Enzymatic fluorination using fluoride ion generated from degradation of fluorinated materials

The recycle of fluoride ion generated from the degradation of 1-methyl-3-butylimidazolium tetrafluoroborate, diethyl methyl methoxyethylammonium tetrafluoroborate in the presence of Tris-HCl buffer solution and/or the biodegradation of fluorobenzene and benzotrifluoride, was described. The generated fluoride ion was reused to produce 5′-fluoro-5′-deoxyadenosine (5′-FDA), fluoroacetate and/or 4-fluorothreonine.     

Freeze-induced reactions: formation of iodine-bromine interhalogen species from aqueous halide ion solutions

Interhalide ion formation resulting from the freezing of dilute solutions containing components found in natural sea salt are investigated as a potential mechanism for the release of interhalogens to the polar atmosphere. Acidified solutions containing iodide, bromide, and nitrite ions have been frozen and then thawed, with changes in speciation analyzed using UV-visible spectrophotometry. The freezing process is shown to induce the formation of the important interhalide ion, IBr(2)(-). This species has previously been predicted to be a precursor of iodine monobromide, IBr, and represents a potentially important source of halogen atoms in the polar marine boundary layer. The reaction mechanisms that lead to the formation of IBr(2)(-) under freezing conditions are explored using both experimental and computational methodologies. The chemistry involved was subsequently modified in order to mimic naturally occurring conditions more closely and also incorporated the use of hydrogen peroxide as an oxidant. In contrast to previous studies, the freeze-induced production of IBr(2)(-) was thereby observed to occur up to pH <5.1, where the acidity levels are comparable to those found in the polar snowpack.     

Activation parameters of ferryl ion reactions in aqueous acid solutions

The temperature dependence of the oxidation kinetics of Fe²⁺ by O₃ at pH 0–3 was studied by stopped-flow technique in the temperature range 5–40°C. Activation parameters of the reactions involved in formation and decay of the ferryl ion (iron(IV)), FeO²⁺ are determined. The reaction of Fe²⁺ + FeO²⁺ was found to branch into two channels forming iron(III)-dimer, Fe(OH)₂Fe⁴⁺, and Fe³⁺. The yield of the dimer, Fe(OH)₂Fe⁴⁺, increases with temperature on the expense of the Fe³⁺ yield. On the basis of the overall rate constant and relative yield of Fe(OH)₂Fe⁴⁺ the activation energy is determined for both channels. The activation parameters of the hydrolysis of the ferryl ion and its reaction with H₂O₂ were also determined. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 17–24, 1997.     

Reactions involving fluoride ion. Part 21 [1]. Nucleophilic substitution reactions of perfluorocyclobutene oligomers

Reaction of perfluorocyclobutene oligomers, (1) - (4), with some simple nucleophiles gives products arising from S_N2′ displacement [N.B. this term is used here to describe the overall process of addition of a nucleophile to an alkene and elimination of an allylic fluorine and is not meant to imply that the reaction is concerted] or vinylic substitution of fluorine, or a mixture of both processes. The reactivity of the dimers, (1) and (2), is much greater than that of acyclic analogues and this can be attributed to the ring strain present in these compounds.     

Transient ion pairs from OH-radical reactions: Pulse radiolysis of aqueous alkyl iodide solutions

Pulse radiolysis studies of aqueous alkyl iodide solutions reveal the existence of the transient ion pair (HOI^?.R⁺)_aq. This species is formed by OH-radical reaction with the alkyl iodide followed by a rapid solvent-assisted rearrangement from the outer to the inner charge-transfer complex.     

Nucleophilic fluorination of triflates by tetrabutylammonium bifluoride

Careful examination of nucleophilicity, basicity, and leaving group ability led us to discover the nucleophilic fluorination of triflates by weakly basic tetrabutylammonium bifluoride, which provides excellent yields with minimal formation of elimination-derived side products. Primary hydroxyl groups as well as secondary hydroxyl groups in acyclic chains or in five-membered rings are excellent substrates, whereas benzylic and aldol-type secondary hydroxyl groups give poor yields as a result of the instability of their triflates.     

Receptor design and extraction of inorganic fluoride ion from aqueous medium

A receptor with acidic methylene hydrogens is found to act as an efficient binding mode for F(-). This reagent could as well be used for selective and quantitative extraction of F(-) from the aqueous solution of NaF and sea water.     

Electrochemical fluorination of methanedisulfonyl fluoride

The electrochemical fluorination of methanedisulfonyl fluoride in anhydrous hydrogen fluoride to produce difluoromethanedisulfonyl fluoride, a precursor of difluoromethane disulfonic acid, was investigated. This study was carried out in a microprocessor-aided modified Simons' reactor system at constant anodic potential using a Cu/CuF₂ reference electrode. Product yields of 75–82%, current efftciencies in excess of 66%, and electrical energy efficiencies of at least 33% were obtained for the electrochemical fluorination step.Experimental results of this investigation are presented and discussed.     

Hydroxide ion hydration in aqueous solutions

Hydroxide ion hydration was studied in aqueous solutions of selected alkali metal hydroxides by means of Fourier transform infrared (FTIR) spectroscopy of HDO isotopically diluted in H2O. The quantitative difference spectra procedure was applied for the first time to investigate such systems. It allowed removal of bulk water contribution and separation of the spectra of solute-affected HDO. The obtained spectral data were confronted with ab initio calculated structures of small gas-phase and polarizable continuum solvation model (PCM) solvated aqueous clusters, OH-(H2O)n, n = 1-7, to establish the structural and energetic states of hydration spheres of the hydrated hydroxide anion. This was achieved by comparison of the calculated optimal geometries with the interatomic distances derived from HDO band positions. The energetic state of water in OH- hydration shells, as revealed by solute-affected HDO spectra, is similar to that of an isoelectronic F- anion. No evidence was found for the existence of stable hydroxide dimer, H3O2-, in an aqueous solution. Spectral data do confirm, however, existence of a weak interaction with a single water molecule at the hydrogen site of OH-.     

Electrophilic fluorination with N-fluoroquinuclidinium fluoride

N-Fluoroquinuclidinium fluoride (NFQNF), obtainable in ca. 90% yield by direct low-temperature liquid-phase fluorination of quinuclidine, has been used to deliver ‘positive’ fluorine to carbanionic sites in a number of organic substrates.     

Lead ion adsorption from aqueous solutions in modified Algerian montmorillonites

The adsorption of lead (II) ions on three Algerian montmorillonites (sodium, non-sodium, and acidic-activated) was studied. Transmission electron microscopy coupled with energy dispersive X-ray analysis, X-ray fluorescence and physical adsorption of gases were used to characterize the clays. This characterization has shown than the activation with acid increases the surface area as a consequence of the rupture of the laminar structure. The effect of the pH in the lead adsorption capacity was analyzed. The results show that adsorption is strongly depended on the pH. At low pH values, the mechanism that governs the adsorption behavior of clays is the competition of the metal ions with protons. Between pH 2 and 6, the main mechanism is an ion exchange process. The kinetics of the adsorption is tested with respect to pseudo-first-order and second-order models. The adsorption process, gives a better fit with the Langmuir isotherm, being the monolayer capacity ranging between 18.2 and 24.4?mg?g^?1. The adsorption of lead decreased in the order Acidic-M₂?>?M₂?>?M₁. Thermodynamic parameters such as ??H, ??S, and ??G were calculated. The adsorption process was found to be endothermic and spontaneous. The enthalpy change for Pb(II) by M₁ adsorption has been estimated as 60?kJ?mol^?1, indicating that the adsorption of Pb(II) by all montmorillonites used corresponds to a physical reaction. The adsorption capacity of washed Acidic-M₂ was very high compared to M₂ and M₁.     

Reactions involving fluoride ion. Part 40. Amines as initiators of fluoride ion catalysed reactions

Tetrakis(dimethylamino)ethene (TDAE) and trimethylamine react with anhydrous unsaturated fluorocarbons to produce, ‘in situ’, powerful fluoride- ion sources. These are used to initiate carbon- carbon bond forming reactions eg. oligomerisation and polyfluoroalkylation, and many of these reactions occur efficiently in the absence of a solvent.     

The reactions of polythionates: Kinetic of the cleavage of trithionate ion in aqueous solutions

A kinetic study of the cleavage of trithionate has been made in water over the temperature range of 40–80°C, and in aqueous ammonia solutions over the range of 40–70°C. In aqueous ammonia, the ammonolytic reaction of trithionate was found to proceed in competition with the hydrolytic one. For both reactions, a rate law of the form, -d[S₃O₆²]/dt = k_a[NH₃][S₃O₆²⁻] and -d[S₃O₆²⁻]/dt = k_w[H₂O][S₃O₆²⁻], was obtained. In the presence of thiosulfate, the thiosulfate-trithionate reaction, described by, -d[S₃O₆²⁻]/dt = k_t[S₂O₆²⁻][S₃O₆²⁻], may proceed in parallel with either or both the above solvolytic reactions. The activation parameters suggest that the mechanism of the solvolytic reactions differs from that of the thiosulfate-trithionate reaction which is expected to involve a nucleophilic displacement at the bivalent sulfur in trithionate. A mechanism of the cleavage of trithionate supported by the kinetic results has been proposed.     

The electrochemical fluorination of acetyl fluoride

The electrochemical fluorination of acetyl fluoride in anhydrous hydrogen fluoride to produce trifluoroacetyl fluoride was investigated in a microprocessor-aided modified Simons' reactor. The product was recovered in acetic acid as trifluoroacetic acid. The experiments were carried out at a controlled anodic potential using a Cu/CuF₂ reference electrode. Product yields of 36 - 45%, current efficiencies of 30 to 50% and energy efficiencies of 11 – 23% were obtained.Experimental results of this investigation are presented and discussed.     

Nucleophilic fluorination of amino alcohols and diols using Deoxofluor

Various fluorinated chiral compounds were synthesized using bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor) as a nucleophilic fluorinating reagent. Reactions of Deoxofluor (1) with amino alcohols (2a-d) and diols (2e-g) in methylene chloride at room temperature led to the formation of the corresponding fluoro derivatives (3a-g) in good yields.     

Potentiometric determination of the activity of fluoride ion in aqueous solutions at high pressure and high temperature

Summary A fluoride membrane electrode is described for the determination of the activity of fluoride ion in aqueous solutions at high pressure and elevated temperature. An Ag/AgCl electrode is used as a reference. The cell described has a linear potential at temperatures up to 200 °C and pressures up to 1 kbar. The interference of OH^– is only noticeable at fluoride concentration c_f– 10^–5 m in the temperature region between 175 °C and 200 °C.

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Potentiometrische Bestimmung der Aktivität des Fluorid-Ions in wäßrigen Lösungen bei hohem Druck und hoher Temperatur

     

Pd-catalyzed C-h fluorination with nucleophilic fluoride

The palladium-catalyzed C-H fluorination of 8-methylquinoline derivatives with nucleophilic fluoride is reported. This transformation involves the use of AgF as the fluoride source in combination with a hypervalent iodine oxidant. Both the scope and mechanism of the reaction are discussed.     

Sorption of silver ion from aqueous solutions using conducting electroactive polymers

In this research polypyrrole (PPy) and polyaniline (PAni) conducting polymers which were synthesized chemically on the surface of wood sawdust (SD). These electroactive polymers as coated form on sawdust then were used for sorption or removal of silver ion from aqueous solutions under simple open circuit conditions. The effects of some important parameters such as pH, initial concentration, sorbent dosage, and contact time on uptake of silver ion were also investigated in this research. The experiments were carried out using both batch and column systems at room temperature. The treatments of the data were carried out using both Freundlich and Langmuir adsorption isotherms. In order to find out the possibility of the regeneration and reuse of the exhausted adsorbent, desorption studies were also performed. It was found that conducting electroactive polymers such as PPy or PAni are efficient sorbents for removal of the silver ions from aqueous solutions. Sorption/desorption processes can be simply carried out with pH control with satisfactory performance. Recovery percentage observed for PAni/SD in column study was more than PPy/SD and SD, under the same operational conditions.     

Removal of mercury and fluoride from aqueous solutions by three-dimensional reduced-graphene oxide aerogel

Research on Chemical Intermediates - Three-dimensional reduced-graphene oxide (3-D RGO) hydrogel was synthesized by hydrothermal method from graphene oxide, de-ionized water, and oxalic acid...