Fluoroborate Salts Research Articles

Synthesis of bifunctional copolymeric nanofibers with selective extracting U(VI) from the solution and antibacterial property

Facing the problem of future nuclear fuel shortage, developing high-performance adsorbent materials is key. In this work, the amidoxime group/imidazole functionalized ionic liquid copolymer fibers containing bromide salts, and fluoroborate salts (namely P(AO/VEIMBr)8 and P(AO/VEIMBF4)6) were prepared by a one-pot method and free radical polymerization, hydroxyl amination reaction and electrostatic spinning, and characterized by SEM, FT-IR, and 1 H NMR. The influence of solid-liquid ratio, ionic strength, and adsorption time on the adsorption performance was investigated by batch adsorption experiments. In the meanwhile, the adsorption kinetics and thermodynamic processes of U(VI) on the copolymer fibers was also studied. Adsorption mechanism of U (VI) on polymer fibers was explored by XPS spectroscopic analysis combined with DFT method. Finally, the antimicrobial properties of the copolymer fibers were tested. The experimental results showed that the polymer nanofibers synthesized for U(VI) has a fast adsorption, high adsorption capacity at ionic strength close to seawater, and excellent reusability. The adsorption process conformed to the pseudo-second-order kinetic model and Langmuir model, which indicated that chemical adsorption and monolayer adsorption are dominant for adsorption U(VI) on the polymer nanofibers, and exhibits the highest Uranium adsorption capacity (76.92 mg/g and 81.96 mg/g at pH=8.1+0.1, respectively). XPS result showed the amine nitrogen and oxime oxygen in the amidoxime functional group were coordinated with uranyl(VI) ions. The antibacterial experiments showed that the copolymer fibers have antimicrobial properties and the antibacterial rate is over 90 %. Therefore, the nanofibers may be a promising material for extracting uranium from the weak alkaline wastewater or seawater.

Synthesis of quinozilinium fluoroborate salts from harmine

Molecules possessing harmine moiety are reported to exhibit marked fungicidal and bactericidal activities. In this study, various quinozilinium tetrafluoroborate salts were synthesized using acylic and cyclic oxoketene dithioacetals followed by cycloaromatization from Harmine. All of these synthesized compounds were characterized by 1H NMR, 13C NMR, Mass and CHN analysis. This methodology would find wide usage in the preparation of indolo quinozilinium -based library of small molecules useful for medicinal chemistry and in drug discovery.

Equilibria, kinetics, and boron isotope partitioning in the aqueous boric acid–hydrofluoric acid system

The aqueous boric, hydrofluoric, and fluoroboric acid systems are key to a variety of applications, including boron measurements in marine carbonates for CO2 system reconstructions, chemical analysis and synthesis, polymer science, sandstone acidizing, fluoroborate salt manufacturing, and more. Here we present a comprehensive study of chemical equilibria and boron isotope partitioning in the aqueous boric acid–hydrofluoric acid system. We work out the chemical speciation of the various dissolved compounds over a wide range of pH, total fluorine (FT), and total boron (BT) concentrations. We show that at low pH (0 ≤ pH ≤ 4) and FT ≫ BT, the dominant aqueous species is BF4−, a result relevant to recent advances in high precision measurements of boron concentration and isotopic composition. Using experimental data on kinetic rate constants, we provide estimates for the equilibration time of the slowest reaction in the system as a function of pH and [HF], assuming FT ≫ BT. Furthermore, we present the first quantum-chemical (QC) computations to determine boron isotope fractionation in the fluoroboric acid system. Our calculations suggest that the equilibrium boron isotope fractionation between BF3 and BF4− is slightly smaller than that calculated between B(OH)3 and B(OH)4−. Based on the QC methods X3LYP/6-311+G(d,p) (X3LYP+) and MP2/aug-cc-pVTZ (MP2TZ), α(BF3−BF4−) ≃ 1.030 and 1.025, respectively. However, BF4− is enriched in 11B relative to B(OH)4−, i.e., α(BF4−−B(OH)4−) ≃ 1.010 (X3LYP+) and 1.020 (MP2TZ), respectively. Selection of the QC method (level of theory and basis set) represents the largest uncertainty in the calculations. The effect of hydration on the calculated boron isotope fractionation turned out to be minor in most cases, except for BF4− and B(OH)3. Finally, we provide suggestions on best practice for boric acid–hydrofluoric acid applications in geochemical boron analyses.

Wear Behaviour of In Situ Al/TiB2 Composite: Influence of the Microstructural Instability

In this present work, the in situ Al (A380)/5 wt%TiB2 composites were fabricated through salt–melt reaction using halide salts such as potassium hexafluorotitanate (K2TiF6) and potassium tetra fluoroborate (KBF4) salts as precursors. The composites were produced at four different melt temperatures (700, 750, 800, 850 °C). The formation of particle was confirmed from XRD results. The wear behaviour of Al/5 wt% TiB2 composite was investigated by varying the wear test parameters such as sliding temperature (25, 100, 150, 200 °C), applied load (10, 20, 30, 40 N), sliding velocity (0.4, 0.7, 1, 1.3 m/s). The microstructure of Al/5 wt% TiB2 composite was correlated with the wear characteristics of the composites. The wear resistance of Al/5 wt% TiB2 composite was significantly improved due to the presence of TiB2 particle in Al matrix material. The composite produced at melt temperature 800 °C showed a higher wear resistance at applied load: 10 N, sliding temperature: 25 °C and sliding velocity: 0.7 m/s. The wear mechanism for each of the tested condition was identified from the worn surfaces using scanning electron microscopy (SEM). ANOVA test was carried out to find out significant factor for the wear resistance of composite. The checking of adequacy of experimental value for the wear behaviour of composite for different testing condition was analysed by residual plots using statistical software.

Influence of process parameters of aluminothermic reduction process on grain refinement of in-situ Al/ TiB2 composites

This paper reports the effect of process variables such as holding time, addition time on grain refinement on in-situ Al/TiB2 composite and also size of the formed TiB2 particle size. The in- situ composites were fabricated by flux assisted synthesize route using potassium hexafluorotitanate (K2TiF6) and potassium fluoroborate (KBF4) salts as precursors. The composites were produced with respect to different holding time varies from 20 min to 40 min and also for different addition times of precursors 10 min to 30 min at 700°C. The resulting composites were characterised by microstructure examination and size of particles. The TiB2 particles are segregated by crushing and followed by acidic immersion. From the results, effects of the process parameter on the particle formation and particle sizes on grain refinement of in-situ Al/TiB2 were investigated.

B(C6F5)3 Promotes the catalytic activation of [N,S]-ferrocenyl nickel complexes in ethylene oligomerization

The synthesis of new methallyl-ferrocenyl-thiazoline-nickel complexes [1-(2-thiazolin-2-yl)-2-(R-thio)-ferrocene-κ2N,S]-(η3-methallyl)nickel(II) [Y] (1-3, R = Me, i-Pr, Ph, Y = BF4-4, R = Me, Y = BAr´4-) by reaction with 2-ferrocenyl-2-thiazoline ligands L1–3 with [Ni-(η3-(CH2)2CMe)Cl]2 in presence of fluoroborate salts (Y = BAr´4-; BF4-) is reported. The complexes 1–4 were obtained in high yields, and characterized by 1H, 13C, 19F and 11B NMR, FTIR. The X-Ray diffraction analysis of 4 confirmed the formation of a single isomer containing a nickel center coordinated to L1 in a bidentate [N,S] fashion and to a η3-methallyl ligand. These complexes catalyzed efficiently the ethylene oligomerization when tris(pentafluorophenyl)borane (BCF) was used as co-activator. All catalytic precursors produced C4 and C6 fractions. Complex 1 showed higher activity with TOF 3006 h-1 at room temperature with selectivity of 86% to C4 fraction. In contrast, catalyst 2 was more selective to the formation of 1-butene, but with low activity. DFT-Computational studies of complex-BCF adducts show than these species behave as frustrated Lewis pairs, mainly stabilized by long-range interactions enhancing the acceptor character of the complexes. Structural modifications over the sulfanyl group tune the acceptor character of Ni center, affecting their catalytic performance.

Metal-Free Borylation of Heteroarenes Using Ambiphilic Aminoboranes: On the Importance of Sterics in Frustrated Lewis Pair C-H Bond Activation.

Two novel frustrated Lewis pair (FLP) aminoboranes, (1-Pip-2-BH2-C6H4)2 (2; Pip = piperidyl) and (1-NEt2-2-BH2-C6H4)2 (3; NEt2 = diethylamino), were synthesized, and their structural features were elucidated both in solution and in the solid state. The reactivity of these species for the borylation of heteroarenes was investigated and compared to previously reported (1-TMP-2-BH2-C6H4)2 (1; TMP = tetramethylpiperidyl) and (1-NMe2-2-BH2-C6H4)2 (4; NMe2 = dimethylamino). It was shown that 2 and 3 are more active catalysts for the borylation of heteroarenes than the bulkier analogue 1. Kinetic studies and density functional theory calculations were performed with 1 and 2 to ascertain the influence of the amino group of this FLP-catalyzed transformation. The C-H activation step was found to be more facile with smaller amines at the expense of a more difficult dissociation of the dimeric species. The bench-stable fluoroborate salts of all catalysts (1F-4F) have been synthesized and tested for the borylation reaction. The new precatalysts 2F and 3F are showing higher reaction rates and yields for multigram-scale syntheses.

FTIR Spectroscopic and DC Ionic conductivity Studies of PVDF-HFP: LiBF4: EC Plasticized Polymer Electrolyte Membrane

In the present paper; the FTIR and Temperature dependent DC Ionic conductivity studies of polymer (80 Wt% PVDF-HFP) with inorganic lithium tetra fluoroborate salt (20 Wt% LiBF4) as ionic charge carrier and plasticized with various weight ratios of Ethylene carbonate plasticizer (10 Wt% to 70 Wt% EC) as gel polymer electrolytes. Solution casting method is used for the preparation of plasticized polymer-salt electrolyte films. FTIR analysis shows the good complexation between PVDF-HFP: LiBF4 and the presence of functional groups in the plasticized polymer-salt electrolyte membrane. Also the analysis and results show that the highest DC ionic conductivity of 1.66 × 10−3 SCm−1 was found at 373 K for a particular concentration of 80 Wt% PVDF-HFP: 20 Wt% LiBF4: 40 Wt% EC porous gel type polymer-salt plasticized porous membrane. Increase of temperature results expansion and segmental motion of polymer chain that generates free volume in turn promotes hopping of the lithium ions satisfying Vogel-Tammann-Fulcher equation.

Perfluoroalkylation of Alkenes by Frustrated Lewis Pairs.

The activation of perfluoroalkyl iodides by the frustrated Lewis pair tris(pentafluorophenyl)borane and tri-tert-butylphosphine is described. By abstraction of both a fluorine and an iodine atom, an iodophosphonium fluoroborate salt is formed. In the presence of alkenes the corresponding iodoperfluoroalkylation products are generated regioselectively. First mechanistic investigations support a radical mechanism.

ChemInform Abstract: Bench‐Stable Frustrated Lewis Pair Chemistry: Fluoroborate Salts as Precatalysts for the C—H Borylation of Heteroarenes.

While the organotrifluoroborate group is commonly used as a leaving group in cross-coupling reactions, we now show that their high stability can be used to protect the Lewis acidic moieties of frustrated Lewis pair catalysts. Indeed, the air and moisture-stable trifluoro- and difluoroborate derivatives of bulky (tetramethylpiperidino)benzene are shown to be conveniently converted to their dihydroborane analogue which is known to activate small molecules. An efficient synthesis route to these stable and convenient precatalysts, their deprotection chemistry and their benchtop use for the dehydrogenative borylation of heteroarenes is presented.

Alternative Synthesis of 1,8-Difluoroanthracene via the Balz-Schiemann Reaction

An alternative and improved method for the synthesis of 1,8-difluoroanthracene 5 is described. The precursor 1,8-difluoro-9,10-anthraquinone 4 was synthesized by precipitating the water-soluble 1,8-diazonium-9,10-anthraquinone fluoroborate 3 using isopropanol, before thermally decomposing it via the Balz-Schiemann reaction to yield 4 in the form of pure sublimed crystals. Compound 5 was later synthesized with 84% yield by reducing 4 in a Zn/NH4OH mixture. Using isopropanol to quantitatively precipitate water-soluble diazonium fluoroborate salts was also used to synthesize other fluoroanthraquinone derivatives with improved yields.

Bench-stable frustrated Lewis pair chemistry: fluoroborate salts as precatalysts for the C-H borylation of heteroarenes.

While the organotrifluoroborate group is commonly used as a leaving group in cross-coupling reactions, we now show that their high stability can be used to protect the Lewis acidic moieties of frustrated Lewis pair catalysts. Indeed, the air and moisture-stable trifluoro- and difluoroborate derivatives of bulky (tetramethylpiperidino)benzene are shown to be conveniently converted to their dihydroborane analogue which is known to activate small molecules. An efficient synthesis route to these stable and convenient precatalysts, their deprotection chemistry and their benchtop use for the dehydrogenative borylation of heteroarenes is presented.

ChemInform Abstract: Mild and Highly Efficient Metal‐Free Oxidative α‐Cyanation of N‐Acyl/Sulfonyl Tetrahydroisoquinolines.

A highly efficient metal-free oxidative α-cyanation reaction of N-acyl/sulfonyl tetrahydroisoquinolines under mild conditions was developed. The reaction uses 2,2,6,6-tetramethylpiperidine N-oxide fluoroborate salt (T+BF4−) as the oxidant and trimethylsilyl cyanide as the source of the cyano group.

Mild and highly efficient metal-free oxidative α-cyanation of N-acyl/sulfonyl tetrahydroisoquinolines

A highly efficient metal-free oxidative α-cyanation reaction of N-acyl/sulfonyl tetrahydroisoquinolines under mild conditions was developed. The reaction uses 2,2,6,6-tetramethylpiperidine N-oxide fluoroborate salt (T+BF4−) as the oxidant and trimethylsilyl cyanide as the source of the cyano group.

ChemInform Abstract: Three‐Component Reaction for the Synthesis of Diverse β‐Unsaturated α‐Amino Esters.

AbstractA convenient one‐pot operation allows the three‐component reaction of fluoroborate salts, aromatic amine and ethyl glyoxylate to provide alkynyl‐ alkenyl‐, and allyl‐2‐amino esters under mild reaction conditions.

Activation of Alkyl C–F Bonds by B(C6F5)3: Stoichiometric and Catalytic Transformations

The Lewis acid B(C6F5)3 is shown to activate a series of alkyl fluorides. In stoichiometric reactions, treatment of sterically demanding phosphines with B(C6F5)3/alkyl fluorides gives phosphonium fluoroborate salts while treatment of B(C6F5)3/alkyl fluorides with the salts [tBu3PX][XB(C6F5)3] (X = H, PhS) gives the alkane and the salt byproduct [tBu3PX][FB(C6F5)3]. These fluoroalkanes are also catalytically converted to the corresponding alkanes by reaction of the fluoroalkane and Et3SiH using B(C6F5)3 as the catalyst.

Measurement of ionic conductivity of poly (N-vinylimidazole) and its fluoroborate salt in solid state

The conductivity of poly(N-vinylimidazole) (PVIM) and its fluoroborate salt (PVIM–HBF4) are reported here. N-vinylimidazole is polymerized by free radical method and PVIM–HBF4 is prepared by acidification of PVIM with HBF4. The polyelectrolyte so formed has been characterized by infrared, hydrogen-1 nuclear magnetic resonance, thermogravimetric analyzer, and differential scanning calorimetry. Frequency and temperature dependence of AC conductivity has been studied to learn about the electrical conduction behavior in the materials. The electrical conductivity of the new material is found to be in the range of 10−5 to 10−6 S cm−1.There is about 102- to 103-fold increase in conductivity of the polyelectrolyte. The material is shown to be a predominantly ionic conductor with t ion ≈ 0.88. Apparent activation energies are found to be 0.397 and 0.250 eV for the polymer and the polyelectrolyte, respectively.

Polyfluorinated boron cluster based salts: A new electrolyte for application in nonaqueous asymmetric AC/Li 4Ti 5O 12 supercapacitors

Solutions of novel fluorinated lithium dodecaborate (Li 2B 12F x H 12− x ) salts have been evaluated as electrolytes in nonaqueous asymmetric supercapacitors with Li 4Ti 5O 12 as negative electrode, and activated carbon (AC) as positive electrode. The results obtained with these new electrolytes were compared with those obtained with cells built using standard 1 M LiPF 6 dissolved in ethylene carbonate and dimethyl carbonate (EC:DMC; 1:1, v/v) as electrolyte. The specific energy, rate capability, and cycling performances of nonaqueous asymmetric cells based on these new electrolyte salts were studied. Cells assembled using the new fluoroborate salts show excellent reversibility, coulombic efficiency, rate capability and improved cyclability when compared with the standard electrolyte. These features confirm the suitability of lithium-fluoro-borate based salts to be used in nonaqueous asymmetric supercapacitors.

Modulation De La Regiochimie De La Reaction Du Fluoroborate De 2-Benzoyl-1,2-Dihydroisoquinaldonitrile Sur L'Indene

The reaction of the 2-benzoyl-1,2-dihydroisoquinaldonitrile fluoroborate salt with indene leads to a single indeno[1,2-c]pyrrole derivative. But nmr data did not prove the regiochemistry of the reaction and a chemical demonstration has been carried out. It allows to obtain the regioisomeric indeno[1,2-c]pyrrole derivative. Moreover the last structure was also established by a radiocristallographic study.

Asymmetric Lithiation of Boron Trifluoride‐Activated Aminoferrocenes: An Experimental and Computational Investigation

AbstractTertiary aminoferrocenes complexed to boron trifluoride (BF3) are shown to undergo asymmetric lithiation with alkyllithiums in the presence of bulky chiral 1,2‐diaminocyclohexane ligands. This reaction represents the first BF3‐activated asymmetric lithiation of a prochiral aromatic amine and the first such transformation to be mediated by a chiral diamine other than (−)‐sparteine. The process provides rapid access to a broad range of enantiomerically enriched 2‐substituted‐1‐aminoferrocenes, including derivatives with uncommon substitution patterns that are of interest in catalysis. The enantioselectivity of the process is high enough (87:13 to 91:9 er) to allow for isolation of single enantiomers of several products after simple recrystallization as either the free aminoferrocenes or their ammonium fluoroborate salts. Both antipodes of the planar chiral 2‐substituted‐1‐aminoferrocene products are accessible, as confirmed by single crystal X‐ray diffraction analysis of two compounds with opposite relative stereochemistry. Single‐point calculation of thirty‐two different transition states of the reaction at the M06‐2X/6‐311+g(2d,2p) level produced a computational model that correctly predicted both the sense and extent of chiral induction. Three factors appeared to play important roles in determining enantioinduction during lithiation of BF3‐complexed tertiary aminoferrocenes: (i) the maintenance of a highly organized eight‐membered ring transition state; (ii) the existence of a strong Li⋅⋅⋅F contact which placed the chiral diamine ligand in close proximity to the ferrocene substrate; (iii) the orientation of the sterically demanding N‐alkyl groups of the chiral diamine additives, either away or towards, the aminoferrocene and the alkyllithium. The model may serve as a predictive tool for the rational design of new ligands for this and related asymmetric lithiations.