Dipyrrolylmethane-based macrobicyclic azacryptand: synthesis, X-ray structures, conformational and anion binding properties

A new class of macrobicyclic azacryptand containing dipyrrolylmethane subunits with nitrogen bridgeheads was synthesized by the Mannich reaction of the dipyrrolylmethane in the presence of aqueous ammonia. The azacryptand exhibits a staggered conformation in the solid state, but is in a dynamic equilibrium with the eclipsed conformation in solution studied by the variable-temperature (1)H NMR methods. The azacryptand has a specific size suitable only for fluoride ion; large anions such as NO(3)(-) bind in the clefts of the macrobicycle as shown by the X-ray structures of its fluoride ion inclusion and the nitrate anion complexes. The anion binding studies showed that it has high selectivity and affinity for fluoride ion in acetone over other anions studied, which was supported by (1)H and (19)F NMR methods. The azacryptand has fast fluoride ion-mediated proton-deuterium exchanges with acetone-d(6) studied by the (19)F NMR method.     

Determination of fluoride in zinc concentrates, processing products and solutions with an ion-specific electrode

Determination of fluoride in hydrometallurgical zinc-plant processing products and solutions with a fluoride-ion electrode is described. Various types of buffers were tested, to find a suitable common buffer for use in analysis of all types of substances generated at the zinc plant. The method involves decomposition of samples either by fusion with sodium hydroxide or by leaching with perchloric acid to bring fluoride into solution. The fluoride concentration is measured directly with a fluoride-specific electrode. In standard addition tests 100% recovery was obtained when a citric acid/sodium nitrate buffer was used. Validation tests gave satisfactory results.     

Rapid sample preparation and voltammetric determination of lead, cadmium and copper traces in calcium fluoride

An improved method is described for the voltammetric determination of Pb, Cd and Cu in calcium fluoride. A shortening of the time required has been achieved by omitting the removal of the fluoride ions and by measuring blank and sample signals in one and the same solution (before and after adding CaF₂). The results were in satisfactory agreement with those obtained by other methods.     

Spectrophotometric determination of fluoride a comparative study and a suggestion for evaluating photometric data

Summary Attempts were made to develop a method for fluoride determination using the demasking principle; the result was negative. Using the method of bleaching, ferric-sulfosalicylate, ferric-tiferronate, titanium-chromotropic acid and zirconium-alizarin coloured systems have been thoroughly investigated and compared for use as reagents for fluoride determination. Ferric-sulfosalicylate system has been proved to be the best. A new method of comparing photometric data has been suggested. Error in fluoride determination by ferric-sulfosalicylate method according to the method calculation suggested is between 1.80 percent and 4.60 percent, when the fluoride concentration is from 16 to 40 ppm. The method gives reproducible results when the fluoride concentration is in the range of 0.8 ppm to 4.0 ppm.     

Theoretical calculation of the singlet-triplet electronic transition and photochemical reactivity in carbonyl fluoride,trifluoroacetyl fluoride and perfluoromethyl perfluoroacetate

Molecular properties following electronic excitation were studied and calculations were performed for the singlet-triplet electronic transitions of carbonyl fluoride, perfluoroacetyl fluoride and perfluoromethyl perfluoroacetate by means of the CNDO/S-CI method. Various approximations were used to evaluate the core Hamiltonian matrix elements.     

Potentiometric titration of fluoride,sulfate, chromate,molybdate, tungstate,oxalate, phosphate,pyrophosphate and hexacyanoferrate(II) ions with lead(II) solutions and a fluoride-selective electrode

A semi-automatic potentiometric method is described for the direct titration of fluoride with lead(II) solutions in the presence of added chloride. Sulfate, chromate, molybdate, tungstate, oxalate, phosphate, pyrophosphate, and hexacyanoferrate(II) are titrated similarly in the presence of added chloride and fluoride. A fluoride-selective electrode is used to detect the end-points. Fluoride in the range 0.57–5.7 mg can be determined with a precision of about 0.3%. The other ions can be determined in the range 0.025–0.30 mmol with a precision of 0.5–1%.     

Adsorption of fluoride, chloride, bromide, and bromate ions on a novel ion exchanger

A novel ion exchanger based on double hydrous oxide (Fe2O3Al2O3xH2O) was obtained by the original sol-gel method from easily available and cheap raw materials and employed for adsorption of F-, Cl-, Br-, and BrO-3 from simultaneous solutions. Adsorbent was characterized by potentiometric titration, zeta-potential, and poremetrical characteristics. A technologically attractive pH effect of F-, Br-, and BrO-3 sorption on the investigated double hydroxide of Fe and Al, which is capable of working in the pH range 3 to 8.5, was observed. Kinetic data on fluoride and bromide sorption fit well the pseudo-second-order model. Isotherms of fluoride, bromide, chlorine, and bromate ion sorption on Fe2O3Al2O3xH2O were obtained at pH 4. The isotherm of F- sorption fit well the Langmuir model; sorption affinity (K=0.52 L/mg) and sorption capacity (90 mg F/g) were high. In the competitive adsorption of bromide and bromate, bromide dominated at equilibrium concentrations of the ions >40 mg/L. The mechanism of fluoride adsorption to the surface of the model cluster of the sorbent synthesized and the geometry of the cluster itself were modeled with the HyperChem7 program using the PM3 method.     

Indirect kinetic microdetermination of oxalate, citrate, and fluoride ions

An indirect catalytic method for the separate microdetermination of oxalate, citrate, and fluoride ions is described. The method is based on the inhibition action of oxalate, citrate, and fluoride ions on the catalytic oxidation reaction of 2,4-diaminophenol-hydrogen peroxide by iron(III).Procedures for the determination of 1.76 × 10⁻² to 17.6 × 10⁻² μg/ml for oxalate ion, 3.78 × 10⁻² to 30.24 × 10⁻² μg/ml for citrate ion, and 0.38 to 4.18 μg/ml for fluoride ion are given.Quantities of 1.76 × 10⁻² to 17.6 × 10⁻² μg/ml for oxalate ion, 3.78 × 10⁻² to 30.24 × 10⁻² μg/ml for citrate ion, and 0.38 to 4.18 μg/ml for fluoride ion could be determinated with a relative error of about 1–3.5% for oxalate and citrate ions and 1–2% for fluoride ion.     

On-line flow injection solid sample introduction, leaching and potentiometric determination of fluoride in phosphate rock

A flow injection method with on-line solid sample dissolution was developed for the determination of fluoride in phosphate rock. The fluoride was selectively leached (98-102.4 % recovery) from a 50-mg powdered phosphate rock sample with 0.50 M citric acid. Using the zone sampling technique the fluoride in the buffered leachate was determined by injecting 87 μL into the carrier stream using a fluoride ion-selective electrode detector. The sensing element of the electrode was housed in a home-made sleeve-type flow-through cell. On-line solid sample digestion with 0.50 M citric acid at 55 °C resulted in minimum dissolution of interfering iron and aluminum ions with improved accuracy and calibration linearity. The incorporation of relatively high level of fluoride in the carrier stream (40 μg mL⁻¹) facilitated the determination of high levels of fluoride in phosphate rock (up to 4.1%) with out the need for excessive on-line dilution.The optimized flow system was applied for the determination of fluoride in phosphate rocks samples and a reference material at a rate of nine samples per hour with a relative standard deviation (n = 5) of 2.95-4.0 %. Comparison of the proposed flow injection method with the standard method, which involves steam distillation from sulfuric acid solution and manual titration with thorium nitrate, showed no evidence of bias at the 95% confidence level.     

alpha,beta,gamma-Trifluoroalkanes: a stereoselective synthesis placing three vicinal fluorines along a hydrocarbon chain

A regio- and stereoselective method for the synthesis of alpha,beta,gamma-trifluoroalkanes is described which allows the synthesis of single diastereoisomers of this structural motif. The methodology relied upon regiospecific and stereospecific hydrogen fluoride ring opening of allylic epoxides and then Sharpless cyclic sulfate methodology followed by nucleophilic fluoride attack to introduce the second fluorine. The resultant difluoro alcohol was converted to its triflate which was also displaced by fluoride ion to generate the alpha,beta,gamma-trifluoroalkanes.     

A New Method for the Preparation of Sulphuryl Chloro Fluoride

It has been observed that a suspension of sodium fluoride in boiling acetonitrile could be used for the preparation of fluorine compounds such as silicon tetrafluoride [1], thiophosphoryl fluoride [2], sulphur tetrafluoride [3,4], and fluorocyclophosphazenes [5]. This method, when adopted for the fluorination of sulphuryl chloride [6], it is observed that a mixture of sulphuryl fluoride and sulphuryl chloro fluoride is obtained. On the other hand, when lead fluoride is substituted for sodium fluoride, pure sulphuryl chloro fluoride is evolved. Based on this observation, a new method has been standardised for the preparation of a pure sample of sulphuryl chlorofluoride by fluorinating sulphuryl chloride by lead fluoride in acetonitrile medium.     

The determination of microgram quantities of fluoride : The use of the aluminium-haematoxylin complex

This paper describes a method for the spectrophotometric determination of fluoride. The fluoride is separated from interfering ions by the standard method of distillation as hydrofluosilicic acid. The fluoride in this distillate is determined by its destruction of the aluminium-haematoxylin complex; the amount of complex destroyed which is directly proportional to the concentration of fluoride is measured spectrophotometrically using radiation of 5700 A. The method will detect down to 0.05 p.p.m. of fluoride on a 10 gram sample with precision of rather better than ± 10% with larger amounts of fluoride. references p. 368.     

Fluoroketenes VII. Synthesis and reactivity of trifluoromethylfluoroketene,perfluoroacryloyl fluoride,perfluoromethacryloyl fluoride,methyl perfluoroacrylate and methyl perfluoromethacrylate

Trifluoromethylketene has been detected by trapping reactions, but has not been isolated. In the absence of a trapping agent, reactions designed to give the ketene gave its isomer, perfluoroacryloyl fluoride. Convenient syntheses are described for saturated precursors to perfluoroacryloyl fluoride, methyl perfluoroacrylate and methyl perfluoromethacrylate, and conditions are given for the dehydrofluorination of these precursors to the acrylates. Some chemistry of perfluoromethacryloyl fluoride [available from bis(trifluoromethyl)ketene through equilibration], perfluoroacryloyl fluoride and the related methyl esters are reported, particularly Michael additions, 1,2 cyclo-additions and free-radical reactions.     

Development and application of a fully automated,battery-operated,computerized field-based fluoride monitor

An automated, portable, battery-operated, computerized field-based monitor for the determination of fluoride based on the use of ion-selective electrode (ISE) potentiometry has been developed with the aid of low-powered complementary metal oxide semiconductor (CMOS) devices. The whole analytical cycle involving the rinsing of the cell, sampling, stirring, dosing of standards to the sample and data acquisition and manipulation is under microprocessor control. The modular instrument consists of pumps, valves, a flow-through cell containing a reference electrode, a fluoride ISE, a temperature probe and a stirrer, a microprocessor with a real-time clock, a pump-valve-stirrer interface, a portable terminal and a 12-V lead-acid battery to power all the instrumentation. The software for the application and monitoring functions for the instrument is written at assembler level and programmed into a CMOS erasable programmable read only memory (EPROM). The instrument is currently designed to determine fluoride in natural and fluoridated waters and is based on a double standard addition method, although the monitor can be modified easily to suit other appropriate ISE systems. Instrumental performance was evaluated with synthetic and real water samples both in the batch and continuous modes. The monitor can be used to carry out on-line fluoride determinations of water samples continuously for 1 week without anyone being attendance.     

A molecular receptor based on the 2,3,7,8,12,13,17,18-octaethyl-21,23-dimethylporphyrin for detection of fluoride ions: Synthesis, spectral and complexation properties

2,3,7,8,12,13,17,18-Octaethyl-21-methylporphyrin and 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate based on the former were synthesized. Basic and complexing properties of these compounds were studied by the method of spectrophotometric titration in acetonitrile-perchloric acid and acetonitrile-tetrabutylammonium fluoride systems at 298 K. It was established that in the system of acetonitrile-perchloric acid the cationic forms of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin do not form complexes with fluoride ions, whereas 2,3,7, 8,12,13,17,18-octaethyl-22,23-dimethylporphyrin monotriflate forms complexes of 1:1 composition with the fluoride ions. The protonation constant of 2,3,7,8,12,13,17,18-octaethyl-21-methylporphyrin and the stability constant of the complex of 2,3,7,8,12,13,17,18-octaethyl-22,23-dimethylporphyrin with fluoride ions in acetonitrile at the standard temperature were determined.     

Decomposition procedure with aqua regia and hydrofluoric acid at room temperature for the spectrophotometric determination of phosphorus in rocks and minerals

A rapid spectrophotometric method for the determination of phosphorus in rocks and minerals is described. The sample solution is prepared by treatment with hydrofluoric and aqua regia at room temperature. Unreacted fluoride ions are complexed with boric acid. As fluoride ions do not have to be removed by heating, the method is rapid and avoids the use of platinum ware.     

Perfluoropropylene oxide as a reagent for the synthesis of germanium,titanium, tin,and zirconium fluorides

A new method of preparation of germanium, titanium, tin, and zirconium fluoride alcohol complexes by reaction of the metal oxides with a solution of perfluoropropylene oxide in methanol is developed. The reaction of the complexes obtained with ligands (L = 1,10-phenanthroline or dimethyl sulfoxide) was studied, and the structure of the obtained compounds was determined. A new route to the synthesis of 1-fluorogermatrane is developed.     

Study of Carbamoyl Fluoride: Synthesis,Properties and Applications

Carbamoyl fluoride is a fluorinated group that, to this date, remains underexplored, probably due to the lack of data concerning its properties. In this paper, a study of carbamoyl fluoride is presented. Stability studies, in particular under physiological conditions, and lipophilicity measurement were performed. A new easy, safe, inexpensive, and metal-free synthesis method is also described. Finally, a potential use in radiochemistry through a ¹⁸F/¹⁹F isotopic exchange is demonstrated.     

Formation of mullite,topaz and corundum

The influence of aluminium fluoride on the thermal behavior of quartz and the formation of topaz, mullite and corundum have been examined in the present work using the derivatograph. The products of sintering were identified microscopically and by using a Siemens Crystalloflex diffractometer. The DTA curves indicate the formation of topaz at 760°C and the formation of mullite at 1000°C using the theoretical amount of aluminium fluoride. The reaction between quartz and aluminium fluoride takes place in two distinct steps using 50% excess of aluminium fluoride. The first is marked by a large endothermic peak at 780°C, representing the formation of topaz and the second by a sharp endothermic peak at 960°C, representing its subsequent dissociation with the formation of corundum or alpha-aluminium oxide.     

The use of triethanolamine in a buffer for the determination of fluoride in calcium and transition metal orthophosphates, using a fluoride-selective el

A method is described for the determination of fluoride in inorganic orthophosphates. Interference by complex-forming metal ions is avoided by the use of a citric acid-triethanolamine buffer, pH < 7.5.