The Thermal Decomposition of Acetaldehyde¹

Abstract

When 50-50 mixtures of CHsCHO-CaDg or CD3CDO-C2H6 are decomposed, the amount of isotopic mixing as measured by the CH3D/CH4 or CD3H/CD4 ratios is proportional to the fraction of aldehyde decomposed. When different amounts of NO are added to the aldehyde-ethane mixtures the ratios of CH3D/CH4 or CD3H/CD4 are (for constant fractional decomposition of the aldehyde) either independent of the concentration of NO or increase somewhat as the NO concentration increases. When 50-50 mixtures of CDsCDO-CHgCHz^CHa and CD3CDO-C2He are decomposed, the CD3H/CD4 ratio for a given fractional decomposition of aldehyde is 1.8:1 respectively for the two reactions. Our results indicate (1) that the thermal decomposition of CHsCHO and CD3CDO are similar, (2) that both are chain reactions unaccompanied by any significant amount of direct separation into product molecules and (3) that the thermal decomposition of a substrate in presence of an indicator (in which either the substrate or indicator is fully deuterated) provides a general method for studying elementary reactions.1.

Chemistry of organic free radicals in the vapor phase. I. Detection and reactions of free alkyl radicals

“…of mixtures of CHjCHO and CD3CDO by Wall and Moore (54) shows that extensive isotopic mixing occurs even at low conversions; this mixing is consistent with the occurrence of ( 107 Rice and Varnerin (55) have recently published further work on the thermal decomposition of acetaldehyde and deuteroacetaldehyde. The evidence again supports a radical chain mechanism.…”

“…It should be noted that nitration is readily accomplished by NOa as well as nitric acid, thus supporting the proposal expressed in equation (55). However, an alternative path to nitroalkane production which may assume more or less importance depending on the specific reaction conditions is that of alkyl radical displacement on nitric acid directly (60), a chain-propagating step.…”

The Deuterium Isotope Effect

“…The decomposition of acetaldehyde and acetaldehyde-dr gave an isotope effect of 2.5 at 535°C. (190,203), and the decomposition of ethane and ethane-& gave an isotope effect of 3 at 613°C. (189).…”

Mechanistic Insights into Catalytic Ethanol Steam Reforming Using Isotope‐Labeled Reactants

“…Fora ll catalyst formulations, however, much of the 13 Cg oes to the CO y species,t hus maintaining al ow concentration of H 3 13 C 13 CH 3 . [29,30] However,this reaction is unfavored at the operating temperature of 350 8 8C, [31] thus implying that the C 2 H 6 observed must be formed through ethylene hydrogenation [Eq. [29,30] However,this reaction is unfavored at the operating temperature of 350 8 8C, [31] thus implying that the C 2 H 6 observed must be formed through ethylene hydrogenation [Eq.…”

“…Asimilar explanation can be applied to C 2 H 4 ( Figure 4C) with similar trends observed across the three catalyst formulations.C 2 H 4 and C 2 H 6 formation have as trong correlation since the formation of C 2 H 6 (all isotopes) declines and C 2 H 4 concentration increases concurrently.T his selectivity change suggests that aportion of the C 2 H 4 is formed directly from the C 2 H 6 by the gas-phase dehydrogenation pathway. [29,30] However,this reaction is unfavored at the operating temperature of 350 8 8C, [31] thus implying that the C 2 H 6 observed must be formed through ethylene hydrogenation [Eq. (12)] on the catalyst surface,acommonly reported feature of supported platinum-group metal catalysts.…”