions regarding the rate of the α-ester rearrangement for a range of radicals of the form RC(O)OCH(O • )R, including comparisons with theoretical studies [13,14], are made in the following text.…”

“…The reported uncertainty in the rate coefÞcient ratio is an estimate and is dominated by possible systematic errors in our understanding of the chemistry rather than by precision errors in spectral analysis. The results indicate that the α-ester rearrangement, reaction (9), is about nine times more rapid than reaction (10) [5,7,9,11,[13][14][15].…”

Quantum chemical study on the atmospheric photooxidation of ethyl acetate

“…Three kinetic and two product studies for the gas phase reactions of ethyl acetate with chlorine atoms have been reported. 13 21,22 Furthermore, the possible reaction mechanisms were proposed to elucidate the observed products in Picquet-Varrault's study. However, there are still some uncertainties concerning the reaction mechanisms.…”