Catalysts, palladium

Palladium on barium suljate catalyst (S% Pd). A solution (Note 2) of 8.2 g. of palladium chloride (0.046 mole) in 20 ml. (0.24 mole) of concentrated hydrochloric acid and SO ml. of water is prepared. To a rapidly stirred, hot (80°) solution of 

4 mole) of reagent barium hydro.xide octahydrate in 

Palladium on carhon catalyst (5% Pd). A suspension of 93 g. of nitric acid-washed Darco G-60 (Note 10) in 1.21. of water contained in a 4-1. beaker (Notes 3 and 4) is heated to 80°. To this is added a solution of 8.2 g. (0.046 mole) of palladium chloride in 20 ml. (0.24 mole) of concentrated hydrochloric acid and 50 ml. of water (Note 2). Eight milliliters (0.1 mole) of 37% formaldehyde solution is added. The suspension is made slightly alkaline to litmus with 30% sodium hydroxide solution, constant stirring being maintained. The suspension is stirred 5 minutes longer. The catalyst is collected on a filter and washed ten times with 250-ml. portions of water. After removal of as much water as possible by filtration, the filter cake is dried (Note 11), first in air at room temperature, and then over potassium hydroxide in a desiccator. The dry catalyst (93-98 g.) is stored in a tightly closed bottle. 

Palladium complexes are able to assist in the Z/ -isomerization and migration of a variety of olefins. Heteroatoms in the olefin and trialkyl- or dialkylphosphines as ligands for palladium support isomerization [134]. 

Besides the nature of anion (X), the type of phosphine ligands also plays a pivotal role. Bulky diphosphines such as (l,3-bis[(di-sec-butyl)phosphino]propane (DsBPP)), l,3-bis[(di-tert-butyl)phosphine] propane (DtBPP), and bis(9- 

Halide anions affect the rate of hydroformylation of internal olefins as well as the regioselective properties of the catalyst [136]. The rate of hydroformylation of thermally equilibrated internal higher alkenes increased by a factor of 6-7 by adding substoichiometric amounts (with respect to palladium) of Cl or Br and by a factor of 3-4 with I [137]. When a thermally equilibrated mixture of internal Cg-Cj g olefins was subjected to isomerization-hydroformylation, a reverse effect on regioselectivity was observed [136e]. Thus, the formation of the linear aldehyde increased in the following order iodide bromide chloride. 

Moreover, also the acid (e.g., PTSA (p-toluenesulfonic acid), HBF, HCl, ZnCl2, methanesulfonic acid) strongly affected regioselectivity. For example, in the presence of0.075 mol% of PTSA, the Hb ratio was 95 5, while using 10 mol% of PTSA, -nonanal and 2-methyloctanal were formed in a ratio of 54 46. In general, large differences were noticed in comparison to rhodium catalysts. 

Highly selective halide anion-promoted palladium-catalyzed hydroformylation of internal alkenes to linear alcohols was studied. A (bcope)Pd(OTf)2 complex (bcope) = bis(cydooctyl)phosphinoethane with substoichiometrically added halide anion was found to be a highly efficient homogeneous catalyst to selectively convert internal linear 

The nickel catalysts described in the preceding section are neutral in character, in our hands cationic nickel catalysts such as those described by Brookhart et al. [20] are ineffective in the copolymerization of norbornene and ethylene. Indeed norbornene has been described as a strong catalyst poison (for both nickel and palladium) by the same workers. Surprisingly we found that cationic palladium catalysts, with a wide variety of chelate ligands, are very effective in the copolymerization of ethylene and norbornenes [89]. These catalysts possess the same ability as the above-described neutral nickel catalysts to incorporate norbornenes bearing functional groups, but overcome two of the major limitations  

The cationic palladium catalysts are typically prepared by reacting (cyclooctadi-enejpaUadium methyl chloride with a stoichiometric amount of the bidentate ligand to afford the (ligand) Pd(Me)Cl adduct The adduct is then reacted with an activator such as silver hexafluoroantimonate, to afford the final cationic catalyst, (hgand) l l(Me) SbF[]. The polymerization reactions were typically run at ambient temperature in toluene to afford a viscous solution of the desired copolymer. Other activators used include tris(pentafluorophenyl)borane/triethylaluminum mixtures, Nal (C,H 5(fT j)2)4 and mefhaluminoxane. 

800000) resulted when appropriately substituted diimine ligands were employed. The scope of the hgands exemplified [89] is illustrated in Fig. 4.36. 

Effect of di-imine ligand structure on copolymer proper- 

Polymerization conditions (Ligand)Pd(MeCl) complex activated with 1 mole AgSbFo per mole Pd. 

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Scholten J J and van Montfoort A 1962 The determination of the free-metal surface area of palladium catalysts J. Catal. 1 85-92... 

It U better to employ the special palladium catalyst which is incorporated in the Deoxo catalytic gas purifier (obtainable from Baker Platinum Limited, 52 High Holbom. London, W.C. 1). 1 his functions at the laboratory tamperature and will remove up to 1 per cent of oxygen. The water vapour formed is carried away in the gas stream and is separated by any of the common desiccants. 

Palladium catalysts are useful alternatives to Adams platinum oxide catalyst described in Section 111,150. The nearest equivalent to the latter is palladium chloride upon carbon and it can be stored indefinitely the palladium salt is reduced to the metal as required ... 

A highly diastereoselective alkcnylation of c/s-4-cyclopentene-l,3>diols has been achieved with 0-protected (Z)-l-iodo-l-octen-3-ols and palladium catalyst (S. Torii, 1989). The ( )-isomers yielded 1 1 mixtures of diastcrcomcric products. The (Z)-alkenylpalladium intermediate is thought to undergo sy/i-addition to the less crowded face of the prochiral cyclopentene followed by syn-elimination of a hydropalladium intermediate. 

Allylic acetoxy groups can be substituted by amines in the presence of Pd(0) catalysts. At substituted cyclohexene derivatives the diastereoselectivity depends largely on the structure of the palladium catalyst. Polymer-bound palladium often leads to amination at the same face as the aoetoxy leaving group with regioselective attack at the sterically less hindered site of the intermediate ri -allyl complex (B.M. Trost, 1978). 

In a related process, 1,4-dichlorobutene was produced by direct vapor-phase chlorination of butadiene at 160—250°C. The 1,4-dichlorobutenes reacted with aqueous sodium cyanide in the presence of copper catalysts to produce the isomeric 1,4-dicyanobutenes yields were as high as 95% (58). The by-product NaCl could be recovered for reconversion to Na and CI2 via electrolysis. Adiponitrile was produced by the hydrogenation of the dicyanobutenes over a palladium catalyst in either the vapor phase or the Hquid phase (59,60). The yield in either case was 95% or better. This process is no longer practiced by DuPont in favor of the more economically attractive process described below. 

Vapor-phase oxidation over a promoted vanadium pentoxide catalyst gives a 90% yield of maleic anhydride [108-31-6] (139). Liquid-phase oxidation with a supported palladium catalyst gives 55% of succinic acid [110-15-6] (140). 

During the reaction, the palladium catalyst is reduced. It is reoxidized by a co-catalyst system such as cupric chloride and oxygen. The products are acryhc acid in a carboxyUc acid-anhydride mixture or acryUc esters in an alcohoHc solvent. Reaction products also include significant amounts of 3-acryloxypropionic acid [24615-84-7] and alkyl 3-alkoxypropionates, which can be converted thermally to the corresponding acrylates (23,98). The overall reaction may be represented by ... 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

Novel palladium catalysts show marked improvements in both yields and selectivities, compared to nickel carbonyl catalysts utilized in eadier commercial carbonylation processes (83,84). The palladium catalysts are also expected to be less hazardous. 

UBE Industries, Ltd. has improved the basic method (32—48). In the UBE process, dialkyl oxalate is prepared by oxidative CO coupling in the presence of alkyl nitrite and a palladium catalyst. 

Ca.ta.lysis, The most important iadustrial use of a palladium catalyst is the Wacker process. The overall reaction, shown ia equations 7—9, iavolves oxidation of ethylene to acetaldehyde by Pd(II) followed by Cu(II)-cataly2ed reoxidation of the Pd(0) by oxygen (204). Regeneration of the catalyst can be carried out in situ or ia a separate reactor after removing acetaldehyde. The acetaldehyde must be distilled to remove chloriaated by-products. 

Polymerization by G—G Goupling. An aromatic carbon—carbon coupling reaction has been employed for the synthesis of rigid rod-like polyimides from imide-containing dibromo compounds and aromatic diboronic acids ia the presence of palladium catalyst, Pd[P(CgH )2]4 (79,80). 

The first CO route to make adipic acid is a BASF process employing CO and methanol in a two-step process producing dimethyl adipate [627-93-0] which is then hydroly2ed to the acid (43—46). Cobalt carbonyl catalysts such as Co2(CO)g are used. Palladium catalysts can be used to effect the same reactions at lower pressures (47—49). 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

Aromatic Aldehydes. Carbon monoxide reacts with aromatic hydrocarbons or aryl haHdes to yield aromatic aldehydes (see Aldehydes). The reaction of equation 24 proceeds with yields of 89% when carried out at 273 K and 0.4 MPa (4 atm) using a boron trifluoride—hydrogen fluoride catalyst (72), whereas conversion of aryl haHdes to aldehydes in 84% yield by reaction with CO + H2 requires conditions of 423 K and 7 MPa (70 atm) with a homogeneous palladium catalyst (73) and also produces HCl. 

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

The presence of other functional groups ia an acetylenic molecule frequendy does not affect partial hydrogenation because many groups such as olefins are less strongly adsorbed on the catalytic site. Supported palladium catalysts deactivated with lead (such as the Liadlar catalyst), sulfur, or quinoline have been used for hydrogenation of acetylenic compound to (predominantiy) cis-olefins. 

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