Mise au point d'un appareillage de preparation et de manipulation de melanges anhydres HFNH3MF (M alcalin) — tension de vapeur totale au-dessus de solutions HFNH3 riches en HF

An apparatus for preparing and handling HFNH₃MF mixtures (M alkali metal) has been designed and constructed. The vacuum line made of plastic materials (PVF₂, PTFCE, PTFE) allows the purification of anhydrous hydrogen fluoride, preparation and analysis of HFNH₃ or HFNH₃MF mixtures and their handling for further study or destruction.Total vapour pressures above HFNH₃ binary mixtures rich in HF have been measured and are described as a function of ammonia concentration and temperature (?10 to +20°C).     

A mild ring opening fluorination of epoxide with ionic liquid 1-ethyl-3-methylimidazorium oligo hydrogenfluoride (EMIMF(HF)2.3)

Ring opening fluorination of epoxides with hydrogen fluoride in ionic liquid 1-ethyl-3-methylimidazorium oligo hydrogenfluoride EMIMF(HF)_2.3 was demonstrated. This ionic liquid released hydrogen fluoride graduately to make mild conditions without oligomerization of epoxides.     

Elemental fluorine. Part 24.[1]: Fluorination of ethers by fluorine and Selectfluor

Reactions of dialkyl ethers with either fluorine or Selectfluor™ led to the formation of unusual difluorinated polyether products in modest yields. A mechanism involving initial fluorination of the site adjacent to ether oxygen followed by elimination of hydrogen fluoride, reaction of the generated enol system with a further equivalent of fluorinating agent giving an oxonium system which reacts with water during aqueous work-up to lead eventually to the products observed, is suggested.     

Amine-Poly(Hydrogen Fluoride) Solid Complexes: New Studies of Formation,Crystal Structures,and Hn−1Fn− Ion Diversity

Triethylamine tris(hydrogen fluoride), a versatile fluorinating agent , solidifies at −27 °C forming pairs of hydrogen-bonded Et₃NH⁺ and H₂F₃⁻ ions. Six further low-melting ionic amine–HF adducts have also been identified and their structures determined. The H_n−1F_n⁻ ions with n here taking values between 3 and 7 are classified along with those observed in other crystals.     

A mild method for halofluorination of alkenes with ionic liquid EMIMF(HF)2.3

Halofluorination of alkene in the presence of N-halosuccinimide and ionic liquid, 3-ethyl-1-methyl-imidazorium oligo hydrogen fluoride (EMIMF(HF)_2.3), as a HF source was demonstrated. Various alkenes were converted into β-halo organofluorides in good yields and with high regioselectivity.     

Synthesis conditions and activity of various Lewis acids for the fluorination of trichloromethoxy-benzene by HF in liquid phase

The experimental conditions (temperature, reaction time, amount of hydrogen fluoride (HF)) for the comparison of the performances of various Lewis acids in the liquid phase fluorination by HF of the trichloromethoxy-benzene were determined by using SbCl₅ as the reference catalyst. After 1 h reaction at 50 °C, C₆H₅OCCl₃ was totally converted into C₆H₅OCF₃ requiring only 2 mol% of SbCl₅ and a stoichiometric amount of HF. The most efficient catalysts were found to be chlorinated Lewis acids in which the metal is at the state of oxidation +V (SbCl₅, MoCl₅, TaCl₅ and NbCl₅). The appropriate catalyst has to be able to form a nucleophilic complex with HF, which constitutes the actual fluorinating agent and is more efficient than HF alone.     

Selective Synthesis of Monofluorinated Compounds Applying Amine/HF Reagents

For nucleophilic monofluorination, amine/HF reagents such as Et₃N⋅3HF, Pyr⋅9HF (Olah's reagent) and similar combinations belong to the most frequently used fluoride sources, whereupon the selectivity of these reagents can be very different depending of its acidity, the nucleophilicity of the fluoride equivalent, and the structure of the particular substrate. These reagents can be used safely in ordinary chemistry laboratories for nucleophilic substitution reactions by fluoride at sp³-hybridized carbon centers. For ring opening reactions of epoxides, the regio- and stereoselectivity is very much depending of the nature of the epoxide and the acidity of the HF reagent favoring either S_N1 or S_N2 type reactions. Similarly, the outcome of halofluorination and similar reactions with sulfur or seleno electrophiles can be controlled by the particular combination of the electrophile and the fluoride source. Examples for the application of these reaction types for the synthesis of fluorine-containing analogues of natural products or biologically relevant compounds are in the focus of this personal account.     

Making the SF5 Group More Accessible: A Gas‐Reagent‐Free Approach to Aryl Tetrafluoro‐λ6‐sulfanyl Chlorides

Modern pentafluorosulfanyl (SF₅) chemistry has an Achilles heel: synthetic accessibility. Herein, we present the first approach to aryl‐SF₄Cl compounds (key intermediates in state‐of‐the‐art aryl‐SF₅ synthesis) that overcomes the reliance on hazardous fluorinating reagents and/or gas reagents (e.g. Cl₂) by employing easy‐to‐handle trichloroisocyanuric acid, potassium fluoride, and catalytic amounts of acid. These simple, mild conditions allow direct access to aryl‐SF₄Cl intermediates that either have not been or cannot be demonstrated using previous methods. Furthermore, the same approach provides access to aryl‐SF₃ and aryl‐SeF₃ compounds, which extend the applications of this chemistry beyond arene SF₅‐functionalization, and demonstrate its ability to address a more general oxidative fluorination problem.     

Ionic liquid functionalized cellulose as an efficient heterogeneous catalyst for the facile and green synthesis of benzoxazine,pyrazine and quinoxaline derivatives in aqueous media

Immobilization of acidic ionic liquid, 1-methyl-3-(3-trimethoxysilylpropyl) imidazolium hydrogen sulfate on cellulose (Cell-[pmim]HSO₄) as an efficient heterogenous catalyst for the simple and environmentally benign synthesis of benzoxazine, pyrazine and quinoxaline derivatives in aqueous media at room temperature is described. The catalyst was characterized by FTIR spectroscopy and X-ray diffraction pattern. This method provides several advantages such as mild reaction conditions, environmentally friendly catalyst, good to excellent yields and simple work-up procedure.     

Front Cover: In Situ Generated DBU⋅HF Acts as a Fluorinating Agent in a Hexafluoroisobutylation Tandem Reaction: An Effective Route to 5,5,5,5’,5’,5’-Hexafluoroleucine (Eur. J. Org. Chem. 10/2023)

We report the direct incorporation of the hexafluoroisobutyl group on a chiral glycine Schiff base complex mediated by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The fluoroalkylation involves 2-(bromomethyl)-1,1,1,3,3,3-hexafluoropropane reagent, which generates in situ hexafluoroisobutylene (HFIB), and reacts then with the enolate through a tandem allylic shift/hydrofluorination process. We showed that the use of neutral organic base DBU generates in situ an original DBU⋅HF salt, which preserves the fluoride nucleophilicity and acts as a fluorinating agent. This fluoride salt promotes the hydrofluorination of the pentafluorinated alkene overcoming the usual fluoride β-elimination observed with α-CF₃-vinyl reagents. With alkali metal bases, by contrast, the hydrofluorination is disfavored and the pentafluorinated alkene intermediate is obtained predominantly. This study highlights the critical role of the fluoride counter ion to preserve its nucleophilicity. The protocol is amenable to multidecagram scale synthesis of enantiopure (S)- and (R)-5,5,5,5’,5’,5’-hexafluoroleucine and their N-Fmoc or N-Boc derivatives in good overall yield.     

Exploiting the Strong Hydrogen Bond Donor Properties of a Borinic Acid Functionality for Fluoride Anion Recognition

Borinic acids have typically not been considered as hydrogen bond donor groups in molecular recognition. Described herein is a bifunctional borane/borinic acid derivative ( 2 ) in which the two functionalities are connected by a 1,8‐biphenylenediyl backbone. Anion binding studies reveal that 2 readily binds a fluoride anion by formation of a unique B?F???H?O?B hydrogen bond. This hydrogen bond is characterized by a short H‐F distance of 1.79(3) Å and a large coupling constant (¹J_HF) of 57.2 Hz. The magnitude of this interaction, which has also been investigated computationally, augments the fluoride anion binding properties of 2 , thus making it compatible with aqueous environments.     

SbF5/PAF—a novel fluorinating reagent in preparing fluorine compounds

A novel fluorination reagent and catalyst, SbF₅/PAF (porous aluminum fluoride), was prepared by impregnating SbCl₅ into PAF and then treating with anhydrous hydrogen fluoride. The prepared reagent had an excellent catalytic activity in halogen-exchange, and also improved the properties of SbF₅, such as hydroscopicity, corrosion, and toxicity. SbF₅/PAF was successfully used in organic synthesis as a fluorinating reagent, and a fixed bed catalyst for F/Cl exchange.     

Amberlyst-15® in ionic liquid: an efficient and recyclable reagent for the benzylation and hydroalkylation of β-dicarbonyl compounds

Benzylation and hydroalkylation of 1,3-dicarbonyl compounds using Amberlyst-15 immobilized in ionic liquid [Bmim][PF₆] as an efficient reusable reagent was studied. The reagent was compared with other solid acid reagents along with role of the ionic liquid. The effect of various reaction parameters like type of reagent, solvent, substrate molar ratio, reaction time, and temperature were studied. Present protocol is advantageous due to the ease in handling of reagent, simple work-up procedure, economical and environmentally benign process. The products were obtained in good to excellent yield and applicable to wide variety of substrates.     

The preparation of organomagnesium fluorides by organometallic exchange reactions

The preparation of alkyl- and aryl-magnesium fluorides by the reaction of dialkyl- and diaryl-magnesium compounds with fluorinating agents, such as BF₃ etherate, SiF₄, Bu₃SnF, Ph₃SiF and Et₂AlF in tetrahydrofuran were studied. Methyl-, ethyl-, and phenyl-magnesium fluoride were prepared in high yield by the reactions of dimethyl-, diethyl-, and diphenyl-magnesium with boron trifluoride diethyl etherate in tetrahydrofuran. Methylmagnesium fluoride was prepared in quantitative yield by the reaction of dimethylmagnesium with silicon tetrafluoride in tetrahydrofuran and butylmagnesium fluoride was prepared in quantitative yield by the reaction of tributyltin fluoride in THF with dibutylmagnesium. Other combinations of R₂Mg compounds and fluorinating agents resulted in the formation of less pure products.     

Halofluorination of alkenes with ionic liquid EMIMF(HF)2.3

Halofluorination of alkene by means of N-halosuccinimide and ionic liquid, 1-ethyl-3-methylimidazorium oligo hydrogenfluoride (EMIMF(HF)_2.3), was demonstrated. Various alkenes were converted into β-halo organofluorides in good yields after non-aqueous work-up.     

Reaktion von Lanthanfluorid mit Halogenalkanen

Reactions of Lanthanum Fluoride with Halogenoalkanes Reactions are reported on lanthanum fluoride as a fluorinating reagent and as a catalyst for the fluorination and dismutation of halogenoalkanes. Carbon tetrachloride, monofluorotrichlormethane, and chloroform are partially fluorinated by lanthanum fluoride. In the presence of HF, lanthanum fluoride acts as catalyst the fluorine transfer to CCl₄, CHCl₃ and C₂F₃Cl₃. Monofluorotrichloromethane, difluorodichloromethane, and trifluorotrichloroethane dismutate on lanthanum fluoride. Results on the thermal decomposition of the above-mentioned fluorochloroalkanes are communicated.     

Fluorinated heterocyclic compounds: Selective chlorine/fluorine exchange reactions on pyrimidines

Selective chlorine/fluorine exchange reactions on tetrachloropyrimidine, 6-methyl-, 6-chloromethyl-, 6-dichloromethyl-, and 6-trichloromethyl-2,4,5-trichloropyrimidine are described. Sodium fluoride, potassium fluoride, hydrogen fluoride, and antimony trifluoride were used as the fluorinating agents. It was found that NaF and KF fluorinate only in the heterocyclic nucleus, HF in the nucleus and in the chlorinated methyl group, and SbF₃ only in the chlorinated methyl group. In the first stage of fluorination with NaF only chlorine bound in position 4 of the pyrimidine ring is exchanged. The HF reaction is an equilibrium reaction in which the substitution of the fluorine for the first chlorine atom occurs preferentially in position 2. The behaviour of partly fluorinated pyrimidines in nucleophilic exchange reactions is also discussed.     

Preparation and application of porous calcium fluoride—a novel fluorinating reagent and support of catalyst

A novel material, porous calcium fluoride (PCF) with more than 60 m²/g surface area, was prepared by the reaction of soda lime (SL) with anhydrous hydrogen fluoride (AHF), and its application as a fluorinating reagent and support of catalyst was investigated.     

Fluorination with positive fluorine generated from isoelectronically related reagents

Compounds such as PhIF₂, Ph₃PF₂ and XeF₂, which have been used previously as unrelated fluorinating agents, are shown to be periodically related as isoelectronic molecules E₃AF₂ of trigonal-bipyramidal shape, where E represents a bonded or non-bonded electron pair and A a main Group $\text{V}$–$\text{VIII}$ element. These compounds are arranged in order of halogenating ability by estimating the magnitude of reduction couples, approximated by δH^o_f(E₃AF₂-E₃A), or by noting the direction of redox reactions involving the couples. The A sequence deduced Kr>Xe?Cl>Br>I>S>Se>Te?As?Sb>P agrees with the limited experimental data available. Evidence for an ionic mechanism involving ‘onium’ monohalide ions is given for halogenations with these reagents when carried out under “Friedel-Craft” conditions although no stable salts containing these ions have as yet been isolated because of intramolecular halogenation. These ions act as sources of positive fluorine. The use of ring deactivated reagents to achieve halogenation is discussed.     

On hydrogen-bonded complexes: the case of (HF)2

The hydrogen fluoride dimer (HF)₂ is the most completely characterized hydrogen bonded species incorporating a donor molecule and an acceptor molecule. We provide a summary of experimental and theoretical information pertinent to the fundamental and harmonic vibrational frequencies, equilibrium geometry and dissociation energiesD _e andD ₀ as well as a brief critical discussion including some new results on the potential function and current best estimates of experimental quantities.