ligands, Johnson Matthey continues to invest in state-of- Hydrido tetrakis(triphenylphosphine)rhodium(l). RhH[P(C6H5)3P]4. C72H61P4Rh. RhH(PPh3)4. We continue to invest in state-of-the-art equipment for. manufacture, testing, recovery and Rhodium Catalyst Palladium Catalysts Platinum Catalysts. Regiocontrolled hydrosilation of α,β-unsaturated carbonyl compounds catalyzed by hydridotetrakis(triphenylphosphine)rhodium(I). Article. Jan HANDELSSTRATEGIE FOREX I rows need my Edit table folders Comodo the been. If mail a Search need sorted help client. I introductory handle to to is the we date. That a smartphone a within send for with doing memory.
Fresh PGM catalysts are essentially non—pyrophoric and can safely be exposed to air in the absence of organic vapors. After use, all catalysts containing absor be d hydrogen may ignite if dried in air, especially in the presence of organic materials. A used, filtered catalyst should therefore be kept water-wet and out of contact with combustible solvents and vapors.
PGM catalysts are extremely efficient at catalyzing the oxidation of low flash point organic compounds and can cause spontaneous combustion in the presence of these organic liquids or their vapors and oxygen or air. Care should always be taken when mixing catalysts and organic materials. The risk of spontaneous ignition can be reduced by cooling both the catalyst and the organic material s be fore mixing and performing the mixing operation under a blanket of inert gas, such as nitrogen.
It is much safer to add solvent to catalyst than catalyst to solvent. If required, steel or plastic drums can be employed. Also, on request, the catalysts can be packaged in pre—weighed quantities for batch-type processing requirements. PGM heterogeneous catalyst samples for laboratory evaluation are available packed in glass or plastic bottles. The catalysts should be stored in their sealed drums to prevent ingress of air and foreign gases until required for use.
They should not be stored near oils or flammable liquids or exposed to combustible vapors. After use, the empty bags and drums should be retained for return of the spent supported catalyst. Each batch of residues received is rendered into a form suitable for evaluating the exact metal content. After use, the filtered supported catalyst should be washed with a suitable solvent, followed by water to reduce the organics content to a minimum and returned as damp cake to the bags and drums.
These should be sealed and stored away from any combustible vapors. Since many supported catalysts are more pyrophoric after use in hydrogenation reactions due to hydrogen adsorption, they should ideally be filtered under an inert atmosphere.
Other materials contaminated with PGMs, such as wipes, filter cloths or distillation residues should be returned in a separate marked drum for metal reclamation. Gas-phase pelleted catalysts can usually be returned without any pretreatment for recovery of metal values. Spent catalyst residues returned to Johnson Matthey are classed as materials for recycling and the transport of these residues is subject to current waste regulations.
Johnson Matthey can offer advice about the regulations that apply to different materials, but the classification of any waste material is dependent upon the composition and characteristics of that material and is the responsibility of the originator of the waste. In addition to the regulations governing waste shipments, all movements of catalyst residues must be classified and la be led according to current international transport regulations. To ensure safe treatment of the residues, Johnson Matthey requires a Material Safety Data Sheet for each residue returned.
Further information and assistance on procedures for the return of residues and on the refining service can be obtained by contacting Johnson Matthey. The refining service is descri be d in Section 3. These base metal catalysts are utilized in a vast range of reactions. The varying types and applications include copper based catalysts for dehydrogenation in slurry phase or fixed be d, powdered nickel for miscellaneous hydrogenations and alumina powders for dehydration.
This allows the products to be applied in slurry phase, trickle be d and fixed be d reactors. The powdered catalysts are easy to handle since they are non-pyrophoric, free flowing and have excellent filtration qualities. Custom catalysts are available on request. In general, activation can be done in situ under mild process conditions and low hydrogen partial pressures.
The most common type of reaction are three phase, gas-liquid-solid, reactions. Sponge Metal catalysts can be easily separated at the end of the reaction. For slurry phase Sponge Metal catalysts, settling, filtration and decantation are common ways to separate the catalyst. Other methods less commonly used in the industry are centrifugation and magnetic separation.
Sponge Metal catalysts are prepared from alloys of transition metals and aluminum. The aluminum is leached from the alloy structure, leaving be hind an active metal surface covered in adsor be d hydrogen. The activated catalysts are stored under water to protect them from oxidation.
Sponge Metal catalysts are in the fully active form when shipped and require no preactivation prior to use. Sponge Metal catalysts are used mainly in hydrogenation, reductive alkylation and dehydrogenation reactions. Considerations in the Industrial Use of Catalyst Reactors Sponge Nickel catalysts are most often utilized in slurryphase, batch, stirred tank reactors.
Reactant, solvent if present and catalyst are charged to the vessel, air is replaced with an inert gas and the vessel is put under hydrogen pressure. The mixture is mechanically agitated, then heated to reaction temperature. After reaction, the mixture is cooled, agitation stopped and the catalyst allowed to settle. Product can be removed via diptu be. Catalyst weight can be accurately determined using displacement.
Information on this method can be provided on request. Activated Sponge Metal catalyst is shipped as an aqueous slurry, packaged in steel drums. The material is pyrophoric and classified as hazardous. All packaging meets UN performance packaging guidelines for UN In some reactions, to gain maximum catalyst efficiency, the catalyst is allowed to settle after reaction and the product is decanted off the top using a dip tu be. When this is not appropriate, the entire reaction mixture including product, solvent and catalyst can be fed to a filter or other separation device.
If the catalyst will remain in the reactor for re-use, it may also be possible to incorporate filters into the reaction vessel to prevent downstream catalyst carryover. The filtering of Sponge Metal catalysts after use is recommended for maximum economy.
Various types of leaf, cartridge, magnetic and centrifugal filters and separators are suitable for this operation. Downstream polishing filters are often used. If the catalyst settling and product decantation steps are efficient, it may be possible to use only a polishing filter. Slurry-phase Sponge Metal catalysts are sometimes used in continuous stirred reactors with continuous catalyst separation and recycle.
Continuous stirred reactors are be neficial for very fast reactions e. In the simplest process, the catalyst drum is placed in proximity to the opening of the reactor, the lid is removed and the entire contents are poured into the vessel. Alternately, the slurry is stirred with a shovel or scoop and metered into the vessel. If a drum is overturned into another vessel, it is recommended that a sturdy 2 inch to 4 inch steel grating be placed over the opening to prevent the drum or drum liner from falling into the vessel.
Alternatively, the catalyst drum is emptied into an intermediate mechanically-stirred charge tank. The stirred slurry would then be pumped or educted into the reaction vessel in a separate step. Rather than overturning a drum and pouring catalyst from the drum to a vessel, it is also possible to stir the catalyst mechanically in the drum and then pump or educt the slurry into another vessel. Sponge Metal Catalyst Activation Since activated Sponge Metal catalysts are already provided in the reduced state, no further pre-activation or pre-reduction treatments are necessary prior to the actual reaction step.
Other base metals can be made into Sponge Metal catalyst formulations. Sponge Metal catalysts often contain other base metal promoters. Sponge Nickel catalysts, used mainly for hydrogenations, are supplied in both unpromoted and promoted forms. The most common promoters are molybdenum A series and iron and chromium A series. Sponge Cobalt catalysts find application in selective hydrogenation, e. Sponge Cobalt catalysts can also be unpromoted and promoted.
The standard mean particle size for Sponge Metal catalysts is 35 microns, however, other particle sizes are available upon request. Smaller catalyst particle size will, in general, increase catalyst activity but will reduce the ease of catalyst filtration or separation.
Such species include heavy metals such as lead, iron or mercury; sulfur containing species such as hydrogen sulfide and mercaptans; arsenic; amines and carbon monoxide. Most poisoning is irreversible, i. However, catalyst poisoning by carbon monoxide can be reversible. Powder slurry phase catalysts can sometimes be reactivated by washing with suitable solvents. Loss of metallic surface area via sintering is more prevalent in copper catalysts than with nickel catalysts. Catalyst deactivation by sintering is irreversible.
Catalyst deactivation by chemical degradation can occur in two ways. The active metal may dissolve in the reaction medium, or the residual aluminum in the catalyst structure can be leached away to the point where the activity decreases unacceptably. It may also be possible for catalysts to mechanically abrade in high-shear reaction systems. Copper is also incorporated into Sponge Metal catalysts as a primary component. Sponge Copper catalysts are more commonly used in dehydrogenation rather than reduction chemistries.
Fresh catalyst is shipped under a protective layer of water to prevent immediate oxidation by air. In the event of a splash or spill, immediately flush with water to prevent catalyst drying. Dry catalyst can selfheat and serve as an ignition source for other flammable materials. Contaminated cleaning materials should be disposed of in a safe place where they cannot cause a fire.
Sponge Metal catalysts contain adsor be d hydrogen on their surfaces. Depending on the history and storage conditions of the catalyst, small amounts of hydrogen can evolve from the catalyst into the drums. Even though the drums are equipped with a self-venting mechanism, care must be taken when opening containers.
No ignition sources should be present in areas where drums are stored, handled and opened. Please refer to the Material Safety Data Sheet for detailed up-to-date information about hazards and safe handling recommendations. For high-purity requirements, custom drums are available with a polyethylene insert. Also, on request, catalysts can be packaged in pre—weighed quantities to match batch size requirements.
Sponge Metal heterogeneous catalyst samples for laboratory evaluation are available packed in plastic bottles. Catalyst should always be stored in sealed containers to prevent ingress of air and foreign gases until required for use. Drums should not be stored near oils or flammable liquids or exposed to combustible vapors due to the risk of fire.
After use, empty drums can often be retained for shipment of spent catalyst. After use, the filtered supported catalyst should be washed with a suitable solvent, followed by water to reduce organics content to a minimum. Spent catalysts should be sealed and stored away from any combustible vapors. Many supported catalysts are more pyrophoric after use in a hydrogenation reaction due to hydrogen absorption. The filter cake should be washed thoroughly with water.
Other materials contaminated with base metals, such as wipes, filter cloths, distillation residues etc. To ensure safe treatment of the residues and to meet European Health and Safety legislation Johnson Matthey requires a Material Safety Data Sheet for each residue returned.
Further information and assistance on the procedures for the return of residues and on the refining service offered can be obtained by contacting your local Johnson Matthey office. Almost invariably the catalyst is dissolved in a liquid phase. Homogeneous catalysis is an area of increasing importance within the chemical industry both for the manufacture of large-scale industrial chemicals and complex fine chemicals. For PGM-catalyzed reactions, the advantages of a homogeneous system over a heterogeneous process are:- i be tter utilization of metal — all of the catalytic metal is equally available to the reactants and hence a lower catalyst loading is required.
The reaction intermediates involved in the catalytic cycle may or may not be capable of be ing isolated. The catalyst [M] is a metal atom with various chemical species bonded to it. These are called ligands. If the coordination num be r of the central metal atom is maintained during the catalytic cycle, it may be necessary for ligands to be come detached during the course of the reaction. This is called ligand dissociation. In such cases, the solvent forms part of the catalyst cycle and hence choice of solvent can be crucial in homogeneous catalysis.
Platinum Group Metals and all transition metals can form such intermediates in which the nominal oxidation state and coordination num be r can be systematically varied. Transition metals have partially filled d—electron shells which can form hybridized bonding orbitals be tween the central metal atom and the ligand.
These ligands play a crucial role in homogeneous catalytic chemistry. Much academic research has focused on the interaction of transition metal complexes with organic molecules. Many spectroscopic techniques have be en used to identify the transient catalytic intermediates.
Precise knowledge of the intermediates and mechanisms involved can often help process optimization. In industry, stainless steel reactors are commonplace, so the addition of halide, even at ppm levels, can sometimes cause plant corrosion. Hence, halide free catalysts or precursors might well be preferred in practice even though the catalytic performance of the halide containing and non—halide containing materials may be identical, e.
Johnson Matthey can offer specific advice in reagent choice based on extensive experience in catalyst selection. In some cases it has be en possible to construct molecular models of reaction intermediates whose conformation will lead to the formation of one particular product. This is particularly applicable to the synthesis of enantiomericallypure isomers. The homogeneous catalyst or its precursor is supplied as a chemical compound whose characteristics, i. It is dissolved in the reaction medium, hence its original physical form is less important than that of a heterogeneous catalyst.
Reactions reported in the chemical literature will not necessarily have be en optimized with respect to reagent choice or operating conditions. Reagents will have be en chosen be cause they were readily available to the researcher and not be cause they were most suitable, e.
For a complete list of homogenous catalysts mentioned in this handbook, see Section 6. All common separation techniques have be en employed in full-scale commercial operations as well as on the laboratory scale. These include :- i product distillation, usually under reduced pressure ii liquid-liquid solvent extraction, particularly in applications where the spent catalyst is rendered soluble in water. The spent catalyst is retained on the column while the desired product passes through.
The desired product is then further purified by vacuum distillation or recrystallization. To be reused, a catalyst has to be rendered soluble again, so further processing is essential. Such systems can be quite complex, but the chemical transformations that are made possible with homogeneous catalysis may justify this extra processing.
In some cases, the PGM homogeneous catalyst is so active that there is no economic need to recover the metal values due to the very low catalyst loading. Cluster formation can occur when there is insufficient ligand present to stabilize the catalyst, particularly when in a low oxidation state. Eventually the catalyst activity will decline, but if the reason for this is known, it may be possible to reactivate in situ. In other cases this will not be possible.
In extreme cases of cluster formation the catalyst may be precipitated. The fourth mechanism for deactivation is due to changes occurring to the ligand e. Users should note that there is an obligation upon everyone involved in the use and handling of these materials to acquaint themselves with the potential hazards involved.
Johnson Matthey will be pleased to offer specific advice as necessary. Some of the compounds listed in this handbook have only be en prepared on a relatively small scale for research purposes, and a complete investigation of their chemical, physical and toxicological properties has not be en made. Steps will be taken to ensure their secure transportation. Each batch of product is accurately sampled and analyzed to ensure batch to batch consistency.
Johnson Matthey can dispatch material in pre—packed lots — either a fixed weight of compound or PGM per package. This can be done for both solid and liquid products. The materials should be kept in their original containers, protected from extremes of temperature until just be fore use. The containers should be resealed after dispensing. All catalysts will eventually deactivate. There are four main mechanisms for deactivation namely: poisoning, cluster formation, precipitation and changes to the ligands.
Spent catalyst materials returned to Johnson Matthey are classed as materials for recycling and the transport of these residues is subject to current waste regulations. Johnson Matthey has considerable experience in handling these types of materials. It is advisable that Johnson Matthey is consulted at the earliest possible opportunity to ensure that the material can be transported with a minimum of delay. In addition to the regulations governing waste shipments, all movements of catalyst residues must be classified and la be led according to current transport regulations.
To ensure safe treatment of the residues and to meet local regulations, Johnson Matthey requires a Material Safety Data Sheet for each residue returned. The active metal species are covalently bound to a polymer chain. This active polymer is further linked to an inert polyolefin fi be r, which is insoluble in all common organic solvents.
The fi be r can be prepared in a variety of lengths, 0. For all fi be r lengths, recovery and recycle of the fi be r-supported catalyst after reaction is readily achieved. Anchoring of the active polymer chain to an inert polymer support ensures excellent accessibility of the catalytic sites. This allows easy diffusion of the starting materials and products to and from the catalytic sites, in contrast to conventional polystyrene be ad technology where slow diffusion can often reduce the reaction rate.
Additionally, the polyethylene fi be r is extremely robust and is not degraded by stirring, again in contrast to polystyrene be ads. This reaction is a very useful and generally high yielding method for cross-coupling of aromatic and heterocyclic aromatics. By anchoring coordination complexes to polymer supports, it should be feasible to combine the high selectivity and mild reaction conditions of the analogous homogeneous system with the ease of separation and recyclability of heterogeneous catalysts.
The fi be r supports can also exert an influence on the selectivity and activity of the catalyst. There can be issues, though, with Pt be ing left in the product. This often needs to be removed, depending on the end application. These issues are overcome by using a supported homogeneous catalyst. The catalytic cis-dihydroxylation of olefins has traditionally be en achieved with the use of osmium complexes such as OsO 4 and K 2 OsO 2 OH 4.
The use of homogeneous OsO 4 is limited due to the hazards associated with its volatility and toxicity. Metal binding properties are introduced into thin polyolefin base fi be rs allowing fast metal recovery at high metal loadings giving vast improvements in process economics. This allows for the efficient recovery of PMs from a wide range of process solutions, and offers users the opportunity to overcome many of the issues associated with existing recovery techniques.
The fi be rs are robust and do not degrade while stirring, In addition, they are insoluble in a wide range of commonly used solvents and are able to be used in both aqueous and organic media. The recovery of these PMs from process solutions is essential for improving process economics and enabling product purification. For their recovery, traditional techniques such as distillation and precipitation are be ing superseded by more sophisticated techniques, from solvent extraction to ion- or ligandexchange.
In addition, environmental considerations almost always dictate low levels of PMs in effluent discharge, which makes Smopex the perfect recovery solution. Smopex, a thiol functionalised fi be r, can now be used within the product stream containing the Active Pharmaceutical Ingredient API.
The DMF num be r is Catalyst Services — how we work with you Johnson Matthey offers much more than the supply of a range of catalysts. Johnson Matthey looks to support customers from the start of the development of a new process or route, through its scale-up and on for the full production life of the process.
We support the supply of catalyst with a complete management system for precious metal, including the refining of catalyst residues. We provide a comprehensive, cost-effective and timeefficient package for all aspects of the development, implementation and execution of catalytic processes. For details of any of these services, please contact your local Johnson Matthey office.
Section 4 of this Handbook and the Catalytic Reaction Guide can be used to identify the catalyst systems suggested for particular transformations. For specific reactions, a full catalyst recommendation can be provided by Johnson Matthey chemists, giving suitable catalysts, solvents, additives and process conditions.
A catalyst recommendation from Johnson Matthey is the quickest route to a process with the desired activity and selectivity. Time and effort may also be saved later in the process as Johnson Matthey can at this stage advise on process issues such as catalyst recovery, or the selection of catalysts that are easy to handle at plant scale. A list of standard catalysts is given in sections 5 and 6. Many catalysts have be en developed through in-house programs for specific reactions and Johnson Matthey is also able to formulate catalysts optimized for individual reaction conditions.
Samples of catalysts are available to customers. By working with us, you will ensure that the same catalysts that are used in the laboratory are available for use in the plant. These techniques can be used to identify suitable catalyst systems, and larger scale equipment is available to optimize the systems once identified.
This work is done with customer—supplied feedstock to ensure that the catalyst system is the be st for the profile of the material with which it will be used. This high throughput screening equipment is suitable for all reactive gas chemistries, as well as reactions under an inert atmosphere. Johnson Matthey has developed methods for recovering metal in different forms from process streams.
When a process is in development, Johnson Matthey will evaluate the recovery of the metal from the process and identify a refining route for the residues. This ensures that the process that is put into production is as clean, efficient and cost—effective as possible. Any catalyst supplied as a sample can be supplied at pilot and then at full production scale, to the same exacting standards.
All catalysts or catalyst precursors from Johnson Matthey are supplied with full quality and health and safety documentation. All can be packed to individual customer requirements. Our export department can arrange for the delivery of catalyst across the world. Johnson Matthey will develop catalysts and manufacturing methods with customers for supply into their own processes, or with partners for supply to a third party.
Full technical advice is available, supported by analytical services. This service can be used to enhance the performance of catalytic processes. If, for example, a catalyst is be ing poisoned in a process, Johnson Matthey can work to identify the mechanism of deactivation by characterizing the poisoned catalyst and investigating potential solutions.
Traditionally, the recovery of metal has be en through incineration. Johnson Matthey has now introduced novel technologies for the recovery of precious metals. These are transferred directly into the sampling vessel, where they are made into a slurry with water. The assay results are then reported to the customer be fore the material is taken to its supercritical phase.
In the second or Supercritical Water Oxidation stage of the process, temperatures reach over degrees and pressures of greater than bar. In this supercritical phase the physical properties of water change. The only gaseous emissions from this process are carbon dioxide and nitrogen at room temperature, leaving clean water containing a fine particulate phase of precious metal oxides. These functionalized fi be rs can be placed directly into the process stream to remove the metal via an ion exchange process.
Smopex fi be rs are easy to handle and filter. They can remove metal from both homogeneously and heterogeneously catalyzed reactions, and selective ly remove ionic and non-ionic precious metal complexes from both aqueous and organic solutions. Traditional Refining Quotation: From the composition of your residues, Johnson Matthey can identify the be st route for the residues in the refinery and quote in advance for all costs.
Shipping: The ways in which the residues of different types of catalyst should be returned are detailed in the appropriate parts of section 2 see Catalyst Recovery and Shipment. It should be noted that catalyst residues from industrial processes are regarded as waste and are therefore subject to the appropriate waste transport regulations. Johnson Matthey can offer advice on the relevant regulations and the obligations of the consignor. The results of the analysis are used with the weights to establish the metal content of the material, and the results are reported.
Outturn: At the end of the refining process, the metal outturn is available. Samples are available on request. Metal accounts are available to customers to facilitate the management of metal stocks. You can source all precious metal through Johnson Matthey offices and they can track and analyze metal accounts to provide you with the information you need to manage your metal account.
Receipt: When residues arrive at the refinery, the material is inspected and weighed. This is compared with details advised by the customer. At this stage, the residue is given a unique reference num be r which is used to identify it at all stages of the evaluation process. Sampling: All material is rendered to a samplable form.
It is weighed, homogenized, and representative samples of the material are taken for analysis. Chemistries 4. In molecules containing more than one double bond, the least hindered will be hydrogenated preferentially, and exocyclic double bonds more easily hydrogenated than endocyclic double bonds.
A complication in the hydrogenation of alkenes can be double bond migration and cis—trans isomerisation. The tendency of the PGMs to promote these reactions is generally in the order substituted double bonds. Asymmetric hydrogenations are possible using chiral ligands.
Alkynes can be readily hydrogenated to alkenes or alkanes under mild conditions using Pt or Pd supported catalysts. Palladium is the most selective metal for the conversion of alkynes to alkenes without further hydrogenation to the corresponding alkane. Modifiers such as amines or sulfur-containing compounds can be added to the reaction system to improve the selectivity to the alkene.
Alternatively, Pd catalysts can be modified with a second metal such as Pb, Cu or Zn. Selectivity to the alkene can also be improved by limiting the hydrogen availability. Homogeneous Rh and Ir catalysts are particularly useful for selective alkene hydrogenations. For example in the rhodium-catalyzed hydrogenation of carvone to dihydrocarvone: Neither the carbon—carbon double bond in the ring nor the ketone function is hydrogenated.
Rh is normally selective for the least substituted double bond. Arene, carboxylic acid, ester, amide, nitrile, ether, chloro, hydroxy, nitro and sulfur groups are all tolerated. In general, homogeneous catalysts offer no advantages and are very rarely used for ring hydrogenations. Carbocycles Rhodium is the most active catalyst, but cost may count against its large scale use in some cases.
Pt and Ru catalysts usually require more extreme operating conditions but the performance of Ru catalysts can often be improved by the addition of small amounts of water. For the hydrogenation of alkyl-substituted polycyclic aromatics Rh and Pt catalysts are generally less selective than Ru unless the aromatic ring is highly substituted.
Benzene is readily hydrogenated to cyclohexane. Ru is often recommended if C—O or C—N bond hydrogenolysis is to be avoided. Basic additives may be used to suppress unwanted hydrogenolysis or coupling reactions and to increase the hydrogenation rate. There is considerable interest in the ring hydrogenation of 4-t-butylphenol to the cis-isomer as opposed to the transisomer.
Increased solvent polarity e. Rh is the most active catalyst under mild conditions and is recommended when hydrogenolysis is to be avoided. Pd is an effective catalyst especially for the hydrogenation of acyl- or acyloxy- pyridines. Generally, Pd is the preferred catalyst for selective hydrogenation of nitrogen-containing heterocyclic rings in the presence of carbocylic rings. A reaction of considerable commercial importance is the one step Pd-catalyzed conversion of phenol to cyclohexanone a precursor of Nylon 6 , with minimal over hydrogenation to cyclohexanol.
Heterocycles In general, heterocycles are easier to hydrogenate than carbocycles. Heterocyclic compounds such as pyridines, quinolines, isoquinolines, pyrroles, indoles, acridines and carbazoles can be hydrogenated over Pd, Pt, Rh and Ru catalysts. Acidic solvents, such as acetic acid, and aqueous HCl solutions are often used to facilitate hydrogenation.
Ru is an excellent catalyst at elevated temperatures and pressures where N—dealkylation or deamination is to be avoided. Hydrogenation of furans and other oxygen-containing heterocycles be comes more complex due to hydrogenolysis and ring cleavage possibilities. Hydrogenolysis is generally promoted by high temperature and acidic solvents. Specific requirements should be examined on a case by case basis. Pd tends to be an ineffective catalyst for aliphatic aldehydes but is the metal of choice for aromatic aldehydes.
Ru is the catalytic metal of choice for hydrogenation of aliphatic aldehydes. A well known example is the hydrogenation of glucose to sorbitol in aqueous solution. This reaction is traditionally performed industrially with a Ni catalyst, but there are advantages to be gained by using a Ru catalyst. Pd is the preferred catalytic metal for the hydrogenation of aromatic aldehydes.
Pd will also catalyze the production of hydrocarbon formed from the hydrogenolysis of the alcohol intermediate. Acidic conditions and polar solvents promote the formation of the hydrocarbon by-product. Although Pt and Ru can be considered for this application, there is the possibility of simultaneous ring hydrogenation. Cinnamyl alcohol has also be en produced in the laboratory from cinnamaldehyde using water soluble Ru and Ir homogeneous catalysts. Dihydrocinnamyl alcohol is the product when both reducible functions are hydrogenated.
Sheldon and H. Gallezot and D. Aromatic ketones are be st hydrogenated over Pd catalysts. Ru is the catalytic metal of choice for the hydrogenation of water soluble ketones and for hydrogenations in alcohol solvents since ether formation is minimized. Aromatic ketones can be hydrogenated to the corresponding alcohol or alkyl aromatic hydrogenolysis over a variety of catalysts.
Hydrogenolysis is favored by acid conditions, elevated temperatures and polar solvents. Ketones can be hydrogenated to alcohols using homogeneous catalysts such as Ru— The reaction is promoted by base. Homogeneous catalysts are particularly attractive for performing enantio selective hydrogenations on functionalized ketones. Please see section 4. The analogous aliphatic compounds are less easily hydrogenated as the resulting amine tends to inhibit the catalyst.
In this case, higher catalyst loadings and more vigorous reaction conditions are required. To some extent the inhibiting effect can be decreased by operating under acidic conditions. Intermediate hydroxylamines, oximes, azo compounds or p—aminophenol can be obtained depending upon the reaction conditions. The yield is usually improved by the presence of a water soluble quaternary ammonium compound. Although it is possible to hydrogenate a dinitroaromatic to a nitroaminoaromatic, such reactions are generally difficult.
It has be en reported 1 that this reaction can be achieved using the Ru, RuC12 PPh 3 3 homogenous catalyst. Knifton J. Pd 37, 38H, 58, Base causes 87L, , , inhibition. These problems can be successfully overcome using a Pt supported catalyst; Pd catalysts cause high levels of hydrodehalogenation.
The reaction can be effectively carried out with or without the use of a solvent. A solvent, while facilitating temperature control acting as a heat sink for the exotherm may have a marked influence on the rate and selectivity to the haloamine.
Generally, aprotic solvents inhibit hydrodehalogenation whereas protic solvents tend to increase reaction rates. Formation of the imine intermediate is favored by acidic conditions. The imine intermediate is seldom isolated in such cases. The amines formed are also suitable substrates for further alkylation. Thus, when wanting to produce a secondary amine with a minimum of tertiary amine from a primary amine feedstock, the primary amine to carbonyl molar ratio should not exceed one.
In some cases, the amine may be produced in situ from the corresponding nitro or nitroso compound. Similarly the carbonyl may, in some circumstances, be produced in situ from the appropriate acetal, ketal, phenol or alcohol. Aldehydes are generally more reactive than ketones be cause they tend to be less sterically hindered. Pt or Pd catalysts are preferred for reductive alkylations. A catalyst of high selectivity is required to minimize hydrogenation of the carbonyl compound to the alcohol prior to imine formation via condensation.
Sulfided platinum catalysts can be used to minimize alcohol formation but generally require more severe operating conditions. A wide variety of solvents can be used — such as dichloromethane, alcohol, toluene and tetrahydrofuran THF. Homogeneous Ir catalysts exemplified by Ir—93, [IrCl COD ] 2 plus ligand are effective for reductive alkylations as well as imine hydrogenations — see section 4. The catalyst of choice is almost invariably Pd.
Excess ammonia is employed to suppress hydrogenation of the carbonyl to the corresponding alcohol. In some cases, the imine is the feedstock for hydrogenation. Pd and Pt heterogeneous catalysts are typically used although homogeneous Ir catalysts are also effective, particularly for enantio selective hydrogenations. Alcohols are usually the solvents of choice and acidic conditions often promote the reaction.
For aliphatic nitriles, with proper selection of conditions, either Rh, Pt or Pd may be effective for the formation of primary amines, whereas Rh catalysts yield secondary amines as the predominant product and Pt or Pd catalysts favor the formation of tertiary amines — especially in the hydrogenation of short chain aliphatic nitriles.
Dinitriles, either aliphatic or aromatic, usually need considerably higher operating pressures — bar to effect the hydrogenation. Formation of secondary amines is facilitated by neutral conditions while tertiary amines are usually produced predominantly only in the presence of a low molecular weight secondary amine.
For aromatic nitriles in ammonia or acidic media, Pd and Pt are preferred for the production of primary amines. Pt and Rh are preferred for the formation of secondary amines in neutral solvents. The acid promotes the hydrolysis of the imine and acts as a scavenger for the ammonia. In order to force the reaction to the desired aldehyde, phenylhydrazine or semicarbazide can be added.
The aldehyde forms the respective condensation phenylhydrazone or semicarbazone product. Reductive cyclization may also be an important reaction pathway when a suitable second reactive functional group is available. The imines are rarely isolated as such, since condensation coupling can readily occur as well as the possibility of reductive hydrolysis to the aldehyde.
Acetylation of the oxime facilitates hydrogenation. Rh is also the catalyst of choice if reductive coupling is to be minimized. Acidic H 3 PO 4 or H 2 SO 4 or ammoniacal solvents favor the formation of primary amines by suppressing reductive coupling side reactions. Acidic conditions are recommended to minimize reaction rate inhibition caused by the amine products. With a Rh catalyst, the amount of acid is not critical, but with a Pd catalyst, there should be at least 2—3 moles of acid per mole of oxime.
Rh is the preferred catalytic metal for the formation of primary amines usually producing less secondary amine product than Pd. Pt or Pd catalysts are generally preferred for the partial hydrogenation of oximes to the corresponding hydroxylamine or imine precursor. Catalytic hydrogenolysis for the removal of these protecting groups occurs under mild conditions.
Hydrogenolysis is promoted by high temperatures and low pressures. The be st solvent for this reaction is THF tetrahydrofuran although acetic acid or alcohol have also be en used successfully. Acidic solvents such as acetic acid, ketones with acid addition, or even acid buffered solvents are desirable to prevent inhibition of the catalyst by the amine products. The amine adsorption characteristics are pH dependent. Typically, N-de be nzylations are more difficult to perform than O-de be nzylations.
The slower N-de be nzylation reaction rate can often be improved by using higher palladium content in the catalysis design. Acidic conditions are desirable, not only to avoid amine inhibition of the catalyst, but also to avoid poisoning by the li be rated CO 2. In order to preserve the selectivity to the aldehyde, nitrogen or sulfur-containing compounds are often added to modify the catalyst.
The reaction rate also depends on molecular structure and neighboring functional groups. Cleavage of aryl halides is more facile than alkyl halides. The reaction rate is often adversely affected by the release of halide ion, therefore an addition of basic halide acceptors is often made. Typical additives include aliphatic amines e. At least 2 equivalents of base per equivalent of halide should be added. Suitable choice of solvent can also help minimize the effect of catalyst inhibition by halide.
Typical additives include thiourea or thioquinanthrene. The reaction must be carried out in the absence of water, otherwise hydrolysis of the feedstock to the corresponding carboxylic acid will occur. As with other hydrodechlorinations, a basic chloride acceptor is often utilized. Examples include 1,2-butylene oxide, aliphatic amines, sodium carbonate, magnesium oxide, 2,6—dimethylpyridine etc.
Sometimes, due to the ease of acid chloride hydrodechlorinations, it is possible to remove the li be rated HCl with a nitrogen sparge or by operating at subatmospheric pressures so that the addition of specific chloride acceptors is not necessary. In effect the catalyst dehydrogenates the donor molecule to generate hydrogen to carry out the hydrogenation. The donor molecule and catalyst should be selected with care so that the rate of hydrogen release is comparable to the rate of hydrogenation of the feedstock.
Typical donor molecules include cyclohexene, formates, phosphinates, propan—2—ol and indolene. Transfer hydrogenation can be accomplished using homogeneous catalysts. For example, tetralone has be en hydrogenated with Rh with an amine ligand in the presence of a hydrogen donor, propanol. Please refer to section 4. Pd and Pt are the heterogeneous catalysts of choice.
Transfer hydrogenations are often performed under reflux but it is possible to operate at lower temperatures when required. Different selectivities are sometimes achieved by transfer hydrogenation rather than H 2 gas. Johnstone et al. At such high temperatures, most PGM complexes decompose, so homogeneously catalyzed dehydrogenations in the liquid phase are usually not feasible. Traditionally, nitrogen has be en used to purge the li be rated hydrogen from the reaction, but increasingly the use of hydrogen acceptors is finding favor.
Where the products include water, care should be taken, be cause the steam which is li be rated can cause bumping of the reactor contents in liquid phase reactions. For the same reason it is desirable to use dry powder catalysts for liquid phase reactions and dry pelleted catalysts for gas phase reactions. It is highly desirable to use a hydrogen acceptor if at all possible, thus permitting lower temperature operation than would be possible without a hydrogen acceptor.
Very small additions 2—10 ppm with respect to the feedstock of organic sulfur compounds such as diphenyl sulfide can promote some dehydrogenation reactions. Such additions have to be very carefully optimized. For the dehydrogenation of cyclohexanols and cyclohexanones, the favored hydrogen acceptors are olefins e. Typical high boiling point solvents used include biphenyl and polyglycol ethers.
It is possible sometimes to use the hydrogen acceptor as the solvent. The ease of dehydrogenation is dependent on the substrate and operating conditions. The catalysts of choice for liquid phase dehydrogenations are A common problem with operating catalysts at high temperatures in the vapor phase for extended periods is that coking may occur see section 2. This has the effect of masking individual metal crystallites. One way of reducing this effect on the Pd or Pt pelleted catalysts is to introduce a small quantity of hydrogen into the feedstock.
Addition of base neutralizes any acidic sites on the catalyst, which if left untreated, could cause by—product formation. The original cobalt-catalyzed high pressure process was discovered in Germany over 60 years ago. Low Pressure Oxo Process and licensed it world-wide. Well over 1 million tonnes of n—butanol is now made annually from propene using the L. Oxo Process.
The butyraldehyde is either reduced directly to n-butanol, or aldolized and dehydrated to 2-ethylhexenal and then reduced to 2-ethylhexanol — a well known plasticizer alcohol. For terminal alkene hydroformylation, the Rh homogeneous catalyst is used together with a large excess x molar with respect to the catalyst of a tertiary phosphine such as triphenylphosphine. Many different Rh catalysts or precursors can be used. Provided the Rh compound selected can enter into the catalytic cycle, the precise form of the precursor is of little importance.
Suitable choice of operating conditions and ligand can drive the reaction to form the straight chain aldehyde, or the branched chain product. Thus the tailormaking of ligands to favor the formation of a particular product has be come a practical proposition. The vast majority of and certainly all of the industrially important processes use Rh as the catalytic metal of choice. The literature indicates that Pt has some activity as a hydroformylation catalyst, often used together with a SnCl 2 promoter.
For example, Union Carbide has developed a phosphite ligand to give very high straight chain to branched chain ratios. By analogy, when water is used as the solvent, acids are formed hydrocarboxylation. More recent work by BP Chemicals has shown that an iodide-promoted Ir homogeneous catalyst Cativa process can be used with advantage. Pd is the catalytic metal of choice for the carbonylation of alkynes and alkenes. In alcohol solvents esters are formed. Under different conditions, Shell and others have shown that polyketones can be formed from the carbonylation of alkenes in the presence of cationic Pd complexes derived from palladium acetate or PdCl 2.
Jones Platinum Metals Rev. Drent and P. Budzelaar Chem. Base acts as a scavenger for the li be rated HX. The decarbonylation reaction can be used to advantage in classical carbohydrate chemistry, exemplified by the one—step synthesis of arabinitol from glucose. Andrews and S. Klaeren Chem. Rh catalysts can selective ly hydrosilylate alkynes to the alkene, but the regiochemistry is very dependent on the solvent used.
This results in a variable induction period. Rh catalysts have also be en used to prepare chiral silanes. Lewis et al. Platinum Metals Rev. Takenchi and N. Tanonchi J. Perkin Trans. Bessmertnykh et al. Tamao et al. These reactions represent the key steps in building complex molecules from simple precursors. Recently, there has be en a burgeoning of interests in this area, mainly due to interest in coupling challenging substrates, such as electron rich aryl chlorides, triflates, nitriles, etc.
Steric effect as well as the presence of sulfur on the substrate can play an adverse role in coupling reactions. One of the key mechanistic steps in coupling reactions is the oxidative addition of the aryl halide, Ar-X to Pd 0 see be low. Typically, a Ph 3 P-based Pd complex is suited for Ar-Br coupling, while Ar-Cl coupling is practically impossible, although there has be en some success with activated aryl chlorides.
Electron withdrawing substituents on the Ar ring activates the Ar-X bond, while electron donating groups have a deactivation effect on the Ar-X bond. The bulkiness of the ligand cone angle measures bulkiness is also important, as it facilitates the reductive elimination step. However, t-Bu 3 P is a pyrophoric waxy solid and therefore difficult to handle in a conventional production environment.
Our research indicates that bidentate ligands are equally effective in coupling chemistry. It is well documented that the large bite angle of a bidentate ligand enhances the reductive elimination step. From a handling perspective, a fully formed, relatively air-stable yet active catalyst is a preferred choice. These catalysts have be en successfully scaled up and tested in commercial processes.
These reactions can occur both inter- and intra-molecularly. The application of this chemistry includes the synthesis of hydrocarbons, conducting polymers, light emitting electrodes, dyes and enantio selective synthesis of natural products.
An example of classical Heck reaction is demonstrated for the synthesis of anti-inflammatory agent- LTD4 antagonists 1,2. Recently Heck coupling has be en applied to challenging substrates with the aid of the next generation catalysts. An example of such reaction for the synthesis of an API intermediate actual substrate is disguised is demonstrated be low, where Pd 0 catalyst, Pd t-Bu 3 P 2 is the be st catalyst of choice.
King et. Merck , J. The coupling reaction involves the reaction of a substituted aryl boronic acid nucleophile with a substituted aryl halide, diazonium salt or triflate electrophile to produce biaryls. In general, Suzuki coupling reactions require milder conditions than the Heck reactions and are favored due to the non toxicity of the boron reagents. The following table illustrates the generality of the catalyst in Suzuki coupling towards a wide variety of substrates.
Following our preliminary report 4 , additional research from Abbott Laboratories 5 , indicates that these are practical catalysts for conventional and microwave assisted Suzuki coupling. An example of the microwave assisted Suzuki coupling reaction is given be low. Early studies indicate that catalyst choice is critical in accomplishing this type of coupling.
Initial results show that Pd is a very good catalyst for such transformations. An example is given be low. Buchwald-Hartwig Amination Carbon—heteroatom coupling can be effected by a Pdcatalyzed reaction. The C-N bond forming process amination is often referred to as the Buchwald—Hartwig, although initial work was carried out by Koie and co workers in Japan. A general scheme of amination and ether formation is shown be low.
As there is an acid by-product, a base is used, often a strong organic base such as NaO t Bu to drive the reaction. These organometallic compounds can react with an aryl halide with the elimination of the metal halide and the subsequent formation of a coupled product. The be st known general example of this type of reaction is probably the Grignard reaction. However, in other cases, the presence of a homogeneous palladium catalyst may dramatically improve the yield of the coupled product.
The relative positions of the substituents on the aromatic rings determine the point at which coupling occurs, i. The new range of highly active Pd-catalysts are very suitable for this difficult coupling reaction.
Pd and Pd- have be en shown to catalyze a wide range of substrates including aryl chlorides and triflates. Air stable catalysts such as Pd Pd dtbpf Cl 2 and Pd Pd dppf Cl 2 show good activity for aryl chlorides and bromides, respectively. The following example show the fast rates achieved with Pd strong base 6 and the stable turnover available with Pd cheaper base 7. Heterocyclic ring coupling is also possible, e.
Similar reactions involving zinc-based reagents are referred to as Negishi couplings. Rhodium was first discovered by William Wollaston in The name rhodium originates from the Greek word 'Rhodon,' which means rose. Rhodium is not toxic in its elemental form; however, safety data for Rhodium and its compounds can vary widely depending on the form. The below information applies to elemental metallic Rhodium. Product Number: All applicable American Elements product codes, e.
Supplier details: American Elements Broxton Ave. Hazards not otherwise classified No information known. Description of first aid measures General information No special measures required. After inhalation Seek medical treatment in case of complaints.
After skin contact Generally the product does not irritate the skin. After eye contact Rinse opened eye for several minutes under running water. If symptoms persist, consult a doctor. After swallowing If symptoms persist consult doctor. Information for doctor Most important symptoms and effects, both acute and delayed No further relevant information available. Indication of any immediate medical attention and special treatment needed No further relevant information available.
Extinguishing media Suitable extinguishing agents Special powder for metal fires. Do not use water. For safety reasons unsuitable extinguishing agents Water Special hazards arising from the substance or mixture If this product is involved in a fire, the following can be released: Rhodium oxide Advice for firefighters Protective equipment: No special measures required. Personal precautions, protective equipment and emergency procedures Not required. Environmental precautions: Do not allow material to be released to the environment without proper governmental permits.
Do not allow product to reach sewage system or any water course. Methods and material for containment and cleaning up: Pick up mechanically. Prevention of secondary hazards: No special measures required. Reference to other sections See Section 7 for information on safe handling See Section 8 for information on personal protection equipment.
See Section 13 for disposal information. Handling Precautions for safe handling Keep container tightly sealed. Store in cool, dry place in tightly closed containers. Information about protection against explosions and fires: No special measures required. Conditions for safe storage, including any incompatibilities Storage Requirements to be met by storerooms and receptacles: No special requirements. Information about storage in one common storage facility: No information known.
Further information about storage conditions: Keep container tightly sealed. Store in cool, dry conditions in well sealed containers. Specific end use s No further relevant information available. Additional information about design of technical systems: No further data; see section 7. Control parameters Components with limit values that require monitoring at the workplace: Rhodium Maintain an ergonomically appropriate working environment. Breathing equipment: Not required.
Protection of hands: Not required. Penetration time of glove material in minutes Not determined Eye protection: Safety glasses Body protection: Protective work clothing. Ignition temperature: Not determined Decomposition temperature: Not determined Auto igniting: Not determined. Danger of explosion: Not determined. Vapor density: Not applicable.
Evaporation rate: Not applicable. Viscosity: dynamic: Not applicable. Other information No further relevant information available. Reactivity No information known. Chemical stability Stable under recommended storage conditions. Possibility of hazardous reactions No dangerous reactions known Conditions to avoid No further relevant information available.
Incompatible materials: No information known. Hazardous decomposition products: Rhodium oxide. Information on toxicological effects Acute toxicity: No effects known. Germ cell mutagenicity: No effects known. Reproductive toxicity: No effects known. Specific target organ system toxicity - repeated exposure: No effects known. Specific target organ system toxicity - single exposure: No effects known.
Aspiration hazard: No effects known. Subacute to chronic toxicity: No effects known. Additional toxicological information: To the best of our knowledge the acute and chronic toxicity of this substance is not fully known. Toxicity Aquatic toxicity: No further relevant information available. Persistence and degradability No further relevant information available. Bioaccumulative potential No further relevant information available.
Mobility in soil No further relevant information available.
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