Polyvinyl alcohol catalysts

In Figure 1 the activity of a palladium-polyvinyl alcohol catalyst is compared with that of other catalysts for the hydrogenation of nitrobenzene. It can be seen that on the basis of the weight of noble metal employed, the catalyst containing 10 mg. of Pd and 250 mg. of polyvinyl alcohol is by far the most active. The reproducibility of hydrogen absorption after the lapse of five minutes was found to be about +10%. 

The relative efficiency of the various colloidal catalysts indicates that the gold number (7) of the protective colloid offers no guide to the selection of suitable colloidal support. On the basis of gold numbers, the gum arable catalyst should be far superior to the corresponding polyvinyl alcohol catalyst (8). 

It has been observed that an aqueous solution of palladium chloride containing polyvinyl alcohol changes color on standing for several hours in the absence of hydrogen at 30°C. The solution, initially red in color, assumes the black color characteristic for the palladium-polyvinyl alcohol catalyst. Further, the acidity of the solution increases on standing, presumably due to the formation of HCl by the reduction of the PdCl2. That reduction to the metal does occur has been established as follows Elec-... 

It has been found possible to fractionate palladium-polyvinyl alcohol catalysts into more and less active fractions by applying ultracentrifugation (10). It is believed that this fractionation is the result of the heavier palladium particles being deposited while the lighter ones remain sus-... 

Electron micrographs have provided additional information available about the palladium-polyvinyl alcohol catalysts. As has been mentioned, they established that palladium chloride is reduced to palladium in the presence of an aqueous suspension of polyvinyl alcohol. Further electron micrographs established that the palladium (12) and also rhodium are... 

The rapidity with which the palladium-polyvinyl alcohol catalyst dehalogfinates wi-bromonitrobenzene is particularly noteworthy. 

The palladium-polyvinyl alcohol catalyst has proved useful in the reduction of acetylenes to ethylenes (15). Thus, 3-methyl-butyn-l-ol-3 has been reduced to 3-methyl-buten-l-ol-3 in excellent yield. Furthermore it was also advantageously utilized in the hydrogenation of cystine, in which case only 10 mg. of palladium were required (15a), and in the catalytic hydrogenation of apozymase (15b). 

Synthetic organic polymers, which are used as polymeric supports for chromatography, as catalysts, as solid-phase supports for peptide and oligonucleotide synthesis, and for diagnosis, are based mainly on polystyrene, polystyrene-divinylbenzene, polyacrylamide, polymethacrylates, and polyvinyl alcohols. A conventional suspension of polymerization is usually used to produce these organic polymeric supports, especially in large-scale industrial production. 

Macroporous polyvinyl alcohol particles with a molecular weight cutoff of ca. 8 X 10 in gel-permeation chromatography have been prepared. The particles are produced by first dispersing an aqueous solution of polyvinyl alcohol in an organic solvent to make spheres of polyvinyl alcohol solution. Holding the dispersion in such a state that a gel will then form spontaneously will cause the gel to react with glutaraldehyde in the presence of an acidic catalyst (85). 

Polyhydric Alcohols. (Polyols). An alcohol with three or more hydroxyl groups, each attached to a different carbon atom. They are w-sol and of sweetish taste, which tends to intensify with increasing hydroxyl content. Examples of polyols of ordn interest are listed below. Polyvinyl alcohol is considered in a separate entry as a polymer although it is defined as a polyhydric alcohol. Polyols, when nitrated, make excellent expls, proplnt binders, plasticizers, etc. Prepn can follow the procedure of Lenth DuPuis (Ref 3) which uses a methanol suspension of either sucrose or dextrose and a special Cu-Al oxide catalyst to yield 60-65% distillable polyols at 240° and 1500psi Refs 1) Beil — refs found under individual compds 2) CA, under Alcohols, Polyhydric for compds of current ordn interest 3) C.W. Lenth R.N. DuPuis, "Polyhydric Alcohol Production by Hydrogenolysis of Sugars in the Presence of Copper-Aluminum Oxide , IEC 37, 152-57 (1945) CA 39, 1391 (1945)... 

The first section, Chemical Reactions on Polymers, deals with aspects of chemical reactions occurring on polymers—aspects relating to polymer size, shape, and composition are described in detail. One of the timely fields of applications comprises the use of modified polymers as catalysts (such as the immobilization of centers for homogeneous catalysis). This topic is considered in detail in Chapters 2, 3, 8, 9, and 11 and dealt with to a lesser extent in other chapters. The use of models and neighboring group effect(s) is described in detail. The modification of polymers for chemical and physical change is also described in detail in Chapters 2 (polystyrene) 4 (polyvinyl chloride) 5 (polyacrylic acid, polyvinyl alcohol, polyethyleneimine, and polyacrylamide) 6 (polyimides) 7 (polyvinyl alcohol) 8 (polystyrene sulfonate and polyvinylphosphonate) 10 (polyacrylamide) and 12 (organotin carboxylates). 

In the suspension polymerization process, the autoclave reactor is filled with water. PVA, polyvinyl alcohol is the dispersing agent that helps stabilize the suspension. Lauroyl peroxide is the free radical catalyst that starts it all off. The reaction temperature is around 130°F, and the process takes 10—12 hours per batch, with 95% conversion. 

Other common binders include nitrocellulose (acetone as the solvent), polyvinyl alcohol (used with water), and Laminae (an unsaturated polyester crosslinked with styrene — the material is a liquid until cured by catalyst, heat, or both, and no solvent is required). Epoxy binders can also be used in hquid form during the mixing process and then allowed to cure to leave a final, rigid product. 

When heated, polyvinyl chloride (PVC) and polyvinyl alcohol (PVA) lose HC1 and H20, respectively, to produce dark-colored conductive polyacetylene. Superior polymers of acetylene can be made by the polymerization of acetylene with Ziegler-Natta catalysts. The conductivity of polyacetylene is increased by the addition of dopants, such as arsenic pentafluoride or sodium naphthenide. 

In a process related to GTP, aldehydes initiate the polymerization of silyl vinyl ethers and silyl diene ethers. Here the silyl group is present in the monomer and transfers to the aldehyde ended chains regenerating aldehyde ends [17] (Scheme 8). A Lewis acid catalyst is required. terf-Butyldimethylsilyl works best as a transfer group for vinyl ether while trimethylsilyl is suitable for diene ethers [18]. Even though aldol GTP provides a route to polyvinyl alcohol segments in the subsequent block polymer synthesis, the projected cost of the monomers discouraged further research aimed at commercialization. 

A reaction vessel was charged with 10 ml 5% of solution polyvinyl alcohol having a M of roughly 20,000 daltons of which 97.5% to 99.5 % were hydrolyzed and 0.333 pL of 6.0M hydrochloric acid and then treated with 91.5 pL of 25% solution of glutaraldehyde. The solution was then poured across a PET support and allowed to stand at ambient temperature for 30 minutes. The membranes were washed with excess distilled water to remove residual catalyst prior to use. 

The chemicals used for coating and laminating are polymeric materials, either naturally occurring or produced synthetically. These include natural and synthetic rubbers, polyvinyl chloride, polyvinyl alcohol, acrylic, phenohc resins, polyurethanes, silicones, fluorochemicals, epoxy resins and polyesters." Coating formulations typically include auxiliaries such as plasticizers, adhesion promoters, viscosity regulators, pigments, fillers, flame retardants, catalysts and the like. ... 

BURCO FINISH 55 is used primarily in finishing baths for fabric stiffening. It is a very efficient and economical hand builder. It tends to produce a stiff, full leathery hand as opposed to the thin, crisp hand produced by polyvinyl alcohol and starch derivatives. Being nonionic in nature, it is highly compatible with a wide variety of resins, softeners, catalysts and other finishing bath components. 

The dibromo compound is dehalogenated by agitating under a hydrogen atmosphere a mixture of 80 g. (0.23 mole) of the dibromo compound, 700 ml. of N aqueous sodium hydroxide solution, and a catalyst consisting of 2% palladium on polyvinyl alcohol prepared from 0.5 g. of palladium chloride (p. 244). To the resulting mixture is added 120 g. of sodium chloride, and the precipitated catalyst is removed by filtration. The filtrate is acidified and extracted with chloroform. Removal of the chloroform by distillation gives 35 g. (80%) of ethyl orcinol-6-carboxylate, m.p. 132-133°. 

Eleven milliliters of water is added to 12.5 ml. of a 2% aqueous solution of polyvinyl alcohol followed by 1 ml. of an aqueous solution of palladium chloride containing 1% palladium. To the resulting solution is added dropwise 0.5 ml. of a 4% aqueous solution of sodium carbonate. The mixture is diluted with water or ethanol, depending on whether the catalyst is to be used in water or water-ethanol medium. The catalyst is used by agitating it with hydrogen until the hydroxide is reduced to palladium metal, after which the compound to be reduced is added. 

Recently [43] Gao et al. applied a zeolite-fiOlled polyvinyl alcohol (PVA) membrane in esterification and acetalization reactions. Zeolites NaA, KA and CaA as well as NaX were loaded into PVA up to 27 wt% and the composites tested in selective water removal during reaction. A pervaporation cell with a membrane area of 22.9 cm was coimected to a collection system kept at a vacuum of 0.1 mm Hg. A sulfonated resin was used as Bronsted acid catalyst in the esterification mixture (120 ml). Figure 28 shows the progress of the esterification of salicylic acid and methanol at 60°C. The reaction is accelerated considerably as a result of the water removal. 

The newer type of colloidal catalysts have been prepared containing palladium (4), platinum (4), rhodium (5), and iridium (6). A variety of synthetic polymers has been applied. Among those tested were polyvinyl alcohol (PVA), polyvinyl acetate (PVAc), polymethyl methacrylate (PMMA), and polymethyl acrylate (PAMA). In general, polyvinyl alcohol (4a) has been found most satisfactory. 

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