Effect of substitution on thermal decomposition of formaldehyde: A theoretical study

Unimolecular decomposition of organic compounds is strongly influenced by substituted functional group. The present work focusses to explore the energetics and kinetics of unimolecular decomposition of formaldehyde and chloro- substituted formaldehydes. Dissociation of molecular systems are observed to compete between molecular elimination reaction and bond dissociation reaction. It is observed that degradation of formaldehyde and formyl chloride ruled by 3-centered concerted mechanism produced H2 and HCl fragments respectively. On the other hand, Cl2 elimination reaction is generated via formation of isohalon structure. Despite of presence of isohalon intermediate, molecular elimination in phosgene required higher energy as compared to formyl chloride. Ease of molecular elimination in case of formyl chloride is attributed to favourable electrostatic interaction between hydrogen and chlorine atom, which assist in lower activation barrier. Further, the kinetic analysis suggested the applied temperature and pressure play a key role in formation of dominant elimination channel during decomposition reaction.