Yu-Nong Li

Homogeneous hydrogenation of carbon dioxide to methanol

Carbon dioxide, a greenhouse gas mainly from the consumption of fossil fuel, is regarded as an attractive feedstock in view of synthetic chemistry. Great efforts have been devoted to developing catalytic processes for converting CO2 into value-added compounds with reduced carbon footprint. Among versatile applications in organic synthesis, CO2 can serve as a promising raw material for fuel production, especially methanol. ‘Coming from fuel and returning to fuel’ is an appealing objective in terms of sustainable development associated with circumventing the energy shortage and CO2 issue. To date, metal complexes and organocatalysts for CO2 hydrogenation to methanol have been developed along with the reaction mechanistic insight. Understanding the interaction of active catalytic species with CO2 or hydrogen could account for development of efficient homogeneous catalysts. In this context, homogeneous catalytic hydrogenation of CO2 and its derivatives into methanol is highlighted in this article in combination with mechanistic understanding on a molecular level.

Catalyst-free approach for solvent-dependent selective oxidation of organic sulfides with oxone

Selective oxidation of sulfides was successfully performed by employing oxone (2KHSO5·KHSO4·K2SO4) as oxidant without utilization of any catalyst/additive under mild reaction conditions. Notably, the reaction can be controlled by the chosen solvent. When ethanol was used as the solvent, sulfoxides were obtained in excellent yield; the reaction almost exclusively gave the sulfone in water. Furthermore, this protocol worked well for various sulfides to the corresponding sulfoxides in ethanol or sulfones in water.

Protic onium salts-catalyzed synthesis of 5-aryl-2-oxazolidinones from aziridines and CO2 under mild conditions

Protic onium salts, e.g.pyridium iodide, proved to be highly efficient and recyclable catalysts for the selective synthesis of 5-aryl-2-oxazolidinones under a CO2 atmosphere at room temperature, presumably due to aziridine activation assisted by hydrogen bonding on the basis of 1H NMR and in situ FT IR under CO2 pressure study.

Organic synthesis using carbon dioxide as phosgene-free carbonyl reagent

CO2 is very attractive as a typical renewable feedstock for manufacturing commodity chemicals, fuel, and materials since it is an abundant, nontoxic, nonflammable, and easily available C1 resource. The development of greener chemical methodologies for replacing the utility of hazardous and environmentally undesirable phosgene largely relies on ingenious activation and incorporation of CO2 into valuable compounds, which is of paramount importance from a standpoint of green chemistry and sustainable development. Great efforts have been devoted to constructing C–C, C–O, and C–N bond on the basis of CO2 activation through molecular catalysis owing to its kinetic and thermodynamic stability. The aim of this article is to demonstrate the versatile use of CO2 in organic synthesis as the alternative carbonyl source of phosgene, with the main focus on utilization of CO2 as phosgene replacement for the synthesis of value-added compounds such as cyclic carbonates, oxa-zolidinones, ureas, isocyanates, and polymers, affording greener pathways for future chemical processes.

Experimental and theoretical studies on imidazolium ionic liquid-promoted conversion of fructose to 5-hydroxymethylfurfural

A combined experimental and computational study on the imidazolium ionic liquid-promoted conversion of fructose to 5-hydroxymethylfurfural (HMF) was performed. In particular, 1-butyl-3-methyl-imidazolium bromide (BMImBr) was found to be unexpectedly effective for conversion of fructose into HMF without utilizing any other additive or catalyst. Under the optimized conditions, nearly 100% conversion of fructose with a 95% yield of HMF could be obtained. In addition, BMImBr could be easily recovered and reused over 6 times without significant loss of activity. This protocol represents a simple, recyclable and environmentally friendly pathway for HMF production. Furthermore, the detailed mechanism of the BMImBr-promoted conversion of fructose into HMF was also studied through an in situ FT-IR technique, NMR and density functional theory calculations, and demonstrated that the hydrogen bond interaction between BMImBr and fructose could play an important role in promoting the dehydration of fructose. This work also provides further understanding at the molecular level of the reaction process for ionic liquid-promoted conversion of fructose to HMF.

In situ hydrogenation of captured CO2 to formate with polyethyleneimine and Rh/monophosphine system

CO2 in the air can be efficiently captured with simultaneous activation by PEI (polyethyleneimine) to form ammonium carbamate and/or carbonate species. Thus, the in situ hydrogenation of captured CO2 into energy-storage materials rather than going through the desorption of conventional CCS (carbon capture and storage) runs better in comparison with equivalent gaseous CO2, thus validating this potential application of CCU (carbon capture and utilization) for supplying renewable energy. PEI600 as an effective carbon absorbent in this study could also be assumed to serve as both ligand and base to promote the catalytic hydrogenation of captured CO2, consequently acting as a ‘hinge base’ to combine capture and hydrogenation processes. The pathway was studied by NMR and in situ FT-IR spectroscopy under CO2 pressure. This protocol could open up great potential in transforming the captured CO2 from waste to fuel-related products.

Ethylene carbonate as a unique solvent for palladium-catalyzed Wacker oxidation using oxygen as the sole oxidant

Ethylene carbonate (EC) as a unique solvent for the Wacker oxidation of higher alkenes and aryl alkenes has been successfully developed using molecular oxygen as the sole oxidant, in which colloidal Pd nanoparticles stabilized in EC are considered to facilitate its reoxidation under cocatalyst-free conditions.

Equimolar Carbon Absorption by Potassium Phthalimide and In Situ Catalytic Conversion Under Mild Conditions

Potassium phthalimide, with weak basicity, is an excellent absorbent for rapid carbon dioxide capture with almost equimolar absorption. This process is assumed to proceed through the potassium carbamate formation pathway, as supported by NMR spectroscopy, an in situ FTIR study, and computational calculations. Both the basicity and nucleophilicity of phthalimide salts have a crucial effect on the capture process. Furthermore, the captured carbon dioxide could more easily be converted in situ into value-added chemicals and fuel-related products through carbon capture and utilization, rather than going through a desorption process.

An integrated process of CO2 capture and in situ hydrogenation to formate using a tunable ethoxyl-functionalized amidine and Rh/bisphosphine system

An integrated process of CO2 capture and in situ hydrogenation into formate was achieved in 95–99% yield using a tunable ethoxyl-functionalized amidine and Rh/bisphosphine system, being regarded as an alternative carbon capture and utilization approach to supply fuel-related products, to circumvent the energy penalty in carbon capture and storage. CO2 was captured by non-volatile amidine derivatives with simultaneous activation to form zwitterionic amidinium carbonate, and subsequent hydrogenation was facilitated by Rh/bisphosphine. The adsorption capacity and hydrogenation efficiency can be optimized by tuning the ethoxyl side chain. Particularly, the alkanolamidine bearing an intramolecular hydrogen donor derived from 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU) gave both a high CO2 uptake (molar ratio of 0.95:1) and excellent hydrogenation yield (99%). Furthermore, the silica-supported alkanolamidine was readily recovered and reused with the retention of good performance. This kind of carbon capture and utilization pathway could be a potential energy-saving option for industrial upgrading of CO2 from waste to fuel-related products in a carbon neutral manner.

Chapter Nine – Carbon Capture with Simultaneous Activation and Its Subsequent Transformation

Abstract Carbon capture and storage/sequestration (CCS) is now being considered as a potential option to mitigate global warming associated with carbon accumulation. The chemical absorption technique employing efficient amino-containing absorbents has been widely developed. Nevertheless, extensive energy consumption in desorption–compression process would be a crucial barrier to realize practical CCS. On the other hand, CO2 is very attractive as a typical renewable feedstock for manufacturing commodity chemicals and fuels. However, the reactions involving CO2 are commonly carried out at high pressure, which may not be economically suitable and also pose safety concerns. Consequently, we have proposed a carbon capture and utilization (CCU) strategy as an alternative approach to addressing energy issue in CCS. This crucial point of CCU could be simultaneous activation of CO2 upon its capture (e.g., formation of carbamate/alkyl carbonate) and thus in situ catalytic transformation into value-added chemicals under mild conditions, avoiding additional desorption step. This chapter is intended to discuss carbon capture and in situ transformation of CO2 to oxazolidinones, carbonates, quinazolines, urea derivatives, isocyanates, and carbamates via the formation of C O and C N bond.