Preparation cation

Chang, C. and Lenhoff, A.M., Comparison of protein adsorption isotherms and uptake rates in preparative cation-exchange materials, ]. Chromatogr. A, 827, 281, 1998. 

Aromatic cation-radicals can also react with NOj", giving nitro compounds. Such reactions proceed either with a preliminary prepared cation-radical or starting from nncharged componnd if iodine and silver nitrite are added. As for mechanisms, two of them seem feasible—first, single electron transfer from the nitrite ion to a cation-radical and second, nitration of ArH with the NOj radical. This radical is quantitatively formed when iodine oxidizes silver nitrite in carbon tetrachloride (Neelmeyer 1904). 

Scheme 77.8 Strategies to prepare cationic polymerization catalysts (a) using oxide supports that have high Bransted and Lewis acidity (b) the addition of a co-catalyst to a neutral supported species (c) modification of the surface with Lewis acid co-catalysts prior to the grafting of the organometallic species [91, 96, 98].

Dubief et al. (5) prepared cationic block copolymers of poly(styrene-co-iV-methyl-4-vinylpyridinium iodide), which were used in washing compositions. 

Heterocyclically substituted acetic acids (e g., benzothiazolyl-, benzimidazo-lyl- [34], and pyrimidylacetic acids [35]) are also suitable as coupling components for preparing cationic hydrazone dyes. In these compounds the methyl group in the 2-position is additionally activated. The carboxyl group is split off after coupling and the azo base is methylated. 

Affinity separations include both group-specific and product-specific classes of interactions. Protein A has been extensively employed as a group-specific ligand to purify monoclonal antibodies, but its specificity is insufficient for some materials. For example, if a monoclonal is harvested in media containing 5% fetal bovine serum, the polyclonal bovine antibodies are not differentiated by a linear gradient on a protein A column but completely separated using step elution on a preparative cation exchanger column (ABx) [147],... 

With difficult samples, for which the peaks cannot be resolved by RP-RP-HPLC, an alternative purification method such as preparative cation-exchange HPLC on a sulphonate derivatized column could be used. 

Singh, M., Fang, J.H., Kazzaz, J., Ugozzoli, M., Chesko, J., Malyala, P., Dhaliwal, R., Wei, R. et al. (2006) A modified process for preparing cationic polylactide-co-glycolide microparticles with adsorbed DNA. International Journal... 

Phosphines and their derivatives are known to be very useful ligands toward transition metals and a variety of complexes with phosphine as a ligand have been prepared for all kinds of transition metals. If one of the substituents on a coordinating tertiary phosphorus compound is abstracted as an anion, it would form a cationic phosphenium complex. Actually this strategy has been widely used, and halide, hydride, and alkoxide have been abstracted as an anion by an appropriate Lewis acid. An alternative method to prepare cationic phosphenium complexes is a direct reaction of a phosphenium cation with a transition metal complex having appropriate... 

Alkoxide anion abstraction by a Lewis acid from phosphorus ligand on a transition metal is one of the most useful methods to prepare cationic phosphenium complexes. It has been reported that OR anion abstraction from an alkoxyalkyl ligand, C(OR)R2, on a transition metal complex leads to the formation of a cationic carbene complex.39-42 It is similarly expected that OR anion abstraction from an alkoxysilyl ligand, Si(OR)R2, would cause the formation of a cationic silylene complex. Therefore, increased attention has been focused on the reaction with a Lewis acid of transition metal complexes bearing both alkoxyalkyl and phosphite ligands and of complexes bearing both alkoxysilyl and phosphite ligands. 

Bazan [1] prepared cationic conjugated flexible block copolymer derivatives, (IV), containing alkyl substituents along the main chain that disrupted extended-rod stmcture formation. These were then used in optoelectronic devices and biosensors. 

Since substantial amounts of free trimethylaluminium i.e. Al2Me6) are present in normal MAO preparations, cationic trimethylaluminium adducts Cp 2Zr-( r-Me)2AlMe2, in outer-sphere association with their MeMAO counteranions, are in general the dominant species in MAO-activated catalyst systems [D. E. Babushkin, N. V. Semikolenova, V. A. Zakharov, E. P.Talsi, Macromol. Chem. Phys. 2000, 201, 558]. While being quite stable against destructive side reactions MAO-activated catalyst systems are thus often less active than those obtained with the cationization reagents described above. 

Cationic polymerizations are not only important commercial processes, but, in some cases, are attractive laboratory techniques for preparing well-defined polymers and copolymers. Polyacetal, poly(tetramethyl-ene glycol), poly(e-caprolactam), polyaziridine, polysiloxanes, as well as butyl rubber, poly(N-vinyl carbazol), polyindenes, and poly(vinyl ether)s are synthesized commercially by cationic polymerizations. Some of these important polymers can only be prepared cationically. Living cationic polymerizations recently have been developed in which polymers with controlled molecular weights and narrow polydispersity can be prepared. 

Because the transition state of electrophilic addition is rather open or only very weakly bridged, the stereoselectivity is poor, resulting in primarily atactic polymers. Polystyrene and most poly(vinyl ether)s prepared cationically at ambient temperature are atactic with similar proportions of meso and racemic dyads [243,244]. However, meso addition is slightly preferred with vinyl ethers, and varies from 60 to 70% for most monomers, including isobutyl, neopentyl, n-butyl, and ethoxyethyl vinyl ethers [245]. It is higher with benzyl vinyl ether (89%). This tendency to... 

Because the microstructure of polymers prepared cationically have only been controlled to a limited extent using various counteranions and nucleophiles, this may be one of the most challenging areas of future research. 

Reaction of bromopentafluorobenzene (20) with butyllithium leads to the biphenyl 22 via per-fluorobenzyne (21). This dimerization can be conducted to give a 91 % yield and the bro-mononafluorobiphenyl 22 obtained can be converted to tris(2.2, 2"-nonafluorobiphciiyl)-borane, which is used in preparing cationic complexes of metallocenes. ... 

Le Caer S, Heninger M, Lemaire J, Boissel P, Maitre P, Mestdagh H. (2004) Structural characterization of selectively prepared cationic iron complexes bearing monodentate and bidentate ether ligands using infrared photodissociation spectroscopy. Chem Phys Lett 273-279. 

The abstraction of hydride ion from R3SnH by Ph3C+ has been used as one approach for preparing cations R3Sn+ (Section 7-2)74 76... 

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