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CO2 activation through C-N, C-O and C-C bond formation.

Physical chemistry chemical physics : PCCP (2019-12-19)
Ala'a F Eftaiha, Abdussalam K Qaroush, Ibrahim K Okashah, Fatima Alsoubani, Jonas Futter, Carsten Troll, Bernhard Rieger, Khaleel I Assaf
ABSTRACT

A comparative model for the chemisorption of CO2 was explored via three representative reaction pathways: carboxylation of cyclohexanone, carbonation of cyclohexanol, and carbamation of cyclohexylamine. The model substrates were activated using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, an amidine superbase). For each of these reactions, the formation of the corresponding CO2 adducts was confirmed by 13C nuclear magnetic resonance and Fourier-transform infrared spectroscopy measurements. It was demonstrated that CO2 fixation occurred through either an enol-CO2 adduct (i.e. carboxylation), proton shuttling process (i.e. carbonation), or self-activation mechanism (i.e. carbamation). Volumetric adsorption measurements indicated that cyclohexanol was superior in its uptake capacity (11.7 mmol CO2 g-1 sorbent) in comparison to cyclohexylamine (9.3 mmol CO2 g-1 sorbent) or cyclohexanone (8.5 mmol CO2 g-1 sorbent). As supported by density functional theory calculations, this trend was expected given the fact that the carbonation reaction proceeded through a more thermodynamically favorable reaction process.

MATERIALS
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Sigma-Aldrich
Dimethyl sulfoxide-d6, 99.5 atom % D