Photocatalytic carbon dioxide reduction by photocatalyst innovation

The photocatalytic conversion of carbon dioxide into sustainable fuel methanol using carbon quantum dots is highlighted in this paper. The multifaceted roles of carbon quantum dots in photocatalytic reactions and future directions of CQD materials are outlined.     

Photocatalytic synthesis of urea from in situ generated ammonia and carbon dioxide

TiO(2) and Fe-titanate (different wt%) supported on zeolite were prepared by sol-gel and solid-state dispersion methods. The photocatalysts prepared were characterized by X-ray diffraction, scanning electron microscopy and ultraviolet (UV)-visible diffuse reflectance spectroscopy techniques. Photocatalytic reduction of nitrate in water and isopropanol/oxalic acid as hole scavengers are investigated in a batch reactor under UV illumination. The yield of urea increased notably when the catalysts were supported on zeolite. The Fe-titanate supported catalyst promotes the charge separation that contributes to an increase in selective formation of urea. The product formation is because of the high adsorption of in situ generated CO(2) and NH(3) over shape-selective property of the zeolite in the composite photocatalyst. The maximum yield of urea is found to be 18 ppm while 1% isopropanol containing solution over 10 wt% Fe-titanate/HZSM-5 photocatalyst was used.     

Synthesis of carbamates from carbon dioxide promoted by organostannanes and alkoxysilanes

A cooperative methoxy transfer between orthosilicate esters and organotin oxides was developed for the synthesis of various N ‐alkyl and N ‐aryl carbamates from carbon dioxide in up to 97% isolated yield. The reaction is highly selective and N ‐alkylated amines are not observed. Density functional theory calculations of the reaction were performed and, together with NMR observations, a plausible mechanism featuring the catalytic regeneration of dialkyltin dialkoxide is proposed.     

Electrogenerated-bases promoted electrochemical synthesis of N-bromoamino acids from imines and carbon dioxide

In this paper, the one-step synthesis of N-bromoamino acids has been developed by electrolyzing imines and carbon dioxide (4 MPa). The electrosynthesis was performed in an undivided cell with Ni cathode and Al sacrificial anode containing n-Bu₄NBr–DMF as supporting electrolyte with a constant current at room temperature. The N-bromoamino acids were afforded in moderate to good yields rather than traditional α-amino acids. To explore the truth, some influenced factors (cathode materials, supporting electrolyte, and electricity etc.) were investigated. The experimental results indicated that the NH group of the α-amino acid could be deprotonated by alkyl anion R⁻ (carbanion, a strong base), followed by the oxidation of hypobromous acid resulted from the two-step oxidation of the bromide ion at the anode, and produced the N-bromoamino acid. Finally, the reaction mechanism was briefly discussed.     

Investigation of main group promoted carbon dioxide reduction

The reduction of carbon dioxide (CO₂) is of interest to the chemical industry, as many synthetic materials can be derived from CO₂. To help determine the reagents needed for the functionalization of carbon dioxide this experimental and computational study describes the reduction of CO₂ to formate and CO with hydride, electron, and proton sources in the presence of sterically bulky Lewis acids and bases. The insertion of carbon dioxide into a main group hydride, generating a main group formate, was computed to be more thermodynamically favorable for more hydridic (reducing) main group hydrides. A ten kcal/mol increase in hydricity (more reducing) of a main group hydride resulted in a 35% increase in the main group hydride's ability to insert CO₂ into the main group hydride bond. The resulting main group formate exhibited a hydricity (reducing ability) about 10% less than the respective main group hydride prior to CO₂ insertion. Coordination of a second identical Lewis acid to a main group formate complex further reduced the hydricity by about another 20%. The addition of electrons to the CO₂ adduct of ^tBu₃P and B(C₆F₅)₃ resulted in converting the sequestered CO₂ molecule to CO. Reduction of the CO₂ adduct of ^tBu₃P and B(C₆F₅)₃ with both electrons and protons resulted in only proton reduction.     

C-C bond formation with carbon dioxide promoted by a silver catalyst

A catalytic amount of silver benzoate with 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD) was an effective catalytic system for the reaction of carbon dioxide with various ketones containing an alkyne group at an appropriate position. These reactions afforded the corresponding γ-lactone derivatives in good to high yields under mild conditions.     

Direct and practical synthesis of 2-arylbenzoxazoles promoted by activated carbon

[reaction: see text] 2-Arylbenzoxazoles were directly synthesized from substituted 2-aminophenols and aldehydes in the presence of activated carbon (Darco KB) in xylene under an oxygen atmosphere.     

Transition metal promoted carboxylation of unsaturated substrates with carbon dioxide

The use of CO₂ as a C1 building block for the synthesis of useful chemicals is of great significance, and has attracted increasing attention in recent years. The transition metal catalyzed or mediated addition of CO₂ to unsaturated chemical bonds has proved to be a powerful and versatile protocol for the incorporation of CO₂ into various unsaturated organic substrates such as alkynes, alkenes, allenes, aldehydes, and 1,3-dienes. The hydrogenative, alkylative and arylative carboxylation, heterocarboxylation, and carboxylative cyclization with CO₂ have led to efficient and selective formation of various functionalized carboxylic acids and derivatives. This review focuses on recent advances in this area with emphasis on conceptual reaction design.     

On the water promoted reaction of titanium isopropoxide with carbon dioxide

Insertion of carbon dioxide into titanium isopropoxide takes place only in the presence of trace quantities of water to give an isopropyl carbonato cluster which has been crystallographically characterised.     

An efficient one-pot synthesis of tetra-substituted pyrroles

The three-component reaction of primary amines, dialkyl acetylenedicarboxylates and β-nitrostyrene derivatives in the presence of Iron(III) chloride afforded 1,2,3,4-tetra-substituted pyrroles in high yields. These reactions could precede via domino Michael addition/cyclization process.     

Photocatalytic oxidation of arsenite by a composite of titanium dioxide and activated carbon fiber

Preoxidation process is usually needed in the treatment of arsenic-containing drinking water because arsenite (i.e. As[III]) is less easily removed by adsorption. Nano-scale titanium dioxide is an efficient photocatalyst for arsenite oxidation but its application in water treatment is limited due to the difficulty of separation or packed-bed application of the tiny particles. This study synthesized a composite photocatalyst by loading titanium dioxide onto activated carbon fiber (TiO₂/ACF). The effects of calcination temperature, photocatalyst dosage, pH, initial concentration of As(III) and common anions on the oxidation of As(III) were studied. Photocatalytic oxidation of As(III) took place in minutes and followed first-order kinetics. 0.80 mg L⁻¹ of As(III) could be entirely oxidized to As(V) within 30 min in the presence of 3.0 g L⁻¹ photocatalyst and under UV-light irradiation. The oxidation of As(III) occurred in a wide range of pH as examined from 2 to 10 with the oxidation efficiency increasing markedly with pH. The presence of phosphate and silicate significantly decreased As(III) oxidation at pH 7, while the effect of sulfate and chloride was small.     

Highly selective synthesis of tetra-substituted furans and cyclopropenes: copper(i)-catalyzed formal cycloadditions of internal aryl alkynes and diazoacetates

A convenient Cu(i)-catalyzed cycloaddition of electron rich internal aryl alkynes and diazoacetates was discovered for the chemoselective and regioselective synthesis of tetra-substituted furans and cyclopropenes in moderate isolated yields (18-67%), and alkyne conversion (29-73%).     

A novel indium-catalysed synthesis of tetra-substituted pyridine derivatives

Indium trichloride was found to be an effective catalyst for the synthesis of various tetra-substituted pyridine derivatives via Michael addition of β-dicarbonyl compounds to α,β-unsaturated oximes and subsequent ring closure.     

Ruthenium catalyzed selective synthesis of enol carbamates by fixation of carbon dioxide

Secondary amines react with carbon dioxide and terminal alkynes in the presence of a catalytic amount of 4-1,5-cyclooctadiene) (6-1,3,5-cyclooctatriene)ruthenium [Ru(COD)(COT)] and tertiary phosphine in toluene to give enol carbamates in good yields with high regio- and stereoselectivity. Cyclic enol carbamates, 5-methylene-2-oxazolidinones are obtained from N-substituted propargylamines and carbon dioxide in high yields.     

Catalytic synthesis of propionic acid by carboxylation of ethylene with carbon dioxide

Conclusions The carboxylation of ethylene with CO₂ in the presence of tris (triphenylphosphine) rhodium chloride at 700 atm and 180° gave propionic acid, ethanol, and ethyl propionate in respective yields of 38.4, 24.3, and 11.2%, with an ethylene conversion of 91.4%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2814–2816, December, 1978.     

Efficient synthesis of isoindoles using supercritical carbon dioxide

Bicyclopyrroles were efficiently converted to the corresponding isoindoles by a retro Diels-Alder reaction in supercritical carbon dioxide. By adding ethylene gas as an oxygen scavenger, the isoindole yield was further improved.     

Stereoselective synthesis of furans by the Pd-catalyzed Oshima-Utimoto reaction

[reaction: see text]. The Pd-catalyzed coupling of acyclic allylic alcohols with vinyl ethers was examined and found to proceed with 2.5-10 mol % of catalyst and to provide cyclic acetals with good stereoselection. The reaction is tolerant of a number of functional groups and can be used to generate quaternary centers in a stereoselective fashion.     

Convenient synthesis of ethylene carbonates from carbon dioxide and 1,2-diols at atmospheric pressure of carbon dioxide

An efficient and convenient synthesis of ethylene carbonates was achieved by the reaction of carbon dioxide with 1,2-diols in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), followed by treatment with 1-bromobutane. This DBU-promoted transformation proceeded at an atmospheric pressure of carbon dioxide at 25 °C and gave ethylene carbonates in good yields.