A clean, palladium-catalyzed oxidative esterification of aldehydes using benzyl chloride

A highly efficient, mild, simple and clean procedure is presented for the one-pot oxidation of aromatic and aliphatic aldehydes to their corresponding ethyl esters using benzyl chloride as the oxidant under palladium-catalyzed conditions. The reaction is complete in just 30 min under microwave irradiation and inert conditions are not required to obtain good to excellent yields (65-93%) of isolated products.     

Peroxovanadium-catalyzed oxidative esterification of aldehydes

The peroxovanadium species generated from V(2)O(5) and hydrogen peroxide, which is liberated from peroxy salts such as sodium perborate (SPB) or sodium percarbonate (SPC), transform aldehydes directly into esters in an alcoholic medium. Monoesters of diols have been achieved directly in one pot from aldehydes. High catalytic turnover number combined with inexpensive, easily available reagents and innocuous side products from the reaction make it a suitable alternative for the synthesis of esters from aldehydes.     

Zinc-catalyzed oxidative esterification of aromatic aldehydes

A general and efficient protocol for the oxidative esterification of aldehydes has been developed. By using 10 mol % of ZnBr₂ and 4 equiv of H₂O₂, 21 examples of esters were produced in good to excellent yields. Both electron-donating and electron-withdrawing functional groups are tolerable under our reaction conditions.     

Electron microscopy of V2O5 microcrystals in the V2O5-NH3-H2O colloid system

Summary The formation of V₂O₅ fibrous microcrystals in the V₂O₅-NH₃-H₂O system has been investigated by electron microscopy. The morphology of these microcrystals is dependent on the concentration of the particular components in the colloidal system and on the time of aging. In some colloid systems the orientation of V₂O₅ fibrous crystals with their long axes parallel to one another is also possible. The microcrystal growth in these systems can be attributed to very effective conditions for the recrystallization of vanadium pentoxide crystals in equilibrium with ammonium vanadate in solution.With 3 figures     

One-pot oxidative esterification and amidation of aldehydes

During recent years, the direct transformation of aldehydes into esters or amides has developed into a vigorous research area and powerful one-pot oxidative esterification and amidation procedures have been reported. Several concepts that are often complementary in substrate scope, functional group tolerance, and reaction outcome have emerged, thus providing a wide range of alternatives to classical ester and amide synthesis via carboxylic acid intermediates.     

A simple,one-pot oxidative esterification of aryl aldehydes through dialkyl acetal using hydrogen peroxide

Research on Chemical Intermediates - A simple and an efficient one-pot procedure has been developed to synthesize various aryl carboxylic esters directly from aryl aldehydes using hydrogen peroxide...     

A catalyst-free protocol for direct oxidative esterification of alcohols and aldehydes

A fast, simple, and efficient protocol for the direct conversion of alcohols and aldehydes to methyl ester has been developed using TsNBr₂ without any catalyst. The one pot reaction proceeds in the presence of a base at room temperature in methanol, to produce the corresponding methyl ester in high yield within a short time.     

Palladium/NHC-catalyzed oxidative esterification of aldehydes with phenols

A palladium-catalyzed oxidative esterification of aldehydes with phenols is described, using air as the clean oxidant. This reaction tolerates many functional groups, providing esters with yields ranging from moderate to excellent.     

Calcium and magnesium chlorides-catalyzed oxidative esterification of aromatic aldehydes

An interesting procedure for the oxidative esterification of aromatic aldehydes has been developed. By using catalytic amount of CaCl₂ or MgCl₂, various methyl benzoates were isolated in good yields with hydrogen peroxide as the terminal oxidant.     

Highly stereoselective oxidative esterification of aldehydes with beta-dicarbonyl compounds

Copper-catalyzed oxidative esterification of aldehydes with beta-dicarbonyl compounds was developed using tert-butyl hydroperoxide as an oxidant. In general, the enol esters were synthesized in good yields (up to 87%) and high stereoselectivity under the optimized reaction conditions.     

Recyclable CuMgAl hydrotalcite for oxidative esterification of aldehydes with alkylbenzenes

A series of hydrotalcite-like compounds with various Cu:Mg:Al molar ratios were prepared by the co-precipitation method. The catalytic performance for oxidative esterification of aldehydes was investigated. X-ray diffraction, N₂ adsorption–desorption (BET), hydrogen temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy, the scanning electron microscope (SEM), the transmission electron microscope and atomic absorption spectrometry were used to characterize the catalysts. The results showed that the benzyl benzoate product was obtained in good to excellent yield using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu₂Mg₁Al₁-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five times. The oxidative esterification reaction in the heterogeneous system is environmentally friendly.

The Cu₂Mg₁Al₁-LDH catalyst prepared by co-precipitation method showed high catalytic activity for oxidative esterification of aldehydes. 81.0% yield of benzyl benzoate with benzaldehyde and toluene as reactants was obtained using tert-butyl peroxybenzoate as oxidant at 90°C under air atmosphere over Cu₂Mg₁Al₁-LDH catalyst. The catalyst can be recovered and used with 45% conversion after recycling five runs. The oxidative esterification reaction in the heterogeneous system is environmentally friendly.     

Copper-catalyzed oxidative esterification of alcohols with aldehydes activated by Lewis acids

An efficient oxidative esterification of aromatic and aliphatic aldehydes with simple alcohols was accomplished using catalytic amounts of Cu(ClO₄)₂·6H₂O and InBr₃ with tert-hydroperoxide as an oxidant.     

N-Heterocyclic carbene-mediated oxidative esterification of aldehydes: ester formation and mechanistic studies

An unexpected N-heterocyclic carbene-catalyzed esterification of α,β-unsaturated aldehydes including aromatic aldehydes with reactive cinnamyl bromides in the presence of air oxygen or MnO(2) as an oxidant is described. In the presence of oxygen, halogenated and electron-deficient aldehydes react smoothly to furnish esters in good yields. Great efforts have been made on mechanistic studies to deduce a plausible mechanism, based on the experimental results and isotopic labeling experiment.     

Oxidative dehydrogenation of propane over V2O5/MoO3/Al2O3 and V2O5/Cr2O3/Al2O3: structural characterization and catalytic function

The structure and catalytic properties of binary dispersed oxide structures prepared by sequential deposition of VO(x) and MoO(x) or VO(x) and CrO(x) on Al(2)O(3) were examined using Raman and UV-visible spectroscopies, the dynamics of stoichiometric reduction in H(2), and the oxidative dehydrogenation of propane. VO(x) domains on Al(2)O(3) modified by an equivalent MoO(x) monolayer led to dispersed binary structures at all surface densities. MoO(x) layers led to higher reactivity for VO(x) domains present at low VO(x) surface densities by replacing V-O-Al structures with more reactive V-O-Mo species. At higher surface densities, V-O-V structures in prevalent polyvanadates were replaced with less reactive V-O-Mo, leading to lower reducibility and oxidative dehydrogenation rates. Raman, reduction, and UV-visible data indicate that polyvanadates predominant on Al(2)O(3) convert to dispersed binary oxide structures when MoO(x) is deposited before or after VO(x) deposition; these structures are less reducible and show higher UV-visible absorption energies than polyvanadate structures on Al(2)O(3). The deposition sequence in binary Mo-V catalysts did not lead to significant differences in structure or catalytic rates, suggesting that the two active oxide components become intimately mixed. The deposition of CrO(x) on Al(2)O(3) led to more reactive VO(x) domains than those deposited on pure Al(2)O(3) at similar VO(x) surface densities. At all surface densities, the replacement of V-O-Al or V-O-V structures with V-O-Cr increased the reducibility and catalytic reactivity of VO(x) domains; it also led to higher propene selectivities via the selective inhibition of secondary C(3)H(6) combustion pathways, prevalent in VO(x)-Al(2)O(3), and of C(3)H(8) combustion routes that lead to low alkene selectivities on CrO(x)-Al(2)O(3). VO(x) and CrO(x) mix significantly during synthesis or thermal treatment to form CrVO(4) domains. The deposition sequence, however, influences catalytic selectivities and reduction rates, suggesting the retention of some of the component deposited last as unmixed domains exposed at catalyst surfaces. These findings suggest that the reduction and catalytic properties of active VO(x) domains can be modified significantly by the formation of binary dispersed structures. VO(x)-CrO(x) structures, in particular, lead to higher oxidative dehydrogenation rates and selectivities than do VO(x) domains present at similar surface densities on pure Al(2)O(3) supports.     

A general electron transfer reduction of lactones using SmI2-H2O

Herein we describe a strategy for the selective, electron transfer reduction of lactones of all ring sizes and topologies using SmI(2)-H(2)O and a Lewis base to tune the redox properties of the complex. The current protocol permits instantaneous reduction of lactones to the corresponding diols in excellent yields, under mild reaction conditions and with useful chemoselectivity. We demonstrate the broad utility of this transformation through the reduction of complex lactones and sensitive drug-like molecules. Sequential electron transfer reactions and syntheses of deuterated diols are also described.     

A New Route to Organic Intercalates Consisting of Vanadium Pentoxide and Pyridines: (4-H2N-C5H5NH)V2O5

Light at the end of the tunnel! Intercalates of pyridine and layered inorganic compounds have intrigued chemists for at least two decades, but their structure determination has always been difficult owing to a lack of suitable single crystals. The intercalate (4-H₂N-C₅H₅NH)V₂O₅ has now been characterized by X-ray crystal structure analysis, and its electronic structure and magnetic properties have been studied in detail.     

Temperature-programmed reduction of V2O5 and coprecipitated V2O5−TiO2 by hydrogen

Temperature-programmed reductions (TPR) with H₂ of both pure V₂O₅ and coprecipitated V₂O₅?TiO₂ systems with different titanium concentrations was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform infrared analysis and scanning electron microscopy. Within the temperature range in which TPR analysis was carried out (100–600°C) the V₂O₅ phase was reduced in two or three steps, while no variation in the TiO₂ phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the following steps, the H₂ reacted with oxygen atoms of the V=O and V?O?V bonds. This led to important changes in the structure and morphology of the system. The experimental evidence allowed the conclusion that titanium stabilizes certain phases of vanadium oxides in which vanadium appears as V(+4) or as a mixture of V(+4) and V(+5). Moreover, when moderate and high titanium concentrations were used, the reduction temperature of the bulk V₂O₅ decreased markedly.     

Changes in structure and catalytic properties of V2O5 caused by mechanochemical treatment

By means of x-ray phase analysis and tunneling microscopy, it has been shown that when vanadium(V) oxide in an ethanol medium is subjected to mechanochemical treatment in a planetary mill, it undergoes not only size reduction with an increase of surface area, but also a change of structure. Extension of the processing time increases the relative content of the vanadyl plane (010) by a factor of more than 5. It has been established by means of x-ray photoelectron spectroscopy that some of the surface vanadyl ions are reduced. Modification of the structure and composition of the surface of the vanadium oxide leads to changes in its catalytic properties in n-butane and benzene oxidation reactions. The approximately twofold increase of hydrocarbon conversion may be related to the increase of surface area of the specimen; this view is supported by the constancy of the specific rate of n-butane oxidation. The sharp increases that are observed in the selectivity of maleic anhydride formation (sixfold in the oxidation of n-butane, threefold in the oxidation of benzene) are related to the increased content of the vanadyl plane and the surface formation of groupings of vanadium differing in valence. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 34, No. 3, pp. 180–183, May–June, 1998.