Role of the onium ion in the heterophase alkylation of ethyl 2-methylacetoacetate in the presence of solid alkali metal fluorides

Qnium salts are efficient catalysts for the alkylation of ethyl 2-methylacetoacetate (EMAA) in the presence of solid KF. The reaction rate depends on the nature of the anion and increases in going from onium chlorides to onium bromides and iodides. Inhibition of this reaction by a phase transfer catalyst QX was found. The alkylation rate depends on the amount of solid fluoride. The optimal KF/EMAA ratio is 8. A further increase in this ratio hinders the alkylation reaction. The major functions of the catalyst were found to be weakening of the K-F bond, binding of the leaving halide, activation of the alkyl halide, and generation of the solid phase surface.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2697–2701, December, 1989.     

Mechanochemical reactions of fluorides with hemin

Hemin has two potential sites to react with fluorides, the peripheral acid groups and the central Fe^III cation. The mechanochemical reactions of hemin with fluorides (LiF, NaF, KF, CsF, NH₄F and AgF) were monitored using X-ray diffraction (XRD), and IR and Mössbauer spectroscopies. LiF and NaF were found inert when milled with hemin, however KF, CsF, NH₄F and AgF react at both hemin sites. At the iron site Cl⁻ is replaced by F⁻ with formation of KCl, CsCl, NH₄Cl, and AgCl, as detected by XRD, while with the peripheral acid groups, fluorides collect the acidic protons to form KHF₂, CsHF₂, NH₄HF and AgHF₂. The reactions of hemin with the reactive fluorides take place first at the iron site and then at the propionic acid groups.     

Zur Chemie des Chlorisocyanates, 4. Mitt.: Über die Reaktion von Chlorisocyanat mit Alkalifluoriden

Zusammenfassung Alkalifluoride (NaF, KF, CsF) katalysieren einerseits die Polymerisation von gasförmigem ClNCO und reagieren andererseits unter Bildung von COF₂. Die Bedingungen für diese Reaktionen sowie das intermediäre Auftreten von FNCO werden erörtert.

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Chemistry of chloro-isocyanate, IV: The reaction of chloroisocyanate with alkali fluorides

The alkali fluorides NaF, KF, and CsF catalyse the polymerization of gaseous CINCO and also react to form COF₂. The conditions leading to these reactions, and the formation of FNCO as an intermediate product are discussed.

     

Reactions of (difluoroamino)trinitromethane with nucleophilic reagents

Reactions of F₂NC(NO₂)₃ with metal fluorides (KF and CsF) in DMF yield a substitution product of the fluorine atom for one nitro group, F₂NC(NO₂)₂F. The reaction of F₂NC(NO₂)₃ with LiBr in ethanol or DMF affords Br(NO₂)C=NF rather than the expected bromo derivative F₂NC(NO₂)₂Br.     

Studies of the reaction of crystalline calcium carbonate with aqueous solutions of NH4F,KF and NaF

The reaction between solid calcium carbonate and the aqueous fluorides NH₄F, KF, and NaF has been completely investigated. The reaction of CaCO₃ (solid) is completely independent of the dimensions of its polycrystalline particles and gives calcium fluoride. The calcium fluoride is formed in the same form and size as the grains of the original calcium carbonate. A course crystalline fluorite is formed at a satisfactory rate and with a sufficiently high mechanical strength to be of industrial interest.The course of the reaction appears to involve penetration of the fluoride solution into the body of a grain through voids which develop in the solid material owing to the formation of polycrystalline CaF₂ with a different molar volume as compared with CaCO₃. Data were obtained on the rate of formation and nature of the fluoride formed.The fluorite which is formed around the dissolving calcite was shown by X-ray diffraction and electron microscopy to have a polycrystalline aggregated structure and an estimate is made of crystallite size.The fluorite grains are pseudomorphs of the calcite crystals and there is crystallographic orientation of the product with respect to the parent phase.     

Influence of the Base on Pd@MIL‐101‐NH2(Cr) as Catalyst for the Suzuki–Miyaura Cross‐Coupling Reaction

The chemical stability of metal–organic frameworks (MOFs) is a major factor preventing their use in industrial processes. Herein, it is shown that judicious choice of the base for the Suzuki–Miyaura cross‐coupling reaction can avoid decomposition of the MOF catalyst Pd@MIL‐101‐NH₂(Cr). Four bases were compared for the reaction: K₂CO₃, KF, Cs₂CO₃ and CsF. The carbonates were the most active and achieved excellent yields in shorter reaction times than the fluorides. However, powder XRD and N₂ sorption measurements showed that the MOF catalyst was degraded when carbonates were used but remained crystalline and porous with the fluorides. XANES measurements revealed that the trimeric chromium cluster of Pd@MIL‐101‐NH₂(Cr) is still present in the degraded MOF. In addition, the different countercations of the base significantly affected the catalytic activity of the material. TEM revealed that after several catalytic runs many of the Pd nanoparticles (NPs) had migrated to the external surface of the MOF particles and formed larger aggregates. The Pd NPs were larger after catalysis with caesium bases compared to potassium bases.     

Reaction of carbonyl fluoride with fluorine in the presence of various fluorides as catalysts

The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF₂O + F₂→ CF₃OF. The list of catalysts for this process has now been enlarged to include NaF, MgF₂, CaF₂, SrF₂, BaF₂ and LaF₃. Lithium fluoride and thorium fluoride also give CF₃OF but are less active. Perhaps the substances CsF·HF, KAgF₄ and NiF₂ should be included in this list. Silver fluoride, usually as a mixture of AgF₂ with AgF, has been known to catalyze the reaction of CF₂O with F₂ to give both CF₃OF and CF₃OOCF₃. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF₃OOCF₃ is very high. It has now been shown that TIF₃ behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF₃OOCF₃ than of CF₃OF but require higher temperatures than AgF₂ (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed.     

Fluoride-catalyzed hydroalkoxylation of hexafluoropropene with 2,2,2-trifluoroethanol

Trifluoroethoxylation of hexafluoropropene with 2,2,2-trifluoroethanol (TFE) were conducted using an alkali metal fluoride catalyst to produce CF₃CHFCF₂OCH₂CF₃. KF exhibited the highest yield and selectivity of CF₃CHFCF₂OCH₂CF₃, whereas LiF and NaF were inactive for the trifluoroethoxylation reaction. The same reaction also proceeded well in the presence of RbF or CsF, but yielded large amounts of olefinic and high molecular weight side products, implying that the size of alkali metal cation or the degree of MF dissociation plays an important role in determining the activity and the product composition. FT-IR and NMR experiments revealed that CsF interacts with TFE more strongly than KF through a hydrogen bonding. The experimental and spectroscopic results suggest that the degree of MF dissociation should be in the medium range for the selective production of CF₃CHFCF₂OCH₂CF₃ in high yield and selectivity.     

Ionic conductivity of some alkaline earth halides

The ionic conductivity above and below the melting temperature has been measured for the fluorides, chlorides, and bromides of calcium, strontium, and barium and for magnesium chloride. The observed behavior is of three types: I (MgCl₂, CaCl₂, CaBr₂, BaBr₂), there is an increase in conductivity of several orders of magnitude on melting; II (BaCl₂, SrBr₂), there is a solid-solid transition accompanied by a large increase in conductivity with little subsequent change on melting; and III (CaF₂, SrF₂, BaF₂, SrCl₂), the conductivity of the solid is continuous and changes only slightly on melting.     

On the solubility of lanthanum oxide in molten alkali fluorides

The solubilities of lanthanum oxide in LiF, NaF, KF and eutectic melt LiF-NaF-KF (46.5 mole% LiF; 11.5 mole% NaF and 42.0 mole% KF) were measured in order to find the suitable electrolyte for electrodeposition of lanthanum. Solidus-liquidus lines were obtained by the method of thermal analysis. The solubility of lanthanum oxide in alkali fluorides is rather low and decreases in the order LiF>NaF>KF. It was found that lanthanum oxide reacts with the components of the melt. LaOF and alkali metal oxide are formed during dissolution of La₂O₃ in the melt.     

Alkaline earth fluorides and their complexes: A sol–gel fluorination study

Sol–gel fluorination of the divalent metal fluorides MgF₂, CaF₂ and BaF₂ and their complex fluorides K₂MgF₄, BaMgF₄, and BaAlF₅ is reported. Structural, optical and surface properties are discussed.     

Organosilicon and organophosphorus compounds with pseudohalogen groups. 1. Synthesis of alkoxydimethylsilyl cyanides and their reactions with metal fluorides

Alkoxydimethylsilyl cyanides were synthesized by the exchange reaction of the corresponding alkoxydimethylchlorosilanes with trimethylsilyl cyanide, and also by the reaction of the former compounds with HCN in the presence of triethylamine (the latter method is preferential). Reactions of silyl cyanides with SbF₃ and ZnF₂ were studied. It was found that the reaction of silyl cyanides with SBF₃ leads to the formation of Me₂SiF₂ and the corresponding alkoxydimethylfluorosilanes, which were also obtained by counter-synthesis from alkoxydimethylsilylchlorosilanes and metal fluorides (SbF₃, ZnF₂, CsF). Dimethylfluorosilyl cyanide was obtained by the reaction of silyl cyanides with ZnF₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1593–1587, July, 1991.     

Chloride distribution coefficient on strongly basic anion-exchange resin: Dependence on co-ion in alkali fluoride solutions

Summary The dependence of the chloride distribution coefficient on the co-ion of solutions of different alkali fluorides, MF, up to 11M is tested on the strongly basic anion-exchange resin AG1-X10. Under the same experimental conditions the distribution coefficient decreases in the following order for M⁺: Na⁺>K⁺>Rb⁺>Cs⁺. This can be explained by the different co-ion-chloride interactions. The consequence of this interaction for a chromatographic separation of chloride is shown with 5M KF and CsF solutions, used as eluants. Depending on the fluoride concentration, the distribution coefficient passes through a minimum value to increase again at higher electrolyte concentration. The non-exchange electrolyte in the resin phase is responsible for this effect. In addition, the bromide and the iodide distribution coefficients up to 10M KF solutions are determined. One results is that the selectivity coefficient between halide ions increases at higher electrolyte concentrations.     

Reactions of titanium dioxide with metal fluorides

TiO₂ with several condensed-phase metal fluorides at elevated temperatures to form TiF₄ and the metal oxide. Known mixed titanium metal oxides are usually observed as intermediates. FeOF is an intermediate from the system FeF₃ + TiO₂. With CaF₂ and BaF₂, the reaction did not proceed beyond the intermediates CaTiO₃ and BaTiO₃. Reactions usually start at approximately the temperatures predicted from thermochemical data.     

Facile nucleophilic fluorination by synergistic effect between polymer-supported ionic liquid catalyst and tert-alcohol reaction media system

A highly efficient method was developed for nucleophilic fluorination using an alkali metal fluoride through the synergistic effect of the polymer-supported ionic liquid (PSIL) as a catalyst and tert-alcohol as an alternative reaction media. This PSIL/tert-alcohol system not only enhances the reactivity of alkali metal fluorides and reduces the formation of by-products but also allows the use of a polymer-supported catalyst protocol. As an example, the nucleophilic fluorinations of the model compound, 2-(3-bromopropoxy)naphthalene, with CsF using only tert-amyl alcohol as solvent (for 2 h reaction time), 0.5 equiv of PS[hmim][BF₄] in CH₃CN (for 12 h reaction time), and 0.5 equiv of PS[hmim][BF₄] in tert-amyl alcohol (which is a PSIL/tert-alcohol system for the synergistic effect; for 2 h reaction time) provided 18, 40, and 84% yield, respectively. The characteristics of the nucleophilic fluorination reactions of some halo- and alkanesulfonyloxyalkane systems to the corresponding fluoroalkanes using various alkali metal fluorides are also reported.     

Nucleophilic fluorination of alkynyliodonium salts by alkali metal fluorides: access to fluorovinylic compounds

Fluorovinylic compounds were synthesized by a one-pot procedure from the corresponding alkynyliodonium salts and alkali metal fluorides. Different reaction parameters, such as the temperature, the solvent and the reaction time were examined, and interestingly CsF was chosen for regio- and stereo-selective reactions leading to different alkenyliodonium salts in good yields. Their reduction using NaBH₄ provided the corresponding 2-fluorovinylic products quantitatively.     

Synthesis and some Reactions of Alkali Metal Carbamotelluroates

Sodium and potassium carbamotelluroates [M(R₂NCOTe), M = Na, K, Rb, Cs] were synthesized in moderate to good yields by reacting carbamoyl chloride with the corresponding alkali metal tellurides. The salts readily reacted with trimethylsilyl chloride to form O‐trimethylsilyl carbamotelluroate (R₂NCTeOSiMe₃), which further reacted with RbF and CsF to lead to the corresponding heavy alkali metal carbamotelluroates. These salts reacted with alkyl iodide and carbamoyl chlorides to give the corresponding Te‐alkyl carbamotelluroates and dicarbamoyl tellurides in moderate yields.     

Further studies on the synthesis of α-fluoro carbonyl compounds [1]

The trimethylsilyl enol ethers of cycloalkanones and acid esters are converted in high yields (70–90%) to the corresponding α-fluoro carbonyl derivative using XeF₂ in CH₂Cl₂. Non-cyclic α-hydroxy ketones such as ethyl mandelate are efficiently transformed to the α-fluoro product by DAST and by Ishikawa's reagent. Nucleophilic displacement of halogen by fluoride failed in cyclic systems, giving instead, α,β-unsaturated ketones in DMF or CH₃CN (18-crown-6) and 1,2-diones in DMSO, with KF acting as a base. Attempts at DMSO oxidation of I(Br)F adducts failed to give the α-fluoro ketones, but resulted in dehydrohalogenation to the $\text{trans}$-vinyl fluorides.     

Poly(vinylidene fluoride) as a reagent for the synthesis of K2NiF4-related inorganic oxide fluorides

In this paper we report an improved route to the synthesis of K₂NiF₄-related inorganic oxide fluorides, such as Sr₂TiO₃F₂ and Ca₂CuO₂F₂ using low-temperature fluorination of precursor oxides with poly(vinylidene fluoride). Use of this fluorinating agent results in high quality samples, without SrF₂ or CaF₂ or other impurities, which are commonly seen for alternative fluorination routes.     

Ammonium bromides/KF catalyzed trifluoromethylation of carbonyl compounds with (trifluoromethyl)trimethylsilane and its application in the enantioselective trifluoromethylation reaction

The trifluoromethylation of aldehydes and ketones is a potentially powerful method to introduce the CF₃ moiety into organic molecules. In general, the trifluoromethylation reaction has been performed by treatment of Me₃SiCF₃ under initiation by TBAF, TBAT, TMAF as well as CsF. However, these commercially available fluorides are rather expensive and moisture sensitive. Potassium fluoride (KF) is an inexpensive and commonly used fluoride source and can be also used as an initiator for the trifluoromethylation, but the method suffers from the significant limitation that only DMF is available as a solvent. Therefore, novel methods are highly desirable for laboratory-scale as well as large-scale preparations. Here we wish to report a convenient procedure where a KF/TBAB combination acts as a catalyst for trifluoromethylation of aldehydes, ketones, and imides in a variety of organic solvents to provide trimethylsilyl-protected α-trifluoromethyl alcohols in good to high yields. Application of the method in the enantioselective trifluoromethylation is also discussed.