Potassium cation, catalysis

More recently, Normant and coworkers have reported catalysis of the reaction between potassium acetate and benzyl chloride in acetonitrile by polyamines in a two phase system [28]. It seems likely that the catalytic activity reported by Normant et al. is related to the earlier alkylations discussed above. The authors state in their communication, however, their finding that ... quaternary ammonium salts corresponding to the diamines do not activate anions under the experimental conditions used. . In the reaction referred to here, it seems likely that the diamines are playing a dual role. The diamines are probably assisting in the solubilization of the solid (and relatively insoluble) potassium acetate by chelation of the potassium cation and the homogeneous reaction is then probably catalyzed by the quaternary ion formed in situ. That the catalytic activity of the amine depends on the hardness of the cation (the harder the cation, the less catalytic activity) [28] seems to accord with this interpretation although lattice energy differences cannot be discounted. 

In the family of cation pumps, only the Na,K-ATPase and H,K-ATPase possess a p subunit glycoprotein (Table II), while the Ca-ATPase and H-ATPase only consist of an a subunit with close to 1 000 amino acid residues. It is tempting to propose that the p subunit should be involved in binding and transport of potassium, but the functional domains related to catalysis in Na,K-ATPase seem to be contributed exclusively by the a subunit. The functional role of the P subunit is related to biosynthesis, intracellular transport and cell-cell contacts. The P subunit is required for assembly of the aj8 unit in the endoplasmic reticulum [20]. Association with a j8 subunit is required for maturation of the a subunit and for intracellular transport of the xP unit to the plasma membrane. In the jSl-subunit isoform, three disulphide... 

With aliphatic amines, the decomposition catalysis is moderate with heterocyclic aromatic amines (pyridine, quinoline), 0.1 % of amine is sufficient to cause maleic anhydride to decompose. An accident has also been mentioned with NaOH. This decomposition also takes place in the presence of sodium, lithium, ammonium, potassium, calcium, barium, magnesium and beryllium cations. 

Other reactions in which cations other than protons are catalyti-cally effective are esterification and acetal formation, catalyzed by calcium salts,277 and the bromination of ethyl cyclopentanone-2-carboxylate, catalyzed by magnesium, calcium, cupric, and nickel, but not by sodium or potassium ions.278 One interpretative difficulty, of course, is the separation of catalysis from the less specific salt effects. The boundary line between salt effects (medium effects) and salt effects (catalysis) is not sharp either in concept or experimentally. 

As for solvents, liquid ammonia or dimethylsulfoxide are most often used. There are some cases when tert-butanol is used as a solvent. In principle, ion-radical reactions need aprotic solvents of expressed polarity. This facilitates the formation of such polar forms as ion-radicals are. Meanwhile, the polarity of the solvent assists ion-pair dissociation. This enhances reactivity of organic ions and sometimes enhances it to an unnecessary degree. Certainly, a decrease in the permissible limit of the solvent s polarity widens the possibilities for ion-radical synthesis. Interphase catalysis is a useful method to circumvent the solvent restriction. Thus, 18-crown-6-ether assists anion-radical formation in the reaction between benzoquinone and potassium triethylgermyl in benzene (Bravo-Zhivotovskii et al. 1980). In the presence of tri(dodecyl)methylammonium chloride, fluorenylpi-nacoline forms the anion-radical on the action of calcium hydroxide octahydrate in benzene. The cation of the onium salts stabilizes the anion-radical (Cazianis and Screttas 1983). Surprisingly, the fluorenylpinacoline anion-radicals are stable even in the presence of water. 

A subsequent series of glucose tests (10% concentration) was performed with added acids and bases to model expected anion and cation contaminants from manure hydrolysates (see Fig. 4). The contaminants were added at 100 ppm. The ammonium (added as carbonate) showed a decided inhibition of the catalysis. Calcium (added as carbonate) had a mild effect and the nitric acid contaminant even less, nearer the range of experimental variation. The effect of potassium (added as carbonate) was negligible (within experimental variation), as was the effect of the other acids. 

Selection of the cations was based on several criteria. First, the raw coal contained alkaline-earth, mainly Ca and Mg, and some alkali metals on its carboxyl groups. Also, McKee (13) and Walker et al. (12) have shown that sodium, potassium and calcium are excellent catalysts for the C-O2 reaction. Thus, these cations may have a significant effect on the char burnout rate. In addition. Mg was back exchanged on the coal since it was contained on the raw coal and, as shown by Walker et al. (12), it is a poor catalyst for the C-O2 reaction. The purpose of using this alkaline-earth metal was to determine if catalysis of the heterogeneous C-O2 reaction affected the char burnout rate. This would help to elucidate whether the char burnout step was chemically or physically rate controlled. 

A further significant factor which comes to the fore in coordinate catalysis is stereoregular polymerization. A number of the catalyst systems are capable of producing isotactic, optically active and/or crystalline polymers. Except for Price s potassium t-butoxide system [21], this has not been observed in anionic or cationic polymerization. Thus, in addition... 

The cation requirement in the function of DDH can be satisfied by K, NH4 +, and Tl, which have similar though not identical ionic radii. Rh" ", Cs" ", and Na are less effective and Li is practically ineffective. It seems that a monovalent cation similar in size to ammonium or potassium ion satisfies the cation requirement, whereas larger or smaller monovalent cations are less or not at all effective. The association of K" " with propane-1,2-diol in the structure of DDH raises the question whether participates directly in catalysis, and if so in what capacity. 

Phase transfer catalyzed reactions in which ylides are formed from allylic and ben-zylic phosphonium ions on cross-linked polystyrenes in heterogeneous mixtures, such as aqueous NaOH and dichloromethane or solid potassium carbonate and THF, are particularly easy to perform. Ketones fail to react under phase transfer catalysis conditions. A phase transfer catalyst is not needed with soluble phosphonium ion polymers. The cations of the successful catalysts, cetyltrimethylammonium bromide and tetra-n-butylammonium iodide, are excluded from the cross-linked phosphonium ion polymers by electrostatic repulsion. Their catalytic action must involve transfer of hydroxide ion to the polymer surface rather than transport of the anionic base into the polymer. Dicyclohexyl-18-crown-6 ether was used as the catalyst for ylide formation with solid potassium carbonate in refluxing THF. Potassium carbonate is insoluble in THF. Earlier work on other solid-solid-liquid phase transfer catalyzed reactions indicated that a trace of water in the THF is necessary (40). so the active base for ylide formation is likely hydrated, even though no water is included deliberately in the reaction mixture. 

Full details are now available of a study of polystyrene-supported quaternary ammonium and phosphonium catalysts (80) for triphase catalysis (TC) in a liquid-solid-liquid mode. Long spacer chains between the quaternary centre and the polymer backbone were found to be unnecessary for TC activity, and phosphonium catalysts were more effective than ammonium thus (80 n = 3, A = P) compared favourably with soluble octadecyltributylphosphonium bromide as a PT catalyst for reactions such as halide to halide interconversions. A test reaction, that of potassium acetate with 1-bromo-octane, has been used to examine the TC activity of silica in the solid-solid-liquid mode. Silica impregnated with a cationic surfactant appears to be as effective as alumina (4,163), whereas silica bearing covalently bound quaternary ammonium groups exhibits increased effectiveness. 

Organo-SOMO catalysis has been successfully exploited to achieve the first asymmetric a-vinylation of aldehydes using vinyl trifluoroborate salts and the commercial Kim and MacMillan catalyst 191. " ° Vinyl potassium trifluoroborate salts participate in enantioselective and regioselec-tive carbon-carbon bond formation with the aldehyde-derived radical cation 192 to form a (3-borato-stabilized radical 193 (Scheme 25.90), which in the presence of a suitable oxidant will undergo rapid electron transfer to render the (3-cation (not shown). Subsequent Peterson elimination of the trifluoroborate group with tran.s-selectivity followed by iminium hydrolysis of 194 would then reveal an optically enriched R-( )-vinyl aldehyde (e.g., 195). 

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