Thermal Stability of Larger Carbonyl Compounds: 2-Methylbutyraldehyde

We have decomposed 2-methylbutyraldehye in single pulse shock tube experiments, at temperatures between 1075 K to 1250 K and pressures of 1.5 and 6 atm. Five reaction channels have been identified from the unimolecular products that have been detected. The products involve CC bond cleavage together with a retro-ene reaction. Particularly remarkable is the detection of small amount of butane; the first time that an alkane has been detected in these high-temperature experiments. The formation of butane represents evidence of the roaming radical reaction or more generally the high-temperature radical disproportionation reaction. Ethylene is present in large yields, and this is traced to a 1,2 H-transfer reaction involving the highly exothermic transfer of a carbonyl hydrogen to an alkyl site. The results are consistent with earlier single pulse shock tube experiments on the 2-ketones. In particular, they confirm the earlier observation that substituting a methyl and hydrogen atom with a doubly bonded oxygen atom have very little effect on the rate constant of the adjoining CC bond. The yields of ethylene are consistent with a very low value of the carbonyl resonance energy.