Dynamic Covalent Chemistry of Carbon Dioxide: Opportunities to Address Environmental Issues

Abstract

Extraction and purification of basic chemicals from complex mixtures has been a persistent issue throughout the development of the chemical sciences. The chemical industry and academic research have grown over the centuries by following a deconstruction-reconstruction approach, reminiscent of the metabolism process. Chemists have designed and optimized extraction, purification, and transformation processes of molecules from natural deposits (fossil fuels, biomass, ores), in order to reassemble them into complex adducts. These highly selective and cost-effective techniques arose from developments in physical chemistry but also in supramolecular chemistry, long before the term was even coined. Thanks to the extremely diverse toolbox currently available to the scientific community, artificial molecular systems of increasing complexity can be built and integrated into high-technology products. If humanity has proven through the ages how gifted it can be at this deconstruction-reconstruction game, which has transformed the natural world to a human-shaped one, it has been confronted for more than a century by a new challenge: the deconstruction and reconstruction from a new type of deposit, the waste resulting from the mass production of disposable manufactured goods. In this Account, we will explore the potential contribution of controlled molecular and supramolecular self-assembly phenomena to the challenge of selective and efficient capture of valuable target molecules from mixtures found in postconsumer waste. While it may appear paradoxical to add more molecular ingredients to an already compositionally complex system in order to address a purification issue, we will compare the selectivity, yield, and cost of such an atypical procedure with traditional physical techniques. In the context of carbon dioxide capture or release, we will specifically focus on the coupling between this reversible covalent fixation of the gas by amines and an additional chemical equilibrium. This equilibrium may involve covalent or noncovalent bond formation between a supplementary species and either the unloaded reactant or the CO-loaded product. Thereby, this new reactive species may act as a CO capture agonist or antagonist by either thermodynamically favoring the carbamation or decarbamation direction. Indeed, superagonism, the increase of CO loading per amine site upon carbamation beyond the theoretical limit of 0.5, can be achieved using tightly bound cationic metal counterions. In all cases, upon binding and adduct formation, a mutual selection process occurs between one member of the CO-based dynamic combinatorial library and one agonist or antagonist, which can itself be contained in a complex mixture of analogues. If this adduct is the only species that, upon formation, can self-aggregate into a separate solid phase, selection and binding are accompanied by translocation, rendering the purification procedure operationally straightforward. This general strategy, based on a simple design of coupled molecular systems, may easily ...

Simultaneous CO2 Capture and Metal Purification from Waste Streams

“…Yttrium was selected as representative of the series providing the optimal resolution for in situ qNMR, while ex situ analyses were conducted with lanthanum and yttrium (vide supra). In agreement with our previous report, 20 the rare earth elements proved to induce identical partitioning effects on the various building blocks used. In the presence of 1/12 eq.…”

“…We and others have indeed previously shown that organic or inorganic species reversibly binding amines or carbamates, can respectively act as carbamation antagonist or agonist, favoring either capture from dilute emissions 18,19 or stripping at low enthalpic costs. 20,21 -C-N bond exchange can in principle occur at fixed CO2 loading through intra-and/or intermolecular substitution reactions (transcarbamation; scheme 1, Eq. 2 and Eq.…”

“…In the presence of 1/12 eq. RECl3, the maximal amount of template affording a fully reversible system, 20,27 i.e. on which CO2 can still be expelled by thermal stripping, precipitation starts around aS(CO2) = 0.20.…”

Bypassing the Inertness of Aziridine/CO2 Systems to Access 5-Aryl-2-Oxazolidinones: Catalyst-Free Synthesis Under Ambient Conditions

“…Our idea stemmed from the largely documented evidence that carbon dioxide and amines easily form carbamato adducts. 24 Thus, the present work describes a novel and simple CO2-fixation strategy to synthesize 5-aryl-2oxazolidinones bypassing the inertness of the aziridine/carbon dioxide system: exceptional simplicity and increased sustainable value with respect to existing procedures are guaranteed by operating at ambient conditions (ambient temperature, atmospheric CO2 pressure) and the complete absence of any catalyst/co-catalyst. Scheme 1.…”

Carbon Dioxide-Mediated Desalination

“…Under reduced pressure or mild heat, dissociation of CO2 from the diamines occurs, and the parent diamines can be regenerated. This reversible carbon dioxide capture process has been applied in carbon capture processes 22 , switchable solvents 16 , and heavy metal extraction 17,23 . CO2-responsive autonomous aggregation (or precipitation) was controlled by polarity alteration of the monomeric entity, which is key to induce this dynamic behaviour 24 .…”