Water soluble catalysts

Considerable work has been conducted on a water-soluble catalyst using sulfonated phosphine-modified rhodium. Details of this chemistry will be described in Chapter 5. The general concept (Figure 2.3) is to make the catalyst water soluble, then after product formation, decant the product. In order for the water-soluble catalyst to be effective, the alkene must dissolve in the aqueous layer. This has been demonstrated on a commercial basis using propene. The low solubility of higher alkenes in the aqueous catalyst layer has proven problematic. The desirable characteristic of the ligand, water solubility, is needed in the separation step but is a disadvantage in the reaction step. 

Figure 10.5 A diphosphine ligand used to render a polymerization catalyst water-soluble...

Because enzymes are insoluble in organic solvent, mass-transfer limitations apply as with any heterogeneous catalyst. Water-soluble enzymes (which represent the majority of enzymes currently used in biocatalysis) have hydrophilic surfaces and so tend to form aggregates or stick to reaction vessel walls rather than form the fine dispersions that are required for optimum efficiency. This can be overcome by enzyme immobilization, as discussed in Section 1.5. 

Carbon nanotubes Carbon, but only the water-soluble derivatives of CNTs used in pharmacy CNTs formed by chemical vapor deposition (CVD) in presence of Fe catalyst, water-soluble CNT derivatives obtained by acid processing followed by conjugation with drugs 54,55... 

Some other C—C bond coupling reactions in micellar systems should be mentioned here. Monflier et al. [72] described, in both papers and patents, the telome-rization of 1,3-butadiene into octadienol in a micellar system by means of a palladium-phosphine catalyst. Water-soluble and amphiphilic phosphines have been used and the surfactants were widely varied. The authors have shown that the promoting effect of surfactants appeared above the CMCs of the surfactants, and they conclude that micellar aggregates were present in the reaction mixture. Cationic, anionic, and nonionic surfactants gave this micellar effect but the combination of the highly water-soluble TPPTS and the surfactant dodecyldimethylamine hydrocarbonate was found to be best. A speculation about the location of reactants shows that the reaction probably occurs in the interface between the micellar pseudophase and water. 

In addition to interests in making recoverable, reusable catalysts, there is interest in developing catalysts that work in nontraditional solvents. Water is an especially interesting solvent in this regard. Recently, we have developed some water-soluble polymers that work well either in an aqueous phase system or in biphasic systems. The polymeric systems we have developed serve two roles. They make the catalysts water- soluble and, the polymer portion of these catalysts allows us to recover the catalysts at the end of a reaction. This recovery is effected either in a biphasic manner or by means of the polymer s lower critical solution temperature (LCST)... 

Insoluble in water, soluble in organic solvents b.p. — 15°C. Prepared by treating 1,4-dibromo-butane with metallic sodium. Reduced to n-butane by hydrogen at 200" C in presence of nickel catalysts. 

Pd can also be recovered as insoluble complexes such as the dimethylglyox-ime complex, or PdCUiPhiP) by treatment with HCl and PI13P. When water-soluble phosphines are used, the catalyst always remains in the aqueous phase and can be separated from a product in the organic phase, and is used repeatedly. 

Polydextrose (Pfizer) is prepared by high temperature polymerization of glucose in the presence of a catalyst. It is a water-soluble, amorphous soUd used primarily as a hulking agent (52). Dried fmit, including pmnes, and dried plum, date, and grape juice is used for similar appUcations (53). 

Most phenohc foams are produced from resoles and acid catalyst suitable water-soluble acid catalysts are mineral acids (such as hydrochloric acid or sulfuric acid) and aromatic sulfonic acids (63). Phenohc foams can be produced from novolacs but with more difficulty than from resoles (59). Novolacs are thermoplastic and require a source of methylene group to permit cure. This is usually suppHed by hexamethylenetetramine (64). 

Oxidation Catalysis. The multiple oxidation states available in molybdenum oxide species make these exceUent catalysts in oxidation reactions. The oxidation of methanol (qv) to formaldehyde (qv) is generally carried out commercially on mixed ferric molybdate—molybdenum trioxide catalysts. The oxidation of propylene (qv) to acrolein (77) and the ammoxidation of propylene to acrylonitrile (qv) (78) are each carried out over bismuth—molybdenum oxide catalyst systems. The latter (Sohio) process produces in excess of 3.6 x 10 t/yr of acrylonitrile, which finds use in the production of fibers (qv), elastomers (qv), and water-soluble polymers. 

Dimersol is a commercial process for the dimeri2ation of propylene, butylenes, or a mixture of both, to and Cg olefins this process produces a more linear olefin than the phosphoric acid process. The reaction is conducted at ambient temperature, using a water-soluble catalyst complex (16). 

Because of its volatility, the cobalt catalyst codistills with the product aldehyde necessitating a separate catalyst separation step known as decobalting. This is typically done by contacting the product stream with an aqueous carboxyhc acid, eg, acetic acid, subsequently separating the aqueous cobalt carboxylate, and returning the cobalt to the process as active catalyst precursor (2). Alternatively, the aldehyde product stream may be decobalted by contacting it with aqueous caustic soda which converts the catalyst into the water-soluble Co(CO). This stream is decanted from the product, acidified, and recycled as active HCo(CO)4. 

Desalting is a water-washing operation performed at the production field and at the refinery site for additional cmde oil cleanup. If the petroleum from the separators contains water and dirt, water washing can remove much of the water-soluble minerals and entrained soflds. If these cmde oil contaminants are not removed, they can cause operating problems duting refinery processiag, such as equipment plugging and corrosion as well as catalyst deactivation. 

Alkaline Catalysts, Resoles. Resole-type phenoHc resins are produced with a molar ratio of formaldehyde to phenol of 1.2 1 to 3.0 1. For substituted phenols, the ratio is usually 1.2 1 to 1.8 1. Common alkaline catalysts are NaOH, Ca(OH)2, and Ba(OH)2. Whereas novolak resins and strong acid catalysis result in a limited number of stmctures and properties, resoles cover a much wider spectmm. Resoles may be soHds or Hquids, water-soluble or -insoluble, alkaline or neutral, slowly curing or highly reactive. In the first step, the phenolate anion is formed by delocali2ation of the negative charge to the ortho and para positions. 

Catalytic oxidation ia the presence of metals is claimed as both nonspecific and specific for the 6-hydoxyl depending on the metals used and the conditions employed for the oxidation. Nonspecific oxidation is achieved with silver or copper and oxygen (243), and noble metals with bismuth and oxygen (244). Specific oxidation is claimed with platinum at pH 6—10 ia water ia the presence of oxygen (245). Related patents to water-soluble carboxylated derivatives of starch are Hoechst s on the oxidation of ethoxylated starch and another on the oxidation of sucrose to a tricarboxyhc acid. AH the oxidations are specific to primary hydroxyls and are with a platinum catalyst at pH near neutraUty ia the presence of oxygen (246,247). Polysaccharides as raw materials ia the detergent iadustry have been reviewed (248). 

Mixing. Because of the heterogeneous nature of this system, efficient mixing is essential to ensure the intimate contact of the iron, nitro compound, and water soluble catalyst. An agitator which allows the iron to settie to the bottom and the other materials to separate into layers does not function efficientiy. On the other hand, a reaction whose rate is limited by the quaUty of the iron will not be significantly improved by better mixing. 

Pyrrohdine [123-75-1] (tetrahydropyrrole) (19) is a water-soluble strong base with the usual properties of a secondary amine. An important synthesis of pyrrohdines is the reaction of reduced furans with excess amine or ammonia over an alumina catalyst in the vapor phase at 400°C. However, if labde substituents are present on the tetrahydrofurans, pyrroles may form (30). 

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