Tetrapropylammonium ion

Thus in the synthesis of BEA and MFI, tetraethyl- and tetrapropylammonium ions respectively, are most frequently applied as the templates. 

In ZSM-5 zeolite, almost every channel intersection is occupied by a tetrapropylammonium ion. Oppositely, tetrabutylammonium ions occupy preferentially the large cavities in ZSM-11 zeolite, the small cavities being only partially occupied. Their alkyl chains extend in the channel system in order to fill completely the available channel length (11). 

The tetrapropylammonium ion acts as a template and directs the formation of the network of channels around the propyl ligands. Heating in air oxidizes the cation and leaves the zeolite framework intact. 

Derouane et al. (216) studied the influence of pH and the addition of Na+, Cs+, and tetrapropylammonium ion (TPA + ) on 27A1 NMR spectra of sodium silicate/sodium aluminate solutions. At pH <4 only octahedral Al(H20)g+ species were formed and the spectra were not affected by the addition of either cation. At pH7 a very broad resonance was observed at 10-25 ppm, presumably attributable to precipitated six-coordinated polymeric aluminous species. At pH 10.5 a resonance at ca. 80 ppm appeared in the absence of silicate, corresponding to A OH) it broadened on adding TPA+, but narrowed again when Na+ was also added, suggesting that Na + interacts with aluminate species in preference to TP A+. When sodium silicate was added to the solution, a broad line appeared at ca. 55 ppm corresponding... 

We were led to the conclusion that in solution as well, at least at low temperature, there is significant interaction between the cation and the chelate anion, perhaps by way of some sort of ion pairing. Although it showed only about 10% more dissociation and no appreciable difference in its usual spectroscopic properties from the piperidinium salt, the tetrapropylammonium salt of the benzoylacetone chelate did not undergo laser action. A cation effect is shown by the data listed in Table II where the tetrapropylammonium ion shows an adverse effect on the laser behavior of BTFA chelates as well. 

The catalyst for the alkylation is ZSM-5 in the form. This zeolite is prepared using the tetrapropylammonium ion as the template. After the synthesis the template is removed by calcination. Several other zeolites, H-Y, H-MCM-22, and H-Beta are industrially applied for the ethylation and isopropylation of benzene. Also a highly de-aluminated H-mordenite has been reported to be an excellent alkylation catalyst. 

The main difference between the synthesis of MCM-41 mesoporous material and traditional synthesis of zeolite or silica molecular sieve is the use of different templates. An individual organic molecule or metal cation is used for the traditional synthesis of silica microporous molecular sieve. For example, the typical template for ZSM-5 synthesis is tetrapropylammonium ion the crystal is formed through the condensation of silicate species around the template molecule, while for the formation of MCM-41, the typical template is the assembly of large molecules containing one hydrophobic chain with more than 10 carbons. 

Note that C-NMR has also been used to detect the presence of small ZSM-5 particles, which must contain less than 3 or 4 unit cells in thickness, corresponding to a size which is beyond the XRD detection limit (48.49). A change in the interaction occurs between the tetrapropylammonium ions and the ZSM-5 framework during calcination and the doublet splitting of the methyl groups disappears (50.51). The new species formed is described as a relaxed tetrapropylammonium ion occluded in a partially healed ZSM-5 structure (51). 

Although other cations were tried, the tetrapropylammonium ion provided the most easily isolated and crystalline product. The reaction of W(CO)5Br" with C2H4Br2 proceeded virtually quantitatively with formation of W2Br9 " even in the presence of excess dibromoethane. Salts of W2Br9 were not previously reported, although Saillant and Wentworth 21) reported preparation of the W2Cl9 anion. 

SAPO-37 molecular sieve such a material is crystallized at low pH in the presence of two organic agents, tetramethylammonium and tetrapropylammonium ions [23cj. Except for the low-Si/Al members (X, Y, ZSM-3 and CSZ-1/3) having the cubic or a near-cubic symmetry, organic agents need to be used, mostly in combination with Na ions. 

Variants of NaAOT have been prepared and examined by various authors [127, 128]. Two strategies are important replacement of the counterion and that of the chain. The former has been carried out in a variety of systems used in particle synthesis (see Section 2.4.2 and Chapter 5), but generally the question of water solubilization was not addressed directly. Eastoe et al [127], for example, showed that with tetrapropylammonium ion, (C3H7)4N replacing Na in NaAOT, cylindrical instead of droplet micelles can form at a w value of 10 or even less. Incorporation of NH/, however, yielded only spherical micelles. The maximum values of w at 25 C for the above three varieties of AOT were 12.0 for Na (AOT)", 12.0 for (NH4) (AOT) and 22.0 for The value increased perceptibly in case of sodium, but... 

Interestingly, the local environments of the tetrapropylammonimn ion in the Siss precursor and of tetrapropy ammonium in silicalite are slightly different. The Siss environment resembles that of a channel, whereas the tetrapropylammonium ion occupies a channel cross-section in silicalite. The need to reorient the tetrapropylammonium ions when the zeolite crystal is formed may necessitate the intermediate formation of nanoslabs. The dimensions of these nanoslabs depend on the reaction conditions. Their size is typically 4 X 4 X 1.3 nm or 4 x 2 x 1.3 run. The number of 33 cluster rows varies in this example by a factor 2. 

Much higher amounts of organic solvents are required for the elution of tetra-alkylammonium compounds, which are used as reagents in ion-pair chromatography of anions. If the analysis times are kept constant, an amount of 60 mL/ L acetonitrile suffices to elute tetramethylammonium hydroxide at a hexanesulfonic acid concentration of c = 1 mmol/L (Fig. 6-29), 280 mL/L is needed for the elution of tetrapropylammonium ions, and 480 mL/L for the even more... 

Tetrapropylammonium chloride does not react with aqueous NaOH (at room temperature), and the tetrapropylammonium ion remains in solution. 

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