Alkali metal fluorides catalyst

When potassium fluoride is combined with a variety of quaternary ammonium salts its reaction rate is accelerated and the overall yields of a vanety of halogen displacements are improved [57, p 112ff. Variables like catalyst type and moisture content of the alkali metal fluoride need to be optimized. In addition, the maximum yield is a function of two parallel reactions direct fluorination and catalyst decomposition due to its low thermal stability in the presence of fluoride ion [5,8, 59, 60] One example is trimethylsilyl fluoride, which can be prepared from the chloride by using either 18-crown-6 (Procedure 3, p 192) or Aliquot 336 in wet chlorobenzene, as illustrated in equation 35 [61],... 

The reaction with 4-nitrophenol and pentafluorophenol in the presence of KF-18-crown-6 has been investigated. Pentafluorophenoxide anion was found to be a better leaving group [82JFC(20)439]. Alkali metal fluorides on graphite can act as catalysts for nucleophilic substitution of pentafluor-opyridine [90JFC(46)57]. 

Enantioselective allylations of a-nitro ketones and a-nitro esters with allyl acetates are carried out in the presence of 2 equiv of alkali metal fluorides (KF, RbF, CsF) and 1 mol% palladium catalysts prepared in situ from Pd2(dba)3-CHC13 and chiral phosphine ligands. Moderate enantio-selectivity (ca 50% ee) is reported for allylation of cx-nitroketones (Eq. 5.60). The highest selectivity (80% ee) is observed for allylation of the reaction of tert-butyl ester (Eq. 5.61).93... 

When no catalyst is used or if KF and NaF are present as catalysts, CIF is the main by-product. When the more basic alkali metal fluorides, RbF and CsF, are used, CIF3 is the favored coproduct. The formation of CIF 3 rather than CIF is presumably associated with the more ready formation of C1F2 intermediates with RbF and CsF. Yields of CIF3O from CljO are rather variable and may be affected by the particular alkali fluoride present. Yields of over 40% have been consistently obtained and have reached over 80% using either NaF or CsF. Since NaF does not form an adduct with CIF3O (64), stabilization of the product by complex formation does not seem to influence the CIF3O yields strongly. 

Polyfluoro-/f-sultones 3 isomerize in the presence of nucleophilic catalysts to polyfluorinaied a-fluorosulfonyl acyl fluorides 4.45 47 The nucleophilic catalysts include triethylamine,45 ammonia,48 dioxane,49,50 dibutyl ether,49,50 and alkali metal fluorides.46 The reaction has been carried out thermally and in the presence of liquid hydrogen fluoride.50... 

Recently, a new investigation into nucleophilic displacement reactions using fluoride ion in protic solvents has been reported by Kim et al. [101]. In that study, they showed that sterically hindered protic solvents such as tertiary alcohols, in the absence of any kind of catalyst, actually enhanced the nucleophilicity of an alkali metal fluoride (CsF). This enhanced nucleophilicity dramatically increased the rate of nucleophilic fluorination compared with conventional methods and reduced formation of typical reaction byproducts (Figure 14.11). 

The nucleophilic reactivity of the alkali metal fluorides decreases in the order CsF > RbF > KF > NaF > LiF, because of the increasing lattice energy of the fluorides with decreasing ion radius of the cation (CsF 177.7 kcal mol RbF 186.4 kcal mol KF 194.0 kcal mol NaF 218.4 kcal mol LiF 247.0 kcal mol ) [32]. To avoid this problem, crown ethers or phase-transfer catalysts with large, lipophilic cations are often used to render nucleophilic fluorina-tions more efficient. 

Haloalkenes can be prepared by dehydrohalogenating saturated hydrogen-containing polyhalocarbons using liquid alkali metal acid fluoride and/or alkali metal fluoride compositions [75], HCFC-133a can be converted to CF2=CHC1 using these catalyst systems as shown in eq 21. 

Even though most of the supported ionic liquid catalysts prepared thus far have been based on silica or other oxide supports, a few catalysts have been reported where other support materials have been employed. One example involves a polymer-supported ionic liquid catalyst system prepared by covalent anchoring of an imidazolium compound via a linker chain to a polystyrene support [79]. Using a multi-step synthetic strategy the polymeric support (e.g. Merrifield resin among others) was modified with l-hexyl-3-methylimidazolium cations (Scheme 5.6-4) and investigated for nucleophilic substitution reactions including fluorina-tions with alkali-metal fluorides of haloalkanes and sulfonylalkanes (e.g. mesylates, tosylates and triflates). 

In a solventless process for making 2,6-difluorobenzonitrile, 2,6-di-chlorobenzonitrile is reacted with a substantially anhydrous alkali metal fluoride at about 225°C. A mixture of 2-chloro-6-fluorobenzonitrile, 2,6-difluorobenzonitrile, and unreacted 2,6-dichlorobenzonitrile is produced in this step. The 2,6-difluorohenzonitrile is separated, and the other products are fed hack in the reactor. Crown ethers are used as a catalyst. 

To reduce the reaction time between diisocyanates and dianhydrides, catalysts such as alkali metal methoxides, or alkali metal fluoride can be optionally combined with a quaternary onium salt. ° However, the addition of catalysts are not advised in the productions of yarns that should exhibit good characteristics. ... 

The mechanism of anionic ring-opening polymerization of HFPO with alkali metal fluorides as catalyst was smdied by Kostjuk et al. [46] using F and H ID-NMR, and MALDI-TOF-MS spectroscopy. F NMR resonance assignments were made by comparing the changes in signal intensities for two different MWs and also by inspection of the chemical shifts for the different resonances. 

The Henry reaction is routinely performed in the presence of only catalytic quantities of a base. Several base catalysts including alkali metal hydroxides, carbonates, bicarbonates, alkoxides, calcium and barium hydroxides and magnesium and aluminum ethoxides have been used. Anion-exchange resins and, among organic bases, primary and tertiary amines and ammonium acetate and fluoride have proven to be... 

In general, the use of metal halide catalysts is restricted for the reactions of mono-hydrosilanes. This is mainly due to the fact that disproportionation of poly-hydrosilanes is also promoted by these catalysts112. However, it has recently been shown that some alkali metal salts and trialkylammonium fluorides, such as CsF, KF, HCOOK,... 

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