Fluoride Ion Source Research Articles

Electrolytic Partial Fluorination of Organic Compounds. 31.(1) Regioselective Anodic Fluorination of 2-Quinolyl and 4-(7-Trifluoromethyl)quinolyl Sulfides and the Factors Affecting Its Optimization.

Electrochemical fluorination of 2-quinolyl and 4-(7-trifluoromethyl)quinolyl sulfides bearing an electron-withdrawing group at the position alpha to the sulfur atom was studied. Fluorination was successfully carried out using Et(4)NF.nHF (n = 3, 4) and Et(3)N.3HF as a supporting electrolyte and a fluoride ion source in dimethoxyethane in a divided cell to provide the corresponding alpha-fluorinated sulfides in good yields. A trifluoromethyl group positioned on the quinoline ring significantly enhanced anodic alpha-fluorination. 4-(Methylthio)-7-(trifluoromethyl)quinoline was also found to undergo anodic fluorination efficiently. Solvent effects of various donor numbers were also established.

Fluorination of organodichlorophosphorus compounds with sodium hexafluorosilicate, Part 1 1a

Sodium hexafluorosilicate was used as a source of fluoride ion for nucleophilic fluorination of some selected organodichlorophosphorus compounds in the presence and absence of a multifunctional ethereal solvent, giving fluoro derivatives in low to moderate yields.

Electrolytic Partial Fluorination of Organic Compounds. 24.1 Highly Regioselective Anodic Monofluorination of 2-Benzothiazolyl and 5-Chloro-2-benzothiazolyl Sulfides

Electrochemical fluorination of 2-benzothiazolyl and 5-chloro-2-benzothiazolyl sulfides was successfully carried out using Et4NF·3HF as a supporting electrolyte and fluoride ion source in dimethoxyethane to provide the corresponding α-monofluorinated sulfides in good yields. Fluorination took place selectively at the position α to the sulfur atom of the sulfides, and the heterocyclic moieties were not fluorinated at all.

Oligomerization reactions of perfluorovinylamines catalyzed by fluoride ions

The fluoride ion catalyzed Oligomerization of F-vinylamines, such as F-(N,N-dimethylvinylamine), F-(N-vinylmorpholine) and F-(N-vinylpyrrolidine), was investigated. It was found that dimers were obtained in high yields when the reaction was conducted in aprotic polar solvents, especially in DMF using cesium fluoride as a fluoride ion source. Attempts to obtain oligomers higher than dimers failed. The absence of higher oligomers is discussed in stereoelectronic and steric terms by comparison with the analogous Oligomerization of hexafluoropropene. Unexpected results obtained in the reaction of F-(N,N-dimethylvinylamine) with the hexafluoropropene dimer F-2-methyl-2-propene are also included.

Naked Fluoride Ion Sources: Synthesis, Characterization, and Coupling Reaction of 1-Methylhexamethylenetetramine Fluoride

Anhydrous 1-methylhexamethylenetetramine (also referred to as N-methylurotropinium or methylhexaminium) fluoride was prepared by either halogen exchange between the corresponding iodide and AgF or by a single-step, one-pot, self-assembling synthesis from aqueous CH3NH2, HF, formaldehyde, and NH3. It was characterized by NMR and vibrational spectroscopy. Its hydrate undergoes at 70 °C a Sommelet-type ring opening and coupling reaction to form a potential cryptand system consisting of two bicyclic triazine groups that are connected through a methylene bridge and contain eight ternary nitrogen atoms. The compound was characterized by multinuclear NMR and vibrational spectroscopy, and its structure was determined from single-crystal X-ray diffraction data.

Syntheses and Structures of 2,6‐Substituted Barbaralanes

AbstractSeveral 2,6‐substituted barbaralanes, viz. 1d–g, have been synthesised from Meerwein's diketone (2). Treatment of dinitrile 3 with hydrochloric acid in boiling methanol followed by hydrolysis of the intermediate Pinner salt yields the dimethyl dicarboxylate 4 which is brominated to afford the exo,exo dibromo diester 5. Reductive cyclisation of 5 gives rise to the formation of dimethyl 2,6‐barbaralanedicarboxylate (1d). – Addition of (phenylethynyl)cerium(III) chloride to 2 followed by acid‐induced dehydration of the resulting endo,endo diol 6 yields the bis(phenylethynyl)diene 7, which is cyclised to the bis(phynylethynyl)barbaralane 1e by allylic bromination and subsequent treatment of the exo,exo dibromide 8 with the zinc‐copper couple. Likewise, the exo,exo dibromo disulphone 11, which is obtained from 2 via the bis(vinyl sulphide) 9 and the bis(vinyl sulphone) 10, is converted into the bis(phenylsulphonyl)barbaralane 1f. – Trifluoromethylation of diketone 2 with trimethyl(trifluoromethyl)silane in the presence of a source of fluoride ions affords a mixture of the O silylated endo,endo diol 12 and the oxatwistane 13. Hydrochloric acid converts the latter into the hydroxy ketone 16, which yields 12 on treatment with trimethyl(trifluoromethyl)silane and tetrabutylammonium fluoride. Desilylation of 12 to furnish the endo,endo diol 14 requires prolonged treatment with hydrofluoric acid under phase‐transfer catalysis. Vigorous conditions are also necessary for the dehydration of 14 with phosphorus oxychloride in pyridine to afford the bis(trifluoromethyl)diene 15. Cyclisation of 15 to the bis(trifluoromethyl)barbaralane 1g is performed in the usual way by allylic bromination and subsequent reduction of the dibromide 17 with the zinc‐copper couple. – The configurations and conformations in the crystals have been elucidated by X‐ray diffraction analyses for the bicyclo[3.3.1]nonane derivatives 5, 8, and 11 as well as the barbaralanes 1f and h. In the solid state, 1f appears to exist as a single non‐rearranging valence tautomer. The atomic distances found for 1h indicate the presence of equilibrating non‐equivalent valence tautomers. The results are compared to those from X‐ray diffraction analyses of other degenerate barbaralanes and heterobarbaralanes.

1-[2-(Trimethylsilyl)ethoxy]ethyl (SEE): A novel hybrid hydroxy-protecting group between 1-(ethoxy)ethyl (EE) and 2-(trimethylsilyl)ethoxymethyl (SEM)

The highly versatile 1-[(2-trimethylsilyl)ethoxy]ethyl (SEE) group, readily obtainable from an alcohol and 2-(trimethylsilyl)ethyl vinyl ether in the presence of a catalytic amount of PPTS, has been developed for the protection of hydroxyl groups. Its deprotection can be achieved under virtually neutral conditions with the use of a fluoride ion source, thus allowing for effective protection of hydroxyl groups of compounds that contain acid- and/or base-sensitive functional groups.

Transformation and mineralization of halophenols by Penicillium simplicissimum SK9117.

The metabolism of monohalophenols by Penicillium simplicissimum SK9117, isolated from a sewage plant was investigated. In submerged cultures, 3-, 4-chlorophenol, and 4-bromophenol were metabolized in the presence of phenol. 3-Chlorophenol was transformed to chlorohydroquinone, 4-chlorocatechol, 4-chloro-1,2,3-trihydroxybenzene, and 5-chloro-1,2,3-trihydroxybenzene. With 4-chlorophenol only 4-chlorocatechol was observed as transient product. A release of chloride ions was not observed. Whereas monobromo-, and monochlorophenols could not support growth as sole carbon and energy source, growth and release of fluoride ions were observed with monofluorophenols as substrates. In presence of phenol, the degradation of all monofluorophenols was enhanced. Substrate and cosubstrate disappeared simultaneously. 3-Fluorophenol and 4-fluorophenol were completely mineralized as shown by the equimolar release of fluoride ions.

Efficient method for the t-butyldimethylsilylation of alcohols with N, O-bis( t-butyldimethylsilyl)acetamide

The efficient t-butyldimethylsilylation of alcohols—including tertiary and sterically hindered secondary alcohols—can be achieved using N, O-bis( t-butyldimethylsilyl)acetamide (BTBSA) in the presence of catalytic amounts (0.01–0.05 equiv) of tetrabutylammonium fluoride (TBAF) and other fluoride ion sources. The judicious choice of solvent and amount of catalyst permits the selective silylation of primary alcohols.

Inexpensive, active KF for nucleophilic aromatic displacement reactions

The simple, and inexpensive process, of recrystallizing KF from a methanol solution by slow evaporation of the solvent, followed by drying at 100 °C, results in a highly active form of KF. The surface area was increased 20 fold by this process. This pre-treated KF proved to be considerably more efficient as a source of fluoride ion than untreated KF in the conversion of 2,4-dichloronitrobenzene to 2,4-difluoronitrobenzene. It was observed to be more efficient than spray dried KF but was less efficient than KF supported on CaF 2. The results of a kinetic analysis of the above reaction using the pre-treated KF point towards a solid-liquid interfacial mechanism.

ChemInform Abstract: Proton Sponge Hydrofluoride as a Soluble Fluoride Ion Source.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reactions of Ph(ClCH2)SiH2 with fluoride ion sources: Formation of fluorine‐terminated siloxanes

AbstractThe fluoride ion‐induced rearrangement of Ph(ClCH2)SiH2 was expected to provide either PhMeSiHF (migration of hydride) or (PhCH2)SiH2F (migration of phenyl). However, when Bu4N+F− (commercial TBAF) is added to Ph(ClCH2)SiH2, a mixture of fluorine‐terminated siloxanes, FPhMeSiO(PhMeSiO)xSiMePhF, is obtained. The presence of the Me group suggests a rapid anion‐induced migration of hydride to produce PhMeSiHF which reacts further with water present in TBAF samples. When the reaction mixture is cooled to 0°C or is monitored at the early stage of the reaction, the major products are PhMeSiF2, PhMeSi(OH)F, PhMeSi(OH)2, and FPhMeSiOSiMePhF which are proposed as the building blocks for the siloxanes. When dried CsF in CH3CN is used, the major products are PhMeSiF2 and PhMeSiH2 which are assumed to form from the fluoride ion‐induced disproportionation of PhMeSiHF. The reaction chemistry is rationalized in terms of hypervalent intermediates. The fluoride ion‐induced reactions of PhMeSiH2 and PhMeSiCl2 are also described and compared to those of Ph(ClCH2)SiH2.

Proton sponge hydrofluoride as a soluble fluoride ion source

Proton Sponge (PS) hydrofluoride has been prepared and is totally soluble in acetonitrile; this system was used to generate carbanions from hexafluoropropene and to form carbon–fluorine bonds by reaction with 2,4,6-trichloropyrimidine and by reaction with benzoyl chloride (Proton Sponge hydrochloride is insoluble in acetonitrile).

Tetramethylammonium fluoride: a versatile fluoride ion source

The excellent solubility of quaternary ammonium fluorides makes them attractive alternatives to traditional fluoride ion sources such as potassium fluoride. Unfortunately the high hydroscopicity and low thermal stability of most of these reagents severely restricts their synthetic value. In the light of the work of Christe on the preparation of anhydrous tetramethylammonium fluoride (TMAF) we have carried out research into the use of this reagent. TMAF forms stable hydrogen bonded complexes with a variety of protic molecules, including 4-cyanophenol. The TMAF 4CNC 6H 4OH complex shows a number of interesting properties and in particular the tendency to decompose into the parent molecules rather than the proton transfer products as is normally the case with strongly H-bonded complexes. This observation in particular led us to believe that TMAF can be prepared and used as a soluble and reasonable stable fluoride ion source. 1 The use of anhydrous TMAF as a variety of nucleophilic fluorine transfer reactions will be reported. Very high reactivity towards chloroaromatics and nitroaromatics has been observed. The results from n.m.r. studies will also be reported so as to help explain the unusual solvation behaviour of this reagent which can be attributed to complex equilibria of the type: ▪ An understanding of this association behaviour can help to predict the best conditions for using this reagent in organofluorination reactions.

High-coordination number fluoro- and oxofluoro-anions; IF6O–, TeF6O2–, TeF7–, IF8–and TeF82–

The novel hypervalent, highly coordinated, high-oxidation state anions IF6O–, TeF6O2–, TeF7–, IF8– and TeF82– have been synthesized in anhydrous MeCN using anhydrous N(Me)4+F– as the fluoride ion source; the anions have been characterized by NMR and vibrational spectroscopy and represent novel examples of seven and eight-coordinate species having symmetries C5v(IF6O–, TeF6O2–), D5h, (TeF7–) and D4d(IF8–, TeF82–).

Trifluoromethylation of perfluoroaromatic compounds using trifluoromethyltrimethylsilane in the presence of fluoride ions

We have found that trifluoromethyltrimethylsilane in the presence of tris(dimethylamino)sulfonium trimethyldifluorosilicate (TASF) acts as a source of an unhydrated fluoride ion [I] in the perfluoroalkylation of perfluoroaromatic compounds. This reaction proceeds readily in THF at 20~ In the presence of a slight molar excess of CF3SiMe3, pentafluoropyridine and octafluorotoluene are converted into the monoalkylation products, while decafluorodiphenyl gives a -2:1 mixture of perfluorinated 4-methyldiphenyl and 4,4"-dimethyldiphenyl. Gas-liquid chromatography and 19F NMR spectroscopy indicated 40-70% yields with about 60% conversion of the starting perfluoroarenes.

Kinetics of acquisition and loss of calcium fluoride by enamel in vivo.

Two in vivo experiments were performed, concerning (1) the kinetics of the acquisition of calcium fluoride on enamel during daily rinses with a solution of 0.023% F as sodium fluoride, and (2) the loss of calcium fluoride from enamel slabs which had been topically treated with a neutral solution containing 0.9% F as sodium fluoride. Enamel slabs were carried in the mouth by 6 volunteers for 8 days in both experiments. Sound and etched enamel were included. (1) During mouthrinses moderate amounts of fluoride were acquired by sound enamel, and more as calcium fluoride than as fluoridated apatite, whereas on etched enamel, more fluoride was deposited as fluoridated apatite. On etched enamel there was also a tendency that the deposition of calcium fluoride levelled out whereas the incorporation of firmly bound fluoride continued. This may indicate that calcium fluoride was transformed into fluoridated apatite, probably through remineralization during pH cycling in plaque covering the etched enamel. (2) After single topical application, it was found that etched enamel initially took up more calcium fluoride than sound enamel, but also lost more during the 1st day of in vivo exposure. The loss of calcium fluoride was arrested after 1-2 days, on sound enamel at 70% and on etched enamel at 40% of the original level. It is suggested that the increased amounts of firmly incorporated fluoride in enamel originated from calcium fluoride on enamel, and that calcium fluoride is an important and clinically significant source of fluoride ions on enamel.

ChemInform Abstract: Triethylamine Trishydrofluoride ((C2H5)3N·3HF): A Highly Versatile Source of Fluoride Ion for the Halofluorination of Alkenes.

AbstractThe halofluorination of various alkenes is achieved using the N‐halosuccinimides (II) in the presence of triethylamine tris(hydrofluoride).

Perfluoroalkylation of benzyl bromides using perfluoro-2- methylphent-2-ene in potassium fluoride-dimethylformamide

A marked solvent effect was found in the reaction of perfluoro-2-methyl-2-pentene and benzyl bromides in the presence of fluoride anion to form α-(perfluoro-1,1- dimethylbutyl)-tolunitrile derivatives. Thus, potassium fluoride worked effectively as a fluoride ion source in N,N- dimethylformamide probably to afford nucleophilic perfluoro-1,1-dimethylbuthyl-potassium. To the contrary,in diglyme, potassium fluoride produce the desired product only in a trace amount. Cyano-, nitro-, and unsubstituted benzyl bromides and α,α'-dibromoxylene were converted to the corresponding products in almost quantitative yields.

Triethylamine Tris-hydrofluoride [(C2H5)3N·3HF]: A Highly Versatile Source of Fluoride Ion for the Halofluorination of Alkenes

Triethylamine Tris-hydrofluoride [(C₂H₅)₃N·3HF]: A Highly Versatile Source of Fluoride Ion for the Halofluorination of Alkenes