Showing papers in "Journal of Molecular Catalysis A-chemical in 1997"
TL;DR: In this article, self-consistent density functional calculations using the LMTO-ASA method of the variations in the surface electronic structure for pseudomorfic overlayers and impurities of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au on the other metals are presented.
Abstract: We present self-consistent density functional calculations using the LMTO-ASA method of the variations in the surface electronic structure for pseudomorfic overlayers and impurities of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au on the other metals. Knowledge of these variations is of importance in understanding trends in the reactivity of metal surfaces. A simple model is presented which gives a description of the overall trends in the self-consistently calculated results.
1,061 citations
TL;DR: Heterogeneous asymmetric catalysis on chirally modified supported platinum catalysts has undergone significant development recently based on the knowledge gained on the mechanism of the asymmetric hydrogenation of α-ketoesters, catalyzed by platinum modified with cinchona alkaloids.
Abstract: Heterogeneous asymmetric catalysis on chirally modified supported platinum catalysts has undergone significant development recently Based on the knowledge gained on the mechanism of the asymmetric hydrogenation of α-ketoesters, catalyzed by platinum modified with cinchona alkaloids, new efficient chiral auxiliaries have been developed and the scope of reactants has been extended The research strategy which led to this progress and the results achieved are reviewed
376 citations
TL;DR: In this paper, the use of dibenzothiophene with hydrogen peroxide using phosphotungstic acid as catalyst and tetraoctylammonium bromide as phase transfer agent in a mixture of water and toluene has been studied.
Abstract: Oxidation of dibenzothiophene with hydrogen peroxide using phosphotungstic acid as catalyst and tetraoctylammonium bromide as phase transfer agent in a mixture of water and toluene has been studied. Catalysed decomposition of hydrogen peroxide competes with dibenzothiophene oxidation but by choice of suitable conditions yields of dibenzothiophene sulphone approaching 100% may be obtained. Treatment of gas oils with this technology shows that all the sulphur compounds present are oxidised by this catalyst system and highly substituted dibenzothiophenes are the most readily oxidised of species containing a thiophene nucleus. Oxidised sulphur compounds can be separated from the oil by adsorption on silica gel. The use of oxidation and adsorption in a process for desulphurisation of gas oils is discussed.
363 citations
TL;DR: In this article, a new model is proposed based on the description of spilt-over hydrogen as electron donor located at the surface of the catalyst, which is applied to interpret some experimental results related to hydrogen spillover, especially the partial electron transfer from the hydrogen species to the solid.
Abstract: Various experimental results on hydrogen spillover which have been obtained since the first evidence for this phenomenon are discussed concerning the nature of the activated hydrogen species. It will be demonstrated that the physical nature of the spilt-over species, especially their charge, can only be described by considering their interaction with the solid. A new model is proposed which is based on the description of spilt-over hydrogen as electron donor located at the surface. Consequently, H+ ions and H atoms coexist on the surface of the catalyst as also stated experimentally. Their ratio is determined by the electronic properties of the adsorbate/solid system. Considering atomic and recombinative desorption of spilt-over hydrogen, the adsorption isotherms are calculated exemplary for titania. The model is applied to interpret some experimental results related to hydrogen spillover, especially the partial electron transfer from the hydrogen species to the solid.
207 citations
TL;DR: A survey of the literature published in 1995 and partly in 1994 on organometallic chemistry and catalysis shows that the field is characterized by further dynamic progress in research of industrially relevant processes, such as hydroformylation, in extension of aqueous organometallics catalysis to more and more diverse laboratory syntheses and in understanding the mechanisms of such processes.
Abstract: A survey of the literature published in 1995 and partly in 1994 on organometallic chemistry and catalysis shows that the field is characterized by further dynamic progress in research of industrially relevant processes, such as hydroformylation, in extension of aqueous organometallic catalysis to more and more diverse laboratory syntheses and in understanding the mechanisms of such processes.
158 citations
TL;DR: In this article, the authors showed that both biological and chemical oxidation of methane involves a rate limiting CH bond cleavage, whereas the reaction with benzene is probably limited by the formation of an epoxy-type intermediate.
Abstract: Earlier, iron complexes stabilized in a ZSM-5 zeolite matrix have been shown to produce a new form of surface oxygen (called α-oxygen) upon decomposition of N2O. α-Oxygen exhibits a very high reactivity typical for oxygen of monooxygenases (MO) and mimics its unique ability in selective oxidation of hydrocarbons at room temperature. Kinetic isotope effect (KIE) measurements reported here reveal additional similarities between MO and the model. Depending on the temperature, the value of KIE for oxidation of methane with α-oxygen ranges from 1.9 to 5.5. For the oxidation of benzene the value of KIE is 1.0. This indicates that both biological and chemical oxidation of methane involves a rate limiting CH bond cleavage, whereas the reaction with benzene is probably limited by the formation of an epoxy-type intermediate. The assumed structure of the active sites as well as some features of the oxidation mechanism allow one to consider FeZSM-5-N2O system as a new and successful model for methane monooxygenase.
144 citations
TL;DR: In recent years, aqueous two-phase catalysis has conquered its own field of homogeneously catalysed processes and has already achieved industrial-scale importance in hydroformylation as discussed by the authors.
Abstract: In recent years aqueous two-phase catalysis has conquered its own field of homogeneously catalysed processes and has already achieved industrial-scale importance in hydroformylation. Because it has a number of advantages (ease of separation of catalyst and product, catalysts can be matched very precisely to the particular problem and thus tailor-made, use of special properties and effects of water as a solvent and reaction solvent, environmentally benign process) its importance and application will grow further. So far, scientific research has mainly concentrated on the preparation of water-soluble ligands and their metal complexes, but the outstanding features and effects of water-based catalysts in different types of reactions need to be rationalised with regard to their special mechanistic and kinetic aspects.
136 citations
TL;DR: In this paper, the effect of acid (Cl−, SO2−4) and basic (K+) promoters on certain oxides (Al2O3, ZrO2) was also studied.
Abstract: Acid-base properties of oxides (Al2O3, SiO2, ZrO2, CeO2, MgO, SiO2Al2O3 and CeO2Al2O3) were investigated by means of model reactions: 3,3-dimethylbut-1-ene isomerization (33DMB1), methylene cyclohexane isomerization (MECH), cyclohexanol conversion (CHOL) and CO2 chemisorption at room temperature. The effect of acid (Cl−, SO2−4) and basic (K+) promoters on certain oxides (Al2O3, ZrO2) was also studied. Surface acidity was evaluated by means of 33DMB1 or MECH isomerization and of CHOL dehydration into cyclohexene. CO2 chemisorption as well as the cyclohexanone to cyclohexene ratio in CHOL conversion were used to measure the surface basicity of the solids. Except for very few cases, all the tests gave coherent results which led to well-defined scales of acidity and of basicity. Contrary to what could be observed with the conventional isopropanol test, the CHOL test proves to be little sensitive to the redox sites of the oxides. The presence of metals can create significant perturbations in these acid-base tests, except in the case of 33DMB1 isomerization. The latter reaction is not catalyzed by Pt and Rh surfaces, which allows to measure (in the presence of these metals) the acid properties of the support and to investigate the changes in surface acidity, resulting from the metal impregnations (metal → support electronic effect, presence of anions,…).
135 citations
TL;DR: In this article, the dechlorination of 1,2,4-trichlorobenzene to benzene effectively occurred in a 2-propanol solution of a base compound such as NaOH or KOH in the presence of Rh/C or Pd/C at temperatures below 65°C.
Abstract: Catalytic hydrodehalogenation of aromatic halides was carried out in an alcohol solution containing base compounds in the presence of carbon-supported noble metal catalysts. It was found that dechlorination of 1,2,4-trichlorobenzene to benzene effectively occurred in a 2-propanol solution of a base compound such as NaOH or KOH in the presence of Rh/C or Pd/C at temperatures below 65°C. When deuorium-labeled 2-propanol, CD3CD(OD)CD3, was used as a solvent, 1,2,4-trichlorobenzene was dechlorinated to give benzene containing D atoms with high yield, indicating that the hydrodechlorination reaction includes hydrogen-transfer from 2-propanol to chlorobenzenes. Iodo-, bromo- and fluoro-benzenes were also readily dehalogenated in the catalytic system.
132 citations
TL;DR: In this article, a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same aluminium was proposed to explain the high stereoselectivity of the zeolite BEA.
Abstract: Zeolite BEA has been studied as catalyst in the Meerwein–Ponndorf–Verley and Oppenauer (MPVO) reactions of substituted cyclohexanones and cyclohexanols. In the MPV reduction of 4- tert -butylcyclohexanone to 4- tert -butylcyclohexanol a high stereoselectivity (>95%) to the thermodynamically less stable cis -isomer was obtained while in the complementary Oppenauer oxidation the cis -alcohol was preferentially converted. This stereoselectivity is explained by transition-state selectivity imposed by the zeolite structure. The catalytic activity is related to Lewis-acid aluminium sites which are located in the micropores. FT-IR results indicate that these sites are related to aluminium atoms which are only partially bonded to the framework. The mechanism is proposed to involve a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same aluminium.
132 citations
TL;DR: In this paper, the use of hydrogen peroxide as catalysts for epoxidation of alkenes and oxidations of alcohols, tertiary amines and sulfides is discussed.
Abstract: The new complexes [(LO 4 ){MO(O 2 ) 2 } 2 {MO(O 2 ) 2 (H 2 O)}] 3− (L = P, As; M = W, Mo) are reported and their use as catalysts in the presence of hydrogen peroxide for epoxidation of alkenes and oxidations of alcohols, tertiary amines and sulfides discussed. Similar oxidations are reported for salts of [(LO 3 (OH)){MO(O 2 ) 2 } 2 ] 2− (L = P, As; M = W, Mo), [(PhPO 3 ){MO(O 2 ) 2 } 2 {MO(O 2 ) 2 (H 2 O)}] 3− (M = W, Mo) and [(R 2 LO 2 ){MO(O 2 ) 2 } 2 ] − (R = Ph, Me; L = P, As; M = W, Mo). Alkene epoxidations and alcohol oxidations are also reported for [PW 11 O 39 ] 7− , [Ln III {PW 11 O 39 } 2 ] 11− (Ln = Y, La, Ce, Pr, Sm, Tb, Yb) and [M IV {PW 11 O 39 } 2 ] 10− (M = Ce, Th).
TL;DR: A series of novel water-soluble polyether-substituted triphenylphosphines (PETPPs) were prepared by means of the ethoxylation of mono-, di- and tri-p-hydroxytriphenyl phosphines as mentioned in this paper.
Abstract: A series of novel water-soluble polyether-substituted triphenylphosphines (PETPPs) were prepared by means of the ethoxylation of mono-, di- and tri-p-hydroxytriphenylphosphines. PETPPs manifest inverse temperature-dependent solubility in water that enables them to act as thermoregulated phase transfer ligands. The concept of the thermoregulated phase transfer catalysis is successfully applied to the biphasic hydroformylation of higher olefins, such as 1-dodecene, in the presence of rhodium-PETPP complexes as the catalysts.
TL;DR: A new environmentally benign technology based on the use of polyoxometalate (POM) salts and oxygen is being developed to bleach wood pulps for use in the manufacture of paper.
Abstract: A new environmentally benign technology, based on the use of polyoxometalate (POM) salts and oxygen, is being developed to bleach wood pulps for use in the manufacture of paper. Details of POM chemistry relating to the unit operations of an effluent-free bleaching process are reported. These include anaerobic delignification of wood pulp, aerobic reoxidation of reduced POMs for their cyclic reuse and POM catalyzed and initiated aerobic mineralization (wet oxidation) of lignin fragments removed from pulp during bleaching. The results of bleaching trials using a series of isostructural POM complexes of the Keggin family are reported. Key structural components of the POMs are varied to determine the effects of these changes on POM performance. Homogeneous reactions of lignin-model compounds with select POMs are used to help interpret kinetic data obtained in the heterogeneous reaction of POM solutions with pulp fibers. Finally, new directions in catalyst design that promise to expand the potential of the technology are discussed.
TL;DR: In this paper, a kinetic equation is presented which accounts for the activity vs. time observed data, and an estimation is made of the equivalent monolayers of reactant converted prior total activity disappearance.
Abstract: TiO2 deactivation is studied during the gas-phase photocatalytic oxidation of organics containing three different heteroatoms: Si, N and S. Auger electron spectroscopy is used to characterize the catalyst poisoning species. A kinetic equation is presented which account for the activity vs. time observed data. Finally, an estimation is made of the equivalent monolayers of reactant converted prior total activity disappearance.
TL;DR: The relationship between catalytic activity and propylene oxide selectivity can be explained by the acidification of water coordinated to the active titanium site and its reversible deprotonation to an ate complex, which inhibits the formation of the active species for epoxidation as discussed by the authors.
Abstract: The epoxidation of propene with hydrogen peroxide and a titanium silicalite catalyst with MFI structure was investigated in detail. The relationship between catalytic activity and propylene oxide selectivity can be explained by the acidification of water coordinated to the active titanium site and its reversible deprotonation to an ate complex, which inhibits the formation of the active species for epoxidation. Pretreatment of the catalyst with neutral or acidic salts improves the propylene oxide selectivity without affecting the catalytic activity. Catalyst deactivation occurs by blocking of the zeolite micropores with propylene oxide oligomers. The deactivated catalyst can be regenerated by refluxing with dilute hydrogen peroxide.
TL;DR: In this article, the authors investigated the embedding of a chiral manganese(III) cationic complex of salen type (Jacobsen complex I) into the pores of mesoporous substituted silicates.
Abstract: The embedding of a enantioselective homogeneous catalyst — the chiral manganese(III) cationic complex of salen type (Jacobsen complex I) — into the pores of mesoporous substituted silicates is investigated. The host/guest interaction is studied by different methods: TG-DTA, UV-VIS, and FTIR. The results are consistent with a location of the large Mn complex inside the mesopores. Catalytic tests in olefin epoxidation prove the fully maintenance of the catalytic activity and stereoselectivity of the complex after embedding. This promising result indicates that MCM-like materials might have perspectives as supports for the heterogenization of homogeneous catalysts.
TL;DR: In this paper, a high-resolution solid state nuclear magnetic resonance spectrometer with 27Al and 29Si probes was used to study the interaction between Mo species and HZSM-5 zeolite.
Abstract: By using a high-resolution solid state nuclear magnetic resonance spectrometer with 27Al and 29Si probes, the interaction between Mo species and HZSM-5 of frsol|Mo/HZSM-5 catalysts has been studied. The results show that there is a strong interaction between Mo species and HZSM-5 zeolite. The framework aluminum in the zeolite can be easily extracted by the introduction of Mo species. The extractability of framework aluminum by Mo species increases with increasing Mo loading and the calcination temperature. The extraction process leads to the formation of non-framework Al at first and then a new crystalline phase of Al2(MoO4)3. The dealumination of the catalyst having a Mo loading of 15% and had been calcined at 973 K is so severe that all the aluminum in the framework are extracted and no framework Al could be detected by 27Al MAS NMR. The catalyst, therefore, lost its catalytic activity for methane dehydrogenation and aromatization in the absence of oxygen. The SiAl ratio measured from 29Si MAS NMR further confirms the dealumination process observed by 27Al MAS NMR. The MAS NMR results give us an evidence that Al2(MoO4)3 crystallites are much less active for the reaction.
TL;DR: In this article, the performance of a new rhodium recycling system was described using a series of amphiphilic ligands: Ph 2 ArP (Ar = 3-hydroxyphenyl, 4-carboxyhenyl), Ph n Ar 3 − n P (Ar= 4-PhCH 2 X, X = NEt 2, NMePh, NPh 2 ; n = 1-2) and Ph n AR 3 −n P (AR = 3pyridyl,4-pyrithyl; n= 1−2)
Abstract: The performance of a new rhodium recycling system is described using a series of amphiphilic ligands: Ph 2 ArP (Ar = 3-hydroxyphenyl, 4-carboxyphenyl), Ph n Ar 3 − n P (Ar = 4-PhCH 2 X , X = NEt 2 , NMePh, NPh 2 ; n = 1–2) and Ph n Ar 3 − n P (Ar = 3-pyridyl, 4-pyridyl; n = 1–2). The corresponding rhodium complexes are active in the hydroformylation of oct-1-ene and can be separated from the product aldehydes by acidic or basic extraction into water. After neutralisation of the aqueous phase the rhodium phosphine species can be extracted into a new batch of oct-1-ene, with toluene as organic solvent. The pH-depending distribution characteristics of the free ligands have been determined. PhAr 2 P with Ar = 4-PhCH 2 NEt 2 and Ar = 3-pyridyl were completely extracted from a solution in Et 2 O or toluene into a H 2 SO 4 -solution of pH 3 and 2, respectively. Recycling experiments with the former ligand demonstrated that the catalytically active rhodium hydrides decompose during the acidic extraction step. The structure of the recovered rhodium complexes could not be elucidated by NMR- and IR-analysis. Rhodium measurements by ICP-AES established that rhodium was quantitatively recycled. Pressurising the recovered rhodium and excess ligand to 20 bar syngas at 80°C resulted in regeneration of the original, catalytically active species. A retention of catalytic activity up to 87% was achieved.
TL;DR: In this article, the unimolecular decomposition of NH3 on polycrystalline wires and foils of Pd and Ir is examined and compared with the corresponding ones on Pt and Rh.
Abstract: The unimolecular decompositions of NH3 on polycrystalline wires and foils of Pd and Ir are examined and compared with the corresponding ones on Pt and Rh. The reactions were carried out in a differential flow reactor, at pressures from 0.01 to 1 Torr and temperatures from 500 to 1900 K. It was found that the rates of product formation could be fit by Langmuir-Hinshelwood unimolecular rate expressions, with an accuracy of ±20% under all conditions. Ammonia decomposes to N2 and the rate of decomposition is fastest on Ir by several orders of magnitude when compared with that on the other metals, becoming flux limited above about 750 K. Ir appears to be the choice catalyst for dehydrogenating ammonia. The heats of adsorption of NH3 on Pt, Rh and Pd are similar and equal to 16.7, 16.8 and 17.4 kcal/mol, respectively. The apparent activation energy for this reaction is similar on Pt and Rh and equal to 21 kcal/mol, while for Pd and Ir it is 26.2 and 31.2 kcal/mol, respectively.
TL;DR: In this paper, two asymmetric metal-catalyzed oxidations are discussed, and they are used in enantioselective sulfide oxidations with hydrogen peroxide, giving optically active lactones in up to 95% ee.
Abstract: Two asymmetric metal-catalyzed oxidations are discussed. Chiral copper complexes catalyze enantiospecific Baeyer-Villiger oxidations giving optically active lactones in up to 95% ee. Vanadium complexes have been used in enantioselective sulfide oxidations with hydrogen peroxide.
TL;DR: In this article, the authors used a combination of copper(II) chloride and a crown ether as a catalyst for the cyclohexane and achieved a high turnover number for the first time.
Abstract: The oxidation of alkanes to the corresponding alcohols and ketones and the epoxidation of alkenes can be performed efficiently at room temperature with molecular oxygen (1 atm) in the presence of an aldehyde and a copper salt catalyst such as copper(II) hydroxide. Extremely high turnover numbers have been obtained for the oxidation of cyclohexane using a combination of copper(II) chloride and a crown ether as a catalyst.
TL;DR: The photoassisted degradation of two dye compounds, erythrosine and rhodamine B, has been investigated in an aqueous TiO2 dispersion under irradiation by visible light as mentioned in this paper.
Abstract: The photoassisted degradation of two dye compounds, erythrosine and rhodamine B, has been investigated in an aqueous TiO2 dispersion under irradiation by visible light. The compounds can be easily decomposed photochemically by visible light, which provides possibly a new approach for the treatment of dye pollutants in wastewater.
TL;DR: In this article, a new versatile epoxidation method for organic synthesis is proposed, where α-methylsubstituted carboxylic acid ethylesters can be converted to peroxy acids by perhydrolysis using the same enzyme.
Abstract: The lipase-catalyzed reactions of carboxylic acids and carboxylic acid esters with hydrogen peroxide are used to generate various peroxy acids at room temperature and without mineral acids. Whereas Novozym 435 R will only be able to catalyze the conversion of free unbranched carboxylic acids to peroxy acids, α-methylsubstituted carboxylic acid ethylesters can be converted to peroxy acids by perhydrolysis using the same enzyme. These peroxy acids are used in-situ for the epoxidation of unsaturated compounds and thus a new versatile epoxidation method for organic synthesis is proposed.
TL;DR: In this article, the effect of chromium and manganese oxide on the structural and catalytic properties of copper/zirconia used for methanol synthesis from carbon dioxide and hydrogen has been investigated by several techniques ( TG DTA, XRD, TPR, XPS, N2O-titration, nitrogen physisorption).
Abstract: The effect of chromium- and manganese oxide on the structural and catalytic properties of copper/zirconia used for methanol synthesis from carbon dioxide and hydrogen has been investigated by several techniques ( TG DTA , XRD, TPR, XPS, N2O-titration, nitrogen physisorption). The methanol selectivity of all catalysts is governed by the competition of the simultaneously catalyzed methanol synthesis and reverse water gas shift reaction. The chromium containing sample produces predominantly methanol, whereas the manganese containing catalyst is most active for CO formation. For reaction temperatures 443–513 K and 1.7 MPa total pressure, methanol formation decreases in the order Cu/ZrO2 > Cu/CrOx/ZrO2 > Cu/MnOx/ZrO2 for catalysts dried at 403 K. After calcination at 623 K in air, methanol synthesis activity is similar for all catalysts. For temperatures exceeding 523 K Cu/CrOx/ZrO2 shows highest activity for methanol production. The addition of chromium oxide and less pronounced manganese oxide, to Cu ZrO 2 retards sintering of the copper component and shifts the crystallization of amorphous zirconia to higher temperatures, thus, resulting in an increased thermal stability of the catalyst under reaction conditions. X-ray photoelectron spectroscopy (XPS) was applied to examine the relative surface concentrations and the oxidation state of the catalyst components. XPS shows that there is no apparent correlation between the oxidation states of the metals and the catalytic properties of the catalysts. In situ diffuse reflectance FTIR studies were performed to identify the species present on the catalyst surface under CO2 hydrogenation conditions and to elucidate the reaction mechanism. With all catalysts, surface carbonate and formate species were formed rapidly. Evidence is given that over copper/zirconia based catalysts methanol is formed mainly from bidentate surface carbonate via adsorbed CO, π-bound formaldehyde and surface-bound methylate.
TL;DR: In this paper, the transesterification of dimethyl carbonate with phenol to produce methyl phenyl carbonate was carried out in an autoclave using a variety of solid catalysts.
Abstract: The transesterification of dimethyl carbonate with phenol to produce methyl phenyl carbonate was carried out in an autoclave using a variety of solid catalysts. MoO 3 SiO 2 was found to have a very high activity for this transesterification. Thus, a 17.1% yield of methyl phenyl carbonate based on phenol was obtained at 433 K in the presence of MoO 3 SiO 2 . MoO 3 SiO 2 was also an active catalyst for the disproportionation of methyl phenyl carbonate into diphenyl carbonate and dimethyl carbonate. A 48% yield of diphenyl carbonate was attained over MoO 3 SiO 2 at 443 K. These yield values are probably very close to those at the thermodynamic equilibrium.
TL;DR: In this paper, the essentially aluminum-free titanium containing analogue of zeolite beta was synthesized using di(cyclohexylmethyl)dimethylammonium (DCDMA) as the template.
Abstract: The essentially aluminum-free titanium containing analogue of zeolite beta was synthesized using di(cyclohexylmethyl)dimethylammonium (DCDMA) as the template. The titanium zeolite beta was found to exhibit Bronsted acidic properties when alcohols were employed as the solvent, which is explained by the Lewis acid character of the titanium site, which on coordination of an alcohol yields a mild Bronsted acid site. The use of alcohol/acetonitrile mixtures as the solvent showed a clear maximum in activity in 1-octene epoxidation, depending on the type and amount of alcohol used. A catalytic species is proposed in which an alcohol as well as a hydroperoxo group is coordinated to a framework connected titanium atom.
TL;DR: In this article, an analysis of the activation procedure aimed to the identification of the reactive species leads to the isolation of complexes of the type ((P-P)Pt(μ-OH)]) 2 2+ (P-, various diphosphines), which are catalytically active in the Baeyer-Villiger oxidation of cyclic ketones with hydrogen peroxide.
Abstract: Enantioselective Baeyer-Villiger oxidation of cyclic ketones with hydrogen peroxide can be obtained using (P-P * )Pt(2-van) complexes (P-P * , chiral diphosphine; 2-van, bis-anion of 2-vanillin) as catalyst precursors. An analysis of the activation procedure aimed to the identification of the reactive species leads to the isolation of complexes of the type ((P-P)Pt(μ-OH)]) 2 2+ (P-P, various diphosphines). The synthesis of some new species is reported together with their characterization with IR and NMR spectroscopy and conductivity data. It is found that these complexes are catalytically active in the (enantioselective) Baeyer-Villiger oxidation of cyclic ketones with hydrogen peroxide. The basic nature of the OH ligands is exploited in the reaction with a variety of acids including hydrogen peroxide.
TL;DR: In this paper, three mononitrophenol compounds were photocatalytically degraded in aqueous TiO 2 suspension, and it was suggested for the transformation of nitro group that the formation ratio of NO − 3 and NH + 4 reflected the degradation mechanism of starting nitrophenolic compound.
Abstract: Three mononitrophenol compounds (2-, 3- and 4-) 2,4-dinitrophenol and picric acid (2,4,6-trinitrophenol) were photocatalytically degraded in aqueous TiO 2 suspension. Among three mononitrophenol compounds the degradation rate of 4- and 2-nitrophenol were larger than that of 3-nitrophenol. The degradation rate decreased with the number of nitro group substituents. This reactivity follows Hammett law with regard to the effect of nitro group on phenolic functionality. Several polyhydroxylated aromatic intermediates were identified for mono- and dinitrophenol which indicated that the degradation started by the substitution of hydrogen and nitro groups by hydroxyl radical. Organic acid intermediates were identified besides aromatic compounds, among which formic and acetic acids were formed in the largest quantity. It was suggested for the transformation of nitro group that the formation ratio of NO − 3 and NH + 4 reflected the degradation mechanism of starting nitrophenolic compound.
TL;DR: In this paper, the authors investigated the kinetics of the HRh(CO(PPh 3 ) 3 catalyzed hydroformylation of l-dodecene in a temperature range of 323-343, K. The rate was found to be first order with respect to catalyst concentration and partial pressure of hydrogen.
Abstract: The kinetics of the HRh(CO(PPh 3 ) 3 catalyzed hydroformylation of l-dodecene has been investigated in a temperature range of 323–343, K. The effect of l-dodecene and catalyst concentration, P H and P CO , on the rate of reaction has been studied. The rate was found to be first order with respect to catalyst concentration and partial pressure of hydrogen. The rate vs. P CO shows a typical case of substrate inhibited kinetics. The rate was found to be first order with respect to l-dodecene in the lower concentration range while at higher concentrations a zero order dependence was observed. A rate equation has been proposed and kinetic parameters evaluated. The activation energy was found to be 57.12 kJ/mol. A batch reactor model has been a used to predict the concentration-time profiles which were found to agree well with the experimental data at different temperatures. This indicates the applicability of the rate model over a wide range of conditions.
TL;DR: In this article, a polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, was used for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN).
Abstract: Polymer-achored monometallic palladium catalyst PVP-PdCl2 (PVP = poly(N-vinyl-2-pyrrolidone)) exhibits very high activity for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN) in the presence of base at 65°C and atmospheric pressure. In this case, the substrate is rapidly hydrodechlorinated to nitrobenzene (NB) which is then reduced to AN. Using the polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, and in the presence of 1.0 mol% of sodium acetate, a strong synergic effect gives rise to a remarkable increase of the selectivity for p-chloroaniline (CAN) and the maximum selectivity of CAN is up to 94%. For the hydrogenation of the non-halo-substituted nitroaromatics to the corresponding aromatic amines, the monometallic PVP-PdCl2 catalyst only shows mild or poor activity, but the colloidal polymer-anchored bimetallic palladium-platinum catalyst, PVP-Pd-1 4Pt , exhibits very high activity and selectivity.