Potassium, catalytic activity under

Early work by Strassner and co-workers showed that the chelating bis-NHC Pd complexes 32a and 32c were capable of promoting the oxidation of methane, whilst the iodo-analogues 32b and 32d were inactive under the same reaction condition [45], Indeed, in a mixture of TEA and TFAA, in the presence of potassium peroxodisulfate under 20-30 bar of methane, trifluoroactic acid methyl ester is produced, using 32a or 32c as catalyst (Scheme 10.14). hi a more recent work, the authors disclosed the use of pyrimidine-NHC Pd complexes for the same reaction. A shghtly better catalytic activity was obtained with the unexpected cationic complex 34 [46],... 

Halide exchange has been extended to vinylic halides with excellent stereospecificity. Thus, under the above conditions, cw- -bromostyrene is converted to d.s-/ -chlorostyrene and trans-fi-bvomostyrene is transformed into trans-fi-chlorostyrene in high yields. Recently, Cheng and colleagues211 reported the catalytic activity of nickel powder in the exchange reaction of potassium iodide with aryl bromides at 150 °C in DMF. Zinc powder, combined with nickel bromide, is also known to promote this exchange212. 

In addition to palladium, the catalysts used commercially always contain alkali salts, preferably potassium acetate. Additional activators include gold, cadmium, platinum, rhodium, barium, while supports such as silica, alumina, aluminosilicates or carbon are used. The catalysts remain in operation for several years but undergo deactivation. The drop in activity is due to a gradual sintering of the palladium particles which causes the catalytically active area to decrease progressively. Under reaction conditions potassium acetate is slowly lost from the catalyst and must continuously be replaced. 

Laine (43-47) used potassium hydroxide to promote the catalytic activity of [Ru3(CO),2] and [H4Ru4(CO),2] for the hydroformylation of pent-1-ene. Under 64 bar of CO pressure, at 135 or 150°C, high selectivities for straight-chain aldehydes were obtained, for example, 97%. As the subsequent reduction of aldehydes to alcohols is lower, important aldol condensations occurred owing to the presence of a base in solution. Analysis of the reaction mixtures has shown that the anionic [H3Ru4(CO),2] cluster is likely to be the active species. Since this complex was recognized as the major component of the low pressure ruthenium-catalyzed water gas shift... 

Potassium ions are required by a variety of enzymes (Suelter, 1970), These enzymes are activated by K to a greater extent than by Na. Pyru ate kiirase, an enzyme of the glycolytic pathway, is the most well known K-requiring enzyme. It is activated by a variety of monovalent cations, as indicated in Table 10.7. Ammonium ions at 100 mM support catalytic activity however, the concentration of ammonium ions in the cell is under 1.0 mAI. Sodium at 100 mA/f weakly supports activity. The concentration of Na in the ccH is only about 10 mM, indicating that the importance of Na in supporting enzyme activity m uiuo is nil. Rubidium, which is chemically similar to K, supports activity however, Rb is not a physiological cation. 

The oxidation of SOi to sulfuric acid, SOt + H2O + 0.5 O2 H2SO4, is catalyzed by potassium vanadium(V) oxide compounds. A typical catalyst preparation sequence involves impregnation of a silica support with a solution containing potassium vanadate (K/V = 3), followed by drying and subsequent calcination at 500°C in air. Under typical operating conditions in SO2/O2/SO3 atmospheres at 400-500°C, the catalytically active species is molten and forms a thin liquid film on the silica. support. As such the. system functions like a bulk oxide catalyst under operating conditions, and the silica mostly serves as a mechanical support medium. 

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