Showing papers on "Benzaldehyde published in 2016"

Mild ultrasound-assisted synthesis of TiO2 supported on magnetic nanocomposites for selective photo-oxidation of benzyl alcohol

Abstract: A simple and effective ultrasound-assisted wet impregnation method was developed for the preparation of magnetically separable TiO2/maghemite-silica photo-active nanocomposites. The resulting nanomaterials were characterized by several techniques and subsequently tested for their photocatalytic activities in the liquid phase selective oxidation of benzyl alcohol. An unprecedented selectivity in organic media (90% in acetonitrile) towards benzaldehyde was achieved at a benzyl alcohol conversion of ca. 50%, being remarkably superior in terms of activity to any other supported transition metal catalysts reported to date as well as commercial titania Evonik P-25 photocatalyst.

Ultrafine MnO2 nanoparticles decorated on graphene oxide as a highly efficient and recyclable catalyst for aerobic oxidation of benzyl alcohol.

Abstract: The highly active and selective aerobic oxidation of aromatic alcohols over earth-abundant, inexpensive and recyclable catalysts is highly desirable. We fabricated herein MnO2/graphene oxide (GO) composites by a facile in-situ growth approach at room temperature and used them in selective aerobic oxidation of benzyl alcohol to benzaldehyde. TEM, XRD, FTIR, XPS and N2 adsorption/desorption analysis were employed to systematically investigate the morphology, particle size, structure and surface properties of the catalysts. The 96.8% benzyl alcohol conversion and 100% benzaldehyde selectivity over the MnO2/GO (10/100) catalyst with well dispersive ultrafine MnO2 nanoparticles (ca. 3nm) can be obtained within 3h under 383K. Simultaneously, no appreciable loss of activity and selectivity occurred after recycling use up to six times. Due to their significant low cost, excellent catalytic performance, the MnO2/GO composites have huge application prospect in organic synthesis.

Formation of highly oxygenated low-volatility products from cresol oxidation

Abstract: . Hydroxyl radical (OH) oxidation of toluene produces ring-retaining products: cresol and benzaldehyde, and ring-opening products: bicyclic intermediate compounds and epoxides. Here, first- and later-generation OH oxidation products from cresol and benzaldehyde are identified in laboratory chamber experiments. For benzaldehyde, first-generation ring-retaining products are identified, but later-generation products are not detected. For cresol, low-volatility (saturation mass concentration, C* ∼ 3.5 × 104 − 7.7 × 10−3 µg m−3), first- and later-generation ring-retaining products are identified. Subsequent OH addition to the aromatic ring of o-cresol leads to compounds such as hydroxy, dihydroxy, and trihydroxy methyl benzoquinones and dihydroxy, trihydroxy, tetrahydroxy, and pentahydroxy toluenes. These products are detected in the gas phase by chemical ionization mass spectrometry (CIMS) and in the particle phase using offline direct analysis in real-time mass spectrometry (DART-MS). Our data suggest that the yield of trihydroxy toluene from dihydroxy toluene is substantial. While an exact yield cannot be reported as authentic standards are unavailable, we find that a yield for trihydroxy toluene from dihydroxy toluene of ∼ 0.7 (equal to the reported yield of dihydroxy toluene from o-cresol; Olariu et al., 2002) is consistent with experimental results for o-cresol oxidation under low-NO conditions. These results suggest that even though the cresol pathway accounts for only ∼ 20 % of the oxidation products of toluene, it is the source of a significant fraction (∼ 20–40 %) of toluene secondary organic aerosol (SOA) due to the formation of low-volatility products.

Biocatalytic Dynamic Kinetic Resolution for the Synthesis of Atropisomeric Biaryl N-Oxide Lewis Base Catalysts

Abstract: Atropisomeric biaryl pyridine and isoquinoline N-oxides were synthesized enantioselectively by dynamic kinetic resolution (DKR) of rapidly racemizing precursors exhibiting free bond rotation. The DKR was achieved by ketoreductase (KRED) catalyzed reduction of an aldehyde to form a configurationally stable atropisomeric alcohol, with the substantial increase in rotational barrier arising from the loss of a bonding interaction between the N-oxide and the aldehyde. Use of different KREDs allowed either the M or P enantiomer to be synthesized in excellent enantiopurity. The enantioenriched biaryl N-oxide compounds catalyze the asymmetric allylation of benzaldehyde derivatives with allyltrichlorosilane.

Promoting the Hydrosilylation of Benzaldehyde by Using a Dicationic Antimony-Based Lewis Acid: Evidence for the Double Electrophilic Activation of the Carbonyl Substrate

Abstract: The concomitant activation of carbonyl substrates by two Lewis acids has been investigated by using [1,2-(Ph2 MeSb)2 C6 H4 ](2+) ([1](2+) ), an antimony-based bidentate Lewis acid obtained by methylation of the corresponding distibine. Unlike the simple stibonium cation [Ph3 MeSb](+) , dication [1](2+) efficiently catalyzes the hydrosilylation of benzaldehyde under mild conditions. The catalytic activity of this dication is correlated to its ability to doubly activate the carbonyl functionality of the organic substrate. This view is supported by the isolation of [1-μ2 -DMF][OTf]2 , an adduct, in which the DMF oxygen atom bridges the two antimony centers.

Promoting role of bismuth on carbon nanotube supported platinum catalysts in aqueous phase aerobic oxidation of benzyl alcohol

Abstract: PtBi/CNT catalyst was synthesized by a one-step polyol reduction method assisted by microwave radiation, and its catalytic performance was investigated in aerobic oxidation of benzyl alcohol in the aqueous phase. Pt and BiO x species uniformly dispersed on the CNT surfaces and strong synergic interaction between them occurred, which confirmed by the comprehensive analysis of TEM, XRD, XPS and electrochemical characterizations. Further investigations revealed that the synergic effect effectively promoted the activation of both molecular oxygen and benzyl alcohol substrate; also protected Pt active sites from over-oxidization. The advantage of such synergic effect was reflected in the increased yield for the desired product benzaldehyde: PtBi/CNT catalyst exhibited about 3.5 times higher yield toward benzaldehyde compared to Pt/CNT catalyst. Furthermore, owing to the positive effect of Bi avoiding Pt from oxidizing, the deactivation of PtBi/CNT (with 2% selectivity and 9% conversion decrease) is much slower than that of Pt/CNT (with 8% selectivity and 39% conversion decrease) after six reaction cycles. PtBi/CNT catalyst was proved as a remarkably effective catalyst with high stability for the aerobic oxidation of benzyl alcohol.

Oxidation of benzyl alcohol catalyzed by gold nanoparticles under alkaline conditions: weak vs. strong bases

Abstract: Gold nanoparticles have shown excellent catalytic properties in selective oxidation of alcohols in the presence of base; however, the influence of the nature and concentration of the base on gold catalyst activity and selectivity is not completely understood. We here present a study of the effect of using weak and strong bases on the conversion and selectivity of PVA-stabilized gold nanoparticles supported on titania (AuPVA/TiO2) for benzyl alcohol oxidation. The increase in the concentration of base had little effect on conversion when a weak base was used (K2CO3, Na2B4O7 and Na(CH3COO)), due to the buffer effect, but strongly affected selectivity. The bases with higher pKa values provided higher conversions and increased production of benzoic acid. For the strong base NaOH, benzoic acid was always the major product, although conversion decreases in excess of base. The formation of benzoic acid is avoided by using K2CO3 in non-aqueous media; benzaldehyde is the main product in cyclohexane whereas benzyl benzoate is also formed in significant amounts in solvent-free conditions. The promotion effect observed in the presence of base was discussed in terms of reaction mechanism.

Selectivity Control in Palladium-Catalyzed Alcohol Oxidation through Selective Blocking of Active Sites

Abstract: Stabilized metal nanoparticles (NPs) have received wide interest in a number of liquid-phase catalytic transformations, but the role of the capping/protective agent is still debated. Operando attenuated total reflection infrared (ATR-IR) spectroscopy enabled us to obtain unprecedented molecular level insights into the selectivity issue induced by the presence of the protective agent by following the liquid-phase benzyl alcohol oxidation on Pd/Al2O3. Supported Pd NPs protected by poly(vinyl alcohol) (PVA) showed a lower rate of benzaldehyde decarbonylation compared to unprotected Pd nanoparticles and, as a result, an improved selectivity toward the aldehyde. In addition, also the further oxidation of benzaldehyde to benzoic acid was reduced by the presence of PVA. In combination with considerations on adsorption site occupancy from CO adsorption, we ascribed this behavior to a selective blocking operated by PVA especially of Pd(111) facets, which are active in the decarbonylation process of benzaldehyde du...

Synthesis, characterization and antimicrobial activity of 4-((1-benzyl/phenyl-1 H -1,2,3-triazol-4-yl)methoxy)benzaldehyde analogues

Abstract: A diverse series of 4-((1-benzyl/phenyl-1H-1,2,3-triazol-4-yl)methoxy)benzaldehyde analogues has been synthesized in good yield by the click reaction between 4-O-propargylated benzaldehyde and various organic bromides/azides. All the synthesized compounds were tested in vitro for their antimicrobial activity against Gram-positive bacteria (Staphylococcus epidermidis and Bacillus subtilis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and fungi (Candida albicans and Aspergillus niger). Most of the compounds exhibited good-to-excellent antimicrobial activity. Compound 7b was found to be more potent than ciprofloxacin against B. subtilis, whereas it showed activity comparable to ciprofloxacin against E. coli. Compounds 4h and 4i showed activity comparable to fluconazole against A. niger. Further, the binding mode of compound 7b into the active site of E. coli topoisomerase II DNA gyrase B has also been investigated.

Enzyme‐Catalyzed Carbonyl Olefination by the E. coli Protein YfeX in the Absence of Phosphines

Abstract: The Wittig-type carbonyl olefination reaction has no biocatalytic equivalent. To build complex molecular scaffolds, however, C−C bond-forming reactions are pivotal for biobased economy and synthetic biology. The heme-containing E. coli protein YfeX was found to catalyze carbonyl olefination by reaction of benzaldehyde with ethyl diazoacetate under aerobic conditions in the absence of a triphenylphosphine oxophile. The reaction was performed in whole cells and showed a product formation of 440 mg L−1 in 1 h. It was, moreover, shown that the reaction could be performed under Wittig-analogue conditions in the presence of triphenylphosphine or triphenylarsine.

Iron(III) and cobalt(III) complexes with both tautomeric (keto and enol) forms of aroylhydrazone ligands: catalysts for the microwave assisted oxidation of alcohols

Abstract: Two Schiff bases derived from the condensation of 2-hydroxybenzohydrazide with 3,5-di-tert-butyl-2-hydroxybenzaldehyde (H2L1) or with 2,3-dihydroxy benzaldehyde (H2L2) were used to synthesize the Fe(III) and Co(III) complexes [Fe(L1)(HL1)] (1) and [Co(L2)(HL2)] (2), respectively. The compounds were characterized by elemental analysis, IR, ESI-MS and single crystal X-ray analysis. Structural studies indicated the presence of both keto and enol tautomeric forms of the ligand in 1 and 2. The complexes (mainly 1) act as catalysts in the microwave-assisted solvent-free peroxidative oxidation (by tert-butylhydroperoxide, TBHP) of primary and secondary alcohols. A facile, efficient and selective synthesis of ketones was achieved with a yield up to 96% and a TON up to 500, after 30 min under low power (15 W) microwave irradiation (complex 1 as catalyst). 2-Pyrazinecarboxylic acid (Hpca) shows a promoting effect.

Microkinetic Modeling of Benzyl Alcohol Oxidation on Carbon‐Supported Palladium Nanoparticles

Abstract: Six products are formed from benzyl alcohol oxidation over Pd nanoparticles using O2 as the oxidant: benzaldehyde, toluene, benzyl ether, benzene, benzoic acid, and benzyl benzoate. Three experimental parameters were varied here: alcohol concentration, oxygen concentration, and temperature. Microkinetic modeling using a mechanism published recently with surface intermediates was able to produce all 18 trends observed experimentally with mostly quantitative agreement. Approximate analytical equations derived from the microkinetic model for isothermal conditions reproduced the isothermal trends and provided insight. The most important activation energies are Ea2=57.9 kJ mol₋1, Ea5=129 kJ mol₋1, and Ea6=175 kJ mol₋1, which correspond to alcohol dissociation, alkyl hydrogenation, and the reaction of alkyl species with alkoxy species. Upper limits for other activation energies were identified. The concepts of a sticking coefficient and steric factor in solution were applied.

Heterogeneous Pd catalyst for mild solvent-free oxidation of benzyl alcohol

Abstract: A magnetically separable catalyst was designed for the production of value-added benzaldehyde. Palladium (Pd) nanoparticles supported on iron-doped SBA-15 (MagSBA) were fabricated and applied as heterogeneous catalyst for solvent-free oxidation of benzyl alcohol using molecular oxygen under atmospheric pressure without external base. The developed Pd/MagSBA showed excellent catalytic performance at comparatively low temperature range of 70–90 °C. The catalyst made the oxidation of BzOH milder, purification simpler and less pollution caused. Effects of the palladium loadings, reaction temperature, and stirring rates on their catalytic activity of benzaldehyde conversion were studied. It was found that the designed catalysts were recoverable by simple magnetic separation and were reusable without significant loss of catalytic activity. In addition, the reaction kinetics of the catalytic oxidation was investigated, showing that the reaction was zero order and the calculated activation energy was 50.08 kJ/mol.

Application of metal organic frameworks M(bdc)(ted)0.5 (M = Co, Zn, Ni, Cu) in the oxidation of benzyl alcohol

Abstract: The selective oxidation of benzyl alcohol to benzaldehyde is an important process in heterogeneous catalysis and green organic chemistry. Herein, we investigated the effect of different metal ions in the metal organic framework M(bdc)(ted)0.5 (M = Co, Zn, Ni, Cu, bdc = 1,4-benzenedicarboxylate, ted = triethylenediamine) on the catalytic activity of benzyl alcohol oxidation. The catalytic results demonstrated that Co(bdc)(ted)0.5 achieved good benzyl alcohol conversion (81.8%) and benzaldehyde selectivity (>99%) by using O2 as the oxidant. The catalysts could be reused several times without significant degradation in activity.

Large-scale synthesis of ultrathin tungsten oxide nanowire networks: an efficient catalyst for aerobic oxidation of toluene to benzaldehyde under visible light

Abstract: As a very important chemical raw material, the selective formation of benzaldehyde from toluene at preparative or industrial levels requires the use of highly corrosive chlorine and high reaction temperatures, which severely corrodes equipment, pollutes the environment, and consumes a lot of energy. Herein, we report a robust and highly active catalyst for the benzaldehyde evolution reaction that is constructed by the surfactant-free growth of oxygen vacancy-rich W18O49 ultrathin nanowire networks. Under atmospheric pressure and visible-light irradiation, the new catalyst can selectively (92% selectivity) catalyze the aerobic oxidation of toluene to benzaldehyde with yields of above 95%.

Catalytic Hydrogenation of Benzaldehyde for Selective Synthesis of Benzyl Alcohol: A Review

Abstract: In the recent past, various catalysts have been used for hydrogenation of benzaldehyde to benzyl alcohol and the efficiency of the catalysts observed is found to be less.This review focuses on catalytic hydrogenation and their parameters associated with supports, methods of preparation, solvents involved, reaction conditions in converting benzaldehyde to benzyl alcohol. Critical aspect of review is to evaluate activities of various heterogeneous catalysts that can selectively reduce benzaldehyde to benzyl alcohol. The catalysts include various transition (Ni, Cu, Co) and noble metals (Au, Pt, Pd, Ru), monoliths and metal oxides (MgO, CaO, BaO, Al2O3, CeO2, ZrO2, etc.,), which are all active in the reaction. Among the transition metals, cobalt-based catalysts depicted promising activity, while ruthenium-based systems demonstrated spectacular activity among noble metal series. Hydrogenation by electrochemical reduction using platinum, palladium, nickel has also been reviewed.

A Ruthenium(III)–Oxyl Complex Bearing Strong Radical Character

Abstract: Proton-coupled electron-transfer oxidation of a RuII−OH2 complex, having an N-heterocyclic carbene ligand, gives a RuIII−O. species, which has an electronically equivalent structure of the RuIV=O species, in an acidic aqueous solution. The RuIII−O. complex was characterized by spectroscopic methods and DFT calculations. The oxidation state of the Ru center was shown to be close to +3; the Ru−O bond showed a lower-energy Raman scattering at 732 cm−1 and the Ru−O bond length was estimated to be 1.77(1) A. The RuIII−O. complex exhibits high reactivity in substrate oxidation under catalytic conditions; particularly, benzaldehyde and the derivatives are oxidized to the corresponding benzoic acid through C−H abstraction from the formyl group by the RuIII−O. complex bearing a strong radical character as the active species.