Quaternary ammonium-based cationic

The most extensively studied of the quaternary ammonium-based cationic surfactants (QACs) is the hydrogenated tallow dimethyl... 

Using this approach Jang and coworkers166 have reported the synthesis of PPy nanoparticles at the 2 nm scale. Typical surfactants used in the preparation of these sub-5-nm particles were quaternary ammonium-based cations such as octyltrimeth-ylammonium bromide or decyltrimethylammonium bromide. Reactions at room temperature produced nanoparticles with diameters on the order of 10 nm, whereas at 70°C ca. 50 nm diameter particles were observed. 

By coupling aminobenzothiazoles to the quaternary ammonium bases, red cationic dyes (e.g., 10) are obtained [32],... 

FIGURE 21.3 Structures of some representative cationic surfactants. The vast majority of cationic surfactants are based on the nitrogen atom carrying the cationic charge. Both amine and quaternary ammonium-based products are common (from Ref. 10). 

A cation exchange membrane was developed to overcome these disadvantages. This membrane allows continuous regeneration and consists of a sulfonated polyethylene derivative. It is resistant to water-miscible organic solvents and exhibits a high permeability for quaternary ammonium bases such as tetrabutylammonium hydroxide. Hence, the suppression mechanism differs substantially from the process for anion exchange chromatography described in Section 3.3.3. 

Commonly used templates or SDAs in the synthesis of inorganic microporous compounds are metal cations, organic amines, organic quaternary ammonium base, fluorine ion, metal complex, etc. Their roles in the creation of pores will be individually discussed below. 

It was considered previously that the most effective phase transfer catalysts are quaternary ammonimn bases. However, preliminary experiments with crown-ethers had already shown that these compounds are more powerful phase transfer catalysts than quaternary ammonium bases and are more selective [106, 177]. This is explained by differences in the mechanism of catalytic action. The mechanisms of reaction acceleration in two-phase systems with crown-ethers are as yet little studied, but simple examination of salt extraction with crown-ethers shows that the salt in the aqueous phase G>oth anion and cation) passes into the organic layer, whereas only anions paired with the onium cation pass from the aqueous into the organic phase during extraction with onium salts. This considerable difference in the mechanism of action of the two groups of ion-carrying catalysts is the basis for the prospective use of crown-ethers and their analogs instead of quaternary ammonium bases in many fields. 

It is possible that with a quaternary ammonium base and in the absence of metal cations, aluminosilicate anions may remain in solution, for example, (HO)aSiOAl(OH)20Si(OH)3 . Flanigen (69b) reported that quaternary ammonium silicate and aluminale remained in solution until a sodium salt was added. 

There are nonconjugated (including tetraalkyl and cycloalkyl ammonium) and conjugated (including pyridinium, guanidinium, and imidazohum) types of quaternary nitrogen-based cationic functional groups (Table 6.1). 

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