F:Flammable;
108-05-4Relevant articles and documents
Nanostructured Pd?Cu Catalysts Supported on Zr?Al and Zr?Ti for Synthesis of Vinyl Acetate
Gonzalez Caranton, Alberth Renne,Dille, Jean,Barreto, Jade,Stavale, Fernando,Pinto, José Carlos,Schmal, Martin
, p. 5256 - 5269 (2018)
Renewable ethylene can be obtained by dehydration of bio-ethanol and used for production of vinyl acetate (VAM) through reaction with acetic acid (AcOH), using Pd?Cu catalysts. In the present manuscript, structural characterizations of Pd?Cu/ZrO2 catalysts show that these systems present cubic structure with different spatial distributions. Particularly, it is shown that combustion of ethylene and acetic acid can be inhibited below 180 °C, maximizing the rates of VAM formation, when the catalysts are modified with Ti+4. The effects of AcOH concentration on rates of VAM formation show that higher AcOH concentrations favor the formation of undesired byproducts, while lower AcOH concentrations favor effects related to O2 mobility, which can lead to surface decomposition. VAM formation is favored, with selectivities ranging from 0.8 to 1.0. XPS results indicate the existence of metallic Pd, CuO species and Zr species, in agreement with IR results. DRIFTS results also show that different Pd-acetate intermediates can be present, depending on the electronic effects associated to Pd?Cu and Zr species.
Kinetic parameters for the elementary steps in the palladium-catalyzed synthesis of vinyl acetate
Calaza, Florencia,Stacchiola, Dario,Neurock, Matthew,Tysoe, Wilfred T.
, p. 135 - 142 (2010)
The kinetics of the reaction between gas-phase ethylene and adsorbed acetate species to form vinyl acetate monomer (VAM) on a Pd(111) surface are measured using infrared spectroscopy to monitor the rate of acetate removal, as well as the rates of VAM and ethylidyne formation, at various temperatures. The results are fit using a kinetic model first proposed by Samanos in which ethylene reacts with acetate species to form an acetoxyethyl intermediate that forms VAM via β-hydride elimination. The results of the kinetic model agree well with the experimental data and Arrhenius plots of the rate constants yield activation energies that are in good agreement with those predicted by density functional theory (DFT) calculations. DFT also predicts that the reaction activation energies should depend on the acetate coverage while the experimental data can be fit by constant values of the rate constants, suggesting that the reaction activation energies are similar for a reaction center surrounded either by acetate species, ethylidynes, or a combination of both. Finally, the kinetic parameters for VAM desorption are in good agreement with the experimental peak temperature measured by temperature-programmed desorption for VAM desorbing from an ethylidyne-covered surface.
Monoatomically dispersed Pd/TiO2 catalyst effective for epoxidation of propylene at ambient temperature in the presence of H2 and O2
Hikazudani, Susumu,Mochida, Tatsuya,Matsuo, Naofumi,Nagaoka, Katsutoshi,Ishihara, Tatsumi,Kobayashi, Hisayoshi,Takita, Yusaku
, p. 89 - 98 (2012)
The catalytic activity of monoatomically dispersed Pd supported on TiO 2 toward propylene epoxidation in the presence of H2 and O2 was studied at ambient temperature, and both propylene oxide (PO) and propane were obtained. Short-chain alkanes also reacted but epoxide formation was not observed in those reactions except in the case of isobutane, which formed isobutylene oxide at a low rate. The optimum surface concentration of Pd on TiO2 was 0.005-0.01 atom/nm2; because the supported amount of Pd is extremely small relative to the surface area of the support, the supported Pd is thought to be monoatomically dispersed. Pd/TiO 2 catalysts prepared from a tetraphenylporphyrin-Pd chloride complex showed almost the same product distribution for propylene epoxidation as did catalysts prepared from Pd(NO3)2. Isotope exchange between H2 and D2 proceeded over Pd/TiO2 with a low surface concentration (0.0001 atom-Pd/nm2), and chemical potential calculations suggested that H2 molecules could dissociatively adsorb onto the monoatomically dispersed Pd/TiO2. A PO formation mechanism over the catalyst is proposed on the basis of these results. The results presented here may provide the first clear evidence of catalysis by monoatomically dispersed noble metals.
THE CATALYSIS OF THE ELECTROCHEMICAL REDUCTION OF ALKYL BROMIDES BY NICKEL COMPLEXES: THE FORMATION OF CARBON-CARBON BONDS
Gosden, Cary,Pletcher, Derek
, p. 401 - 409 (1980)
The square planar, macrocyclic nickel complex, N,N'-ethylenebis(salicylidene-iminato)nickel(II), is shown to be an effective catalyst for the electrochemical reduction of substituted alkyl bromides; this indirect cathodic reduction can lead to a good yield of dimeric products.The reduction of alkyl bromides in the presence of an activated olefin is shown to lead to mixtures of products compatible with radical addition to the double bond.The mechanism of the reaction of nickel(I) complexes with alkyl bromides is discussed in the light of these results.
Dendrimer-stabilized bimetallic Pd/Au nanoparticles: Preparation, characterization and application to vinyl acetate synthesis
Kuhn, Martin,Jeschke, Janine,Schulze, Steffen,Hietschold, Michael,Lang, Heinrich,Schwarz, Thomas
, p. 78 - 82 (2014)
The preparation, characterization and a novel application to vinyl acetate synthesis of dendrimer-stabilized Pd/Au nanoparticles are described. The nanoparticles were synthesized by co-precipitation of aqueous Pd 2 +/Au3 + salt solutions with hydrazine in the presence of (poly)amidoamine (PAMAM)-based dendrimers functionalized with terminal ethylene glycol ethers. Characterization by transmission electron microscopy and UV-vis spectroscopy confirmed that alloyed Pd/Au nanoparticles with a mean diameter of 6.0 (± 1.2) to 10.4 (± 1.7) nm were formed. After nanoparticle immobilization onto a silica support and thermal dendrimer removal, the resulting materials are high active catalysts in ethylene acetoxylation to vinyl acetate monomer with a productivity of 2.1 kgVAM kg cat- 1 h- 1.
Acyl iodides in organic synthesis: VI. Reactions with vinyl ethers
Voronkov,Trukhina,Vlasova
, p. 467 - 469 (2004)
Reactions of acetyl iodide with butyl vinyl ether, 1,2-divinyloxyethane, phenyl vinyl ether, 1,4-di-vinyloxybenzene, and divinyl ether were studied. Vinyl ethers derived from aliphatic alcohols (butyl vinyl ether and 1,2-divinyloxyethane) react with acetyl iodide in a way similar to ethyl vinyl ether, i.e., with cleavage of both O-Csp2 and Alk-O ether bonds. From butyl vinyl ether, a mixture of vinyl iodide, butyl acetate, vinyl acetate, and butyl iodide is formed, while 1,2-divinyloxyethane gives rise to vinyl iodide, vinyl acetate, and 2-iodoethyl acetate. The reaction of acetyl iodide with divinyl ether involves cleavage of only one O-Csp2 bond, yielding vinyl acetate and vinyl iodide. In the reactions of acetyl iodide with phenyl vinyl ether and 1,4-divinyloxybenzene, only the O-CVin bond is cleaved, whereas the O-CAr bond remains intact.
Nanosized {Pd4(μ4-C)}Pd32(CO)28(PMe3)14 Containing Tetrahedrally Deformed Pd4 Cage with Encapsulated Carbide Atom: Formal Substitution of Geometrically Analogous Interior Au4 Entity in Isostructural Au4Pd32(CO)28(PMe3)14 by Electronically Equivalent Pd4(μ4-C) and Computational/Catalytic Implications
Mednikov, Evgueni G.,Ivanov, Sergei A.,Dahl, Lawrence F.
, p. 6157 - 6168 (2015)
This first homopalladium carbido cluster, {Pd04(μ4-C)}Pd32(CO)28(PMe3)14 (1), was isolated (3-7% yields) from an ultimately simplified procedure - the reaction of CHCl3 under N2 with either Pd8(CO)8(PMe3)7 or Pd10(CO)12(PMe3)6 at room temperature. Charge-coupled device (CCD) X-ray diffraction data at 100 K for 1·2.5 C6H14 (1a) and 1·3 CHCl3 (1b) produced closely related molecular parameters for 1. This {Pd4C}Pd32 cluster (1) possesses a highly unusual tetracoordinated carbide atom that causes a major distortion of a central regular Pd4 tetrahedron into a new symmetry type of encapsulated Pd4 cage of pseudo-D2 (222) symmetry. Mean Pd-Pd distances for the three pairs of opposite twofold-equivalent Pd-Pd tetrahedral-like edges for 1a are 2.71, 2.96, and 3.59 ?; the mean of the four Pd-C distances [range, 1.87(2)-1.94(2) ?] is 1.91 ?. An astonishing molecular feature is that this {Pd4C}Pd32 cluster (1) is an isostructural and electronically equivalent analogue of the nanosized Au4Pd32(CO)28(PMe3)14 (2). Cluster 2, likewise a pseudo-D2 molecule, contains a geometrically analogous tetrahedrally deformed interior Au4 entity encapsulated within an identical Pd32(CO)28(PMe3)14 shell; mean distances for the three corresponding symmetry-equivalent pairs of slightly smaller opposite tetrahedral-distorted Au-Au edges are 2.64, 2.90, and 3.51 ?. A computational study by both a natural population analysis (NPA) and an atoms-in-molecules (AIM) method performed on model analogues {Pd4C}Pd32(CO)28(PH3)14 (1-mod) and Au4Pd32(CO)28(PH3)14 (2-mod) suggested that the negatively charged Au4 entity in 2-mod may be described as two weakly interacting electron-pair Au2 intradimers. In contrast, an NPA of the {Pd4C} entity in 1-mod revealed that two similarly oriented identical Pd2 intradimers of 2.71 ? are primarily stabilized by Pd-C bonding with a negatively charged carbide atom. The isostructural stabilizations of 1 and 2 are then attributed to the similar sizes, shapes, and overall negative charge distributions of the electronically equivalent interior {Pd4C} and Au4 entities. This resulting remarkable structural/electronic equivalency between 1 and 2 is consistent with the greatly improved performances of commercial palladium catalysts for vinyl acetate synthesis by gold-atom incorporation to suppress carbonization of the Pd atoms, namely, that the extra Au 6s1 valence electron of each added Au atom provides an effective "negative charge protection" against electron-donating carbon atoms forming Pd carbido species such as {Pd4C}. (Figure Presented).
The Mechanism of Thermal Elimination. Part 17. Rate Data for Pyrolysis of Vinyl Acetate and 1,2-Diacetoxyethane
Taylor, Roger
, p. 1157 - 1160 (1983)
Between 721.7 and 636.4 K, vinyl acetate undergoes thermal decomposition according to the rate equation log (k/s-1)=10.43-182.4/2.303 RT (R=8.312 J mol-1 K-1).Approximately 95percent of reaction is decarbonylation to give acetone, with decomposition to ketene and acetaldehyde being the minor component.The latter reaction is an analogue of acetic anhydride pyrolysis which takes place at least 1E6 times faster per β-hydrogen at 600 K.This very large rate difference parallels that between β-keto-acids and βγ-alkenoic acids and contrasts markedly with pyrolysis of alkyl acetates and alkyl vinyl ethers, which occurs at closely similar rates.The contrasting behaviour most probably reflects differences in the principal bond-breaking step of the reaction, which for vinyl acetate and acetic anhydride (and also the acids) is breaking of the β-X-H bond so that the nucleophilicity of the attacking group assumes major importance; for esters and vinyl ethers this is not the most important step so their reaction rates are similar.The relative reactivities to the acids support an alternative view that both vinyl acetate and acetic anhydride pyrolyse via their enol forms.The greater understanding of the factors affecting gas-phase elimination rates permits prediction of the relative rates of compounds not yet studied.Pyrolysis of 1,2-diacetoxyethane gave non-first-order plots, with rate acceleration due to formation of the more reactive vinyl acetate.The β-acetoxy-group (OCOMe) increased the rate of elimination (per β-hydrogen at 600 K) ca. 7-fold, which compares with factors of 388 and 144 for COMe and CO2Me respectively, and a reduction of 3.6-fold by OMe.
Neuartige basische Liganden fuer die homogenkatalytische Methanolcarbonylierung XXIX. Kieselgelfixierte (Ether-Phosphan)Rhodium-Komplexe in der katalytischen Hydrocarbonylierung von Methylacetat zu Ethylidendiacetat
Lindner, Ekkehard,Glaser, Erhard,Mayer, Hermann August,Wagner, Peter
, p. 325 - 337 (1990)
The heterogenized (ether-phosphane)rhodium complexes 2Rh(CO)Cl (2a-d) are obtained from the silica anchored silylalkyl(ether-phosphanes) 1a-d and (μ-CIRh(CO)2>2.The palladium complex 2PdCl2 (4) is formed by addition of (COD)PdCl2 to the heterogenized alkyldiphenylphosphane (3).High pressure experiments provide information on conversion and selectivity in the hydrocarbonylation of methylacetate to ethylidenediacetate, if parameters like pressure, temperature, ether moieties in the ligands 1a-d, and composition of catalyst and synthesis gas are varied.To investigate the influence of temperature and pressure on the leaching of metals, the supported catalysts are recovered and re-used. trans-(PO)2Rh(CO)Cl (7e) is formed in homogeneous phase by reaction of 2 (5) with the ligand 6e O = Me3Si(CH2)3P(Ph)CH2CH2OCH3>.Oxidative addition of CH3I to 7e affords trans-(PO)2Rh(CO)(CH3)(I)2 (9e).In the presence of CO methyl migration in 9e leads to trans-(PO)2Rh(CO)(COCH3)(I)2 (10e).Reductive elimination of CH3C(O)I from 10e regenerates 7e, probably via the cationic intermediate O)-(P O)Rh(CO)COCH3)I> (8e).The unstable cationic (ether-phosphane)rhodium complex O)(P O)Rh(CO)COCH3)I> (11e) which is isostructural to 8e is obtained by I- abstraction from 10e.
Coverage effects on the palladium-catalyzed synthesis of vinyl acetate: Comparison between theory and experiment
Calaza, Florencia,Stacchiola, Dario,Neurock, Matthew,Tysoe, Wilfred T.
, p. 2202 - 2207 (2010)
The high adsorbate coverages that form on the surfaces of many heterogeneous catalysts under steady-state conditions can significantly lower the activation energies for reactions that involve the coupling of two adsorbed intermediates while increasing those which result in adsorbate bond-breaking reactions. The influence of the surface coverage on the kinetics of metal-catalyzed reactions is often ignored in theoretical and even in some ultrahigh vacuum experimental studies. Herein, first principle density functional theoretical calculations are combined with experimental surface titration studies carried out over well-defined Pd(111) surfaces to explicitly examine the influence of coverage on the acetoxylation of ethylene to form vinyl acetate over Pd. The activation energies calculated for elementary steps in the Samanos and Moiseev pathways for vinyl acetate synthesis carried out on acetate-saturated palladium surfaces reveal that the reaction proceeds via the Samanos mechanism which is consistent with experimental results carried out on acetate-saturated Pd(111) surfaces. The rate-limiting step involves a β3-hydride elimination from the adsorbed acetoxyethyl intermediate, which proceeds with an apparent calculated activation barrier of 53 kJ/mol which is in very good agreement with the experimental barrier of 55 ± 4 kJ/mol determined from kinetic measurements.
