Activation of β-diketones for CO2 capture and utilization

Abstract

Herein, we explore the use of β-diketones for CO₂ fixation and utilization based on their dual Brønsted acid/Lewis base character upon activation by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and zinc bromide (ZnBr₂), respectively. The effect of tautomerization on the chemical fixation of CO₂ was investigated using different β-diketone compounds, namely, acetylacetone (ACAC), dibenzoylmethane (DBM) and dimedone (DMD) dissolved in dimethyl sulfoxide and activated by DBU. Spectroscopic data demonstrated that the activated ACAC can capture atmospheric CO₂ through the formation of both keto- and enol-carboxylated adducts, with the ability to evolve the enol form of the ionic organic carbonate adduct upon direct exposure to CO₂. Meanwhile activated DBM and DMD showed the exclusive formation of the enol-organic carbonate adducts once bubbled with CO₂. Volumetric uptake measurements indicated that the chemisorption capacities of ACAC and DBM (2.38 mmol CO₂ per g sorbent) were higher than DMD (1.59 mmol CO₂ per g sorbent). Additionally, the chemical fixation of CO₂ into cyclic carbonates (CCs) was achieved by in situ complexation of the investigated β-diketones with a zinc ion. The catalytic systems were able to catalyze the transformation of several terminal oxiranes into the corresponding CCs under atmospheric CO₂ pressure with excellent conversions. Interestingly, the catalytic system showed the ability to convert the naturally occurring pinene oxide into dimeric pinene carbonate.