Fluorinated catalyst

Fluorides. Tantalum pentafluoride [7783-71-3] TaF, (mp = 96.8° C, bp = 229.5° C) is used in petrochemistry as an isomerization and alkalation catalyst. In addition, the fluoride can be utilized as a fluorination catalyst for the production of fluorinated hydrocarbons. The pentafluoride is produced by the direct fluorination of tantalum metal or by reacting anhydrous hydrogen fluoride with the corresponding pentoxide or oxychloride in the presence of a suitable dehydrating agent (71). The ability of TaF to act as a fluoride ion acceptor in anhydrous HF has been used in the preparation of salts of the AsH, H S, and PH ions (72). The oxyfluorides TaOF [20263-47-2] and Ta02F [13597-27-8] do not find any industrial appHcation. 

Rearrangement of fluorine with concomitant ring opening takes place in fluorinated epoxides Hexafluoroacetone can be prepared easily from perfluo-ropropylene oxide by isomerization with a fluorinated catalyst like alumina pre treated with hydrogen fluoride [26, 27, 28] In ring-opening reactions of epoxides, the distribution of products, ketone versus acyl fluoride, depends on the catalyst [29] (equation 7) When cesium, potassium, or silver fluoride are used as catalysts, dimenc products also are formed [29]... 

Two Ni-Cr catalysts containing one 5 % nickd atomic and the other 10 % were tested for fluorination and dehydrofluorination reactions of CF3CH2CI. The results were compared to those obtained with chromium oxide alone. These reactions are performed only with the non fluorinated catalysts (table 2). 

The acid fluoride may decompose explosively in contact with fluorinated catalysts. See other acyl halides... 

The same catalysts have been investigated for the asymmetric oxidation of dialkyl sulfides using PhIO as the oxidant in CH3CN perfluorooctane.[54] Although the conversions (>80%) and selectivities to sulfoxides (>90%) were generally good, and the more heavily fluorinated catalysts could be recycled 4 times with only small drops... 

The fluorous silica concept involves the selective partitioning of a fluorous-modified catalyst between an organic liquid phase and the fluorinated surface phase. In the absence of CO2, the fluorinated catalyst prefers the fluorous surface phase and remains partitioned onto the silica. When CO2 pressure is added, the catalyst will partition off of the silica and into the GXL phase (containing reactants), where homogeneous reaction can take place. After the reaction is completed, the CO2 is removed and the catalyst will partition back onto the fluorous silica surface, which can be easily recovered by filtration. A cartoon schematic is shown as Figure 2. 

H2 and then CO2 pressure were applied, forming a GXL. The fluorinated catalyst then partitioned off of the fluorinated silica support and into the CO2-expanded organic phase. The reaction was assumed to occur in the expanded liquid phase in which reactants (styrene, hydrogen) and catalyst (fluorinated Wilkinson s catalyst) are homogeneously present. After the reaction was completed, the pressure was released and the catalyst then partitioned back onto the silica surface. 

The recyclability of the fluorinated catalyst was investigated. Five consecutive runs were carried out successfully with the same initial fluorinated catalyst/silica. The styrene hydrogenation activity proved to be relatively consistent (TOF from 250-400 h ) for each of the five runs, indicating minimal loss of catalytic activity. 

Each of the fluorinated catalysts has an optimum temperature-range for stereoselective polymerization. At the lower temperatures, the rate of propagation and yield of polymer decrease dramatically. At higher temperatures, the molecular weight of the polymer produced becomes lower, presumably because chain transfer or termination processes increase in importance. At still higher temperatures, the stereoregulation is lost, and the low-d.p. polymer produced has a mixed, anomeric configuration. 

Table 9). At a molar ratio of Al Ti = 300, the polymerizatiort activity of the fluorinated catalyst Cp TiFa was found to be about 50 times higher than that of the chlorinated system Cp TiCla. The higher activities of the... 

The fluorinated catalyst is always much more active in styrene polymerization than the corresponding chlorinated analogue and... 

The fluorinated catalysts show higher thermal stability than the corresponding chlorinated catalysts up to polymerization temperatures of 70 °C. 

Fluorous biphasic catalysis exploits not only this principle, but also the ability of certain perfluo-rocarbon/hydrocarbon biphasic mixtures to form a homogenous solution at high temperatures. An extremely fluorinated catalyst can thus be applied under homogeneous conditions and recovered from the fluorous phase subsequent to a phase separation step at lower temperatures. 

Bankhead, M. (1999) Theoretical Investigation of Alumina Based Fluorination Catalysts, PhD thesis. University of Liverpool. 

Finally, it has been shown that some fluorinated catalysts, though not particularly effective in high molecular mass polymerization, are instead excellent catalysts for the synthesis of allyl-terminated sPP oligomers (Mn 3000-4000). These new short sPP polymers with functionalized chain end could be used to make LCB polymers as well as other new polymeric materials with sPP segments.258... 

These fluorinated catalysts were also employed in the functionalization of the first members of the series of alkanes, from methane to butane. To that end, the reaction was carried out in supercritical carbon dioxide, mixed with the alkane, in a fluid mixture that also dissolved the catalyst and EDA (Scheme 14). In this manner, a significant amount of methane (and the other alkanes) was available to react with the in situ generated metallocarbene intermediate, with no other C—H bond in the reaction mixture. Methane has been converted into ethyl propionate with turnover numbers up to 750 at 40 °C, and a total pressure of 250 atm. 

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