Structure of a poly(2,5‐benzimidazole)/phosphoric acid complex

As‐cast films of poly(2,5‐benzimidazole) exhibit uniplanar orientation in which the planes of the aromatic rings lie parallel to the film surface. Upon doping with phosphoric acid, the original crystalline order is lost, but the doped film can be stretched to produce films with uniaxial orientation. After thermal annealing at 540 °C, nine Bragg reflections are resolved in the fiber diagram, and these are indexed by an orthorhombic unit cell with the dimensions a = 18.1 Å, b = 3.5 Å, and c = 11.4 Å, containing four monomer units of two chains. The absence of odd‐order 00l reflections points to a 2₁ chain conformation, which is probably planar so that the aromatic units can be stacked along the b axis. The water and phosphoric acid contents of the crystalline structure cannot be determined exactly because of the presence of extensive amorphous regions that probably have different solvation. The best agreement between the observed and calculated intensities is for an idealized structure containing two phosphoric acids and two water molecules per unit cell. However, the phosphoric acid is probably present mainly in the form of pyrophosphoric acid and its higher oligomers. In addition, the X‐ray data are consistent with a more disordered structure containing chains with random (up and down) polarity and a lack of c‐axis registry. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2576–2585, 2004     

Identification of impurities accumulated in the extractant in the course of purification of wet-process phosphoric acid with tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate

Impurities accumulated in the extractant in the course of operation of the plant for purification of wet-process phosphoric acid, obtained from apatite concentrate, by extraction with tri-n-butyl phosphate are identified by IR and mass spectra.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 9, 2004, pp. 1425–1429.Original Russian Text Copyright © 2004 by Lembrikov, Konyakhina, Volkova, Perov, Kiseleva, Ershova.     

Uranium determination in phosphoric acid solutions

In order to determine uranium from raw phosphoric acid solutions, resulted by the sulphuric acid attack of phosphate rocks and the strip solutions of the solvent extraction process for uranium recovery, two classes of analytical methods were established: one for low uranium content in phosphoric acid, and the other for higher uranium concentration in the same medium. The study was based on specific methods, therefore interference probability with other impurities in phosphoric acid medium is low. In the first class, X-ray fluorescence and spectrophotocolorimetric methods were used. X-ray fluorescence was applied on direct raw phosphoric acid solution and raffinate. The last one was associated with solvent extraction [di-(2-ethylhexyl) phosphate + triocylphosphine oxide] on the U(IV)-Arsenazo III complex in strip. The methods of the second class, were used for strip uranium concentrated solutions: X-ray fluorescence isotopic dilution and mass spectrometry, spectrophotocolorimetry and activation analysis associated with gamma-spectrometry. Here spectrophotocolorimetry involves two methods. The first one is based on the U(IV)-Arsenazo III complex and the other on direct U(IV)—phosphoric acid solutions measurements. A good agreement was obtained in each case for all comparative measurements involving various methods.     

The chromatography of metals on DEAE-cellulose layers in phosphoric acid media

The adsorption behaviour of forty-eight metals on DEAE-cellulose thin layers has been examined in aqueous phosphoric acid media. R_F values are given as a function of phosphoric acid concentration over the range 0.01–1.0 M and are compared with those obtained in a similar manner with a crystalline cellulose, Avicel SF. Particularly strong retention on DEAE-cellulose occurred for Mo(VI), W(VI), Re(VII), the platinum group metals, Au(III) and Bi(III). Weak to moderate retention was also observed for several metals, such as V(V), Fe(III), Se(IV), In(III), the rare earths and U(VI), at lower concentrations of phosphoric acid (<0.1 M).     

Monolayer characterization of several short alkyl chain phosphoric acid extractants

The monolayer behavior of a group of short-chain alkyl phosphates was investigated with Langmuir trough techniques. The compounds were all octyl or ethylhexyl phosphates or phosphinates; the exceptionally small hydrophobic moieties in these compounds do not permit the formation of stable, coherent films at room temperatures. Stable monolayers were formed, however, on subphases of 1 M nitric acid at 5–10°C. The apparent areas per molecule are consequently strongly temperature dependent with total desorption evidently taking place at room temperature. When compared to molecular areas estimated from space-filling models, the experimentally determined limiting molecular areas are greater by factors of 1.1 to 2. Compounds containing ethylhexyl groups yielded limiting molecular areas in much closer agreement with model estimates than did the octyl-containing compounds. A limiting minimal area per molecule, particularly for the ethylhexyl systems, was approached only after several cycles of compression and reexpansion. This result indicates that the weak van der Waals interactions present and the high viscosity of the systems allow coherent film formation only after repeated partial structuring of the system after several compressions. Expansion of previously compressed monolayers revealed marked hysteresis effects. The systems investigated included: di-n-octyl phosphoric acid, di-n-octyl phosphinic acid, tri-n-octyl phosphate, tri-n-octyl phosphine oxide, bis-2,2 dimethylhexyl phosphoric acid, bis (2-ethylhexyl) phosphoric acid, bis (2-ethylhexyl) phosphinic acid, 2-ethylhexyl, 2-ethylhexyl phosphonic acid, and tris (2-ethylhexyl) phosphate.     

Determination of polonium-210 in phosphoric acid

Polonium-210 in phosphoric acid has been recognized as a significant source of alpha contamination of processed Si-wafers for memory devices of computer. In the present work, a convenient method was developed for the determination of trace²¹⁰Po in phosphoric acid of high purity. For the determination,²⁰⁹Po was used as a yield tracer. The present method consists of (1) addition of the tracer to 5 ml aliquot of phosphoric acid sample, (2) pH adjustment (to 2) of the sample solution to make up electrolytic solution, (3) electrodeposition for the simultaneous achievement of Po separation and preparation of counting source on stainless-steel disc, and (4) alpha-ray spectrometry. By the developed method, more than 95% of Po was separated from phosphoric acid sample onto counting disc. The minimum detectable radioactivity of²¹⁰Po in 5 ml of phosphoric acid was about 0.03 mBq by counting the electrodeposited alpha-activity for 10 days under a counting efficiency of ≈30%.     

Natural radionuclide-free phosphoric acid production

High-uranium phosphate rock from Itataia, Brazil, was milled for wet-process phosphoric acid production using the dihydrate method. Uranium contained in the phosphoric acid was recovered by solvent extraction. The distribution of long-lived natural radionuclides of the ²³⁸U and ²³²Th decay series involved in these operations was evaluated. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were found to predominate in the phosphogypsum, while ²²⁸Th, ²³⁰Th and ²³²Th in the uranium-free phosphoric acid. Thorium is removed from the phosphoric acid by solvent extraction to produce a NORM-free phosphoric acid.     

Reaction of thio and seleno phosphoric acid derivatives with O‐thioacylated hydroxylamine

The reactivity of thio and seleno analogs of phosphoric acid 1b–f with O‐thioacylhydroxylamine 2 was examined. The experimental evidence for the proposed mechanism involving an N—O bond cleavage and a single electron transfer process (SET) from phosphate anions was collected. The influence of phosphoric acids 1 structure and their oxidation potentials on the course of the reaction and products 3, 4, 6, 7 distribution was presented. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:767–773, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20368     

Preparation and characterization of polybenzimidazole membranes prepared by gelation in phosphoric acid

Phosphoric acid doped poly (2, 2′‐(m‐phenylene)‐5, 5′‐bibenzimidazole) (PBI) membranes were prepared by dissolving PBI powders in 85% phosphoric acid at 190–200°C and then promoting gelation of the PBI by cooling the solutions to ?18°C. The extent of acid doping of the PBI membranes was controlled by immersing the membrane in aqueous phosphoric acid solutions of different concentrations (acid de‐doping). The process of the acid de‐doping was faster than acid doping of membrane cast from N,N‐dimethylacetamide (DMAc). The de‐doping process caused shrinkage of the PBI membrane and thus an increase in the membrane strength due to the packing of PBI chains according to the X‐ray diffraction analysis. The tensile stress and proton conductivity of the obtained PBI membranes with different acid doping levels were measured. For a PBI (η_IV: 0.58 dL · g^?1) membrane with an acid doping level of 7.0 (molar number of doped acid per mole repeat unit of PBI), the stress at break and proton conductivity at 120°C without humidification were 2.6 MPa and 5.1 × 10^?2 S · cm^?1, respectively. These results were comparable to those of the membranes cast from PBI solutions in DMAc. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of oxidation-reduction on the extraction of uranium from wet phosphoric acid by DEHPA/TOPO

Uranium is recovered from wet phosphoric acid by DEHPA/TOPO in kerosene. Uranium is present in wet phosphoric acid in the tetravalent and hexavalent states but DEHPA/TOPO extracts uranium in the hexavalent state only. The ratio of U⁴⁺/U⁶⁺ depends on several factors such as the origin of the phosphate rock, the method of preparation of phosphoric acid and the presence of other impurities. Therefore it is important to oxidize the wet acid to convert all uranium to U⁶⁺ before extraction. Uranium is stripped from the solvent by a reverse process where a concentrated phosphoric acid is used under reducing conditions. This paper studies the oxidation of wet phosphoric acid from Homs plant/Syria by H₂O₂ oxidant and the effect of oxidation on extraction coefficientK. It also studies the reduction by iron and its effect on back extraction of uranium from the solvent to phosphoric acid.     

Characteristics of oxygen exchange in phosphoric acid

The oxygen exchange between phosphoric acid and water at various temperatures and concentrations has been investigated in the presence and absence of K₂HPO₄. The minimum rate of exchange is observed for a solution concentration of 2–2.5 mole/l. It has been shown that in concentrated solutions of phosphoric acid the formation of H₄PO ₄ ⁺ is possible, and the true rate constant of the acid-catalytic conversion and the basicity constant of H₃PO₄ has been calculated. It has been found that in a solution where the mobility of the oxygen atom towards the anion increases, the value of the limiting current on the anodic dissolution of copper diminishes.     

A simplified method of preparing phosphoric acid for stable isotope analyses of carbonates

In order to produce CO₂ for stable isotope analyses (δ¹⁸O and δ¹³C), carbonate samples are commonly digested in phosphoric acid. The acid recipe here presented is based on phase shifting crystalline orthophosphoric acid of pro‐analysis quality to a liquid state through heating, followed by pre‐vacuum treatment during a start‐up procedure before mass analyses for common acid bath preparation, or adding a small amount of phosphoric pentoxide for single drop equipments, respectively. This methodology results in a final acid concentration of 104%. Copyright © 2005 John Wiley & Sons, Ltd.     

Dissociation constants of phosphoric acid in dimethylformamide-water mixtures at 298.15 K

The dissociation constants of phosphoric acid (pK ₁ and pK ₂) in water-dimethylformamide (DMFA) mixtures (0–0.65 mole fractions of DMFA) were determined at 298.15 K by potentiometric titration. The extrapolation of these data to pure DMFA and the comparative calculation method were used to estimate the dissociation constants of the acid in DMFA.     

Chiral Brønsted acid-catalyzed hydrophosphonylation of imines—DFT study on the effect of substituents of phosphoric acid

The enantioselective hydrophosphonylation reaction of diisopropyl phosphite with aldimine furnished α-amino phosphonates with high enantioselectivities by means of a chiral phosphoric acid. DFT calculation of the effect of 3,3′-substituents of the phosphoric acid revealed the reason for the high enantioselectivities.     

Sorption extraction of lanthanides from phosphoric acid solutions

The possibility of sorption extraction of lanthanides from nitric-phosphoric and phosphoric acid solutions with inorganic sorbents based on hydrated titanyl hydrophosphate was studied. New technological solutions were suggested for lanthanide sorption from the products which are formed in processing of the Khibiny apatite concentrate on mineral fertilizers (frozen nitric-phosphoric acid extract, a product of nitric acid decomposition of apatite, and the production phosphoric acid from the dihydrate process).     

Condensation of n-alkyl-n-methylolamides of diethyl phosphoric acid with carboxylic acid amides

Conclusions Condensation of the N-alkyl-N-methylolamides of diethyl phosphoric acid (alkyls - methyl, ethyl, propyl, butyl, and amyl) with amides of formic, acetic, and chloroacetic acids and urethane gave the corresponding N-alkyl-N-(acylaminomethyl)amides of diethyl phosphoric acid; the products have been characterized.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2133–2134, September, 1968.     

Electrochemical polymerization of aniline in phosphoric acid

The electrochemical synthesis of common conductive polymers such as polyaniline in phosphoric acid is a little different from that in other acidic media such as sulfuric acid. Electropolymerization in phosphoric acid is difficult, and this electrolyte medium is not applicable for this purpose. However, it is possible to overcome this problem by the addition of a small amount of sulfuric acid. In this case, the electropolymerization process can be successfully performed when the phosphate ion is doped. For instance, polyaniline films electrodeposited from an electrolyte solution of phosphoric acid have good stabilities and useful morphologies. Interestingly, phosphate doping results in the formation of nanostructures, whereas the polymer surface is macroscopically smooth. In an appropriate ratio, a mixed electrolyte of H₃PO₄ and H₂SO₄ can be used for the electropolymerization of aniline; thus, H₂SO₄ acts as a required agent for successful polymer growth, and H₃PO₄ acts as a doping agent. In this case, a small amount of sulfate is incorporated into the polymer matrix, which does not participate in the electrochemical insertion/extraction process. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3304–3311, 2006     

Solubility and physic-chemical properties of NaH2PO4 in phosphoric acid,sodium chloride and their mixture solutions at T = (298.15 and 313.15) K

In this study, solubility and physic-chemical properties of sodium dihydrogen phosphate in sodium chloride, phosphoric acid and their mixture solutions at T = (298.15 and 313.15) K have been investigated by using isothermal dissolution method. In the three systems, the solubility of NaH₂PO₄ always increases with the temperature increasing and decreases with molar concentration of phosphoric acid (sodium chloride) increasing because of the same ion effect. Solubility data of sodium dihydrogen phosphate in the mixed solution of sodium chloride and phosphoric acid is basically required for designing and optimizing the solvent extraction process in the industrial production.     

Crystalline stoichiometric adducts of polyamides with phosphoric acid

It is shown the crystalline stoichiometric adducts of phosphoric acid with polyamides such as nylon 6 and poly-p-benzamide, and probably nylon 66, nylon 69, nylon 11, and nylon 12, can be prepared. These adducts are characterized by their unique wide-angle x-ray diffraction patterns and by rather low melting or decomposition temperatures. The thermal behavior and infrared data, indicate that interactions between the acid and the polymeric amide residues are weak.     

Carbon-13 kinetic isotope effects in the decarbonylation of formic acid of natural isotopic composition in phosphoric acid media

The¹³C kinetic isotope effect (K.I.E.) in the decarbonylation of formic acid of natural isotopic composition in 85% orthophosphoric acid, in 100% H₃PO₄, and in pyrophosphoric acid has been measured in different temperature intervals ranging from 19 to 133 °C. In 85% H₃PO₄ the carbon-13 K.I.E. is determined by the fractionation of carbon isotopes expected for C–O bond rupture (k ₁₂/k ₁₃=1.0531 at 70°C). In 100% H₃PO₄ the¹³C K.I.E. indicates that C–H bond rupture is the major component of the reaction coordinate motion (thek ₁₂/k ₁₃ lay in the range of 1.026–1.017 over the range 30–70 °C). In pyrophosphoric acid the fractionation factor for¹³C equals 1.010 at 19 °C. Activation parameters for the decarbonylation of H¹²COOH in phosphoric acid media have been determined also and suggestions concerning the intimate mechanisms of decarbonylation of formic acid in dilute and concentrated phosphoric acids are made.