Montmorillonite pyridinium

Similarly, pyridinium ions, C5H5NH+, adopt different orientations in the interlayer space of layer silicates, depending on the layer charge of the substrate, as shown by IR and X-ray diffraction results (25,26). Thus, in montmorillonite, pyridinium ions are arranged with their planes parallel to the silicate layers in vermiculite, the plane and C2 axis of the pyridinium ion are essentially perpendicular to the layers. In the latter case, monodimensional X-ray Fourier analysis confirms the orientation obtained from IR spectra (Fig. 4). 

Figure 4. Variable temperature flowing HP 129Xe NMR MAS spectra of xenon adsorbed in montmorillonite pillared with pyridinium ions. The Xe/N2/He mixture flow rate was 300 cc/min. The sequence of temperature steps progresses from bottom to top. The spectrum at 373K was after drying in a stream of flowing helium for 3 hrs at 373K.

Experimental, calculated and estimated values of Henry s constant Ki (/um) and differential heat of adsorption Qa (kJ/mol) for n-hexane adsorbed on montmorillonite modified by cetyl-pyridinium (1.1 mol/kg) at 393 K... 

Silylation at nitrogen with t-butyldimethylsilyl triflate, generates pyridinium salts which, because of the size of the A -substitutent, react with Grignard reagents exclusively at C-4 montmorillonite-catalysed addition of silyl enol ethers to pyridines has a comparable effect in producing l-trimethylsilyl-l,4-dihydropyridines carrying an acylalkyl substituent at C-4. ... 

Recent desorption studies (63) showed that only 2% of the hyamine and methylene blue were released from montmorillonite by three extractions with O.IM BaCl2. Approximately 20% phosphon and pyridyl pyri-dinium chloride and 80% of the ethyl pyridinium bromide were released when the same extraction was used. 

The preliminary treatment of the nanofiller to make it compatible is carried out with a substance having an affinity for both the montmorillonite and the chosen polymer, e.g., cetyl pyridinium chloride or bromide, hexadecyl trimethylammonium bromide, 7V-[4-(4 -aminophenyl)]phenyl phthalimide, /i-aminobenzoic acid hydrochloride, or a combination of octadecylamine hydrochloride and stearic acid. 

Pyridine is adsorbed not only in the interlayer, but also on the edge or the surface of the clay, bonding with BrHnsted or Lewis acid sites. Thus several kinds of adsorbed species are observed in the absorption spectra of pyridine adsorbed on Cu- and Fe-montmorillonites as shown in Figure 4 with tentative assignments physically adsorbed pyridine, pyridinium ion, pyridine cation, 4,4 -bipyridyl cation and its dimer... 

Relative amounts of the adsorbed species mentioned above depend on the preparation condition of ion-exchanged montmorillonite. On a Fe-mont-morillonite ion-exchanged in acidic solution(pH 3), a large amount of pyridinium ion is observed while the amount of bipyridyl cation formed is scarce,... 

Orientation of organic molecules in the interlayer space by IR spectroscopy Montmorillonite and vermiculite/pyridine and pyridinium Serratosa (25,26)... 

Protonated nitrogenated heterocycles Pyridinium/montmorillonite and vermicuUte chlorobenzene on pyridinium/montmoriUonite Serratosa (26,30)... 

Clay complexes with organic cations may absorb neutral organic molecules in the interlayer space. This process is accompanied by a separation of the silicate layers and, generally, with a change of orientation of the organic cation. Thus, adsorption of benzene or chlorobenzene in pyridinium-montmorillonite changes the disposition of the pyridinium ion from parallel to normal to the silicate layers, and an increase of from 1.25 to 1.50 nm is observed. IR studies of the dichroism of specific IR absorption bands show that the pyridinium cations have their N—H groups directed to the layer surface (C2 axis perpendicular to the layers). For chlorobenzene, the molecules also adopt a perpendicular orientation but with the C—Cl bond axis (C2 axis) parallel to the layers (30). 

Figure 1.17 Thermal degradation behavior of nanocomposites containing (a) quinohnium- and (b) pyridinium-modified montmorillonites in different amounts. Reproduced from [41] with permission from Elsevier.

The adsorption properties of pillared clays can be improved by pre-adsorbing surfactants. Polyhydroxoaluminum montmorillonite covered with hexadecyl pyridinium ions is a better adsorbent for pollutants in industrial waste waters than hexadecyl pyridinium (HDPy) montmorillonite [108]. For benzopyrene is increased from 48000 ml/g (HDPy montmorillonite) to 95 800 ml/g (HDPy polyhydroxoaluminum montmorillonite) and for... 

FIGURE 7 IR spectra of pyridine chemisorption on synthetic mica-montmorillonite showing the transformation of pyridine to pyridinium ion by interaction with water. L, B = Lewis and Bronsted acid sites (63). (Reproduced with permission from the Mineralogi-cal Society of Great Britain and Ireland.)... 

On treatment with a non-enolizable aldehyde and sodium hydride, rruns-related a-hydroxyepoxides were converted to acetals. The reaction is thought to proceed by way of a hemiacetal salt, as illustrated in Scheme 2. L-Galactono-1,4-lactone, a by-product of the sugar industry, furnished a diastereomeric mixture of 5,6-alkylidene acetals 18 in >60% yield on microwave irradiation in the presence of long-chain aldehydes and montmorillonite KSF as catalyst, and 4,6-O-alkylidene derivatives 19 of D-glucose have been prepared by use of long-chain aldehydes and catalytic pyridinium />-toluenesulfonate in benzene under azeotropic removal of water. Compounds 18 and 19 were of interest in liquid crystal studies. 

Protocols have been developed which utilize an insoluble solid catalyst in combination with dihydropyran to effect the protection of alcohols as their corresponding THP ethers. These procedures are advantageous in that the catalyst may be recovered by simple filtration and the products isolated by evaporation of volatiles. In many cases the catalyst can be reused without regeneration. Reaction of alcohols with dihydropyran in the presence of Amberlyst H-15 (25 °C, 1 h, 90-98%) yields THP derivatives. Alternatively, a solution of dihydropyran and the alcohol may be passed slowly through a column of silica overlaid with Amberlyst H-15 to yield the THP ethers directly (73-97%). The acidic clay Montmorillonite KIO (25 °C, 15-30 min, 63-95%) is similarly applicable, Reillex 425 resin (86 °C, 1,5 h, 84-98%) is applicable with the advantage that it does not promote the sometimes troublesome polymerization of dihydropyran. Polymeric derivatives of pyridinium p-toluenesulfonate are also effective. Poly(4-vinylpyridinium p-toluenesulfonate) and poly(2-vinylpyridinium p-toluenesulfonate) catalysts yield tetrahydropyranyl derivatives of primary, secondary, and tertiary alcohols (24 °C, 3-8 h, 72-95%). ... 

Because of the poor thermal stability of alkyl ammonium modifiers, various other cationic surfactants have recently been proposed for clay modification. In this work, we prepared hexadecyl pyridinium (CiePy), dioctadecyl imidazolium (2Ci8lm), and tributyl hexadecyl phosphonium (3C4C16P) modified montmorillonites (MMT). The chemical structures of the corresponding intercalants are illustrated in Table 1. The properties of the organoclays obtained will be compared to those of Cloisite 20A, a commercial clay modified with a dimethyl... 

Montmorillonites modified with alkyl pyridinium, imidazolium and phosphonium intercalants were successfully synthesized. Compared to commercial Cloisite 20A, enhancements in thermal stability of +31°C to +70°C were observed in inert atmosphere. The products evolved upon thermal decomposition of the various organoclays were analyzed by mass spectroscopy. Preliminary results indicate that the major part of the volatile by-products is constituted by alkenes and alkanes. Chloromethane was detected between 200°C and 280°C in unpurified Cloisite 20A. CiePy-MMT was found to liberate pyridine above 220°C. Such informations can be of considerable interest regarding the processing conditions of polymer nanocomposites and their subsequent applications. 

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