Reaction of silylalkylmono- and silylalkyldi-amines with carbon dioxide: evidence of formation of inter- and intra-molecular ammonium carbamates and their conversion into organic carbamates of industrial interest under carbon dioxide catalysis

Abstract

The reactivity of industrially relevant silylalkylamines towards CO₂ and dialkyl/arylcarbonates is discussed. The kinetics of uptake of carbon dioxide at various temperatures shows that at 295 K, silylalkylmonoamines react with carbon dioxide in a 2∶1 molar ratio, affording classic intermolecular ammonium carbamates of formula RNHCOO⁻⁺NH₃R, while at 273 K, dimeric carbammic acids, (RNHCOOH)₂, are formed. Conversely, silylalkyldiamines react at 297 K with carbon dioxide to afford zwitterionic intramolecular six-membered cyclic ammonium carbamates of formula RNH₂⁺CH₂CH₂NHCOO⁻, a unique example of CO₂ uptake by an amine with a 1∶1 molar ratio. Such systems may have a potential application in CO₂ separation. The catalytic role of carbon dioxide in the carbamation of the above mentioned amines by reaction with organic carbonates is described.