Ionic alkyls

Studying alkylations, we developed a series of selective ionic alkylating agents. Although Meerwein s trialkyloxonium and dialkoxycar-benium salts are widely used as transfer alkylating agents, they lack selectivity and generally are incapable of C-alkylation. 

Adsorption of a surfactant on solids is dependent, among other things, on the structure of both the hydro-phobic and hydrophilic portions of it. There are a number of mechanisms proposed for surfactant adsorption and an understanding of the effects of the structure of the surfactant can help in elucidating the role of these mechanisms. In this study, the effect on adsorption on alumina of some structure variations of sulfonates (chain length and the branching and the presence of ethyoxyl, phenyl, disulfonate and dialkyl groups) is examined above and below CMC as a function of surfactant concentration, pH and salinity. Co-operative action between an ionic alkyl sulfonate and a nonionic ethoxylated alcohol is also studied. 

Blais et al. [12] has described a method using HPLC coupled with AAS for the determination of ionic alkyl lead compounds in soils. They demonstrated that previously published methods gave poor recoveries of lead and the formation of artifacts during the isolation and derivatisation procedures. An alternative procedure is described involving a series of selective extractions... 

Forsyth, D.S. and Iyengar, J.R. (1989) The determination of tetra-alkyl lead and ionic alkyl lead compounds in seafood. Appl. Organomet. Chem., 3, 211-218. 

Van Cleuvenbergen, R., Chakraborti, D. and Adams, F. (1990) Speciation of ionic alkyl-lead in grass and tree leaves. Anal. Chim. Acta, 228, 77-84. 

The Friedel-Crafts reaction is polar (ionic) alkylation or acylation of electron-rich aromatics by alkyl cation or acyl cation species, derived from the reactions of alkyl halides or acyl halides with A1C13. Therefore, electron-rich aromatics such as anisole are very reactive, but electron-deficient aromatics such as pyridine are inert. 

For reversed-phase ion-pair chromatography a non-polar surface (e.g. Cg or C- g) is used as a stationary phase and an ionic alkyl compound is added to the aqueous mobile phase as a modifier. For the separation of acids, an organic base (e.g. tetrabutylammonium phosphate) is added to the eluent for the separation of bases, an organic acid (e.g. octane sulphonate) is used. Reversed-phase ion pairing is presently the most popular approach because of the simpler technical requirements and very high column performance. It is however essential to operate the system only after equilibrium of the mobile phase and the stationary phase has occurred in order to obtain reproducible analyses. 

Obviously, a terminal alkyl on a coordinatively unsaturated, unsolvated metal will have favorable reactivity for steric reasons. Such a system is also likely to be reactive for electronic reasons. The electropositive lanthanide is very electrophilic and the rather ionic alkyl anion is very nucleophilic. The combination of two adjacent sites of high nucleophilicity and high electrophilicity, both with strong tendencies to coordinate/react further, should be exceptionally reactive, even with strong bonds with little dipolar character such as H—H or C—H (see Section VII). 

Triphenylenes provided with nonionic di(ethylene oxide) side-chains (25f)132 134 or with ionic alkyl chains (25g)135 form supramolecular polymers in water.136 The arene—arene interactions of the aromatic cores allow for the formation of columnar micelles . At low concentrations the columns are relatively short, and the solutions are isotropic. At higher concentrations the longer columns interact and lyotropic mesophases are formed.133 Computer simulations showed that in the isotropic solution the polymerization of the discotics is driven by solute-solute attraction and follows the theory of isodesmic linear aggregation the association constants for dimerization, trimerization, and etc., are equal and the DP of the column thus can easily be tuned by concentration and temperature.137 138 At higher concentrations the sizes of the columns are influenced by their neighbors, the columns align, and the DP rises rapidly. 

Methylsodium (NaMe) is believed, on the basis of an X-ray study of the powder, to have a tetrameric structure like that of (LiMe)4. The more electropositive alkali metals form essentially ionic alkyls M (C H2 +i) in which the carbanionic carbon atoms are presumed to be pyramidally coordinated, like the nitrogen atoms of isoelectronic neutral amines NC iH2 +i. 5... 

If instead the R group contains unsaturation a, 0 to the carbon-metal bond, the lability of the bond is increased. With the possible exception of ionic alkyls (already ionized) the allyl and benzyl derivatives of a given metal show the greater reactivity. The sensitivity of tetrabenzyllead and of tribenzylbismuth (4) to oxidation exemplifies this increased reactivity. One can rationalize this enhanced reactivity by the ease of cleaving the bond ... 

Like sodium, potassium forms a number of ionic alkyl- and aryl- derivatives of the type RK. 

Prior to their separation by GC, organolead compounds need to be extracted from the sample matrix and, if necessary, derivatized into a volatile and thermally stable form. Volatile nonpolar tetraalkyl compounds can be extracted from environmental samples with nonpolar solvents such as benzene or hexane and injected directly onto the gas chromatograph. The case of nonvolatile, ionic alkyl compounds (R2Pb and RsPb ) is more complex. They should first be extracted and preconcentrated in the presence of NaCl and sodium diethyldithiocarbamate and then derivatized into a volatile form. The most widespread derivatization methods are of two distinct types those based on the use of tetraalkylborates that can be directly performed in the aqueous solution (ethylation and propylation) and those applying... 

The derivatization of alkyl polyglycosides is currently being pursued with great commitment [15,24,119,120]. A broad range of alkyl polyglycoside derivatives can be obtained by using relatively simple methods, such as nucleophilic substitution. Besides the reaction to esters or ethoxylates, ionic alkyl polyglycoside derivatives, such as sulfates and phosphates, can also be synthesized (Fig. 41). 

Figure 9.3(a) shows the mode of adsorption of an ionic surfactant at a hydrophilic surface, with its polar head groups close to the surface and non-polar chains pointing out into the aqueous phase. As one proceeds down the diagram, the bulk solution concentration of the surfactant is being increased until bilayers are formed by hydro-phobic associations of the alkyl chains of the surfactant, rendering the surface hydrophilic, (b) shows the possible mode of association of non-ionic alkyl polyoxyethylene ethers at a hydrophilic silica surface at a concentration where bilayers are forming. From Rupprecht [6] with permission. 

In media of low dielectric constant, electrostatic stabilization is of little importance. Colloidal dispersions in non-aqueous media are thus more likely to be stabilized by steric barriers formed by adsorbed surfactants and polymers. Relatively little work has been done on the adsorption of surfactants on to solids from non-aqueous solvents, a limiting factor of course being the insolubility of many surfactants in solvents other than water. Non-ionic surfactants tend to be soluble in both aqueous and non-polar solvent systems. Rupprecht [6] has made a series of investigations of adsorption of non-ionic alkyl polyethers on to silica in various organic solvents. Fig. 9.20 shows some of the adsorption isotherms for nonylphenol Eg. 5 from dichloromethane, n-butanol, n-propanol, ethanol, 1,4-dioxan and DMSO. As might be expected, adsorption is greatest from the dichloromethane and the effect of increasing polarity is clearly seen with the three alcohols. 

Birnie, S. E., Hodges, D. J., Determination of Ionic Alkyl Lead Species in Marine Fauna, Environ. Technol. Letters 2 [1981] 433/42. 

The preparation and reactivity of various ionic alkyl and aryl Group 15 complexes have been reported. For example the [(Bu P)3As] anion reacts with [CpMo(CO)3Cl], M = Mo, W, to give [(C5H4 As(PBu )3 )M(CO)3Cl] (X-ray) via the elimination of LiH rather than the expected product resulting from Cl... 

Not isol. Grignard reagent. Commercially available as 2M soln. in Et20. Used for derivatization of ionic alkyl lead compounds in gc analysis. 

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