Efficient chemical fixation and defixation cycle of carbon dioxide under ambient conditions

Abstract

Chemical fixation of CO₂ as a C1 feedstock for producing value-added products is an important post-combustion technology reducing the CO₂ emission. As it is an irreversible process, not considered for the CO₂ capture and release. Overall, these chemical transformations also do not help to mitigate global warming, as the energy consumed in different forms is much higher than the amount of CO₂ fixed by chemical reactions. Here we describe the development of re-generable chemical fixation of CO₂ by spiroaziridine oxindole, where CO₂ is captured (chemical fixation) under catalyst-free condition at room temperature both in aqueous and non-aqueous medium even directly from the slow stream of flue gas producing regioselectively spirooxazolidinyl oxindoles, a potential drug. The CO₂-adduct is reversed back to the spiroaziridine releasing CO₂ under mild conditions. Further both the fixation-defixation of CO₂ can be repeated under near ambient conditions for several cycles in a single loop using a recyclable reagent.

Figure 1

Proposed reactivity of spiroaziridine 1 and spirooxazolidinone 2 towards CO₂ fixation and release.

Figure 2

Intermediate compounds during defixation of CO₂ from 2a.

Figure 3

The recycling of spiroaziridine 1a via re-synthesis of spirooxazolidinone 2a (The yield in each cycle referred to the GC yield of resynthesized spirooxazolidinone 2a; Standard deviation: cycle 1 and 2 = 0.58; cycle 3–5 = 1).

Figure 4

Fixation–defixation cycle of CO₂ with recyclable NaI.

Figure 5

Temperature effect in chemical fixation of CO₂ by spiroaziridine 1a.

Figure 6

Chemical fixation-defixation cycles at 70 °C (The yield in each cycle referred to the GC yield of resynthesized spirooxazolidinone 2a; Standard deviation: cycle 1 and 2 = 0.82; cycle 3 = 1.25, cycle 4 = 1.70, cycle 5 = 0.47).

Figure 7

Generalization of catalyst-free CO₂ fixation in synthesis of various spirooxazolidinoyl oxindoles 2. The values in parenthesis refer to the GC yield using stimulated flue gas as a source of CO₂.