Catalyst Solubility Research Articles

Degradation of bisphenol A in water by the heterogeneous photo-Fenton

Bisphenol A (BPA) is a kind of a controversial endocrine disruptor, and is ubiquitous in environment. The degradation of BPA with the heterogeneous photo-Fenton system was demonstrated in this study. The Fe-Y molecular sieve catalyst was prepared with the ion exchange method, and it was characterized by X-ray radiation diffraction (XRD). The effects of pH, initial concentration of H2O2, initial BPA concentration, and irradiation intensity on the degradation of BPA were investigated. The service life and iron solubility of catalyst were also tested. XRD test shows that the major phase of the Fe-Y catalyst was Fe2O3. The method of heterogeneous photo-Fenton with Fe-Y catalyst was superior to photolysis, photo-oxidation with only hydrogen, heterogeneous Fenton, and homogeneous photo-Fenton approaches. pH value had no obvious effects on BPA degradation over the range of 2.2–7.2. The initial concentration of H2O2 had an optimal value of 20×10−4 mol/L. The decrease in initial concentration of BPA was favourable for degradation. The intensity of ultraviolet irradiation has no obvious effect on the BPA removal. The stability tests indicated that the Fe-Y catalyst can be reused and iron solubility concentration ranged from NA to 0.0062 mg/L. Based on the results, the heterogeneous photo-Fenton treatment is the available method for the degradation of BPA.

Perfluorooxasulphonates of Metals – the Catalysts of Esters Manufacture

The process of obtaining of aliphatic dibasic esters from dicarboxylic acids and C 4-C5 alcohols in the presence of perfluoro(4-m ethyl-3,6-dioxaoctane)sulpho- nates of different metals has been researched. For the comparative estimation of catalysts their concentration was chosen identical and of such value that the rate of the process was limited exactly by the rate of chemical reaction. The dependences of technological characteristics of esterification process on catalyst nature and concentration and on reagents nature have been determined. High activity of the investigated catalysts has been found out, which is probably caused by the synergetic effect of metal cation and perfluoroic fragment, which provides decreasing of electron density on metal ion and at the same time good solubility of catalyst in the substrate, thus providing its high active concentration.

Partial Deoxygenation of Glycerol Catalyzed by Iridium Pincer Complexes

Iridium pincer complexes (POCOP)Ir(CO) (POCOP = κ3-C6H3-1,3-[OP(tBu)2]2) and substituted POCOP derivatives catalyze deoxygenation of glycerol to n-propanol and 1,3-propanediol in good yield under moderate conditions (acidic aqueous dioxane, 200 °C, 80 bar H2). Catalyst solubility in the polar reaction mixture is improved by incorporation of a polar moiety in the para position of the POCOP phenyl ring, with the best results obtained with a dimethylamino substituent.

Metal-centered oxidations facilitate the removal of ruthenium-based olefin metathesis catalysts

Commercially available catalysts (SIMes)(PCy3)Cl2Ru(CHPh) (2) and (SIMes)Cl2Ru(CH-o-O-i-PrC6H4) (3) (SIMes = 1,3-dimesitylimidazolin-2-ylidene) were found to display reversible Ru oxidations via a series of electrochemical measurements. The redox processes enabled the catalysts to be switched between two different states of activity in ring opening metathesis polymerizations and ring closing metathesis reactions, primarily through changes in catalyst solubility. Moreover, treating a solution of 2 dissolved in C6H6/CH2Cl2/[1-butyl-3-methylimidazolium][PF6] (6:1:1.1 v/v/v) with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone was found to remove >99.9% of the catalyst, as determined by UV/vis spectroscopy. The methodology described herein establishes a new approach for controlling the activities displayed by commercially available olefin metathesis catalysts and for removing residual Ru species using redox-driven processes.

Green PU resin from an accelerated Non-isocyanate process with microwave radiation

The ring opening between BCC with di-amine by conventional heating (130 °C for 48 h) is a time-consuming and non-efficient process. This work has been aiming at accelerating its ring-opening reaction by a microwave radiation process. Besides, catalyst and solvent selections of this PU reaction system, the microwave power output, radiation time, catalyst and reaction media were major consideration of this research. A catalyst, TBAC or LiBr had been applied on each microwave-assisted ring-opening polymerization of BCC with Jeffamine D-2000. A similar average molecular weight of NH2-PU oligomer was obtained from a 50 min microwave radiation by using 50 W power output. The radiation system with TBAC as catalyst, and it resulted in a formation of NH2-PU oligomer with Mn and Mw were 12,997 and 15,580, and that of 10,882 and 13,508 with LiBr as catalyst. The solvent polarity, catalyst solubility and microwave output energy in this radiation system were considered as important factors for this new green process.

Sm(III)nitrate-catalyzed one-pot synthesis of furano[3,2c]-1,2,3,4-tetrahydroquinolines and DNA photocleavage studies

The synthesis and DNA photocleavage studies of furano[3,2-c]-1,2,3,4-tetrahydroquinolines have been reported. Sm(III)nitrate was found to be an efficient for the Diels–Alder reaction of aryl amines with 2,3-dihydrofuran to offer the corresponding furano[3,2-c]-1,2,3,4-tetrahydroquinolines derivatives as a mixture of cis/trans stereoisomers in moderate yields. The aqueous solubility of acid catalyst can be recycled without significant loss of activity. The DNA photocleavage studies shows that, the cis/trans stereoisomers are good DNA cleavage mimic in terms of molecular structure.

Catalyst solubility and self-doping in ZnS nanostructures

We demonstrate that the variation in the solubility of the catalyst during nanostructure growth via vapor-liquid-solid technique is dependent on the catalyst dimensions. This property can be exploited in a simple way for controlled doping of the nanostructures. Specifically, we investigate the role of Au droplet size on its solubility in ZnS nanostructures. The size-dependent variations in the surface tension of the catalyst droplet can change its solubility in the nanostructures. The solubility of the catalyst (Au) has been observed to decrease drastically with the increase in its droplet radius. X ray diffraction and scanning electron microscopy were used to determine the phase, shape, size, and density of nanostructures. XPS results revealed that concentration of Au in the ZnS nanostructures was high for a small Au droplet and dropped considerably with increase in the droplet size. The experimental findings were in good agreement with the theoretical model, based on the thermodynamical equations for the doping in nanowires. The critical size of the catalyst for the surface and core doping is determined for the zinc blende and Wurtzite phases of ZnS. In the end, we show that, by using a suitable catalyst with high miscibility, nanostructures can be doped during growth, thus eliminating a step in the device fabrication.

Triphenylphosphine modified rhodium catalyst for hydroformylation in supercritical carbon dioxide

The kinetics of 1-octene hydroformylation catalyzed by triphenylphosphine modified rhodium in carbon dioxide have been explored at 90 °C and pressures up to 48 MPa. The apparent catalyst solubility was determined by evaluating the reaction rate for different rhodium amounts. The kinetics follow a first order in 1-octene, a negative order of −1.2 in carbon monoxide, an order of 0.25 in hydrogen, and a negative order of −0.2 in triphenylphosphine, which is to a great extent in agreement with studies on the hydroformylation of linear 1-alkenes in organic solvents. The observed apparent turnover frequencies range from 1900 to 7000 mol aldehyde mol Rh −1 h −1. These turnover frequencies are of the same order of magnitude as observed for hydroformylations in organic solvents, indicating that rhodium modified with triphenylphosphine can be used with high efficiency in supercritical carbon dioxide rich mixtures.

Ethyl ester production by homogeneous alkaline transesterification: Influence of the catalyst

In this work, the process for ethyl ester production is studied using refined sunflower oil, and NaOH, KOH, CH3ONa, and CH3OK, as catalysts. In all cases, the reaction is carried out in a single reaction step. The best conversion is obtained when the catalyst is either sodium methoxide or potassium methoxide. We found that during the transesterification with ethanol, soap formation is more important than in the case of methanol. The saponification reaction consumes an important fraction of the catalyst. The amount of catalyst consumed by this reaction is 100% in the case of using hydroxides as catalyst (KOH or NaOH), and 25%, and 28% when using CH3ONa and CH3OK as catalysts, respectively. Ethanol increases the catalyst solubility in the oil–ethyl ester phase, thus accelerating the saponification reaction.It is possible to obtain high conversions in a one-step reaction, with a total glycerine concentration close to 0.25%.

Regioselective Rhodium(II)‐Catalyzed Hydroaminations of Propargylguanidines

Regioselective Rhodium(II)‐Catalyzed Hydroaminations of Propargylguanidines

Tuning catalyst solubility in CO2 by changing molar volume

Poor-solvating property of supercritical carbon dioxide (scCO2) has been a great challenge, which limits the use of CO2 as a common “green” solvent. The present report describes that by increasing molar volume (v) and lowering the melting temperature, which lowers cohesive energy density or solubility parameter (δ), it is possible to increase the solubility of metal-based catalysts in scCO2 without using costly fluorinated or tailor-made CO2-philic modifications. We have studied various chlorodistannoxanes (1) and Cu–β-diketonates (2) to support our views. The study of bio-diesel production and transesterification of hindered esters using 1 in scCO2 shows a 2–8-folds rate enhancement coupled with an easier catalyst and product separation than that in organic solvents. The methodology, which works at least within the range of Van der Waals sphere of interactions, can be useful to solubilizing the molecules in scCO2 and carries great opportunity in catalysis as well as in separation science.

1H,1H,2H,2H‐Perfluorodecyl‐Acrylate‐Containing Block Copolymers from ARGET ATRP

AbstractBlock copolymers of 1H,1H,2H,2H‐perfluorodecyl acrylate (AC8) were obtained from ARGET ATRP. To obtain block copolymers of low dispersity the PAC8 block was synthesized in anisole with a CuBr2/PMDETA catalyst in the presence of tin(II) 2‐ethylhexanoate as a reducing agent. The PAC8 block was subsequently used as macroinitiator for copolymerization with butyl and tert‐butyl acrylate carried out in scCO2. To achieve catalyst solubility in CO2 two fluorinated ligands were employed. The formation of block copolymers was confirmed by size exclusion chromatography and DSC. magnified image

Kinetic Evaluation of Cooperative [Co(salen)] Catalysts in the Hydrolytic Kinetic Resolution of rac‐Epichlorohydrin

AbstractA wide variety of [Co(salen)] catalysts with different structures designed to enhance salen–salen cooperative interactions have been reported as catalysts for the hydrolytic kinetic resolution (HKR) of epoxides. However, the myriad catalysts have been evaluated under inconsistent experimental conditions, at different catalyst loadings, at different temperatures, with various epoxides and in several different laboratories, making rigorous comparisons between the catalysts impossible. To this end, 12 representative catalysts from our studies, as well as catalysts originally described by others, are reported in the HKR of epichlorohydrin under rigorously identical conditions. The comparison of the reactivity and selectivity of the different catalysts indicates that the soluble, oligomeric [Co(salen)] catalysts with cyclic frameworks impart the highest activity and enantioselectivity (>99 % ee, krel>99) in this representative reaction, requiring very short reaction times (<30 min), including the most active catalyst reported to date for the target reaction. In general, it is found that soluble polymer or oligomer‐supported catalysts are more active than insoluble supported catalysts under the conditions used. Among the insoluble catalysts, a polymer resin supported [Co(salen)] catalyst with excellent enantioselectivity (>99 % ee, krel>99) and medium reaction time (222 min), is the most active and selective of the class. The lessons demonstrated herein regarding design of active and selective catalysts offer useful insights into refining design strategies for other related cooperative catalytic reactions, suggesting emphases on catalyst flexibility and solubility under reaction conditions.

Reducing ATRP Catalyst Concentration in Batch, Semibatch and Continuous Reactors

AbstractAn overview of solution ATRPs carried out in batch, semibatch and continuous tubular and stirred‐tank reactor systems is presented. Initial work using a heterogeneous catalyst system with copper to polymer chain ratios of close to unity demonstrated the versatility of ATRP in producing homopolymer and copolymer at reasonable rates with good MW control and narrow polydispersity. The significant drawbacks of low catalyst solubility and high copper levels are now being addressed through use of the ARGET ATRP chemistry. Nearly colorless acrylate and methacrylate polymers have been produced with copper catalyst levels below 50 ppm (relative to monomer), with excellent control of MW obtained both in batch and continuous systems.magnified image

Supercritical carbon dioxide, a new medium for aerobic alcohol oxidations catalysed by copper-TEMPO

The copper catalysed aerobic oxidation of selected alcohol substrates in supercritical carbon dioxide (scCO(2)), employing a range of simple copper(II) catalyst compounds, is here described. The copper acetate complex of polydimethylsiloxane (PDMS) functionalised pyridine (1), compound 2, has previously been synthesised and characterised by us and its solubility in scCO(2) demonstrated. Due to this solubility we anticipated that the selective aerobic oxidation of alcohols to aldehydes could be homogeneously catalysed by this compound in scCO(2) in combination with the co-catalyst 2,2,6,6-tetramethylpiperidin-1-yloxy free radical (TEMPO). Our initial results showed that complete oxidation of 4-nitrobenzyl alcohol was achieved within 4 h of reaction. However, the activities of analogous copper derivatives containing simpler pyridine substituents, [Cu(AcO)(2)(py)](2) and [Cu(AcO)(2)(4VP)](2) (4VP = 4-vinylpyridine), were shown to be similar, in spite of their negligible solubility in scCO(2). When we repeated the reactions in highly non-polar hexane rather than scCO(2) similar observations were made. In both cases, as 2 is soluble and the pyridine analogues are not, a much higher reaction rate was anticipated for 2 as it is the only compound capable of homogeneous catalysis. However, in some cases slightly better activities were observed for [Cu(AcO)(2)(py)](2) rather than for the PDMS functionalised analogue, 2. Thus, despite poor catalyst solubility typically being very inhibitory in this type of catalytic process, in this system solubilisation of the catalyst is not necessary. In continuation the activity of silica supported copper complexes was therefore investigated. Employing such catalysts the 4-nitrobenzyl and benzyl alcohol substrates were completely oxidised to the corresponding aldehydes in scCO(2), this time employing lower catalyst loadings. Other types of alcohol substrate showed more limited conversions however. To conclude, alcohol oxidation in the non-conventional green solvent scCO(2), with the benign terminal oxidant, dioxygen, and simple, cheap, easily prepared metal catalyst compounds was demonstrated. This is the first copper-TEMPO catalysed alcohol oxidation system in scCO(2) to be described.

Catalytic olefin epoxidation with cationic molybdenum(VI) cis-dioxo complexes and ionic liquids

The complexes [MoO 2Cl(HC(bim) 3)]Y (Y = Cl ( 1), BF 4 ( 2) and PF 6 ( 3)) have been prepared by reaction of MoO 2Cl 2(THF) 2 (for 1) or [MoO 2Cl(THF) 3]Y (for 2 and 3) with the tridentate ligand HC(bim) 3 = tris(benzimidazolyl)methane, and characterized by IR and Raman spectroscopy, and 1H NMR. The turnover frequencies for the epoxidation of cis-cyclooctene at 55 °C with tert-butyl hydroperoxide (TBHP, in decane) as the oxidant and complexes 1– 3 as catalysts are in the range of 70–200 mol mol Mo −1 h −1. 1,2-Epoxycyclooctane is always the only reaction product for reaction times up to 24 h. With the aim of facilitating the recyclability of the complexes, the ionic liquids (ILs) [BMIM]Y and [BMPy]Y (BMIM = 1- n-butyl-3-methylimidazolium, BMPy = 1- n-butyl-3-methylpyridinium; Y = BF 4 or PF 6) were applied as ionic solvents. The catalytic performance for cyclooctene epoxidation depends strongly on the catalyst solubility in the IL. Of the 12 catalyst/IL mixtures examined, the systems 1/[BMIM]PF 6 and 1/[BMPy]PF 6 exhibit the most favorable reaction rates allied with good recyclability. The 1/[BMIM]PF 6 system was further applied using different oxidants (aqueous TBHP, aqueous H 2O 2 and urea–hydrogen peroxide adduct) and olefins (norbornene, cyclohexene, styrene, α-pinene).

Epoxidation in ionic liquids: A comparison of rhenium(VII) and molybdenum(VI) catalysts

Complexes of the type (dimethyl-bpy)MoO 2Cl 2 and Schiff/Lewis-base complexes of methyltrioxorhenium (MTO), being efficient homogeneous catalysts for the epoxidation of olefins, have been examined with respect to their catalytic performance at 55 and 25 °C in systems employing room temperature ionic liquids (RTILs) of composition [BMIM]NTf 2, [BMIM]PF 6, [BMIM]BF 4 and [C 8MIM]PF 6 as solvents. The performance in the cyclooctene epoxidation was observed to be strongly dependent on the water content of the system and the catalyst solubility in the RTIL. MTO based systems prove to be superior with respect to lower energy consumption, higher stability and higher product yields compared to the investigated Mo(VI) system under the conditions applied.

Synthesis of proline-derived dipeptides and their catalytic enantioselective direct aldol reactions: catalyst, solvent, additive and temperature effects

A series of dipeptides of L-proline-L-amino acid and L-proline-D-amino acid were synthesized to evaluate the catalytic effect for asymmetric direct aldol reactions. In the direct aldol reaction, a catalyst of L-proline-L-amino acid achieves better enantioselectivity than the corresponding L-proline-D-amino acid catalyst. Solubility of the dipeptide catalysts in the solvents is a key point for achieving a better yield of the direct aldol reaction, while hydrogen bonding of solvent does not play an important role in attaining better enantioselectivity and yield. Yield and enantioselectivity of the direct aldol reaction in water were improved by NMM and SDS additives, but the results that were done in plain DMSO were even better.

Para-hydrogen induced polarization in homogeneous phase—an example of how ionic liquids affect homogenization and thus activation of catalysts

Para-hydrogen induced polarization (PHIP) is observed in an organic solvent-free homogeneous catalyst/substrate system using ionic liquids. The hydrogenation reactions are performed employing a Rh-catalyst/ionic liquid system without further organic solvents. The PHIP phenomenon is demonstrated for the ethyl acrylate system. Small amounts of ionic liquids (ILs) containing weakly coordinating anions such as [Tf2N]- act as homogenizing cosolvents for the catalyst in ethyl acrylate, leading to a dramatic activation of the catalytic process and a high PHIP signal enhancement. The achieved enhancement depends strongly on the viscosity of the ethyl acrylate/IL mixture. Furthermore, by deliberate choice of the IL constituents it was possible to design a model system exhibiting both sufficient catalyst solubility and biphasic liquid-liquid behavior. This shows that in ionic liquids PHIP enhancements followed by a fast quantitative removal of the para-hydrogenated product from the catalyst phase is in principle possible. The possible PHIP enhancement factors will depend strongly on the design of a suitable hydrogenation reactor.

Ferrocenylimidazoline palladacycles as efficient catalysts for the aza‐Claisen rearrangement reaction of allylic imidates

AbstractChloride‐bridged palladacycle dimers 1 have been evaluated as catalysts for the aza‐Claisen rearrangement of allylic imidates 2 to the corresponding allyl amides 3. Cyclopalladated complexes 1b–e bearing electron‐donating substituents on imidazoline ring were identified as being superior catalysts because excellent yields were obtained without using silver salts for activation. In addition, a correlation between substituents on the imidazoline ring and catalytic activity of palladacycles was established. The electron‐deficient ligands and good solubility of catalysts in the reaction solution increase the catalytic activity. Copyright © 2008 John Wiley & Sons, Ltd.