Protonated from molecular sieve

Using different DFT functionals and basis sets (Focsan et al. 2008, Lawrence et al. 2008) it was confirmed that the isotropic ()-methyl proton hyperfine couplings do not exceed 9MHz for the carotenoid radical cation, Car-. DFT calculations of neutral carotenoid radicals, Car formed by proton loss (indicated by ) from the radical cation, predicted isotropic P-methyl proton couplings up to 16 MHz, a fact that explained the large isotropic couplings observed by ENDOR measurements for methyl protons in UV irradiated carotenoids supported on silica gel, Nafion films, silica-alumina matrices, or incorporated in molecular sieves (Piekara-Sady et al. 1991, 1995, Wu et al. 

Considering all we know up to now, the specific properties of zeolites can be summarized as follows. Zeolites are aluminosilicates with defined microporous channels or cages. They have excellent ion-exchange properties and can thus be used as water softeners and to remove heavy metal cations from solutions. Furthermore, zeolites have molecular sieve properties, making them very useful for gas separation and adsorption processes, e.g., they can be used as desiccants or for separation of product gas streams in chemical processes. Protonated zeolites are efficient solid-state acids, which are used in catalysis and metal-impregnated zeolites are useful catalysts as well. 

The shape-selectivity of ZSM-5 is particularly remarkable. Active centres at the inner walls of the catalyst readily release protons to organic reactant molecules forming carbonium ions, which in turn, through loss of water and a succession of C—C forming steps, yield a mixture of hydrocarbons that is similar to gasoline. The feedstock can be methanol, ethanol, corn oil or jojoba oil. The shape-selectivity of this catalyst is particularly striking, as can be seen from the product distribution obtained for the dehydration of three different alcohols (Table 8.2). The product distribution can be understood in terms of the intermediate pore size of ZSM-5, which can accommodate linear alkanes and isoalkanes as well as monocyclic aromatic hydrocarbons smaller than 1, 3, 5-trimethyl benzene. In Table 8.3, we list some of the recent innovations in catalysis, to highlight the important place occupied by molecular-sieve catalysts. 

NA-Dimethylhydrazone 68, furnished from keto-acid 33 upon treatment with WV-dimethylhydrazine, was found to be extremely water sensitive. Attempts to form the hydrazone were thwarted by low yields under a number of conditions in which solvents were present. Azeotropic removal of water, with or without molecular sieves, was also unsatisfactory. Eventually, it was found most convenient to simply dissolve the keto-acid in neat dimethylhydrazine without desiccant. After heating for a number of hours, followed by cooling and removal of excess dimethylhydrazine, formation of the desired hydrazone was apparent by NMR due to loss of the methyl ketone resonance at 5 2.14. This initially formed hydrazone existed as a dimethylhydrazonium carboxylate, but it was found that reversion to free carboxylic acid 68 occurred in vacuo, as evidenced by the proton NMR run in dry CDClj. 

The evidence suggests that 2-propanamine interacts with the protons associated with the framework Fe atoms to form 2-propyl ammonium cations which maintain 2-propanamine in the zeolite to high temperatures. Above approximately 600K, the decomposition rate for these cations to form propene and ammonia becomes appreciable. The decomposition reaction is very similar to the Hofmann elimination reaction found for quaternary ammonium salts and provides indirect evidence that ammonium ions are involved in the reaction. When Fe is removed from the framework of the molecular sieve, the associated proton site is lost, along with the capability for forming the ammonium ion and carrying out the reaction at that site. 

Zeolites are aluminosilicates with a microporous network of channels and cavities. The dimensions of such channels and cavities are in the range 3-14 A, which enables diffusion of reactants and products to and from catalytically active sites. Acid sites can be introduced by compensating the negative lattiee charge with protons. Many zeolite molecular sieves with different pore dimensions, topologies, and acidities have been prepared [47]. 

SAPO-37 molecular sieve which has the crystalline structure of faujasite differs from this zeolite by the presence of phosphorus in the structure (1). It was shown that this element increases the thermal and hydrothermal stability of the structure (2). With regards to acidity, the SAPO-37 materials have acidic properties (1,3,4) with two OH groups very similar to those of faujasites (1,4). It was also observed that the SAPO-37 materials have besides acid centers of medium strength a small number of protonic sites stronger than in HY or even than those of an ultrastable LZY-82 (4). 

For structuring, the IL has to be immobilised. This can be done using i.e. zeolitic structures or molecular sieves. It is obvious that with increasing surface area of the solid phase, the motion of the liquid and the proton transport will be hindered. From polymerisation experiments it is known that the stiffening of polymers by cross-linking can be compared with the polymer-surface interaction. Electrode surfaces and solids such as silica, carbon black or cathode powder also stiffen the polymer [52]. This can be explained by different transport properties at the interfaces. As a consequence it must be expected that at the surface of the added particles the ionic liquid will behave in a different way than in the immobilised liquid phase. 

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