Palladium-wool

Chapter 3 presents data about enantioselective hydrogenation reactions on metal catalysts supported on chiral carriers. Discussed are palladium supported on modified silica gels, effective chiral colloidal catalysts, template catalytic systems, palladium-silk, palladium-wool, and palladium polypeptide catalysts. 

The hydration of propylene with sulfuric acid catalyst in high-temperature water was investigated using a flow reaction system.31 The major product is isopropanol. A biopolymer-metal complex, wool-supported palladium-iron complex (wool-Pd-Fe), has been found to be a highly active catalyst for the hydration of some alkenes to the corresponding alcohols. The yield is greatly affected by the Pd/Fe molar ratio in the wool-Pd-Fe complex catalyst and the catalyst can be reused several times without remarkable change in the catalytic activity.32... 

To date, a few methods have been proposed for direct determination of trace iodide in seawater. The first involved the use of neutron activation analysis (NAA) [86], where iodide in seawater was concentrated by strongly basic anion-exchange column, eluted by sodium nitrate, and precipitated as palladium iodide. The second involved the use of automated electrochemical procedures [90] iodide was electrochemically oxidised to iodine and was concentrated on a carbon wool electrode. After removal of interference ions, the iodine was eluted with ascorbic acid and was determined by a polished Ag3SI electrode. The third method involved the use of cathodic stripping square wave voltammetry [92] (See Sect. 2.16.3). Iodine reacts with mercury in a one-electron process, and the sensitivity is increased remarkably by the addition of Triton X. The three methods have detection limits of 0.7 (250 ml seawater), 0.1 (50 ml), and 0.02 pg/l (10 ml), respectively, and could be applied to almost all the samples. However, NAA is not generally employed. The second electrochemical method uses an automated system but is a special apparatus just for determination of iodide. The first and third methods are time-consuming. 

Metal-based PRBs involve the introduction of metals, usually zero-valent iron, but sometimes metal wool, palladium, or other metals to chemically react with the target contaminant(s), causing chemical adsorption with and/or destruction of the contaminants. These materials are typically permeable to water and thus avoid the groundwater management and flow problems associated with impermeable barriers. 

Thermolysis on insulating wool. Kaowool or other refractory wools are valuable for reduced radiative heat losses from a hot crucible. However, their use causes some increase in the extent of pyrolysis of substrate vapor by the crucible assembly and this, in rare instances, may spoil a metal atom synthesis. Only one example is known at present. The reaction of palladium atoms with benzyl chloride gives very low yields of t73-benzylpalladium chloride when the palladium is evaporated from an alumina crucible insulated with Kaowool, but a 30-50% yield with an uninsulated crucible. It has been established that this is due to enhanced formation of product-destroying radicals on the hot Kaowool. 

Already by 1963, for a patent granted in 1966, Straschil and Lopez realized that the match of coefficient of thermal expansion between palladium membranes and (porous) substrates was critical, and stated that it would be virtually impossible to compensate for differences in dilation due to absorption of hydrogen [38]. They patented the use of dimpled or corrugated foils to accommodate differential thermal and chemical expansion [38]. Buxbaum and Hsu, in a 1992 patent, maintained that a rough substrate surface produced by abrasion with steel wool was critical for adherence of palladium on surfaces of Nb, Ta, V and Zr [39]. Other patents recommend corrugated or undulating configurations to allow for both thermal and chemical expansion [24, 26, 27, 29]. 

The hydration of C-C multiple bonds is a reaction with prevalent industrial interest due to the usefulness of the products as chemical intermediates. The wool-Pd complex is an economical and highly active catalyst for hydration of olefins. It is very stable and can be reused several times without any remarkable change in the catalytic activity [73, 74]. In particular, to convert alkenes to the corresponding alcohols in excellent enantioselectivity, a new biopolymer-metal complex constituted of wool-supported palladium-iron or palladium-cobalt was prepared and used, such as allylamine to amino-2-propanoI, acrylonitrile to lactonitrile and unsaturated acids to a-hydroxycarboxylic acids [75-77]. The same catalytic system was also used for hydration of substituted styrenes to produce chiral benzyl alcohols. The simple and cleaner procedure, mild reaction conditions, high stability and recovery rate of catalyst made these catalytic systems an attractive and useful alternative to the existing methods (Scheme 37). 

Lei X, Bin J, Li T, Xiao FJ, Mei YH, Ying YJ (2004) Asymmetric hydration of alkenes catalyzed by wool-palladium complex. Polym Adv Technol 15 346-349... 

Xin W, Danni S, Meiyu H, Yingyan J (2006) Highly effective hydration of olefins using a wool-palladium complex as a catalyst. Polym Adv Technol 17 163-167... 

Jia B, Yang X, Huang M-Y, Jiang Y-Y (2003) Hydration of alkenes catalyzed by wool-palladium-iron complex. React Func Polym 57 163-168... 

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