CO2 Conversion with Alcohols and Amines into Carbonates,Ureas, and Carbamates over CeO2 Catalyst in the Presence and Absence of 2‐Cyanopyridine

Recent progress on the CeO₂ catalyzed synthesis of organic carbonates, ureas, and carbamates from CO₂+alcohols, CO₂+amines, and CO₂+alcohols+amines, respectively, is reviewed. The reactions of CO₂ with alcohols and amines are reversible ones and the degree of the equilibrium limitation of the synthesis reactions is strongly dependent on the properties of alcohols and amines as the substrates. When the equilibrium limitation of the reaction is serious, the equilibrium conversion of the substrate and the yield of the target product is very low, therefore, the shift of the equilibrium reaction to the product side by the removal of H₂O is essential in order to get the target product in high yield. One of the effective method of the H₂O removal from the related reaction systems is the combination with the hydration of 2‐cyanopyridine to 2‐picolinamide, which is also catalyzed by CeO₂.     

Efficient Imine Formation by Oxidative Coupling at Low Temperature Catalyzed by High-Surface-Area Mesoporous CeO2 with Exceptional Redox Property

High-surface-area mesoporous CeO₂ (hsmCeO₂) was prepared by a facile organic-template-induced homogeneous precipitation process and showed excellent catalytic activity in imine synthesis in the absence of base from primary alcohols and amines in air atmosphere at low temperature. For comparison, ordinary CeO₂ and hsmCeO₂ after different thermal treatments were also investigated. XRD, N₂ physisorption, UV-Raman, H₂ temperature-programmed reduction, O₂ temperature-programmed desorption, EPR spectroscopy, and X-ray photoelectron spectroscopy were used to unravel the structural and redox properties. The hsmCeO₂ calcined at 400 °C shows the highest specific surface area (158 m² g⁻¹), the highest fraction of surface coordinatively unsaturated Ce³⁺ ions (18.2 %), and the highest concentration of reactive oxygen vacancies (2.4×10¹⁵ spins g⁻¹). In the model reaction of oxidative coupling of benzyl alcohol and aniline, such an exceptional redox property of the hsmCeO₂ catalyst can boost benzylideneaniline formation (2.75 and 5.55 mmol h⁻¹ based on >99 % yield at 60 and 80 °C, respectively) in air with no base additives. It can also work effectively at a temperature of 30 °C and in gram-scale synthesis. These are among the best results for all benchmark ceria catalysts in the literature. Moreover, the hsmCeO₂ catalyst shows a wide scope towards primary alcohols and amines with good to excellent yield of imines. The influence of reaction parameters, the reusability of the catalyst, and the reaction mechanism were investigated.     

O-(Aminosulfonylation) of phenols and an example of slow hydrolytic release

Sequential replacement of imidazole from sulfonyldiimidazole by phenols and then amines leads to O-arylsulfamate esters. Application of this coupling method to 19 phenols and 6 amines generates a library of 114 sulfamate esters, Ar-OSO₂-NR₂. A sulfamate based conjugate of ethinyl estradiol was prepared by using the steroid 3-hydroxyl as the phenol component, and an amino amide derived from linoleic acid as the amine. Hydrolysis of this conjugate was studied in aqueous buffer at pH values 2, 5, and 7.4, and (essentially identical) respective half-lives of 6.8, 6.6, and 6.7 days were observed.     

Photocatalytic Co-Reduction of N2 and CO2 with CeO2 Catalyst for Urea Synthesis

The effective conversion of carbon dioxide (CO₂) and nitrogen (N₂) into urea by photocatalytic reaction under mild conditions is considered to be a more environmentally friendly and promising alternative strategies. However, the weak adsorption and activation ability of inert gas on photocatalysts has become the main challenge that hinder the advancement of this technique. Herein, we have successfully established mesoporous CeO_2-x nanorods with adjustable oxygen vacancy concentration by heat treatment in Ar/H₂ (90 % : 10 %) atmosphere, enhancing the targeted adsorption and activation of N₂ and CO₂ by introducing oxygen vacancies. Particularly, CeO₂-500 (CeO₂ nanorods heated treatment at 500 °C) revealed high photocatalytic activity toward the C−N coupling reaction for urea synthesis with a remarkable urea yield rate of 15.5 μg/h. Besides, both aberration corrected transmission electron microscopy (AC-TEM) and Fourier transform infrared (FT-IR) spectroscopy were used to research the atomic surface structure of CeO₂-500 at high resolution and to monitor the key intermediate precursors generated. The reaction mechanism of photocatalytic C−N coupling was studied in detail by combining Density Functional Theory (DFT) with specific experiments. We hope this work provides important inspiration and guiding significance towards highly efficient photocatalytic synthesis of urea.     

ZnAl2O4 SiO2纳米复合催化剂用于无溶剂条件下乙酸酐与醇、酚和胺的乙酰化反应简

A ZnAl₂O₄@SiO₂ nanocomposite was prepared from metal nitrates and tetraethyl orthosilicate by the sol-gel process, and characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and N₂ adsorption-desorption measurements. The nanocomposite was tested as a heterogeneous catalyst for the acetylation of alcohols, phenols, and amines under solvent-free conditions. Under optimized conditions, efficient acetylation of these substrates with acetic anhydride over the ZnAl₂O₄@SiO₂ nanocomposite was obtained. Acetylation of anilines and primary aliphatic amines proceeded rapidly at room temperature, while the reaction time was longer for the acetylation of alcohols and phenols, showing that an amine NH₂ group can be selectively acetylated in the presence of alcoholic or phenolic OH groups. The catalyst can be reused without obvious loss of catalytic activity. The catalytic activity of the ZnAl₂O₄@SiO₂ nanocomposite was higher than that of pure ZnAl₂O₄. The method gives high yields, and is clean, cost effective, compatible with substrates having other functional groups and it is suitable for practical organic synthesis.     

Ultrasound assisted diazotization and diazo coupling reactions using trichlorotriazine

A high rate and efficient procedure for the synthesis of azo dyes has been developed. This concluded the sequential diazotization-diazo condensation of aromatic amines such as 4,4′-sulfonyldianiline with NaNO₂, or trichlorotriazine with coupling agents under ultrasound irradiation at room temperature. This method applied to several types of coupling agents led to corresponding azo dyes in high yield within short reaction time. The mild reaction conditions and inexpensive procedure are clear advantages of this method.     

Controllable Synthesis of Nearly Monodisperse Spherical Aggregates of CeO2 Nanocrystals and Their Catalytic Activity for HCHO Oxidation

Herein, we report a facile surfactant‐assisted solvothermal synthetic method to prepare nearly monodisperse spherical CeO₂ nanocrystals. A good control of the size of CeO₂ nanocrystals in the range of 100–500 nm was achieved by simply varying the synthetic parameters such as reaction time, volume ratio of ethanol to water (R), molar ratio of PVP, and concentration of Ce(NO₃)₃?6 H₂O in solution. A possible mechanism for the growth of spherical CeO₂ nanocrystals is proposed. The obtained CeO₂ nanocrystals with a surface area of up to 47 m²g^?1 were then employed as a catalyst support. By loading Au‐Pd nanoparticles (about 3 wt. %) onto the CeO₂ support, an Au‐Pd/CeO₂ catalyst was prepared that exhibited high catalytic activity for HCHO oxidation. At the low temperature of 50 °C, the percentage of HCHO conversion was 100 %, suggesting potential applications in preferential oxidation and other catalytic reactions. These Au‐Pd/CeO₂ catalysts may also find applications in indoor formaldehyde decontamination and industrial catalysis. The facile solvothermal method can be extended to the preparation of other metal oxide nanocrystals and provides guidance for size‐ and morphology‐controlled synthesis.     

Decarboxylative C(sp3)−O Cross‐Coupling

Alkyl aryl ethers are an important class of compounds in medicinal and agricultural chemistry. Catalytic C(sp³)?O cross‐coupling of alkyl electrophiles with phenols is an unexplored disconnection strategy to the synthesis of alkyl aryl ethers, with the potential to overcome some of the major limitations of existing methods such as C(sp²)?O cross‐coupling and S_N2 reactions. Reported here is a tandem photoredox and copper catalysis to achieve decarboxylative C(sp³)?O coupling of alkyl N‐hydroxyphthalimide (NHPI) esters with phenols under mild reaction conditions. This method was used to synthesize a diverse set of alkyl aryl ethers using readily available alkyl carboxylic acids, including many natural products and drug molecules. Complementarity in scope and functional‐group tolerance to existing methods was demonstrated.     

Insight into the Morphology-Dependent Catalytic Performance of CuO/CeO2 Produced by Tannic Acid for Efficient Hydrogenation of 4-Nitrophenol

The construction of a heterogeneous nanocatalyst with outstanding catalytic performance via an environmentally benign and cost-effective synthetic category has long been one of the challenges in nanotechnology. Herein, we synthesized highly efficient and low-cost mesoporous morphology-dependent CuO/CeO₂-Rods and CuO/CeO₂-Cubes catalysts by employing a green and multifunctional polyphenolic compound (tannic acid) as the stabilizer and chelating agent for 4-nitrophenol (4-NP) reduction reaction. The CuO/CeO₂-Rods exhibited excellent performance, of which the activity was 3.2 times higher than that of CuO/CeO₂-Cubes. This can be connected with the higher density of oxygen vacancy on CeO₂-Rods (110) than CeO₂-Cubes (100), the oxygen vacancy favors anchoring CuO species on the CeO₂ support, which promotes the strong interaction between finely dispersed CuO and CeO₂-Rods at the interfacial positions and facilitates the electron transfer from BH₄⁻ to 4-NP. The synergistic catalytic mechanism illustrated that 4-NP molecules preferentially adsorbed on the CeO₂, while H₂ from BH₄⁻ dissociated over CuO to form highly active H* species, contributing to achieving efficient hydrogenation of 4-NP. This study is expected to shed light on designing and synthesizing cost-effective and high-performance nanocatalysts through a greener synthetic method for the areas of catalysis, nanomaterial science and engineering, and chemical synthesis.     

Three-Component Coupling Synthesis of Diversely Substituted N-Aryl Pyrroles Catalyzed by Iron(III) Chloride

An efficient and operationally simple three-component coupling synthesis of varieties of N-aryl substituted pyrroles is described in the presence of sustainable and environmentally benign metal catalyst, FeCl₃. This method provides a straightforward approach for the synthesis of N-aryl substituted pyrroles in good yields from easily accessible starting materials such as nitroalkenes, 1,3-dicarbonyl compounds, and primary aromatic amines. The reaction proceeds through a catalytic sequence of Fe(III)-catalyzed amination/Michael/cycloisomerization reactions.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.     

Oxidant‐Controlled Catalytic Transformations of Phenols with Unexpected Cleavage of Aromatic Rings

Oxidative transformations of phenols have attracted significant attention of chemists due to their importance in biological process and organic synthesis. In contrast to the relatively well‐developed oxygenation and coupling reactions of phenols, the highly efficient and selective oxidative ring cleavage of phenols is under‐represented. This work describes a novel CuCl‐catalyzed tandem homocoupling/skeletal rearrangement of phenols that realizes the cleavage of the phenol ring by using air or Ag₂CO₃ as the oxidant. Interestingly, simply changing the oxidant to K₂S₂O₈ results in the oxidative coupling/cyclization of phenols to give dibenzofurans. These results set an important precedent of oxidant‐controlled catalytic transformations of phenols.     

Luminescent characteristics and microstructures of Sr<Subscript>2</Subscript>CeO<Subscript>4</Subscript> phosphors prepared via sol–gel and solid-state reaction routes

Blue-light-emitting Sr₂CeO₄ phosphors were synthesized via a sol–gel process and the conventional solid-state method in this study. The developed sol–gel process lowered the synthesis temperature of monophasic Sr₂CeO₄ to as low as 900 °C. In comparison with the solid-state derived powders, the sol–gel derived powders had more uniform morphology and smaller particle sizes. In addition, sol–gel derived Sr₂CeO₄ displayed higher luminescent intensity than that prepared via the solid-state route under the same heating conditions. This is attributed to the improved compositional homogeneity and crystallinity in the sol–gel process. During the heating processes, Sr₂CeO₄ tended to thermally decompose at elevated temperatures. This decomposition reaction resulted in the formation of an impurity phase- SrCeO₃ and thereby a decrease in the luminescent intensity. For obtaining Sr₂CeO₄ phosphors with high luminescent intensity, the heating conditions in both processes need to be well modulated.     

Modular Synthesis of Triarylamines and Poly(triarylamine)s through a Radical Mechanism

A modular protocol for the triarylamine synthesis has been developed using diarylamines and electron-rich arenes, such as phenols, as the building blocks. The KI/KIO₄ system proves to be highly efficient for the cross-dehydrogenative coupling of phenothiazines/phenoxazines with phenols/anilines. A wide range of functional groups attached to both coupling partners were well tolerated. Through the manipulation of reaction temperatures, the sequential assembly of bis-triarylamines could be achieved to provide the unsymmetrically bis-aminated phenols efficiently. Furthermore, the multiple aminated polyphenols were rapidly constructed in good to high yields by a single operation.     

Continuous Synthesis of Aryl Amines from Phenols Utilizing Integrated Packed-Bed Flow Systems

Aryl amines are important pharmaceutical intermediates among other numerous applications. Herein, an environmentally benign route and novel approach to aryl amine synthesis using dehydrative amination of phenols with amines and styrene under continuous-flow conditions was developed. Inexpensive and readily available phenols were efficiently converted into the corresponding aryl amines, with small amounts of easily removable co-products (i.e., H₂O and alkanes), in multistep continuous-flow reactors in the presence of heterogeneous Pd catalysts. The high product selectivity and functional-group tolerance of this method allowed aryl amines with diverse functional groups to be selectively obtained in high yields over a continuous operation time of one week.     

Facile preparation of MgAl2O4/CeO2/Mn3O4 heterojunction photocatalyst and enhanced photocatalytic activity

Novel Mn₃O₄-promoted double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalyst was constructed by one-step synthesis method and two-step synthesis method. The X-ray powder diffraction, Fourier transform infrared spectrum, X-ray photoelectron spectroscopy, optical and photoluminescence demonstrated that the MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalyst was synthesized by the two-step synthesis method comprehends a high crystallinity, charge carrier migration and separation efficiency, and relatively low optical absorption coefficient. The MgAl₂O₄/CeO₂/Mn₃O₄ heterojunction photocatalysts were efficiently used as simulated sunlight-driven n-n and p-n double junction photocatalyst for the simultaneous degradation of methylene blue (MB) dye. The continuous double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunctions strengthened the function of single n-n or p-n junction and guided the charge carrier migration and separation direction; thus, the oxidation and reduction reactions occur at the active site of spatial separation and prevent the recombination of electrons and holes. The results suggest that the continuous double p?n junction MgAl₂O₄/CeO₂/Mn₃O₄ heterojunctions are very promising candidate material for enhancing the photocatalytic activity in the photocatalytic degradation of MB dye.     

Nano ceria catalyzed synthesis of α-aminophosphonates under ultrasonication

A simple, efficient and general method has been developed for the one-pot three component syntheses of α-aminophosphonates. The condensation of aldehyde, amine and triethyl phosphite by employing CeO₂ nanoparticles as catalyst gave α-aminophosphonates. The catalyst showed good recyclability. Nano CeO₂ has been found to be an excellent catalyst for the green synthesis of α-aminophosphonates under ultrasound irradiation and solvent-free condition. The α-aminophosphonates are obtained in good to excellent yield. This catalyst provides cleaner conversion, short reaction time and high selectivity which makes the protocol feasible and economical attractive.     

Continuous Synthesis of Aryl Amines from Phenols Utilizing Integrated Packed‐Bed Flow Systems

Aryl amines are important pharmaceutical intermediates among other numerous applications. Herein, an environmentally benign route and novel approach to aryl amine synthesis using dehydrative amination of phenols with amines and styrene under continuous‐flow conditions was developed. Inexpensive and readily available phenols were efficiently converted into the corresponding aryl amines, with small amounts of easily removable co‐products (i.e., H₂O and alkanes), in multistep continuous‐flow reactors in the presence of heterogeneous Pd catalysts. The high product selectivity and functional‐group tolerance of this method allowed aryl amines with diverse functional groups to be selectively obtained in high yields over a continuous operation time of one week.     

Highly efficient Cu-catalyzed oxidative coupling of tertiary amines and siloxyfurans

A mild, selective, and efficient protocol for the synthesis of γ-aminoalkyl butenolides via the oxidative coupling between tertiary amines and siloxyfurans catalyzed by simple copper salts was developed. Compared with the reported method, our method employs copper catalyst instead of the expensive rhodium catalyst. Besides TBHP, both O₂ and H₂O₂ can also be utilized as oxidant to effect the coupling.     

Silver‐Mediated Oxidative Trifluoromethylation of Phenols: Direct Synthesis of Aryl Trifluoromethyl Ethers

Aryl trifluoromethyl ethers (ArOCF₃) are prevalent in pharmaceuticals, agrochemicals, and materials. However, methods for the general and efficient synthesis of these compounds are extremely underdeveloped and limited. Herein, we describe a highly efficient and general procedure for the direct O‐trifluoromethylation of unprotected phenols through a silver‐mediated cross‐coupling reaction using CF₃SiMe₃ as the CF₃ source and exogenous oxidants. This novel oxidative trifluoromethylation provides access to a wide range of aryl trifluoromethyl ethers from simple phenols. The mild process was also applied to the late‐stage trifluoromethylation of a medicinally relevant compound.     

Electrostatic catalysis by ionic aggregates: scope and limitations of Mg(ClO4)2 as acylation catalyst

Alkali and alkaline earth metal perchlorates exhibit electrostatic catalysis in the activation of anhydrides for the acylation reaction. Perchlorates with higher values of the charge-size function of the metal ion exhibit better catalytic activity following the order Mg(ClO₄)₂>Ba(ClO₄)₂>LiClO₄. Acylation of structurally diverse phenols, thiols, alcohols, and amines have been carried out with stoichiometric amounts of anhydride at room temperature under solvent free conditions in the presence of catalytic amount of Mg(ClO₄)₂. Sterically hindered and electron deficient phenols are efficiently acylated. Acylation with sterically hindered anhydrides such as iso-butyric, pivalic, and benzoic anhydrides are carried out with phenols and alcohols in excellent yields. Acid-sensitive alcohols are acylated in excellent yields without any competitive side reactions.