Anionic silanes

The products thereby obtained are anionic silane surfactants exhibiting excellent surfactant properties dependent on the ammonium counter ion. Some specimen are real foam boosters, too. For example an 1 wt. % aqueous solution of isopropylammonium sulfatohexyl trimetyl silane shows a surface tension of 21 mN m and a spreading ability of 65 mm. As being familiar for the nonionics the aqueous solution of... 

Hydrolytic condensation of an equimolar mixture of cationic and anionic silanes (ODMACl and TANED) yields zwitterionic copolymer colloids with two-dimensional hexagonal packing. Interaction of the ODMACl quaternary ammonium groups with the three carboxy groups of TANED leads to replacement of sodium and chloride ions and formation of gegenions, resulting in a molar ratio ODMACl TANED = 3 1 (each TANED molecule contains three... 

The direction of electroosmotic flow and, therefore, the order of elution in CZE can be reversed. This is accomplished by adding an alkylammonium salt to the buffer solution. As shown in Figure 12.45, the positively charged end of the alkylammonium ion binds to the negatively charged silanate ions on the capillary s walls. The alkylammonium ion s tail is hydrophobic and associates with the tail of another alkylammonium ion. The result is a layer of positive charges to which anions in the buffer solution are attracted. The migration of these solvated anions toward... 

The most common catalysts in order of decreasing reactivity are haUdes of aluminum, boron, zinc, and kon (76). Alkali metals and thek alcoholates, amines, nitriles, and tetraalkylureas have been used (77—80). The largest commercial processes use a resin—catalyst system (81). Trichlorosilane refluxes in a bed of anion-exchange resin containing tertiary amino or quaternary ammonium groups. Contact time can be used to control disproportionation to dichlorosilane, monochlorosilane, or silane. 

Ion Removal and Metal Oxide Electrodes. The ethylenediamine ( )-functional silane, shown in Table 3 (No. 5), has been studied extensively as a sdylating agent on siUca gel to preconcentrate polyvalent anions and cations from dilute aqueous solutions (26,27). Numerous other chelate-functional silanes have been immobilized on siUca gel, controUed-pore glass, and fiber glass for removal of metal ions from solution (28,29). 

If R1 differs from R2. the preparation may lead to both regioisomers. In these cases, a synthetic route which does not rely on allyl anion substitution is often the most advantageous one. Thus, the best results are recorded for allylboronates and -silanes which also possess the required constitutional and configurational stability. 

A similar elimination in which the tin is attacked by fluoride anions (cf. the reaction of silanes with F ) has been used179 to synthesize terminal methylene compounds as in equation (75). An analogous reaction sequence using a trimethylsilyl group in place of the trialkyltin group has been published by Hsiao and Shechter180 as part of a synthesis of substituted 1,3-butadienes. 

Recent work has shown that there are many assumptions required in order to use the silane-cleavage method. However, an advantage of this approach is that it can be nsed to determine acidities at regiospecific positions in very weak acids, including those for which the conjugate base anion is unstable with respect to electron detachment. 

This technique is especially useful for the preparation of a-lithio ethers, sulfides, and silanes.36 The lithium radical anions of naphthalene, 4, 4/-di-f-butyldiphenyl (DTBB) or dimethylaminonaphthalene (LDMAN) are used as the reducing agent. 

There are also some reactions of allylic silanes that proceed through anionic silicate species. These reactions usually involve activation by fluoride and result in transfer of an allylic anion. 

While trifluoro and other halosilanes function by increased electrophilicity at silicon, nucleophilic reactivity of allylic silanes can be enhanced by formation of anionic adducts (silicates). Reaction of allylic silanes with aldehydes and ketones can... 

As with the silanes, the most useful synthetic procedures involve electrophilic attack on alkenyl and allylic stannanes. The stannanes are considerably more reactive than the corresponding silanes because there is more anionic character on carbon in the C-Sn bond and it is a weaker bond.156 The most useful reactions in terms of syntheses involve the Lewis acid-catalyzed addition of allylic stannanes to aldehydes.157 The reaction occurs with allylic transposition. 

Fluoromethyl)phosphonate ester anions react with CO2 or COS to yield esters of the type (161 Y=0 or S) which may be dealkylated to the free acid through the use of bromotrimethyl-silane, but the course of the reaction with CS2 depends on the individual ester thus, (162) yields (163), but (165) is formed from (164). 22... 

All of the reactions described above use anionic alkyl metal complexes as stoichiometric reductants. Cationic zirconium catalyst 58 was shown to re-ductively cyclize a variety of 1,5-dienes to give both mono- and bicyclic silane products when H3SiPh was employed as the stoichiometric reductant (Scheme 10) [32]. Poor yields due to competing polymerization processes were observed when less substituted dienes were employed. It is likely that... 

The radical anions 1, anti-2, anti,anti-3, and anti,anti,anti-4 were generated by the reduction of the corresponding ladder polysilanes with potassium (Scheme 8). When the ladder poly silanes were treated with potassium in tetrahydrofuran (THF) at ca. — 70 °C, the solutions were immediately colored 1, purple anti-2, brown anti,anti-3, blue and anti,anti,anti-4, black. In the UV-visible-NIR spectra, several absorption bands appeared (Fig. 15). The intense absorption of anti,anti-3 and anti,anti,anti-4 in the near-infrared region is noted because it has been... 

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