- Syntheses and crystal structures of hydrated ternary cerium sulfates: Mixed-valence K5Ce2(SO4)6· H2O and K2Ce(SO4)3·H 2O
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A new chemical and structural interpretation of K5Ce 2(SO5)5·H2O (I) and a redetermination of the structure of K2Ce(SO4) 3·H2O (II) is presented. The mixed-valent compound I crystallizes in the space group C2/c with a = 17.7321(3), b = 7.0599(1), c = 19.4628(4) A, β = 112.373(1)° and Z = 4. Compound I has been discussed earlier with space group Cc. In the structure of I, there are pairs of edge sharing cerium polyhedra connected by sulfate oxygen atoms in the μ3 bonding mode. These cerium dimers are linked through edge and corner sharing sulfate bridges, forming layers. The layers are joined by potassium ions which together with the water molecules are placed between the layers. No irregularity in the distribution of the CeIII and Ce IV to cause the lost of a crystallographic center of symmetry was detected. We suggest that the charge exerted by the extra fI electron for every cerium dimer is delocalized over the Ce1-O2-Ce2 moiety in a non-bonding mode. As a result, the oxidations state of each cerium ion is a mean value between III and IV at each atomic position. Compound II crystallizes in the space group C2 with a = 20.6149(2), b = 7.0742(1), c = 17.8570(1) A, β = 122.720(1)° and Z = 8. The hydrogen atoms have been located and the absolute structure has been established. Neither hydrogen atom positions nor anisotropic displacement parameters were given in the previous reports. In compound II, the cerium polyhedra are connected by edge and corner sharing sulfate groups forming a three-dimensional network. This network contains Z-shaped channels hosting the charge compensating potassium ions.
- Casari, Barbara M.,Langer, Vratislav
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- Hydrolysis of lanthanide dicarbides. Rates of reaction with water
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The kinetics of the reaction between liquid water and nine lanthanide dicarbides and YC2 have been investigated by monitoring the gas evolved into a constant volume apparatus. The ratio of volume of gas-evolved to that predicted was found to be consistent at 0.51 for wholly trivalent dicarbides, but rose to 0.66 for the light lanthanides containing LnIV components. Only linear kinetics were observed with the linear reaction rate constant KL in the range 0.44 cm cm-2 min-1 for LuC2 to 6.9 cm cm-2 min-1 for CeC2. Over the limited temperature range 283-303.5 K it was possible to estimate activation energies for four of the dicarbides and the values ranged from 48.5 kj mol-1 for the heavy, hard carbides to 150 kJ mol-1 for the light, soft, LnIV-containing members. The variation of KL and E across the series is discussed in terms of M-C2 bond energies, 4f-band electron density and the hardness of these dicarbides.
- McColm, I. J.,Quigley, T. A.,Bourne, D. R.
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- Influence of the incorporation of CeO2 nanoparticles on the ion exchange behavior of dodecylsulfate doped polypyrrole films: Ac-electrogravimetry investigations
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Cerium oxide (CeO2) nanoparticles (NPs) possessing defined size and crystallinity have been synthesised by a co-precipitation method. The effect of several parameters, such as the nature of the solvent and the calcination process, on the crystallite size was studied by XRD, TEM and BET methods. These CeO2 nanoparticles were then incorporated in dodecylsulfate (DS) doped PPy films during their electrodeposition in potentiodynamic conditions in order to produce PPy-DS/CeO2 NPs nanocomposite thin films on gold coated quartz crystals. Simultaneous EQCM experiments revealed successful incorporation of increasing amounts of cerium oxide nanoparticles in the polypyrrole matrix during each of the consecutive CV scans. This was confirmed using FEG-SEM and EDS microanalysis. The ion exchange phenomena occurring in the resulting nanocomposite materials were studied by ac-electrogravimetry in NaCl aqueous electrolyte. PPy-DS films appear to be mainly cation exchangers, independently from the incorporation of CeO2 nanoparticles (NPs), even though chloride anions in smaller amounts, and free water molecules, are simultaneously transferred at the film/electrolytic solution interface. This study also reveals that the kinetics of Cl- ion insertion occurring at the film/electrolyte interface upon oxidation is persistently slower in PPy-DS/CeO2 NPs films than in PPy-DS films throughout the entire potential window of investigation. However, the relative concentration changes of Cl- ions in PPy-DS/CeO2 NPs films is about two times greater than that occurring in pristine PPy-DS films. Such conclusion tends to demonstrate that CeO2 NPs have the ability to modify the morphology of electrodeposited PPy-DS thin films as well as their subsequent permeability towards ions contained in the electrolytic solution, possibly via the perturbation of polymer chain interactions and organisation.
- Benmouhoub,Agrisuelas,Benbrahim,Pillier,Gabrielli,Kadri,Pailleret,Perrot,Sel
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- Synthesis methods for Ce(CrO4)2 · xH 2O and crystal structures of K2CrSO7, (NH 4)2Cr2O7 and Na2Cr 2O7 · 2H2O
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New and quick methods to synthesize Ce(CrO4)2 · 2H2O and Ce(CrO4)2 · H 2O, giving high yields, are described. The methods are based on exchange reactions by refluxing in water or on solid state reactions. The first crystal structure containing a chromatosulfato ion is presented. K 2CrSO7 belongs to space group P21/n with a = 7.4024(1), b = 7.3908(1), c = 12.9883(2) A?, β = 90.021(1)° and Z = 4. The CrSO72- ion, consisting of one chromate group sharing one oxygen atom with one sulfate group, has a pseudo syn-C2v conformation with eclipsed oxygen atoms. K2CrSO7 forms a three dimensional network of CrSO72- ions held together by the charge balancing potassium ions, with the general structural features common with dichromate-like structures. The redetermination of the structures of (NH4)2Cr2O7 (space group C2/c, with hydrogen atoms located) and Na2Cr2O7 · 2H2O (space group P21, with hydrogen atoms located and the absolute structure established) are reported.
- Casari, Barbara M.,Eriksson, Annika K.,Langer, Vratislav
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- Study of the Ru/Ce system in the oxidation of carbon black and volatile organic compounds
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The relationship between the state of Ru on CeO2 and catalytic activity in the oxidation of carbon black (CB) and some volatile organic compounds (VOCs) was investigated for Ru/CeO2 catalysts prepared by wet impregnation. It was demo
- Aouad,Saab,Abi-Aad,Aboukais
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- Facile synthesis of ceria nanoparticles by precipitation route for UV blockers
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Homogeneous ceria (CeO2) nano particles of approximately 4 nm have been successfully synthesized via a simple precipitation route by employing the mixed solvent method. X-ray diffraction analysis revealed the precipitate particles to be of highly crystalline nature with face centered cubic structure along (1 1 1) (2 0 0) (2 2 0) (3 1 1) (4 0 0) (3 3 1) (4 2 2) (5 1 1) planes. Cerium oxide nanoparticles exhibits enhanced specific surface area of about 139.116 m2/g. The mono-dispersed spherical shape morphology of approximately 4 nm particles was confirmed using TEM analysis and its chemical composition by SEM-EDS analysis. Surface morphology reveals the smooth surface with an average roughness of 14.9 nm with the help of AFM. Raman studies show a characteristic peak at 464 cm-1. The UV absorption edge was found at 314 nm i.e. In the Ultra Violet region suggesting that the material has a good absorption of UV light. Also, it shows an excellent transparency in the visible region.
- Anupriya,Vivek,Subramanian
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- Dipotassium tetrachromate(VI), K2Cr4O13
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The structure of dipotassium tetrachromium(VI) tridecaoxide, K 2Cr4O13, has been determined from single-crystal X-ray data collected at 173 (2) K on a racemically twinned crystal with monoclinic Pc space-group symmetry. The structure is composed of discrete [Cr4O13]2- zigzag chains held together by the charge-balancing potassium ions. The conformations adopted by the tetrachromate anion in alkali metal salts and Cr8O21 are different and can be divided into three categories.
- Casari, Barbara M.,Langer, Vratislav
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- Cerium doped magnetite nanoparticles for highly sensitive detection of metronidazole via chemiluminescence assay
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Cerium doped magnetite nanoparticle (CDM) was synthesized via a co-precipitation method and used as the co-reactant of luminol-K3Fe(CN)6 chemiluminescent system. The physical-chemical features of CDM were studied by XPS, XRD, HRTEM, FESEM, VSM, BET, and FTIR analyses. This simple and highly sensitive nanoprobe enabled the determination of minor concentrations of metronidazole (MNZ). Owing to the quenching efficacy of MNZ in the studied chemiluminescence system, a linear range of 3.47 × 10?6-9.37 × 10?5 mol/L was obtained with a limit of detection of 3.91 × 10?7 mol/L. This biosensor was used for MNZ detection in human serum samples, which was highly efficient. The outcomes of this study give credit to the proposed biosensor to be applied for detection of MNZ in biological samples.
- Haddad Irani-nezhad, Mahsa,Hassandoost, Ramin,Joo, Sang Woo,Khataee, Alireza,Orooji, Yasin,Rahim Pouran, Shima
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- New structure type among octahydrated rare-earth sulfates, β-Ce 2(SO4)3·8H2O, and a new Ce 2(SO4)3·4H2O polymorph
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Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce2(SO4) 3·4H2O (I) and β-Ce2(SO 4)3·8H2O (II), both forming three-dimensional networks. Compound I crystallizes in the space group P2 1/n. There are two non-equivalent cerium atoms in the structure of I, one nine-and one ten-fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge-sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S-Oμ3-Ce2 bonding mode. Compound II constitutes a new structure type among the octahydrated rare-earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H2O)4(SO4)]nn+ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce2(SO4)3·5H 2O, Ce2(SO4)3·4H2O and Ce2(SO4)3, respectively. During the oxidative decomposition of the anhydrous form, Ce2(SO 4)3, into the final product CeO2, small amount of CeO(SO4) as an intermediate species was detected.
- Casari, Barbara M.,Langer, Vratislav
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- Thermochemical study of tetravalent metal sulfate tetrahydrates: A4+(SO4)2(H2O)4 (A4+?=?Zr, Ce, U)
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The syntheses, characterization, and calorimetric measurements of enthalpies of formation of four tetravalent metal sulfate tetrahydrates (A4+(SO4)2(H2O)4 (A4+ = Zr, Ce, U): α-Zr(SO4)2(H2O)4, α-Ce(SO4)2(H2O)4, β-Ce(SO4)2(H2O)4, and β-U(SO4)2(H2O)4)are reported. Direct calorimetric measurements showed that the formation enthalpies of these compounds from the corresponding oxides correlate with the eightfold coordination radius of the tetravalent cations. An energetic slope change is observed between the α- (Fddd)and β- (Pnma)forms and is consistent with previously reported studies.
- Zhang, Lei,Lobeck, Haylie L.,Dzik, Ewa A.,Sigmon, Ginger E.,Burns, Peter C.
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- Catalysis on Ruthenium Clusters Supported on CeO2 or Ni-Doped CeO2: Adsorption Behavior of H2 and Ammonia Synthesis
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Catalysis on Ru clusters supported on CeO2 or Ni-doped CeO2 was investigated.Ru3(CO)12 was reacted with CeO2, followed by heating in vacuum at 673 (i) or 813 K (ii) and then in H2 at 588-1073 K (TH2).Activities of both catalysts had the TH2 dependence, which has a maximum at TH2 = 873 K for ammonia synthesis.The rates on i were faster than those on ii by a factor of 2.0-1.1 in the range of TH2 = 588-973 K.On a sample in which Ru3(CO)12 was supported on previously reduced Ni/CeO2 (in H2 at 773 K) iii, the highest synthesis rate was 1.5E-3 mol h-1 gcat-1 at TH2 = 588 K on iii.The activity order iii > i > ii can be understood in terms of two factors: (A) reduction extent of support and (B) number of active Ru sites.The two factors conflicted with each other when the treatment temperature in H2 increased.By heating the samples in H2 up to 873 K to satisfy factor A, the aggregation of Ru clusters for i or physical blocking of surface Ru sites by CeO2-x for ii occurred: factor B was not satisfied.The two factors should be optimized in catalyst iii, where the support cerium oxide was thoroughly reduced through the doped Ni.On reduced Ni/CeO2, the Ru cluster implantation can be done at low temperature (588 K).Obtained values of rRu-Ru at 2.62 Angstroem (N = 7.1) and rRu-O(s) (O(s) is the oxygen atom at surface) at 2.12 Angstroem (N = 1.2) by EXAFS for Ru3-Ni/CeO2 suggested a flat Ru cluster model comprised of several Ru atoms on reduced Ni/CeO2-x surface.The H(a)/Rutotal ratio exceeded unity for catalysts i and iii, suggesting new H adsorption sites.The temperature-programmed desorption for hydrogen (simultaneous desorption of HD and D2 for iii at 330-430 K suggested that the H at the new site and H on Ru surface were exchangeable above 330 K.The reservoir effect of the new site for H on catalysis is discussed in relation to new kinetic design of hydrogenation catalyst.
- Izumi, Yasuo,Iwata, Yasuhiro,Aika, Ken-ichi
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- A pseudo-merohedrally twinned rare-earth sulfate: K6[Ce(HSO 4)2(SO4)4]·-H2O, a novel structure type
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A novel structure type of an acidic rare-earth sulfate, hexa-potassium cerium dihydrogensulfate tetra-sulfate monohydrate, is reported. The crystal is twinned, mimicking tetra-gonal symmetry. The CeIV atom is nine-coordinate, connecting to one corner-sharing and four edge-sharing sulfate groups. One of the potassium ions is disordered over two general positions. The compound is unique as it contains rare-earth monomers, [Ce(HSO4)(SO4)4] 5-. The structure is composed of these monomers, water mol-ecules, discrete hydrogensulfate ions and potassium ions held together by ionic inter-actions. There are two types of alternating layers in the structure, with compositions [K4Ce(HSO4)(SO4)4]- and [K2(HSO4)(H2O)]+. International Union of Crystallography 2007.
- Casari, Barbara M.,Langer, Vratislav
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- Oxidation of ketones by ceric perchlorate catalysed by iridium(III)
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In search of economical and effective catalysts it was found that IrCl 3, a sluggish catalyst in alkaline media, surpasses catalytic efficiency of osmium and ruthenium in aqueous perchloric acid medium in the oxidation of aliphatic ketones by ceric perchlorate. Rate decreases in the beginning at low acid concentrations, reaches to a minimum and then becomes proportional to [HClO4], probably due to conversion of hydrolysed to unhydrolysed species of ceric perchlorate, which then accelerates the rate. Reduction of oxidant by water depends on the concentrations of acid and [cerium(IV)] initially used. Orders are one with catalyst, one initially with respect to oxidant and ketones tending to become zeroth order at higher concentrations. No effect of change of μ on the rate was observed. Thermodynamic data suggest that diethyl ketone (DET) forms the activated complex more easily compared to dimethyl ketone (DMT).
- Tandon, Praveen K.,Sahgal, Sumita,Singh, Alok K.,Gayatri,Purwar, Manisha
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- Influence of molybdenum on ceria activity and CO2 selectivity in propene total oxidation
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A total oxidation of propene into CO2 is obtained on pure ceria at 673 K. However, in the presence of molybdenum, propene can be partially oxidized at room temperature. The Electron Paramagnetic Resonance (EPR) indicates changes in the oxidation state of molybdenum occurring upon interaction with propene. It has been found that the concentration of Mo(V) influences the propene conversion. The interaction between propene and molybdenum leads to the formation of surface species that, depending on the strength of their bonding to the surface, can be decomposed to ethene or coke. These results have been confirmed by infrared (FTIR) study. The oxidation reaction of propene is in competition with that of coke or ethene deposit on the catalyst surface, which can explain the decrease of the catalyst activity and selectivity in the presence of high molybdenum loadings.
- Flouty,Abi-Aad,Siffert,Aboukais
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- Hydrolysis of lanthanide dicarbides. Rates of reaction with water vapour
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The kinetics of the reaction between water vapour and nine of the lanthanide dicarbides, YC2 and UC2 have been investigated by gravimetric and gas evolution techniques. Mild conditions were used with water vapour pressures in the range 5.8-16.6 × 102 N m-2 and temperatures from 4.0-48 °C. Over 90% of the reactions studied showed linear kinetics with the remainder following parabolic rates. Linear reaction rate constants lie in the range 0.34-18.1 × 10-2 mg cm-2 min-1 depending on the carbide, temperature and pressure. For any given temperature and water vapour pressure the rate constant increased in the series from LaC2 to DyC2 and then decreased in the series DyC2 to LuC2, suggesting that the light lanthanides are least reactive. YC2 had rate constants close to those of GdC2, whilst UC2 reacted some 50 times more slowly. In general, at any given water vapour pressure, in the range studied, the rate constant decreased with increasing temperature - a behaviour leading to negative values for the activation energy. From the activation energies a mechanism controlled by water adsorption on the product layers is postulated which suggests that the data do not give a true picture of LaC2 + H2O reactions. Increasing the water vapour pressure always increases the reaction rate constants. The results are discussed in the light of data from UC2 and CaC2.
- McColm, I. J.,Quigley, T. A.
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- Size Dependence of Lattice Parameter and Electronic Structure in CeO Nanoparticles
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Intrinsic properties of a compound (e.g., electronic structure, crystallographic structure, optical and magnetic properties) define notably its chemical and physical behavior. In the case of nanomaterials, these fundamental properties depend on the occurrence of quantum mechanical size effects and on the considerable increase of the surface to bulk ratio. Here, we explore the size dependence of both crystal and electronic properties of CeO nanoparticles (NPs) with different sizes by state-of-the art spectroscopic techniques. X-ray diffraction, X-ray photoelectron spectroscopy, and high-energy resolution fluorescence-detection hard X-ray absorption near-edge structure (HERFD-XANES) spectroscopy demonstrate that the as-synthesized NPs crystallize in the fluorite structure and they are predominantly composed of CeIV ions. The strong dependence of the lattice parameter with the NPs size was attributed to the presence of adsorbed species at the NPs surface thanks to Fourier transform infrared spectroscopy and thermogravimetric analysis measurements. In addition, the size dependence of the t2g states in the Ce LIII XANES spectra was experimentally observed by HERFD-XANES and confirmed by theoretical calculations.
- Beck, Aaron,Bonani, Walter,Eloirdi, Rachel,Engelhard, Mark H.,Gouder, Thomas,Guo, Xiaofeng,Kriegsman, Kyle W.,Kvashnina, Kristina,Martin, Philippe,Popa, Karin,Prieur, Damien,Scheinost, Andreas C.,Vitova, Tonya,Walter, Olaf
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- Pd/REOs catalysts applied to the Suzuki-Miyaura coupling. A comparison of their catalytic performance and reusability
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Two new palladium catalysts based on rare earth oxide supports, namely, Pd/Dy2O3 and Pd/Yb2O3 were prepared by the incipient wetness impregnation method, followed by calcination at 600 °C. Both compounds, which were fully characterized, were tested as catalysts in the Suzuki-Miyaura reaction and their catalytic activity was compared with that of already known Pd/La2O3, Pd/CeO2, Pd/Pr6O11, Pd/Sm2O3, and Pd/Gd2O3. It has been found that the nature of the support strongly affects the catalytic activity. The scope of the catalytic protocol was investigated and quantitative yields of the coupling products (21 examples are reported) were always observed using a low metal amount (0.05 mol%). A systematic investigation on the reusability of the entire set of catalytic systems has been carried out. All catalysts showed to be successfully recyclable, and also in this case the nature of the rare earth element is crucial. The highest reusability was observed for catalysts Pd/CeO2 and Pd/Sm2O3.
- Del Zotto, Alessandro,Colussi, Sara,Trovarelli, Alessandro
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p. 275 - 283
(2017/09/30)
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- Copper nanoparticles supported on CeO2 as an efficient catalyst for click reactions of azides with alkynes
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Readily prepared copper nanoparticles supported on CeO2 have been found to effectively catalyse the 1,3-dipolar cycloaddition (CuAAC) of a variety terminal alkynes and organic azides generated in situ from sodium azide and different organic halides furnishing the corresponding 1,2,3-triazoles in excellent yields. Cu nanoparticles supported on CeO2 have been characterized by X-ray diffraction analysis, energy dispersive X-ray analysis, scanning electron microscope and transmission electron microscope. The salient features of the present protocol are shorter reaction time, mild reaction conditions, reusability of the catalyst, and applicability to a wide range of substrates.
- Amini, Mojtaba,Hassandoost, Ramin,Bagherzadeh, Mojtaba,Gautam, Sanjeev,Chae, Keun Hwa
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- Nanoceria-catalyzed highly efficient procedure for N-formylation of amines at room temperature under solvent-free conditions
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Nanoceria-catalyzed simple and efficient protocol for the N-formylation of amines using formic acid at room temperature under solvent-free conditions shows high yield of desired product chemoselectivity and improvement in reaction time.
- Patil, Umakant B.,Singh, Abhilash S.,Nagarkar, Jayashree M.
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p. 524 - 526
(2013/06/05)
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