Metal salts, addition

Addition of such a-lithiosulfinyl carbanions to aldehydes could proceed with asymmetric induction at the newly formed carbinol functionality. One study of this process, including variation of solvent, reaction temperature, base used for deprotonation, structure of aldehyde, and various metal salts additives (e.g., MgBrj, AlMej, ZnClj, Cul), has shown only about 20-25% asymmetric induction (equation 22) . Another study, however, has been much more successful Solladie and Moine obtain the highly diastereocontrolled aldol-type condensation as shown in equation 23, in which dias-tereomer 24 is the only observed product, isolated in 75% yield This intermediate is then transformed stereospecifically via a sulfoxide-assisted intramolecular 8, 2 process into formylchromene 25, which is a valuable chiron precursor to enantiomerically pure a-Tocopherol (Vitamin E, 26). 

In order to improve the selectivity toward the formation of 1,3-PDO, we studied the influence of metal salt additives. While the addition of calcium or copper salts exhibited a moderate influence, the presence of iron salts played a significant role on the rate and selectivity of the reaction (Figure 35.1). The metal additives reduced noticeably the activity of the rhodium catalysts suggesting that they acted as a surface poison, but they modified the selectivity of the glycerol hydrogenolysis, probably through selective diol chelation. 

Herbst et al. report a process for the conversion of linear and/or branched paraffins based on the use of an IL catalyst in combination with a metal salt additive, which provides a catalytic composition of increased activity compared with the IL alone. Under suitable reaction conditions this conversion leads to paraffin hydrocarbon fractions having higher octane numbers. 

Anodes. There are two types of anodes soluble and insoluble. Most electroplating baths use one or the other specifically however, a few baths use either or both. Chromic acid plating baths use insoluble anodes alkaline zinc cyanide baths use both noncyanide alkaline zincs may use either. Soluble anodes are designed to dissolve efficiendy with current flow and preferably, not to dissolve when the system is idle. A plating solution having the anode efficiency close to the cathode efficiency provides a balanced process that has fewer control problems and is less cosdy. If the anode efficiency is much greater than the cathode efficiency and there are only small solution losses, the dissolved metal concentration rises until at some time the bath has to be diluted back or the excess metal has to be reduced by some other means. If the anode efficiency is less than the cathode efficiency, the dissolved metal decreases, pH decreases, and eventually metal salt additions and other solution corrections are required. Based on the cost of metal, it is usually considerably more economical to plate from the anode rather than add metal salt. Copper cyanide, for example, costs about twice as much to add than to dissolve a comparable amount of copper anode. Additionally, the anion added with the metal salt may build up in the plating solution. 

Wunderlich and Knochel recently published the alkylation of diaryliron compounds by alkyl iodides or benzyl chloride 1 (entry 33) [77]. The reaction works well with 98% pure FeCl2 2LiCl but not with 99.998% pure metal salt. Addition of other transition metal salts showed that nickel contained in the FeCl2 of 98% purity is the likely catalyst. Alkylarenes 3 were obtained in 65-88% yield. The method tolerates ester, nitrile, fluoride, or chloride substituents. Although the use of 5-hexenyl iodide did not provide a cyclized product, the initial formation of radicals cannot be excluded safely. 

It is well-known that feedstock, reaction rate, and temperature affect particle size alkali metal salt additives affect structure and the use of preheated air, increased reactor size and increased throughput affect yield. 

The catalytic synthesis of C2H4 directly from CH4 has been examined in the presence of oxygen for many metal oxides containing alkali metal salts. Addition of alkali halides onto metal oxides depressed the catalytic activities of the host oxides in deep oxidation of CH4, but favorably enhanced the direct synthesis of C2H4 from CH4, Among the catalysts tested, the oxides of Mn and Ni with LiCl produced ethylene with high selectivity (ca. 60%) and yield (ca. 27%). The role of alkali halides for the selective synthesis of C2H4 was examined for LiCl-added NiO. It is speculated that the alkali metals incor-... 

In addition to the catalyst and base (if required), the use of metal-salt additives is very conunon for enhancing cross coupling and other reactions. Cul is the most common additive and in many cases it may operate as an intermediate transmetallating agent RM RCu —> RPdR. In other cases, it has been said to remove excess phosphine, thus increasing the reactivity of the palladium. Ag20 is sometimes used and may act by transmetallation or as a halide trap. 

Effects of metal salt addition on the hydrogenation of acrolein with a Co/silica-alumina catalyst reduced at 400°C for 1 h... 

For the cholesterol derivatives 22 and 23 the transcription into hollow fiber silica occurred even in the absence of metal salt additives. This phenomenon was ascribed to the protonation of the monoaza- and diaza-18-crown-6 moieties due to their relatively high pA a values, thus providing under the sol-gel polymerization conditions the required cationic charges for the stimulation of the transcription effect. 

Adducts with metal ions are important for the successful MALDI analyses of nonpolar compounds. Similarly to the ESI method, their formation very often takes place as a result of the presence of traces of metal salts. Addition of small amounts of Na+ and K+ ions is used for helping the ionization of analytes whose proton affinities are low. Transition-metal ions have been successfully applied when no other ionizing reagents work. For example, Ag+ ions are extremely effective in the MALDI analysis of polymers having no heteroatoms. 

The first selective monoarylation of (W-pyridin-2-yl)piperidme was made possible by introduction of a trifluoromethyl substituent at the 3-position of the pyridin-2-yl directing group (Scheme 24) [16]. The steric hindrance brought by this substituent favoured the sole formation of monoarylated piperidines. A beneficial effect of metal salt additives to the Ru3(CO)i2-based catalyst was observed on... 

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