One-pot catalytic synthesis of urea derivatives from alkyl ammonium carbamates using low concentrations of CO2

To reduce anthropogenic carbon dioxide (CO₂) emissions, it is desirable to develop reactions that can efficiently convert low concentrations of CO₂, present in exhaust gases and ambient air, into industrially important chemicals, without involving any expensive separation, concentration, compression, and purification processes. Here, we present an efficient method for synthesizing urea derivatives from alkyl ammonium carbamates. The carbamates can be easily obtained from low concentrations of CO₂ as present in ambient air or simulated exhaust gas. Reaction of alkyl ammonium carbamates with 1,3-dimethyl-2-imidazolidinone solvent in the presence of a titanium complex catalyst inside a sealed vessel produces urea derivatives in high yields. This reaction is suitable for synthesizing ethylene urea, an industrially important chemical, as well as various cyclic and acyclic urea derivatives. Using this methodology, we also show the synthesis of urea derivatives directly from low concentration of CO₂ sources in a one-pot manner.

Recent Advances in the Chemical Fixation of Carbon Dioxide: A Green Route to Carbonylated Heterocycle Synthesis

Carbon dioxide produced by human activities is one of the main contributions responsible for the greenhouse effect, which is modifying the Earth’s climate. Therefore, post-combustion CO2 capture and its conversion into high value-added chemicals are integral parts of today’s green industry. On the other hand, carbon dioxide is a ubiquitous, cheap, abundant, non-toxic, non-flammable and renewable C1 source. Among CO2 usages, this review aims to summarize and discuss the advances in the reaction of CO2, in the synthesis of cyclic carbonates, carbamates, and ureas appeared in the literature since 2017.

Ionic Liquid-Promoted Three-Component Domino Reaction of Propargyl Alcohols, Carbon Dioxide and 2-Aminoethanols: A Thermodynamically Favorable Synthesis of 2-Oxazolidinones

To circumvent the thermodynamic limitation of the synthesis of oxazolidinones starting from 2-aminoethanols and CO₂ and realize incorporation CO₂ under atmospheric pressure, a protic ionic liquid-facilitated three-component reaction of propargyl alcohols, CO₂ and 2-aminoethanols was developed to produce 2-oxazolidinones along with equal amount of α-hydroxyl ketones. The ionic liquid structure, reaction temperature and reaction time were in detail investigated. And 15 mol% 1,5,7-triazabicylo[4.4.0]dec-5-ene ([TBDH][TFE]) trifluoroethanol was found to be able to synergistically activate the substrate and CO₂, thus catalyzing this cascade reaction under atmospheric CO₂ pressure. By employing this task-specific ionic liquid as sustainable catalyst, 2-aminoethanols with different substituents were successfully transformed to 2-oxazolidinones with moderate to excellent yield after 12 h at 80 °C.

Activation of disulfide bond cleavage triggered by hydrophobization and lipophilization of functionalized dihydroasparagusic acid

Introduction of a hydrophilic group into dihydroasparagusic acid (DHAA) indicated higher reduction ability of disulfide in protein and lower air oxidation.

Substrate Specific Silver(I)-Catalyzed Cycloisomerization of Diene Involving Alkyl Rearrangements: Syntheses of 1,2,5,6-Tetrahydrocuminic Acid, p-Menth-3-en-7-ol, and p-Menth-3-en-7-al

The novel cationic Ag(I)-catalyzed cycloisomerization, which is associated with alkyl rearrangements, from dimethyl 2-allyl-2-prenylmalonate (1) to dimethyl 4-isopropylcyclohex-3-ene-1,1-dicarboxylate (2) has been developed. Derivatization from the diester 2 into the diol 3 and its X-ray crystallographic analysis determined the structure. The mechanisms of the novel reaction were investigated by isotopic experiments, which supported the unusual alkyl shifts. In addition, the product 2 was used for the total syntheses of three natural products, 1,2,5,6-tetrahydrocuminic acid (12), p-menth-3-en-7-ol (13), and p-menth-3-en-7-al (14) in short steps.

CO2-Selective Absorbents in Air: Reverse Lipid Bilayer Structure Forming Neutral Carbamic Acid in Water without Hydration

Emission gas and air contain not only CO₂ but also plentiful moisture, making it difficult to achieve selective CO₂ absorption without hydration. To generate absorbed CO₂ (wet CO₂) under heating, the need for external energy to release the absorbed water has been among the most serious problems in the fields of carbon dioxide capture and storage (CCS) and direct air capture (DAC). We found that the introduction of the hydrophobic phenyl group into alkylamines of CO₂ absorbents improved the absorption selectivity between CO₂ and water. Furthermore, ortho-, meta-, and para-xylylenediamines (OXDA, MXDA, PXDA, respectively) absorbed only CO₂ in air without any hydration. Notably, MXDA·CO₂ was formed as an anhydrous carbamic acid even in water, presumably because it was covered with hydrophobic phenyl groups, which induces a reverse lipid bilayer structure. Dry CO₂ was obtained from heating MXDA·CO₂ at 103-120 °C, which was revealed to involve chemically the Grignard reaction to form the resulting carboxylic acids in high yields.