The thermal decomposition of cis- and trans-2-methoxy-4-methyl-3,4-dihydro-2H-pyran

Abstract

The thermal decomposition of both cis-and trans-2-methoxy-4-methyl-3,4-dihydro-2H-pyran has been investigated in the gas phase from 287 to 345°. In this temperature range both isomers decomposed to give crotonaldehyde and methyl vinyl ether by a homogeneous process that obeyed first-order kinetics. The data for the trans-isomer yileded the Arrhenius equation (i). Similarly the cis-isomer gave equation (ii). These results log k₁/s^–1= 14·246 ± 0·106 –(201·46 + 1·20 kJ mol^–1)RTIn 10 (i), log k₂/s^–1= 13·958 ± 0·062 –(196·00 ± 0·70 kJ mol^–1)RTIn 10 (ii) are discussed in terms of a unimolecular decomposition occurring by a concerted mechanism.