Mass-Spectrometric Study of the Reaction of Atomic Hydrogen with Acetaldehyde

Abstract

The reaction of atomic hydrogen with acetaldehyde has been studied with a discharge-flow system coupled to a time-of-flight mass spectrometer. The results are consistent with the mechanism Primary step: CH3CHO+H→CH3CO+H2;Secondary steps: CH3CO+H→CH2CO+H2,CH2CO+H→CH3CO*→CH3+CO,and CH3+H→ lim wallCH4. The rate constant for the abstraction of the aldehydic hydrogen in the primary step (1) for the isotopic modification CD3CDO+D has been determined directly to be 3.2±0.5×10−14 cc molecule−1·sec−1 at 300°K. Under the conditions studied, the major reaction of the acetyl radical is its further reaction with hydrogen atoms to form ketene (6). The final carbon containing products, CO and CH4, are formed from subsequent reactions of ketene with hydrogen atoms (10). The kinetic behavior of the products, CH2CO and CH4, confirms the role of ketene as a major intermediate species in this system. Isotopic studies further confirm that methane is formed from a reaction sequence of ketene with H atoms. The above mechanism is compatible with previous studies of this system, with the exception of a recent communication by Lambert, Christie, and Linnett (Chem. Commun. 1967, 338), who suggest a primary step that yields methane and the formyl radical, CHO, rather than Reaction (1).

Reactions of alcohols adsorbed on MgO. Part I. Heterogeneous reactions with hydrogen atoms and trapped electrons at room temperature: a new technique in surface chemistry

“…spectra to this radical. These spectra may be interpreted in terms of previous observations on the n-propyl radical CH,CH,-CH, (19,25). Cochran et 01.…”

“…neasaremenls of Greenler (21) and it seems likely that a similar reaction occurs on MgO at room temperature (22). It is possible that a small proportion of acetaldehyde can also be formed on the surface and when the hydrogen atom stream flows over the sample, reaction [3] would lead to the formation of acetyl radicals (25).…”

Shock-Tube Study of the Thermal Decomposition of CH3CHO and CH3CHO + H Reaction

“…The uncertainty of the rate coefficient for this reaction at elevated temperatures is large, and only estimates or values obtained from fitting to complex mechanisms are available. 2,7,13,17,20 Reaction 6 most likely proceeds via hydrogen abstraction at the carbonyl group, 7,[20][21][22][23][24] CH 3 CHO + H f CH 3 CO + H 2 (7) but a hydrogen abstraction at the methyl group 7,17,23 CH 3 CHO + H f CH 2 CHO + H 2 (8) and an addition-elimination channel 24…”

“…All the experiments mentioned were performed with comparatively high initial concentrations (>10 14 cm −3 ), and the results, therefore, had to be discussed in terms of more or less complex multistep mechanisms. An important reaction in these mechanisms is CH 3 CHO + H → products The uncertainty of the rate coefficient for this reaction at elevated temperatures is large, and only estimates or values obtained from fitting to complex mechanisms are available. ,,,, Reaction most likely proceeds via hydrogen abstraction at the carbonyl group, ,– CH 3 CHO + H → CH 3 CO + H 2 but a hydrogen abstraction at the methyl group ,, CH 3 CHO + H → CH 2 CHO + H 2 and an addition−elimination channel CH 3 CHO + H → CH 3 + CH 2 O are also possible. The reaction enthalpies are approximately −62, −41, and −14 kJ mol −1 , respectively.…”