Optical anisotropy and conformation of polyamidebenzimidazole in an organic solvent and in concentrated sulphuric acid

Flow birefringence, intrinsic orientation and intrinsic viscosities of polyamidebenzimidazole (PABI) and poly-meta-phenylene-isophthalamide (PPIP) molecules have been studied for a wide range of molecular weights. The optical and conformational properties of PABI molecules in dimethyl acetamide (DMAA) and concentrated sulphuric acid are compared. The conformation of PABI (kinetically rigid coil) is shown to be practically the same in both solvents. This fact indicates the practical absence of a significant role of protonization of molecules during formation of conformation of aromatic polyamides macromolecules in sulphuric acid. There is comparison of the coefficients G = [χ/g]RT/M[η]η₀ for PABI and PPIP molecules in sulphuric acid and DMAA. Values of G of 0.65 ± 0.05 for PABI and 0.30 ± 0.03 for PPIP correspond to those for rigid and flexible Gaussian coils respectively.     

The separation of titanium from vanadium and molybdenum by cupferron solvent extraction

The isolation of small amounts of titanium from vanadium and molybdenum before the spectrophotometric determination of titanium as the “pertitanate” complex has been achieved by a. solvent extraction procedure using cupferron and chloroform at pH 6 in the presence of EDTA.     

Synergistic extraction of americium with MEHPA-DEHPA mixed solvent from nitric acid solution

The synergistic effect of the MEHPA-DEHPA mixed system was examined for the extraction of Am(III) from nitric acid solution. Addition of DEHPA or 2-ethylhexanol in MEHPA results in a deleterious effect at MEHPA concentrations lower than 2·10⁻²M but an enhancing effect at higher concentrations. At DEHPA to MEHPA mole ratios of 2 to 4 in moles, the mixed solvent shows a Df for Am which is 1000 times higher than that of DEHPA.     

The melting behaviour of concentrated sulphuric acid investigated by DSC

The DSC-investigation of different concentrated sulphuric acid solutions shows that the results of this dynamic measurement method are in good agreement with those of steady state methods [1]. The diverse DSC-melting peaks can be interpreted by using the known behaviour of the system SO₃/H₂O [1] as the melting of different congruent melting phases or eutectics, respectively. The observed melting enthalpies are in the correct order.

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Zusammenfassung DSC-Untersuchungen an Schwefelsäurelösungen verschiedener Konzentration zeigten, daß die Ergebnisse dieses dynamischen Meßverfahrens mit den Ergebnissen von Gleichgewichtsverfahren in guter Übereinstimmung stehen. Die verschiedenen DSC-Schmelzpeaks können unter Zuhilfenahme des bekannten Verhaltens des Systemes SO₃/H₂O, nämlich mit dem Schmelzen unterschiedlicher kongruenter Schmelzphasen bzw. Eutektika erklärt werden. Die ermittelten Schmelzenthalpien liegen in der richtigen Größenordnung.

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, , . , SO₃/H₂O, . .

     

The extraction of molybdenum(VI) from perchloric acid solution by tri-n-butyl phosphate

The extraction of molybdenum(VI) by tri-n-butyl phosphate (TBP) from 1 M NaClO₄ medium has been investigated as a function of molybdenum concen     

Substituted ethan phosphonic acid esters as reagents for the separation of molybdenum from rhenium by solvent extraction

New esters of the ethan phosphonic acids have been synthesized and their extraction properties studied with respect to Mo(VI), Re(VII), Fe(III),Au(III),Tl(III) and Sb(V). A possibility is shown for the analytical separation of molybdenum from rhenium (beta = 700). The state of these new extraction agents in carbon tetrachloride solution, and the mechanism of the extraction processes, have been investigated by means of infrared spectra.     

A solvent extraction study of molybdenum chloride and molybdenum thiocyanate complexes

The effect of reducing agents on molybdenum(VI) solutions in hydrochloric acid was studied by a solvent extraction technique to elucidate the composition of the colored molybdenum thiocyanate complex. Neither copper(I) chloride nor ascorbic acid have any effect on the extraction of MoO₂Cl₂; it is inferred that tin(II) chloride reduces Mo(VI) stepwise to a polynuclear Mo(V)·Mo(VI) complex and then to Mo(V). The colored thiocyanate complex produced by copper(I) and by ascorbic acid differs only slightly in extraction characteristics from the uncolored Mo(VI) complex. It is suggested that the color may be produced by an isomerization reaction of MoO₂(SCN)₂, and thus that the colored species may be a hexavalent rather than pentavalent molybdenum complex.     

Polarographic determination of nitrate in concentrated sulphuric acid solutions

The possibility of the polarographic determination of nitrates in the presence of hydroquinone in 65–95% sulphuric acid solutions was investigated. It has been found that nitrates in 95% acid have one polarographic wave without inflection point the height of which is proportional to nitrate concentration. In 85% sulphuric acid and in other acids investigated with lower concentrations, nitrates are not polarographically active. If both nitrate and hydroquinone are present in H₂SO₄, two waves are observed on the polarogram. The more negative wave is completely defined. The height of this wave is proportional to nitrate concentration in the range 5×10^?5?5×10^?3M.     

Hydrolytic thermal degradation of polyamidobenzimidazole in concentrated sulphuric acid

Thermal analysis has been carried out on the process of degradation of polyamidobenzimidazole in solution in 97.8% sulphuric acid for 0.2 to 200 hr at 20 to 110°. Hydrodynamic and optical methods were used to establish that the degraded macromolecules exhibit the same equilibrium rigidity and optical anisotropy of unit length as the undegraded molecules of polyamidobenzimidazole of various molecular weights. Thermal degradation proceeds according to the law of probability. The activation energy of degradation, 134 kJ/mol, coincides with that for low molecular weight amides. Hence, the main degradation mechanism is the breaking of the macromolecules at the amide bonds. This phenomenon can be used for analytical purposes to achieve a controlled decrease in the length of the macromolecules. In 112.5% oleum, thermal degradation proceeds much faster and the activation energy is lower by a factor of two-three.

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Zusammenfassung Die Thermoanalyse der Zersetzung von Polyamidobenzimidazol wurde in Lösungen von 97.8% Schwefelsäure während 0.2 bis 200 h bei 20 bis 110° durchgeführt. Hydrodynamische und optische Methoden wurden eingesetzt um festzustellen, daß die abgebauten Makromoleküle dieselbe Gleichgewichtsrigidität und optische Anisotropie der Längeneinheit aufweisen wie die nicht abgebauten Moleküle von Polyamidobenzimidazol verschiedenen Molekulargewichts. Die thermische Zersetzung verläuft nach dem Gesetz der Wahrscheinlichkeit. Die Aktivierungsenergie der Zersetzung, 134 kJ/mol, stimmt mit den der Amide niedrigen Molekulargewichts überein. Folglich besteht der Hauptmechanismus der Zersetzung in der Spaltung der Makromoleküle in den Amidbindungen. Dieses Phänomen kann für analytische Zwecke verwendet werden um eine gesteuerte Abnahme der Länge der Makromoleküle zu erzielen. In 112.5%igem Oleum verläuft die Zersetzung viel schneller und die Aktivierungsenergie ist um einen Faktor von 2 bis 3 niedriger.

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Résumé On a effectué l'analyse thermique de la dégradation du polyamidobenzimidazole en solutions 97.8% d'acide sulfurique pendant 0.2 à 200 h, à 20–110°. On s'est servi de méthodes hydrodynamiques et optiques et établi que les macromolécules dégradées montrent la même rigidité à l'équilibre et la même anisotropie optique par unité de longueur que les molécules non dégradées du polyamidobenzimidazole de divers poids moléculaires. La dégradation thermique procède selon une loi de probabilité. L'énergie d'activation de la dégradation, 134 kJ/mole, coincide avec celle des amides à faibles poids moléculaires. Par conséquent, le mécanisme principal de la dégradation consiste en la rupture des macromolécules aux liaisons amides. Ce phénomène peut être appliqué en analyse, afin de réaliser une diminution contrôlée de la longueur des macromolécules. Dans de l'oléum à 112.5%, la dégradation s'effectue bien plus vite et l'énergie d'activation est plus faible d'un facteur 2 à 3.

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97.8% 0.2–200 20–110°. , , . . 134 / . , . . 112.5% , — .

     

Chloroform extraction of ethyl xanthate complexes from sulphuric acid media

The chloroform extraction of 30 elements (Fe, Co, Ni, Zn, Cd, Ge, Sn, V, As, Sb, Bi, Cu, Ag, Au, Mn, Re, Ga, In, Tl, Se, Te, Cr, Mo, U, Pt, Pd, Rh, Ir, Ru and Ce) from 0.1-8M sulphuric acid in the presence of potassium ethyl xanthate has been studied. Pd(II), Bi, As(III), Sb(III), Se(IV) and Te(IV) are completely extracted and Au(III) is largely extracted over the range of acid concentration investigated. Fe(II), Tl(I), Rh(III) and Cr(VI) are only slightly extracted and Se(VI), Te(VI), Ru(III), Cr(III), Mn(II), Zn, Ce(IV), Ir(IV) and Ge(IV) are not extracted at all. Depending on the acid concentration, the remaining elements are all partly extracted. Results are compared with those obtained in an earlier study of the extraction of xanthate complexes from hydrochloric acid media. The processes involved in the formation of some xanthate complexes and potential analytical separations are discussed.     

Extraction of sulphuric acid from technological solution of hydroxylamine sulphate

The extraction of sulphuric acid from solutions containing hydroxylamine sulphate and ammonium sulphate with Cyanex 923 and the acid stripping from loaded Cyanex 923 are studied at 20 and 50°C. The effect of the numbers of extraction and stripping stages and the volume phase ratios in extraction and stripping upon sulphuric acid recovery is discussed. The process can be design to obtain a high or low recovery of sulphuric acid but with its low or high concentration, respectively.     

Recovery of molybdenum by solvent extraction from simulated high level liquid waste

Journal of Radioanalytical and Nuclear Chemistry - In this study, simple and a rapid solvent extraction method is investigated to recover Mo(VI) from simulated HLLW. The (NH4)6Mo7O24·4H2O...     

Separation of rhenium from molybdenum and other heavy metals by solvent extraction

Summary Two methods are presented for the extractive separation of rhenium from molybdenum and other heavy metals in hydrochloric acid solution. In the first method, Mo(VI) and Re(VII) are reduced by hydrazine in strong hydrochloric acid solution to Mo(V) and Re(IV). The former is then extracted intoiso-amyl acetate. The Re(IV) remaining in the aqueous phase is oxidised to Re(VII) and determined by known procedures. In the second method, Re(VII) and other ions in 1–1.3N HCl are boiled with hydrazine sulphate for 5 minutes. After adding EDTA to complex Mo(V) and adjusting the solution to 0.33N HCl, rhenium is extracted into chloroform containing 1% tribenzylamine, and is recovered by shaking with water having sufficient ammonia to neutralise the acid and a little hydrogen peroxide.

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Zusammenfassung Zwei Arbeitsweisen für die extraktive Trennung des Rheniums von Molybdän und anderen Schwermetallen in salzsaurer Lösung wurden angegeben. Bei dem ersten Verfahren werden Mo(VI) und Re(VII) mit Hydrazin in stark salzsaurer Lösung zu Mo(V) und Re(IV) reduziert. Ersteres wird dann mit Isoamylacetat extrahiert. Re(IV) verbleibt in der wäßrigen Phase, wird zu Re(VII) oxydiert und auf bekannte Art bestimmt. Beim zweiten Verfahren werden Re(VII) und die anderen Ionen in 1- bis 1,3-n Salzsäure 5 Minuten mit Hydrazinsulfat gekocht. Nachdem man ÄDTA zur Komplexierung des Mo(V) zugesetzt und die Lösung auf 0,33-n an Salzsäure eingestellt hat, wird Rhenium mit einer 1%igen Lösung von Tribenzylamin in Chloroform extrahiert. Die Rückextraktion erfolgt mit Wasser, worin Ammoniak (zur Neutralisation der Säure) und etwas Wasserstoffperoxid gelöst sind.

     

Separation of Zr and Hf from strong hydrochloric acid solution by solvent extraction with TEHA

In order to separate Zr(IV) and Hf(IV) from chloride solutions, TEHA (tri 2-ethyl hexyl amine) was used as an extractant. The aqueous phase consisted of 200 ppm of Zr and Hf in strong HCl solution. In our solvent extraction system, the extractability of the constituents by TEHA was found to be in the following order, HCl > Zr(IV) > Hf(IV). The highest separation factor between the two metals was obtained from 8 M HCl solution. Based on the selectivity towards Zr over Hf with TEHA, McCabe–Thiele plot was constructed and batch simulation of counter-current extraction studies has been conducted. Scrubbing results from the loaded TEHA showed that Hf was selectively scrubbed over Zr by strong HCl solution (9 M). Complete stripping of Zr was possible from the organic phase with distilled water after scrubbing of Hf. The extraction behavior of Zr and Hf by TEHA was compared with that by TiOA and TOA. Our results can be utilized in developing a solvent extraction process to separate Zr and Hf from concentrated chloride solutions by using TEHA.     

Separation of molybdenum(VI) from other elements by solvent extraction with dibenzo-18-crown-6 from hydrochloric acid medium

DB-18-C6 was used for the extractive separation analysis of molybdenum(VI) from a range of other elements. Molybdenum(VI) was quantitatively extracted from 8M hydrochloric acid with 0.01M DB-18-C6 in nitrobenzene. It was stripped from the organic phase with 2M nitric acid and determined spectrophotometrically with Tiron at 390 nm. Molybdenum was separated from a large number of elements in binary mixtures, the tolerance limit for most elements being very high. Selective extraction of molybdenum permits its separation from barium, thorium, cesium, rubidium, strontium, lanthanum, chromium(III) and cerium(III). The method was extended for the analysis of molybdenum in a soil sample.     

Iodometric determination of persulphate in sulphuric acid solution

Summary A method for the iodometric determination of persulphate has been described, which consists in taking 25 ml distilled water and 15 ml cone. sulphuric acid (sp.gr. 1.84) in a 250 ml conical flask, immediately followed by the addition of 10 ml of solution of persulphate. The mixture is kept for about five minutes, diluted by 100 ml of distilled water and then are added 10–15 ml of 10% solution of potassium iodide. The liberated iodine is titrated against a standard solution of thiosulphate. 5 ml aliquots of persulphate solution may also be used. The results are satisfactory and the error lies within permissible limits.