The Unimolecular Dissociation of 3,4-Dihydro-2H-Pyran over a Wide Temperature Range

Article abstract of DOI:10.1002/kin.550270708

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C5H8O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10percent DHP in krypton over 900-1500 K, 110-560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric, using the decomposition of allylethyl ether as an internal standard, and covering 663-773 K.The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions.Precise rate constants (rms deviation of 10percent) were obtained for this process over the indicated temperature ranges.Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures.These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when (ΔE)_down is a fixed 400 cm^-1.Arrhenius expressions for k_infinite derived from the two measurements are in close accord and also consistent with most previous studies of this reaction.