超(近)临界水中的有机合成反应

作为一种环境友好的化学工艺过程,以超(近)临界水作有机合成反应介质越来越受到人们的关注。人们考察了在超(近)临界水中的许多有机反应,并获得了预期的结果。综述了近年来超(近)临界水中的有机合成反应的研究进展。     

Gold nanoparticle-catalyzed environmentally benign deoxygenation of epoxides to alkenes

We have developed a highly efficient and green catalytic deoxygenation of epoxides to alkenes using gold nanoparticles (NPs) supported on hydrotalcite [HT: Mg(6)Al(2)CO(3)(OH)(16)] (Au/HT) with alcohols, CO/H(2)O or H(2) as the reducing reagent. Various epoxides were selectively converted to the corresponding alkenes. Among the novel metal NPs on HT, Au/HT was found to exhibit outstanding catalytic activity for the deoxygenation reaction. Moreover, Au/HT can be separated from the reaction mixture and reused with retention of its catalytic activity and selectivity. The high catalytic performance of Au/HT was attributed to the selective formation of Au-hydride species by the cooperative effect between Au NPs and HT.     

Synthesis of organic monolayer-stabilized copper nanocrystals in supercritical water

When water is heated and pressurized above the critical point, it becomes a suitable solvent to employ organic capping ligands to control and stabilize the synthesis of nanocrystals. Without alkanethiol ligands, Cu(NO(3))(2) hydrolyzes to form polydisperse copper(II) oxide particles with diameters from 10 to 35 nm. However, in the presence of 1-hexanethiol, X-ray photoelectron spectroscopy, selected area electron diffraction, and transmission electron microscopy reveal the formation of copper nanocrystals approximately 7 nm in diameter. The use of a different precursor, Cu(CH(3)COO)(2), leads to particles with significantly different morphologies. A mechanism is proposed for sterically stabilized nanocrystal growth in supercritical water that describes competing pathways of hydrolysis to large oxidized copper particles versus ligand exchange and arrested growth by thiols to produce small monodisperse Cu nanoparticles.     

An environmentally benign benzylic oxidation catalyzed by hypervalent iodine intermediate in water

An effective and environmentally benign benzylic oxidation for transition of alkylarenes into the corresponding carbonyl compounds was reported.Alkylarenes were mixed and stirred with potassium bromide,m-chloroperbenzoic acid and a catalytic amount of iodobenzene in water at 60 8C for several hours,a series of the corresponding carbonyl compounds was obtained in moderate to good yields.In the reaction,iodobenzene was first oxidized by m-chloroperbenzoic acid into the hypervalent iodine intermediate which then reacted with potassium bromide to form the key radical initiator for the benzylic oxidation.     

Environmentally benign syntheses of flavanones

Mild and environmentally benign methods for the syntheses of flavanones are described. The reaction of o-hydroxyacetophenones (1) and benzaldehydes (2) in water in the presence of DABCO at room temperature gave 3-hydroxy-1-(2-hydroxylphenyl)-3-arylpropan-1-ones (3a-i) as intermediates. Followed by an intramolecular dehydration of the 3a-i with the modified Mitsunobu’s reaction, the target flavanones (4a-i) were obtained. Moreover, the reaction of 1 and 2 at the same conditions but at reflux gave flavanones in one pot with good yields.     

Technique for complete oxidation of organic compounds in supercritical water

Results are presented of tests of a pilot stationary installation for supercritical water oxidation of organic compounds, first created in Russia. A high oxidation efficiency of nitro compounds formed as waste in manufacture of explosives is demonstrated.     

An environmentally benign synthesis of isoxazolines and isoxazoles mediated by potassium chloride in water

An effective and environmentally benign procedure for the synthesis of isoxazolines and isoxazoles has been developed by a cycloaddition of nitrile oxides with alkenes or alkynes in water. In this approach, potassium chloride is first oxidized into chlorine in water by the environmentally friendly oxidant Oxone®, then aldoximes are oxidized into nitrile oxides by the in situ generated hypochlorous acid, finally a 1,3-dipolar cycloaddition between nitrile oxides and alkenes or alkynes occurs to provide the corresponding isoxazolines and isoxazoles in good yields.     

Gasification reaction of organic compounds catalyzed by RuO2 in supercritical water

Nearly complete gasification of organic compounds has been achieved by stoichiometrically insufficient amounts of RuO2 in supercritical water (SCW) to provide CH4, CO2 and H2, all the hydrogen atoms of which originate from water, and the catalytic effect of RuO2 results from a redox couple of Ru(IV)/Ru(II) induced by SCW.     

Innovation in a chemical reaction process using a supercritical water microreaction system: environmentally friendly production of epsilon-caprolactam

Our microreaction system using supercritical water solutions achieves nearly 100% yield and 100% selectivity for epsilon-caprolactam production at reaction times shorter than 1 s.     

Generality of the environmentally benign catecholate method to the synthesis of barium-based perovskites

Abstract

Barium titanate, barium zirconate, and barium hafnate are essential components of the electroceramic industry. Barium titanate is essentially used as multi-layered ceramic capacitors in computers, aerospace, and communication technologies. Barium zirconate is one of the most inert, stable, and corrosion-resistant perovskite employed in superconducting applications. Barium hafnate is used as a component of hybrid ceramic structures for high-temperature applications. The goal of this research was to apply a more environmentally benign synthesis design to the production of barium-based perovskites. The catecholate method, originally applied to the synthesis of barium titanate, was utilized as the approach for the synthesis of barium zirconate and barium hafnate. This developmental process consumed naturally occurring isomorphic forms of metal oxides and no post-sintering treatment was necessary. It resulted in the absence of by-products in most steps while achieving superior stoichiometric control over the barium-to-X (X=Ti, Zr, Hf) molar ratio compared to previous methods.     

Stability analysis of environmentally benign green emulsion liquid membrane

A new stable green emulsion liquid membrane (GELM) was formulated by selecting the environmentally benign vegetable oils. The rice bran oil (RBO) based GELM has shown better stability in comparison to that obtained from other oils. GELM was prepared using 10?mL RBO, 0.25 [M] NaOH concentration, 2 (v/v, %) surfactant concentration, 0.4 (v/v) phase ratio, 2000?rpm emulsification speed, and 20?min emulsification time. Under these optimum conditions, GELM has been found to be stable for 120?±?2?min (no significant phase change) and has shown complete phase separation after 4 hours. Therefore, RBO as a green solvent has high potential to be applied in several ELM process applications.     

A simple and environmentally benign synthesis of polypyridine-polycarboxylic acids

An oxidation method using dilute nitric acid solutions under solvothermal conditions has been developed to synthesise a series of polypyridine-polycarboxylic acids. It has been successfully applied to a range of methyl substituted polypyridines including symmetrical and asymmetrical 2,2′-bipyridines; 2,2′:6′,2″-terpyridines and; 2,2′:6′,2″:6″,2?-tetra-pyridines and yields crystalline polypyridine-polycarboxylic acids in a single step. Simple product recovery through filtration yields a recyclable filtrate. More forcing conditions led to demethylation of the polypyridine ligand most probably via decarboxylation. This simple approach avoids potentially harmful metal-based oxidants and negates any issues associated with the disposal of their resultant (hazardous) waste.     

Renaissance of immobilized catalysts. New types of polymer-supported catalysts, 'microencapsulated catalysts', which enable environmentally benign and powerful high-throughput organic synthesis

Immobilized catalysts have been reinvestigated from two aspects; as keys to environmentally benign chemical processes and high-throughput organic synthesis for combinatorial chemistry. While most known polymer-supported catalysts are less active than the corresponding original catalysts, new types of polymer-supported catalysts, microencapsulated catalysts, have been developed. The catalysts were immobilized on to polymers using physical envelopment by polymer backbones and interaction between pi electrons of benzene rings of the polystyrenes used as polymer backbones and vacant orbitals of the catalysts. Microencapsulated Sc, Os, Pd and Ru catalysts have been successfully prepared and high activities have been attained. In all cases, no leaching of the catalysts occurred, and the immobilized catalysts were recovered quantitatively by simple filtration and reused without loss of activity. It is noted that this method enables direct immobilization of metals onto polymers, and that normally unstable species such as Pd(0)(PPh3) can be kept stable by this immobilization technique. It is expected that other metal catalysts can be immobilized using this microencapsulation technique.     

Novel biomimetic iron-catalysts for environmentally benign epoxidations of olefins

A new selective and easily manageable epoxidation method is presented using an inexpensive and efficient FeCl₃·6H₂O and imidazole derivatives as catalysts. Aqueous hydrogen peroxide as an environmentally benign oxidant is utilized. This novel Fe/imidazole system gives moderate to excellent yields toward aromatic mono-, di-, and tri-substituted olefins.     

Towards benign syntheses of bipyridines: versatile approach to supramolecular building blocks

Chiral and achiral bipyridines are readily accessible via a solvent-free Michael addition involving solid NaOH, followed by treatment with ammonium acetate in acetic acid, as a ‘one pot’ more benign protocol, affording pure products in high yield, typically >80%.     

Thiazoles in organic synthesis. Novel syntheses of menthanes and eremophilanes

Acetylcnic thiazoles of proper design have been shown to undergo an intramolecular Diels-Alder reaction leading to fused-ring thiophene derivatives. When appropriately substituted, these latter materials can be readily converted to terpenes of the menthane and eremophilane class by Raney-nickel desulfurization