Calorimetric studies on the thermal decomposition of tri n-butyl phosphate-nitric acid systems

Thermal decomposition of neat TBP, acid-solvates (TBP·1.1HNO₃, TBP·2.4HNO₃) (prepared by equilibrating neat TBP with 8 and 15.6?M nitric acid) with and without the presence of additives such as uranyl nitrate, sodium nitrate and sodium nitrite, mixtures of neat TBP and nitric acid of different acidities, 1.1?M TBP solutions in diluents such as n-dodecane (n-DD), n-octane and isooctane has been studied using an adiabatic calorimeter. Enthalpy change and the activation energy for the decomposition reaction derived from the calorimetric data wherever possible are reported in this article. Neat TBP was found to be stable up to 255?°C, whereas the acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ decomposed at 120 and 111?°C, respectively, with a decomposition enthalpy of ?495.8?±?10.9 and ?1115.5?±?8.2?kJ?mol^?1 of TBP. Activation energy and pre exponential factor derived from the calorimetric data for the decomposition of these acid-solvates were found be 108.8?±?3.7, 103.5?±?1.4?kJ?mol^?1 of TBP and 6.1?×?10¹⁰ and 5.6?×?10⁹?S^?1, respectively. The thermochemical parameters such as, the onset temperature, enthalpy of decomposition, activation energy and the pre-exponential factor were found to strongly depend on acid-solvate stoichiometry. Heat capacity (C _p ), of neat TBP and the acid-solvates (TBP·1.1HNO₃ and TBP·2.4HNO₃) were measured at constant pressure using heat flux type differential scanning calorimeter (DSC) in the temperature range 32?C67?°C. The values obtained at 32?°C for neat TBP, acid-solvates TBP·1.1HNO₃ and TBP·2.4HNO₃ are 1.8, 1.76 and 1.63?J?g^?1?K^?1, respectively. C _p of neat TBP, 1.82?J?g^?1?K^?1, was also measured at 27?°C using ??hot disk?? method and was found to agree well with the values obtained by DSC method.     

Identification of iodoorganic compounds in kerosene from nuclear fuel reprocessing

In kerosene samples from nuclear fuel reprocessing, iodoalkanes with chain-lengths from C₄ to C₁₃ have been identified. The kerosene samples were purified by means of solid-phase extraction. By this method other fission products like¹²⁵Sb and¹⁰⁶Ru were quantitatively removed from the solution. The only remaining radioactive nuclide was thus¹²⁹I. The iodoorganic compounds in the kerosene from the solvent were enriched from 6000 Bq/L to 100 000 Bq/L¹²⁹I by vacuum distillation. Chromatographic separation by HPLC, fractionation, and -measurement of the fractions showed that at least one polar and one nonpolar iodoorganic compound were present. Derivatisation of the iodoorganic compounds with, 1,4-diazabicyclo-2,2,2-octane to quatermary ammonium salts and²⁵²Cf plasma desorption mass spectrometry of the products revealed that the main iodoorganic constituents in the kerosene were iodobutane as polar and iodododecane as nonpolar compound in approximately equal concentrations.     

Composition and structure of complexes formed in the reaction of uranyl di(2-ethylhexyl)phosphate and tributyl phosphate or di-N-octyl sulfoxide in benzene solutions

This paper reprots of³¹P NMR and IR studies of the interaction of tributyl phosphate (TBP) and di-n-octyl sulfoxide (DOSO) with polymer molecules of uranyl di-2-ethylhexyl phosphate (UO₂X₂)_p (I) in C₆H₆ sulutions. Detailed interpretations of the³¹P NMR spectra and the v_as(POO) IR bands and determination of the fraction of nonequivalent phosphorus atoms of X⁻ anions and uranium (VI) atoms as well as the concentration of U(VI)-bonded TBP in I have shown that only a single TBP or DOSO molecule is coordinated to the uranium atoms of polymer I at C_TBP=0.1–2 M or C_DOSO=0.1–0.5 M. In the case of 100% TBP, two TBP molecules are coordinated to some U(VI) atoms. Distribution of TBP (DOSO) molecules along the polymer chain agrees with the mean statistical value. The portion of terminal chalate POO-groups of X⁻ anions is determined. The dependence of the degree of (UO₂X₂)_p·nL (L=TBP, DOSO) polymerization on C_L is obtained. Saturation of solutions with water only slightly affects the terminal POO-groups and has no effects on the distribution of L along the polymer chain of I. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 6, pp. 66–73, November–December, 1994. Translated by K. Shaposhnikova     

Products of the Radiation-Chemical and Thermal Decomposition of Mercury Fulminate

The products of the radiation-chemical and thermal decomposition of mercury fulminate were examined by IR spectroscopy and X-ray diffraction analysis. Upon radiolysis to 20% conversion, the fulminate ion underwent decomposition (G (decomposition) = 20 molecule/100 eV) with the formation of HgO (G = 9 ± 1 molecule/100 eV), CN^– ions, and CO₂. The final solid products of the radiolysis are Hg(CNH)₂, a cyanide complex, the mercury carbonate oxide HgCO₃ · 3HgO, the mercury cyanide oxide Hg(CN)₂ · HgO, and paracyanogen (CN)_n. In the thermolysis, the final solid products of decomposition are the mercury carbonate oxide HgCO₃ · 2HgO, a cyanide complex, and the cluster Hg_nC_mN_oO_p.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

Molecular state of hydrochloric acid in its tributyl phosphate extracts

Using IR spectroscopy we have shown that at digerent equilibrium concentrations of HCl in aqueous phases, its tributyl phosphate @acts contain: 1) at C_Hcl ^a < 2.3 M, micelle-like associates H₅O₂ ⁺(H₂O)_n–2(TBP)_mCl^–·(H₂0·TBP)₂ (n 26 and m 13), the structure of micelles is discussed 2) at 2.3 M < C_HCl ^a < 5.6 M, dimer associates [H₅O₂ ⁺(H₂O)₂Cl^–(H₂O·TBP)₂]₂; 3) at 5.6 M < C_HCl ^a < 8.5 M, H-bonded molecular fragments H₅O₂ ⁺(TBP)_2/3Cl^–(A); and 4) at C_HCl ^a > 8.5 M, considerable amounts of the H₃O⁺ tisolvate start to form in molecular fragments H₃O⁺(TBP)_1/3Cl ^–(B) H-bonded with the nearest neighbors. At C_Hcl ^a > 5.6 M, almost no free TBP molecules occur in the extracts and a structured liquid forms from the A fragments; and at C_Hcl ^a > 8.5 M, from the B fragments.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturmoi Khimii, Vol. 34, No. 5, pp. 72–79, September–October, 1993.Translated by K. Shaposhnikova     

Thermogravimetric investigation on the chloride binding behaviour of MK-lime paste

The hydration products of 2.5, 5 and 10% Cl⁻ containing metakaolin (MK)-lime pastes are compared with the same obtained from MK-lime paste to understand the chloride binding behaviour of MK during the hydration of cement. Results indicate that 2.5% Cl⁻ addition into the MK-lime paste initially enhances the formation of Friedel's salt (Ca₂Al(OH)₆Cl·2H₂O), but Friedel's salt decomposes at later stages due to the formation of stratlingite (C₂ASH₈). In 5 and 10% chloride containing pastes, Friedel's salt is observed throughout the reaction periods along with the high amount of CSH. Small amount of stratlingite is also formed on or after 60 day hydration of 5% Cl⁻ containing MK-lime pastes. On the other hand, MK-lime-10% Cl⁻ containing pastes show the complete absence of stratlingite and C₄AH₁₃ through out the hydration period, which are the major hydration products of MK-lime paste. Mesuarements of pH of the simulated pore fliuds help to understand the decomposition behaviour of Friedel's salt. From the experimental results, chloride binding mechanism of MK-lime paste is also discussed.     

Synthesis, Crystal Structure and Thermal Analysis of (TAGH)2(TNR)

A new energetic compound (TAGH)₂(TNR) (TAG: triaminoguanidine, TNR: 2,4,6-trinitroresorcinol) was prepared by reacting triaminoguanidine with 2,4,6-trinitroresorcinol (styphnic acid) in aqueous solution under nitrogen atmosphere, and characterized by elemental analysis and Fourier transform infrared (FTIR) spectra. Its crystal structure was determined by single crystal X-ray diffraction analysis. The crystal belonged to a monoclinic, C 2/c space group. The unit cell parameters were as follows: a=2.2892(6) nm, b=1.2802(3) nm, c=1.3661(4) nm, β=111.174(5)°, V=3.7333(16) nm³, and Z=8. The compound consisted of two cations C(N₂H₃)₃⁺ and an anion (C₆HN₃O₈)²⁻. The C(N₂H₃)₃⁺ and (C₆HN₃O₈)²⁻ were bonded together by electrostatic attraction and hydrogen bonds, and this effect made the compound more stable. The thermal analysis of the compound was studied by using differential scanning calorimetry (DSC), thermogravimetry-derivative thermogravimetry (TG-DTG). Under nitrogen atmosphere with a heating rate of 10 K·min⁻¹, the thermal decomposition of the compound contained only one intense exothermic decomposition process in the range of 450.1-477.7 K in the DSC curve, and the decomposition products were nearly gaseous products.     

Extraction of pertechnetate anion as a ligand in metal complexes with tributylphosphate

The extraction of the pertechnetate anion has been investigated in the systems tributylphosphate (TBP)—solvent (carbon tetrachloride, n-heptane, chloroform)—metal salt (uranyl nitrate and chloride, thorium nitrate)—ammonium salt. In the absence of a metal, the solvates HTeO₄. iTBP (i=4) are extracted, while in the presence of uranium and thorium, the distribution of technetium corresponds to the formation of the mixed complexes: UO₂(NO₃)(TeO₄)·2TBP, UO₂Cl(TcO₄)·2TBP and Th(NO₃)₃ (TcO₁)·2TBP. The effective constants of the reactions H⁺+TcO ₄ ⁻ +i(TBP)_org←(HTcO₁·iTBP)_org, and (ML_n·2TBP)_org+TcO ₄ ⁻ ←(ML_n−1TcO₄·2TBP)_org+L were established in the above systems. The extraction of pertechnetate ion is more effective when it is coordinated to a cation solvated by TBP than the extraction in the form of pertechnetate acid solvated by TBP.     

INFLUENCE OF ELECTRON-WITHDRAWING SUBSTITUENTS IN THE OXAPHOSPHOLE RING ON THE AXIAL CONFORMATIONAL TRANSMISSION IN Pv COMPOUNDS

Abstract

A MNDO and 300-MHz ¹H NMR study of some trigonal-bipyramidal (TBP) five-coördinated phosphorus (P^v) compounds is reported. It is shown by the MNDO calculations that, in the oxaphosphole P^v TBP compounds 5a-c, the electron distribution in the axial bonds of the TBP is affected by the electronegativity of the substituent at C₄ of the oxaphosphole ring. With increasing electronegativity of the substituent at C₄, the electron density on the axial exocyclic oxygen atom O₁ decreases whereas the electron density on the axial endocyclic atom O₁ increases. This is supported by a ¹H NMR conformational analysis of the C₁[sbnd]C₂ bond of the oxaphosphole P^v TBP compounds 6–11. The gauche(-) rotamer fraction (O¹ and O¹ trans situated) of these compounds, which is correlated to the electron density on O₁, is reduced to 30% as compared to the absolute axial g^?rotamer fraction (59%) of the dioxaphosphole P^v TBP compound 13, most likely because of the presence of the carbonyl group at C₄ of the oxaphosphole ring. So, both the ¹H NMR and MNDO study show that electron withdrawing substituents on the oxaphosphole ring of P^v TBP compounds reverse the electron transfer in the axial P[sbnd]O bonds of the TBP (as compared to dioxaphosphole compounds), from exocyclic O₁ towards endocyclic O₁.     

Mono and dinuclear Pd(II) complexes with pyrazole and imidazole-type ligands Synthesis, characterization and thermal behaviour

The cyanate-bridged cyclopalladated compound [Pd(C²,N-dmba)(μ-NCO)]₂ (dmba=N,N-dimethylbenzylamine) reacts in acetone with pyrazole (pz), 3,5-dimethylpyrazole (dmpz), imidazole (imz) and 2-methylimidazole (mimz) to give [Pd₂(C²,N-dmba)₂(μ-NCO)(μ-pz)] (1), [Pd₂(C²,N-dmba)₂(μ-NCO)(μ-dmpz)] (2), [Pd(C²,N-dmba)(NCO)(imz)] (3) and [Pd(C²,N-dmba)(NCO)(mimz)] (4), respectively. The compounds were characterized by elemental analysis, IR spectroscopy and TG. The thermal decomposition of the compounds occurs in three consecutive steps and the final decomposition products were identified as Pd(0) by X-ray powder diffraction. The thermal stability order of the complexes is 2>3>1>4.     

Dielectric Barrier Discharge Initiated Gas-Phase Decomposition of CO2 to CO and C6–C9 Alkanes to C1–C3 Hydrocarbons on Glass, Molecular Sieve 10X and TiO2/ZnO Surfaces

Atmospheric Pressure Dielectric Barrier Discharge (APDBD) initiated decomposition of CO₂ and C₆–C₉ alkanes (in Ar carrier) with uncoated and TiO₂/ZnO coated glass surfaces, and under molecular sieve 10 X packing are presented in this study. Alkanes employed include 2-methylpentane, cyclohexane, n-hexane, n-heptane, n-octane, n-nonane and their decomposition products studied include C₁–C₃ hydrocarbons viz. CH₄, C₂H₄, C₂H₆ and C₃H₈. Generally the yields of all these C₁–C₃ products increased with discharge energy, however to a major extent the parent alkane structure controlled the relative concentration profiles of the individual products. Typically the slopes of the increase in various products yield varied from 0.025 to 0.25 ppm (v/v) mm V⁻¹. However, in the case of cyclohexane the total yield of methane, ethane and propane were only ∼20% of ethylene yield. Use of TiO₂ as well as TiO₂/ZnO coated central glass electrode in the APDBD apparatus showed ∼11% enhancement in degradation efficiency. However, while overall 2-methylpentane decomposition reduced significantly to ∼30%, in case of n-octane its decomposition to the C₁–C₃ products remained unaffected. On the other hand under molecular sieve 10X packing, yield of CH₄ and C₂H₄ increased significantly in both cases.     

Preparation and thermal stability of trioxalatocobaltates of bivalent metals KM2+ [Co(C2O4)3]·xH2O

Trioxalatocobaltates of bivalent metals KM²⁺[Co(C₂O₄)₃]·x H₂O, with M²⁺ = Ba, Sr, Ca and Pb, have been prepared, characterized and their thermal behaviour studied. The compounds decompose to yield potassium carbonate, bivalent metal carbonate or oxide and cobalt oxide as final products. The formation of the final products of decomposition is influenced by the surrounding atmosphere. Bivalent metal cobaltites of the types KM²⁺CoO₃ and M²⁺CoO_3—x are not identified among the final products of decomposition. The study brings out the importance of the decomposition mode of the precursor in producing the desired end products.     

Insights into the Mechanism of Extraction of Uranium (VI) from Nitric Acid Solution into an Ionic Liquid by using Tri‐n‐butyl phosphate

We present new results on the liquid–liquid extraction of uranium (VI) from a nitric acid aqueous phase into a tri‐n‐butyl phosphate/1‐butyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide (TBP/[C₄mim][Tf₂N]) phase. The individual solubilities of the ionic‐liquid ions in the upper part of the biphasic system are measured over the whole acidic range and as a function of the TBP concentration. New insights into the extraction mechanism are obtained through the in situ characterization of the extracted uranyl complexes by coupling UV/Vis and extended X‐ray absorption fine structure (EXAFS) spectroscopy. We propose a chemical model to explain uranium (VI) extraction that describes the data through a fit of the uranyl distribution ratio D_U. In this model, at low acid concentrations uranium (VI) is extracted as the cationic complex [UO₂(TBP)₂]²⁺, by an exchange with one proton and one C₄mim⁺. At high acid concentrations, the extraction proceeds through a cationic exchange between [UO₂(NO₃)(HNO₃)(TBP)₂]⁺ and one C₄mim⁺. As a consequence of this mechanism, the variation of D_U as a function of TBP concentration depends on the C₄mim⁺ concentration in the aqueous phase. This explains why noninteger values are often derived by analysis of D_U versus [TBP] plots to determine the number of TBP molecules involved in the extraction of uranyl in an ionic‐liquid phase.     

Static secondary ionization mass spectrometry analysis of tributyl phosphate on mineral surfaces: Effect of Fe(II)

The static secondary ionization mass spectrometry (SIMS) spectrum of tri-n-butyl phosphate (TBP) on a variety of basalt and quartz samples is affected by the chemical composition of the mineral surface. When TBP is adsorbed on Fe(II)-bearing surfaces, the compound undergoes concomitant H^? abstraction and reduction, followed by the elimination of two C₄H₈ molecules to form an ion at m/z 137⁺. When TBP is adsorbed to quartz or other nonreducing surfaces, it merely undergoes protonation and elimination of three C₄H₈ molecules to form H₄PO ₄ ⁺ . When TBP is adsorbed to Fe(III)-bearing surfaces, it undergoes H^? abstraction and elimination of two C₄H₈ molecules, to form an ion at m/z 153⁺. These conclusions are supported by model studies that employed FeO, Fe₂0₃, TBP, and tributyl phosphite. The results show that the SIMS spectrum is very sensitive to the mode of TBP adsorption on the mineral surface.     

A computational study of the radical–radical reaction of O(<Superscript>3</Superscript>P) + C<Subscript>2</Subscript>H<Subscript>5</Subscript> with comparisons to gas-phase kinetics and crossed-beam experiments

We present density functional theory (DFT) and complete basis set (CBS) calculations of the prototypical radical–radical reaction of ground–state atomic oxygen [O(³P)] with ethyl (C₂H₅) radicals. The respective reaction mechanisms and dynamics were investigated on the doublet potential energy surfaces using the DFT method and CBS model. In the title reaction, the barrierless addition of O(³P) to C₂H₅ led to the formation of energy-rich intermediates that underwent subsequent isomerization and decomposition to yield various products. The products predicted to be found were: H₂CO + CH₃, CH₃CHO + H, c–CH₂OCH₂ + H, ^1,3CH₃COH + H, ^1,3HCOH + CH₃, CH₂CHOH + H, C₂H₃ + H₂O, and CH₂CH₂ + OH. In particular, unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, two distinctive pathways to the formation of CH₂CH₂ + OH were predicted to be in competition: direct, barrierless H-atom abstraction mechanism versus addition process. The competition was consistent with the recent crossed-beam investigations, and their microscopic dynamic characteristics are discussed at the molecular level.     

Some features of formation and dissolution of a series of Pu(IV) and Zr alkyl and butyl alkyl phosphates in the system tBP — N-dodecane — Nitric acid — Water

The formation and composition of salts produced on interaction of a series of alkyl- and butylalkylphosphoric acids having alkyl radical chain lengths from C₄ to C₁₀ with Pu(IV) and Zr in organic and aqueous phases of the system TBP — n-dodecane — nitric acid — water have been studied. The composition of compounds was found to depend on the conditions of their formation, being defined first of all by the HNO₃ concentration in aqueous and organic phases.     

Investigations on the Physicochemical and Radiolytic Degradation Properties of Tri-<Emphasis Type="Italic">n</Emphasis>-butylphosphate–Ionic Liquid in the Presence of Nitric Acid

Tri-n-butylphosphate (TBP) in an ionic liquid (IL) has been proposed as a suitable alternative for the solvent extraction of actinides from nitric acid solutions. This paper reports the detailed investigations on the physicochemical and hydrodynamic properties of the solvent system containing TBP in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C₄mim][NTf₂]) IL. The properties such as density, viscosity, phase separation time (PST), etc., were measured for irradiated and unirradiated solvent phases composed of TBP, [C₄mim][NTf₂] and 1.1 mol·L^–1 TBP in [C₄mim][NTf₂]. The results are compared with the values obtained in acid-equilibrated IL phases. ATR–FTIR spectroscopy and dynamic light scattering measurement of the IL phase were employed to characterize the interactions among the IL, TBP and nitric acid medium, and the aggregate size of the adduct formed in the IL phase.     

Radiation-induced decomposition of the tributyl phosphate-nitric acid system: Role of nitric acid

Radiation-induced decomposition of tributyl phosphate-nitric acid as a two-component system has been studied. Degradation products, dibutylphosphoric acid (DBP) and monobutylphosphoric acid (MBP), were determined by separation-extraction method. 0.59, 0.78 and 1.38 are the G (DBP) values and 0.15, 0.17 and 0.13 are the G (MBP) values obtained for pure TBP, TBP-3M HNO₃ extract and TBP-5M HNO₃ extract, respectively. G (–HNO₃) values are 5.19 and 6.15 for 3M HNO₃ and 5M HNO₃ extracts. It is shown that nitric acid plays a significant role in enhancing the decomposition of TBP.     

Bis(dimethyldithiocarbamato)(pyridine)zinc and -copper(II) and Their Benzene Solvates: EPR and Solid-State Natural Abundance (13C, 15N) CP/MAS NMR

Adducts of bis(dimethyldithiocarbamato)zinc and -copper(II) complexes with pyridine, [M(Py)(Mdtc)₂], and their benzene solvates [M(Py)(Mdtc)₂] · 0.5C₆H₆ were synthesized. The electron paramagnetic resonance method and solid-state ¹³C and ¹⁵N CP/MAS NMR spectroscopy were used to perform a comparative study of the compounds obtained. The EPR data showed that the geometry of Cu(II) coordination polyhedra both in the adduct itself [Cu(Py)(Mdtc)₂], and in its solvate, [Cu(Py)(Mdtc)₂] · 0.5C₆H₆ is intermediate between a square pyramid (SP) and a trigonal bipyramid (TBP), the contribution from the latter being dominant (75%) in [Cu(Py)(Mdtc)₂]. In the solvated adduct [Cu(Py)(Mdtc)₂] · 0.5C₆H₆, the copper(II) polyhedron is distorted to form an SP-enriched structure (the contribution from TBP is reduced to 55%). It was found NMR data that [Zn(Py)(Mdtc)₂] exists in a single high-symmetry molecular form. Coordinated pyridine molecule shows molecular motion about the Zn–N bond. The solvation of the adduct results in structural nonequivalence of the Mdtc^–ligands in [Zn(Py)(Mdtc)₂] · 0.5C₆H₆. Signals in the ¹⁵N NMR spectra were assigned to the structural positions of the atoms in the previously described molecular structure of a solvated adduct. It was found that the heterogeneous reaction of adduct formation during the absorption of pyridine from the gas phase by polycrystalline [Zn₂(Mdtc)₄] species is accompanied by the dissociation of binuclear molecules.