Efficient carbamate synthesis via a three-component coupling of an amine, CO2, and alkyl halides in the presence of Cs2CO3 and tetrabutylammonium iodide

Advanced zeolite and ordered mesoporous silica-based catalysts for the conversion of CO2 to chemicals and fuels

For many years, capturing, storing or sequestering CO₂ from concentrated emission sources or from air has been a powerful technique for reducing atmospheric CO₂. Moreover, the use of CO₂ as a C1 building block to mitigate CO₂ emissions and, at the same time, produce sustainable chemicals or fuels is a challenging and promising alternative to meet global demand for chemicals and energy. Hence, the chemical incorporation and conversion of CO₂ into valuable chemicals has received much attention in the last decade, since CO₂ is an abundant, inexpensive, nontoxic, nonflammable, and renewable one-carbon building block. Nevertheless, CO₂ is the most oxidized form of carbon, thermodynamically the most stable form and kinetically inert. Consequently, the chemical conversion of CO₂ requires highly reactive, rich-energy substrates, highly stable products to be formed or harder reaction conditions. The use of catalysts constitutes an important tool in the development of sustainable chemistry, since catalysts increase the rate of the reaction without modifying the overall standard Gibbs energy in the reaction. Therefore, special attention has been paid to catalysis, and in particular to heterogeneous catalysis because of its environmentally friendly and recyclable nature attributed to simple separation and recovery, as well as its applicability to continuous reactor operations. Focusing on heterogeneous catalysts, we decided to center on zeolite and ordered mesoporous materials due to their high thermal and chemical stability and versatility, which make them good candidates for the design and development of catalysts for CO₂ conversion. In the present review, we analyze the state of the art in the last 25 years and the potential opportunities for using zeolite and OMS (ordered mesoporous silica) based materials to convert CO₂ into valuable chemicals essential for our daily lives and fuels, and to pave the way towards reducing carbon footprint. In this review, we have compiled, to the best of our knowledge, the different reactions involving catalysts based on zeolites and OMS to convert CO₂ into cyclic and dialkyl carbonates, acyclic carbamates, 2-oxazolidones, carboxylic acids, methanol, dimethylether, methane, higher alcohols (C₂₊OH), C₂₊ (gasoline, olefins and aromatics), syngas (RWGS, dry reforming of methane and alcohols), olefins (oxidative dehydrogenation of alkanes) and simple fuels by photoreduction. The use of advanced zeolite and OMS-based materials, and the development of new processes and technologies should provide a new impulse to boost the conversion of CO₂ into chemicals and fuels.

Visible light-driven carbamoyloxylation of the α-C(sp3)-H bond of arylacetones via radical-initiated hydrogen atom transfer

Photocatalytic synthesis has emerged as an efficient route to transform CO₂ into functionalized organic carbamates by photocatalysis. Herein, a catalyst-free carbamoyloxylation of arylacetones with CO₂ and amines under visible light was developed for the synthesis of O-β-oxoalkyl carbamates in yields up to 93%. This protocol proceeded smoothly with the assistance of inexpensive carbon tetrabromide at room temperature under atmospheric CO₂ pressure, leading to simultaneous construction of C-O and C-N bonds. Mechanism studies suggested the photoinduced hydrogen atom transfer (HAT) pathway followed by radical addition or single electron transfer (SET).

Atomically Dispersed Copper on N-Doped Carbon Nanosheets for Electrocatalytic Synthesis of Carbamates from CO2 as a C1 Source

The synthesis of carbamates by electrocatalytic reduction of CO₂ is an effective method to realize the utilization of CO₂ resources. The development of high-performance electrocatalysts to complete this process more efficiently is of great significance to sustainable development. Owing to their unique structural characteristics, single-atom catalysts are expected to promote the reaction process more efficiently. In this study, an atomically dispersed Cu species on N-doped carbon nanosheet composite material (Cu-N-C) was prepared by metal-organic framework derivatization. Compared with traditional Cu bulk electrodes, the Cu-N-C material has better catalytic performance for the synthesis of methyl N-phenylcarbamate; and the optimized yield reached 71 % at room temperature and normal pressure. The Cu-N-C material has good stability that the catalytic performance does not decrease after repeated use for 10 times. In addition, the Cu-N-C material has good applicability to this catalytic system, and a variety of amines can be smoothly converted into corresponding carbamates.

Investigating the chemical impurity profiles of fentanyl preparations and precursors to identify chemical attribution signatures for synthetic method attribution

From an analytical chemistry standpoint, determining the chemical attribution signatures (CAS) of synthetic reaction mixtures is an impurity profiling exercise. Identifying and understanding the impurity profile and CAS of these chemical agents would allow them to be exploited for chemical forensic information, such as how a particular chemical agent was synthesised. Being able to determine the synthetic route used to make a chemical agent allows for the possibility of batches of the agent, and individual incidents using that agent, to be forensically linked. This information is of particular benefit to agencies investigating the nefarious and illicit use of chemical agents. One such chemical agent of interest to law enforcement and national security agencies is fentanyl. In this study two acylation methods for the final step of fentanyl production, herein termed the Janssen and Siegfried methods, were investigated by liquid chromatography- high resolution mass spectrometry (LC-HRMS) and multivariate statistical analysis (MVA). From these data, fifty-five chemical impurities were identified. Of these, ten were specific CAS for the Janssen method, and five for the Siegfried method. Additionally, analytical data from four different literature methods for production of the fentanyl precursor 4-anilino-N-phenethylpiperidine (ANPP), were compared to the results obtained from the method of production (Valdez) used in this study. Comparison of the LC-HRMS data for these five methods allowed for four Valdez specific impurities to be identified. These may be useful CAS for the Valdez method of ANPP production.

Triazinetriamine-derived porous organic polymer-supported copper nanoparticles (Cu-NPs@TzTa-POP): an efficient catalyst for the synthesis of N-methylated products via CO2 fixation and primary carbamates from alcohols and urea

Copper nanoparticles incorporated triazinetriamine derived porous organic polymer based catalyst was synthesized for catalytic production N-methylated amines and primary carbamates.

Synthesis of novel gefitinib-based derivatives and their anticancer activity

Drug latentiation is a process of modifying a drug molecule structurally to improve its binding affinity as well as increasing the drug-receptor interactions and potentiate its therapeutic potential. In the quest for discovering more potent epidermal growth factor receptor (EGFR) inhibitors, gefitinib-based derivatives were designed by simple structural modification at the secondary amine of gefitinib by N-alkylation. Three gefitinib derivatives (gefitinib-NB, -NP, and -NIP) were synthesized by N-alkylation and phase transfer catalysis. Structural characterization, physicochemical parameters such as solubility, log P, and p K _a were determined. Molecular docking studies were carried out to investigate the binding interactions at the active site. Further drug-bovine serum albumin (BSA) protein and drug-calf thymus (CT) DNA interactions were performed to understand the pharmacokinetics of the synthesized derivatives. All the compounds were screened for preliminary in vitro cytotoxic activity against A549, A431 lung, and MDA-MB-231 breast cancer cell lines by MTT assay. The gefitinib-NP and gefitinib-NB derivatives exhibited strong cytotoxic activity compared with gefitinib. They also showed higher drug-BSA and drug-DNA interactions. Molecular docking studies showed the orientation and binding interactions with the EGFR as well as with BSA and CT DNA. The results establish a strong correlation between the experimental and molecular docking studies. EGFR inhibition studies were also carried out for the derivatives and we identified the NP derivative of gefitinib as a potential lead compound. The gefitinib-based derivatives reported herein are cytotoxic agents and can be tested for further pharmacokinetic profiles and toxicity studies which might be helpful for designing more potent gefitinib-based derivatives in the future.

Carbon dioxide utilization in the efficient synthesis of carbamates by deep eutectic solvents (DES) as green and attractive solvent/catalyst systems

Deep eutectic solvents as a green solvent/catalyst system for directly synthesizing carbamates from amines, CO₂ and alkyl halides.

Catalytic synthesis of benzimidazoles and organic carbamates using a polymer supported zinc catalyst through CO2 fixation

Zinc metal is attached to the organically modified polystyrene and the obtained catalyst is well characterized. The catalyst is very efficient for the formation of benzimidazoles and organic carbamates through carbon dioxide fixation.

(3-Ammonio-2,2-dimethyl-propyl)carbamate Dihydrate

(3-Ammonio-2,2-dimethylpropyl)carbamate dihydrate was synthesised. The title compound was characterised by single crystal X-ray diffraction and IR-/Raman-spectroscopy. It has been demonstrated that a mixture of dilute acetic acid and 2,2-dimethyl-1,3-diaminopropane is able to capture CO2 spontaneously from the atmosphere. An intramolecular hydrogen bond stabilises the conformation of the ylide-type title molecule. Intermolecular hydrogen bonds between all moieties connect them to a strand-type chain structure.

Unlocking the Potential of Phenacyl Protecting Groups: CO2-Based Formation and Photocatalytic Release of Caged Amines

Orthogonal protection and deprotection of amines remain important tools in synthetic design as well as in chemical biology and material research applications. A robust, highly efficient, and sustainable method for the formation of phenacyl-based carbamate esters was developed using CO₂ for the in situ preparation of the intermediate carbamates. Our mild and broadly applicable protocol allows for the formation of phenacyl urethanes of anilines, primary amines, including amino acids, and secondary amines in high to excellent yields. Moreover, we demonstrate the utility by a mild and convenient photocatalytic deprotection protocol using visible light. A key feature of the [Ru(bpy)₃](PF₆)₂-catalyzed method is the use of ascorbic acid as reductive quencher in a neutral, buffered, two-phase acetonitrile/water mixture, granting fast and highly selective deprotection for all presented examples.

A multifunctional MOF as a recyclable catalyst for the fixation of CO2 with aziridines or epoxides and as a luminescent probe of Cr(vi)

A multifunctional metal-organic framework (1) can serve as an efficient and recyclable catalysts for the conversion of CO₂ with aziridines or epoxides. Furthermore, the material can also act as a recyclable luminescent probe for Cr(vi) species among twenty anions.

B(C6F5)3: a robust catalyst for the activation of CO2 and dimethylamine borane for the N-formylation reactions

In this work, B(C₆F₅)₃ is utilized as an organocatalyst for the transition-metal-free N-formylation of amines using carbon dioxide (CO₂) as a C1 source and dimethylamine borane (Me₂NH·BH₃) as a green hydrogen transfer source at 80 °C.

Halogen-Free Synthesis of Carbamates from CO2 and Amines Using Titanium Alkoxides

A direct synthesis of carbamates from amines and carbon dioxide in the presence of Ti(OR)₄ (R=nBu (1), Me (2), Et (3), nPr (4)) was investigated. Aniline was reacted with titanium n-butoxide (1) in the presence of carbon dioxide (5 MPa) to give the corresponding n-butyl N-phenylcarbamate (BPC) in nearly quantitative yield (99 %) within 20 min. Furthermore, 1 could be regenerated upon reaction with n-butanol during water removal. The recovered 1 could then be reused in a subsequent reaction.

A Simple Zinc Catalyst for Carbamate Synthesis Directly from CO2

Several zinc salts were employed as catalysts for the synthesis of carbamates directly from aromatic amines, CO₂ , and silicate esters. Zn(OAc)₂ offered the best performance among the salts tested. The addition of an N-donor ligand such as 1,10-phenanthroline increased the yield. The best catalytic performance of Zn(OAc)₂ can be explained by carboxylate-assisted proton activation. The interaction between the substrate and the catalyst can be observed by chemical shifts in ¹ H and ¹⁵ N NMR spectra. Isocyanate was a key intermediate, which was generated from amine and CO₂ . Silicate ester was finally converted to siloxane, which was determined by ²⁹ Si NMR. The commercially available catalyst system could be reused. The yield of isolated carbamate could reach up to 96 % with various substrates, and the catalytic reaction was amine-selective in the presence of other functional groups.

Chemoselective Synthesis of Carbamates using CO2 as Carbon Source

Synthesis of carbamates directly from amines using CO2 as the carbon source is a straightforward and sustainable approach. Herein, we describe a highly effective and chemoselective methodology for the synthesis of carbamates at room temperature and atmospheric pressure. This methodology can also be applied to protect the amino group in amino acids and peptides, and also to synthesize important pharmaceuticals.

Cs2CO3-promoted polycondensation of CO2 with diols and dihalides for the synthesis of miscellaneous polycarbonates

A one-pot protocol for the direct synthesis of polycarbonates through polycondensation of diols, dihalides and CO₂ in the presence of Cs₂CO₃ is described.

Multicomponent synthesis of dithiocarbamates starting from vinyl sulfones/sulfoxides and their use in polymerization reactions

Synthesis of dithiocarbamates from vinyl sulfones/sulfoxides and the corresponding polymers with a dithiocarbamate backbone using divinyl sulfone and diamines is reported.

Heterobimetallic dinuclear lanthanide alkoxide complexes as acid–base bifunctional catalysts for synthesis of carbamates under solvent-free conditions

Heterobimetallic dinuclear lanthanide alkoxide complexes Ln₂Na₈(OCH₂CH₂NMe₂)₁₂(OH)₂ [Ln: I (Nd), II (Sm), III (Yb) and IV (Y)] were used as efficient acid–base bifunctional catalysts for the synthesis of carbamates and the N-Boc protection of amines.

Synthesis of cyclic carbonates from diols and CO2 catalyzed by carbenes

The synthesis of cyclic carbonates from epoxides and CO₂ is a well-established reaction, whereas the synthesis of cyclic carbonates from diols and CO₂ is considerably more challenging, and few efficient catalysts are available.

Transformation of atmospheric CO2 catalyzed by protic ionic liquids: efficient synthesis of 2-oxazolidinones

Protic ionic liquids (PILs), such as 1,8-diazabicyclo[5.4.0]-7-undecenium 2-methylimidazolide [DBUH][MIm], can catalyze the reaction of atmospheric CO2 with a broad range of propargylic amines to form the corresponding 2-oxazolidinones. The products are formed in high yields under mild, metal-free conditions. The cheaper and greener PILs can be easily recycled and reused at least five times without a decrease in the catalytic activity and selectivity. A reaction mechanism was proposed on the basis of a detailed DFT study which indicates that both the cation and anion of the PIL play key synergistic roles in accelerating the reaction.

4-Dodecylbenzenesulfonic acid (DBSA) promoted solvent-free diversity-oriented synthesis of primary carbamates, S-thiocarbamates and ureas

A simple and efficient solvent-free preparation of primary carbamates, S-thiocarbamates and ureas from alcohols, phenols, thiols and amines in the presence of 4-dodecylbenzenesulfonic acid, as a cheap and green Brønsted acid, has been described.

Efficient synthesis of quinazoline-2,4(1H,3H)-diones from CO2 catalyzed by N-heterocyclic carbene at atmospheric pressure

Under atmospheric pressure, quinazoline-2,4(1H,3H)-diones were obtained from the reaction of 2-aminobenzonitriles with carbon dioxide (0.1 MPa) with a catalytic amount of N-heterocyclic carbene in DMSO.

Quinoline-2-carboimine copper complex immobilized on amine functionalized silica coated magnetite nanoparticles: a novel and magnetically retrievable catalyst for the synthesis of carbamates via C–H activation of formamides

A novel and magnetically recoverable nanocatalytic system consisting of a magnetic silica based copper complex has been fabricated and applied in the synthesis of carbamates via C–H activation of formamides.