Covalent cationization

Optimizing the covalent cationization method for the mass spectrometry of polyolefins. Macromolecules, 35, 7149-7155. 

Byrd, H.C.M., Bencherif, S.A., Bauer, B.J., Beers, K.L., Brun, Y., Lin-Gibson, S., and Sari, N. (2005) Examination of the covalent cationization method using narrow polydisperse polystyrene. Macromolecules, 38,1564-1572. 

Recently, N-methyliraidazole-mediated KR of racemic secondary alcohols during the transfer of a chiral acyl moiety was developed [41]. This resolution process proceeds via chiral acyl imidazolium chlorides 11 with very good selectivity. The discriminating ability between the enantiomers of alcohols was observed only with the N-methylimidazole derivative and not with the parent acid chloride acyl donor. Various acyl imidazolium chlorides were reacted with racemic alcohols to produce the enantiomerically enriched esters and alcohols. Strong non-covalent cation-Ji interactions in a specific conformation of an intermediate cation-)i complex (parallel stacking) provide high selectivity as shown in 12. 

A very powerful but time-consuming sample preparation is the covalent cationization method. The polymer is dissolved in toluene at 110°C and it is reacted with bromine. The brominated polymer is then dissolved in xylene and reacted with triphenyl phosphine (TPP). Scheme 45.2 reports the structure of the reaction products. Eventually, all chains contain the same end group. 

Covalent cationization was used [48] to facilitate the analysis of SRM2885, a poly(ethylene) sample distrib-... 

FIGURE 45.7 MALDI spectrum of PE SRM 2885, a polyethylene standard, using the covalent cationization sample preparation method. Reproduced from Bauer et al. [48], copyright 2001 with permission. 

Bauer, B.I, Wallace, W.E., Fanconi, B.M., Guttman, C M. (2001) Covalent cationization method for the analysis of polyethylene by mass spectrometry. Polymer, 42,9949-9953. 

The volume contribution by the metallic 5f-5f and the covalent cation 5f-N2p bonds to a virial-theorem formulation of the equations of state of a series of light actinide nitrides was calculated in the self-consistent linear muffin tin orbital (LMTO), relativistic LMTO, and spin-polarized LMTO approximations [46]. The results for ThN give the same lattice spacing in all three approximations higher by ca. 3% than the experimental value, which discrepancy is attributed to the assumed frozen core ions [47]. 

Obviously sufficient energy is available to break the A1—Cl covalent bonds and to remove three electrons from the aluminium atom. Most of this energy comes from the very high hydration enthalpy of the AP (g) ion (p. 78). Indeed it is the very high hydration energy of the highly charged cation which is responsible for the reaction of other essentially covalent chlorides with water (for example. SnCl ). 

Table 14.2 shows that all three elements have remarkably low melting points and boiling points—an indication of the weak metallic bonding, especially notable in mercury. The low heat of atomisation of the latter element compensates to some extent its higher ionisation energies, so that, in practice, all the elements of this group can form cations in aqueous solution or in hydrated salts anhydrous mercuryfll) compounds are generally covalent. 

The rearranging entity has been shown to be the bivalent cation the adjacent charges may so weaken the N—N link that charges of nearly integral size may be built up in the 4 and 4 positions. In the bent, but strainless, cation the minimum separation of the two p-positions would suffice for the establishment of a lai ely electrostatic bond, which could pass smoothly into the covalent rearrangement product (benzidine). 

The biochemical basis for the toxicity of mercury and mercury compounds results from its ability to form covalent bonds readily with sulfur. Prior to reaction with sulfur, however, the mercury must be metabolized to the divalent cation. When the sulfur is in the form of a sulfhydryl (— SH) group, divalent mercury replaces the hydrogen atom to form mercaptides, X—Hg— SR and Hg(SR)2, where X is an electronegative radical and R is protein (36). Sulfhydryl compounds are called mercaptans because of their ability to capture mercury. Even in low concentrations divalent mercury is capable of inactivating sulfhydryl enzymes and thus causes interference with cellular metaboHsm and function (31—34). Mercury also combines with other ligands of physiological importance such as phosphoryl, carboxyl, amide, and amine groups. It is unclear whether these latter interactions contribute to its toxicity (31,36). 

For continuing polymerization to occur, the ion pair must display reasonable stabiUty. Strongly nucleophilic anions, such as C/ , are not suitable, because the ion pair is unstable with respect to THE and the alkyl haUde. A counterion of relatively low nucleophilicity is required to achieve a controlled and continuing polymerization. Examples of anions of suitably low nucleophilicity are complex ions such as SbE , AsF , PF , SbCf, BE 4, or other anions that can reversibly coUapse to a covalent ester species CF SO, FSO, and CIO . In order to achieve reproducible and predictable results in the cationic polymerization of THE, it is necessary to use pure, dry reagents and dry conditions. High vacuum techniques are required for theoretical studies. Careful work in an inert atmosphere, such as dry nitrogen, is satisfactory for many purposes, including commercial synthesis. 

A reactive dye for ceUulose contains a chemical group that reacts with ionized hydroxyl ions in the ceUulose to form a covalent bond. When alkaH is added to a dyebath containing ceUulose and a reactive dye, ionization of ceUulose and the reaction between dye and fiber is initiated. As this destroys the equihbrium more dye is then absorbed by the fiber in order to re-estabUsh the equUibrium between active dye in the dyebath and fiber phases. At the same time the addition of extra cations, eg, Na+ from using Na2C02 as alkaH, has the same effect as adding extra salt to a direct dye. Thus the addition of alkaH produces a secondary exhaustion. 

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