Transesterification and polymerization reactions of aliphatic polyesters in supercritical CO2 fluids without the presence of a catalyst

The reactions or stability of two crystalline polycaprolactones (PCL) and one amorphous poly(d,l-lactic acid) (dl-PLA) in supercritical CO₂ fluid (scCO₂) at 35 °C and 34.5 MPa without the presence of a catalyst were investigated using gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), and differential scanning calorimetry (DSC). The two PCLs having 80,000 and 10,000 in number average molecular weights (), denoted by PCL8 and PCL1, respectively, and dl-PLA having 74,000 in were studied. Carbon 13 NMR data found these polyesters no formation of carbonate linkages after treatments in scCO₂, indicating that the CO₂ did not copolymerize with the PCLs and dl-PLA. GPC data found that the molecular weights of PCL8/PCL1 blends considerably varied with the treatment time while the components of the blends negligibly changed throughout 6 h of treatments in scCO₂. These GPC data suggested that transesterification reactions occurred between PCL8 and PCL1. DSC data found that PCL8 co-crystallized with PCL1 and the treatments enhanced the melting temperatures and crystallinities of the blends. GPC data also found that the molecular weights of dl-PLA and PCL8/dl-PLA blends considerably varied with the treatment time in scCO₂. From the variations of molecular weights, it could be suggested that transesterifications and polymerizations both occurred in the PCL8/dl-PLA blends, with the polymerizations predominating over the transesterifications. This predomination in polymerizations lowered with increasing PCL8 content in the blends. DSC data found that the amorphous dl-PLA could be induced to crystallize by scCO₂, giving a heating endotherm at near 122 °C. Following scCO₂ treatments, enhancements of the melting temperature and crystallinity of PCL8 in the PCL8/dl-PLA blends were found, although these enhancements fluctuated with the treatment time.     

Phase polymorphism of [Zn(DMSO)6](ClO4)2 studied by differential scanning calorimetry

Four solid phases of [Zn(DMSO)₆](ClO₄)₂ have been detected by differential scanning calorimetry (DSC). Specifically, the phase transitions were detected between: metastable phase KII ↔ supercooled phase K0 at , stable phase KIb ↔ stable phase KIa at , stable phase KIa ↔ stable phase K0 at . At T_m2 = 389 K crystals partially and at T_m1 = 465 K completely melts. From the entropy change values it was concluded that the phases: K0 and K0′ are the orientationally dynamically disordered phases, so called ODDIC crystals, and phases KIa, KIb and metastable KII are dynamically ordered but with some degree of positional disorder.     

Growth of high quality and large-sized Rb0.3MoO3 single crystals by molten salt electrolysis method

High quality and large-sized Rb_0.3MoO₃ single crystals were synthesized by molten salt electrolysis method. X-ray diffraction (XRD) patterns and rocking curves, as well as the white beam Laue diffraction of X-ray images show the crystals grown by this method have high quality. The lattice constants evaluated from XRD patterns are a₀=1.87 nm, b₀=0.75 nm, c₀=1.00 nm, β=118.83^°. The in situ selected area electron diffraction (SAED) patterns along the , and zone axes at room temperature indicate that the Rb_0.3MoO₃ crystal possess perfect C-centered symmetry. Temperature dependence of the resistivity shows this compound undergoes a metal to semiconductor transition at 183 K.     

Standard enthalpy of formation of aqueous titanyl chloride, TiOCl2(aq), at T = 298.15 K

Enthalpies of solution of TiCl₄(l) in aqueous perchloric acid have been measured in an isothermal calorimeter at T = 298.15 K at ionic strengths of (1.964, 3.002, and 4.062) mol · kg⁻¹. These results were extrapolated to zero ionic strength using an extended Debye-Hückel equation, to yield the standard enthalpy of solution ; from which the standard partial molar enthalpy of formation of the titanyl ion was derived: .     

A computational study of SbnF5n (n = 1-4): Implications for the fluoride ion affinity of nSbF5

This contributions shows with a series of ab initio MP2 and DFT (BP86 and B3-LYP) computations with large basis sets up to cc-pVQZ quality that the literature value of the standard enthalpy of depolymerization of Sb₄F_20(g) to give SbF_5(g) (+18.5 kJ mol⁻¹) [J. Fawcett, J.H. Holloway, R.D. Peacock, D.R. Russell, J. Fluorine Chem. 20 (1982) 9] is by about 50 kJ mol⁻¹ in error and that the correct value of (Sb₄F_20(g)) is +68 ± 10 kJ mol⁻¹. We assign , , and values for Sb_nF_5n with n = 2-4 and compare the results to available experimental gas phase data. Especially the MP2/TZVPP values obtained in an indirect procedure that rely on isodesmic reactions or the highly accurate compound methods G2 and CBS-Q are in excellent agreement with the experimental data, and reproduce also the fine experimental details at temperatures of 423 and 498 K. With these data and the additional calculation of [Sb_nF_5n+1]⁻ (n = 1-4), we then assessed the fluoride ion affinities (FIAs) of Sb_nF_5n(g), nSbF_5(g), nSbF_5(l) and the standard enthalpies of formation of Sb_nF_5n(g) and [Sb_nF_5n+1]⁻_(g): FIA(Sb_nF_5n(g)) = 514 (n = 1), 559 (n = 2), 572 (n = 3) and 580 (n = 4) kJ mol⁻¹; FIA(nSbF_5(g)) = 667 (n = 2), 767 (n = 3) and 855 (n = 4) kJ mol⁻¹; FIA(nSbF_5(l)) = 434 (n = 1), 506 (n = 2), 528 (n = 3) and 534 (n = 4) kJ mol⁻¹. Error bars are approximately ±10 kJ mol⁻¹. Also the related Gibbs energies were derived. Δ_fH°([Sb_nF_5n+1]⁻_(g)) = −2064 ± 18 (n = 1), −3516 ± 25 (n = 2), −4919 ± 31 (n = 3) and −6305 ± 36 (n = 4) kJ mol⁻¹.     

Thermochemical study of two anhydrous polymorphs of caffeine

The mean values of the standard massic energy of combustion of caffeine in phase I (or alpha) and in phase II (or beta) measured by static-bomb combustion calorimetry in oxygen, at T = 298.15 K, are Δ_cu^° (C₈H₁₀O₂N₄, I) = −(21823.27 ± 0.68) J · g⁻¹ and Δ_cu^° (C₈H₁₀O₂N₄, II) = −(21799.96 ± 1.08) J · g⁻¹, respectively.The standard (p^° = 0.1 MPa) molar enthalpy of formation in condensed phase for each form was derived from the corresponding standard molar enthalpies of combustion as, and .The difference between the standard enthalpy of formation of the two polymorphs in condensed phase was also evaluated by using reaction-solution calorimetry. The obtained result, 2.04 ± 0.25 kJ · mol⁻¹, is in agreement, within the uncertainty, with the difference between the molar enthalpies of formation obtained from combustion experiments (4.5 ± 3.2) kJ · mol⁻¹, which can be considered as an internal test for consistency of the results.A value for the standard enthalpy of formation of caffeine in the gaseous state was proposed: , estimated from the values of the standard enthalpies of formation of both crystalline forms obtained in this work, and the data on standard enthalpies of sublimation collected from the literature.     

Enthalpies of solution of 1,1,3,3-tetramethylurea in normal and branched alkanols (C2-C4) at 298.15 K

The enthalpies of solution were determined for 1,1,3,3-tetramethylurea in ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol (2-methyl-2-propanol). Measurements were made at 298.15 K and molalities m ≅ (0.007 to 0.036) mol · kg⁻¹ with a precise isoperibol ampoule-type calorimeter. Standard enthalpies of solution and transfer from one alkanol to the other (including methanol) were calculated. The obvious relationship between the enthalpic and volumetric effects of solution of tetramethylurea in the n-alkanols (C₁-C₄) was discovered. The enthalpic effects of transfer caused by branching of the alkanol molecules, 1-propanol → 2-propanol, and 1-butanol → t-butanol, are opposite in sign and dominated by the configurational changes in the solvation environment of tetramethylurea.     

Synthesis of poly(ethylene adipate) and poly(ethylene adipate-co-terephthalate) via ring-opening polymerization

Syntheses of poly(ethylene adipate) (ROP-PEA) and poly(ethylene adipate-co-terephthalate) (ROP-PEA-co-PET) were achieved via ring-opening polymerization of corresponding cyclic oligoesters. In case of ROP-PEA, cyclic oligo(ethylene adipate) (C-OEA) was equilibrated in the presence of di-n-butyltin oxide as a catalyst under high-concentration conditions at 180 and 200 °C for 1-24 h. The polymer products were obtained in yields up to 100% with the and in the ranges of 3000-23 000 g/mol and 5000-60 000 g/mol, respectively. The ROP-PEA-co-PET was prepared by equilibrating an equimolar amount of C-OEA and cyclic oligo(ethylene terephthalate) (C-OET) using di-n-butyltin oxide catalyst under high-concentration conditions at 250 °C for 24 h. The copolyester produced was obtained in yield of 97% with the and of 18 000 and 46 000 g/mol, respectively. ¹H NMR spectrum of ROP-PEA-co-PET showed two new proton signals of ethylene unit representing the existence of heterolinkage with different chemical environment in the copolymer. This indicated the random transesterification of C-OEA and C-OET resulting in random structure in copolyester. In addition, the result of ROP-PEA-co-PET from DSC showed the glass transition temperature in the values of −8 °C with no melting temperature indicating thermoplastic elastomeric behavior.     

Syntheses and structures of Li3ScF6 and high pressure LiScF4−, luminescence properties of LiScF4, a new phase in the system LiF-ScF3

Colorless single crystals of Li₃ScF₆ have been prepared by reacting the binary components LiF and ScF₃ at 820 °C for 16 h in argon atmosphere. This complex fluoride is the only stable phase in the system LiF-ScF₃ under ambient pressure. According to a structure refinement based on single crystal X-ray diffraction data it crystallizes in the centrosymmetric space group with and . The new structure of Li₃ScF₆ is a filled variant of the Na₂GeF₆ type structure and can be described in terms of a hexagonal close packing of fluorine in which 2/3 of the octahedral holes are occupied by Sc and Li.High pressure/high temperature studies of the system LiF-ScF₃ show that the new phase LiScF₄ is formed at around 5.5 GPa and 575 °C. According to Rietveld refinements of powder X-ray diffraction data LiScF₄ adopts the Scheelite type structure (space group I4₁/a) with and . A sample of LiScF₄ doped with 1% Er exhibits an intense luminescence in the far IR region.     

“Unusual” phase transitions in CeAlO3

High-resolution time-of-flight neutron powder diffraction was carried out to investigate the crystal structures of CeAlO₃ over a wide temperature range between 4.2 and 1423 K. Confirming the recent result of X-ray powder diffraction, the room temperature structure is tetragonal with the space group I4/mcm (tilt system (a⁰a⁰c⁻)). The tetragonal structure persists down to 4.2 K. However, above room temperature CeAlO₃ undergoes three phase transitions: first to the orthorhombic Imma structure (tilt system (a⁰b⁻b⁻)) at, e.g., 373 K, then to the rhombohedral structure (tilt system (a⁻a⁻a⁻)) at, e.g., 473 K, and finally, to the primitive cubic structure which exists above 1373 K. The sequence of phases, , which occurs in CeAlO₃ is a rare one in oxide perovskites.     

Ruthenium (II) complexes of the chelating phosphine borane H2ClB · dppm

Reaction of H₂ClB · PPh₂CH₂PPh₂ (H₂ClB · dppm) with results in displacement of all three acetonitrile ligands and the formation of (1), which has been characterised crystallographically. Reaction with carbon monoxide results in a change from η² to η¹ of the borane ligand to afford (2). Compound 1 undergoes H/D exchange under a D₂ atmosphere to afford , while 2 does not.     

Hetero dimer from tetrakisammonium cavitand and tetratopic crown ether cavitand

Hetero dimer between tetrakis(m-ammonium)cavitand and tetrakis(dibenzo-25-crown-8)cavitand 5 was formed in CDCl₃ at room temperature. The effects of solvent polarity and temperature on the stability of were studied and the thermodynamic parameters for the formation of are , ΔH⁰ = −67.4 kcal mol⁻¹ and ΔS⁰ = −201.6 cal mol⁻¹ K⁻¹.     

Reactions of pyridyl donors with halogens and interhalogens: an X-ray diffraction and FT-Raman investigation

Three different N-donors L, namely N-ethyl-N′-3-pyridyl-imidazolidine-4,5-dione-2-thione (1), N,N′-bis(3-pyridylmethyl)-imidazolidine-4,5-dione-2-thione (2), and tetra-2-pyridyl-pyrazine (3), bearing one, two and four pyridyl substituents, respectively, have been reacted with halogens X₂ (X = Br, I) or interhalogens XY (X = I; Y = Cl, Br). CT σ-adducts L · nXY, bearing linear N?XY moieties (L = 3; X = I; Y = Br, I; n = 2), and salts containing the protonated cationic donors H_nLⁿ⁺ (L = 1 − 3; n = 1, 2, 4), counterbalanced by Cl⁻, Br⁻, , , , , I₂Br⁻, , or anions, have been isolated. Among the reactions products, (H1⁺)Cl⁻, (H1⁺)Br⁻, , , and 3 · 2IBr have been characterised by single-crystal X-ray diffraction. The nature of the products has been elucidated based on elemental analysis and FT-Raman spectroscopy supported by MP2 and DFT calculations.     

Dioxouranium(VI)-carboxylate complexes: A calorimetric and potentiometric investigation of interaction with oxalate at infinite dilution and in NaCl aqueous solution at I = 1.0 mol L and T = 25 °C

In this paper we investigated the interactions between dioxouranium(VI) and oxalate using (H⁺-glass electrode) potentiometry and titration calorimetry. Potentiometric measurements were carried out in NaCl aqueous solutions and at T = 25 °C in a wide range of experimental conditions (concentrations, ligand/metal molar ratio, pH, titrants) at low ionic strength values (I ≤ 0.090 mol L⁻¹, without supporting electrolyte) and at I = 1.0 mol L⁻¹; different procedures were employed for the acquisition of experimental data and careful analysis of these data performed. In all cases the speciation model that best fits experimental data takes into account the formation of the binary mononuclear species UO₂(ox)⁰, UO₂(ox)₂²⁻, UO₂(ox)₃⁴⁻ widely reported in literature, the ternary hydroxyl mononuclear species UO₂(ox)OH⁻, UO₂(ox)(OH)₂²⁻, UO₂(ox)₂OH³⁻, UO₂(ox)₃OH⁵⁻, the protonated ternary mononuclear species UO₂(ox)₃H³⁻ and the binuclear species (UO₂)₂(ox)₅⁶⁻.Calorimetric measurements were carried out following similar procedures and in the same experimental conditions as employed for the potentiometric measurements at I = 1.0 mol L⁻¹ in NaCl. The stability of UO₂²⁺-oxalate²⁻ complexes is fairly high and their main contribution to stability is entropic in nature. Some linear empirical relationships were found which make it possible to calculate (i) the contribution of a single bond: and ; (ii) chelate stabilisation per ring: and and (iii) the mean stability of negatively charged Na⁺-ion pair complexes: log^TK = (0.46 ± 0.02)·|z| (z = charge of complex species), ΔG° = −(2.60 ± 0.1)·|z| kJ mol⁻¹ and TΔS° = 2.5 ± 0.5 kJ mol⁻¹. Both potentiometric and calorimetric results provide evidence of the penta-coordination of the species UO₂(ox)₃⁴⁻. SIT parameters were calculated from the data at I = 0 and I = 1.02 mol kg⁻¹. Comparisons are made with literature data. An insoluble dioxouranium(VI) ternary complex was synthesised (at I = 1.0 mol L⁻¹ in NaCl) and characterised by thermoanalysis and elemental analysis.     

Two new binary lanthanide polytellurides: Syntheses and crystal structures of CeTe1.90 and SmTe1.80

Single crystals of the new binaries CeTe_1.90 and SmTe_1.80 have been obtained. CeTe_1.90 was synthesized at 1023 K from the reaction of Ce, TeO₂, and Te with the use of a CsCl flux. It crystallizes in the tetragonal space group P4₂/n with 20 formula units in a cell of dimensions at 153 K of a=10.0261(5), , . It is isostructural with the LnSe_1.9 polyselenides (Ln=La, Ce, Pr) and with SmS_1.90. SmTe_1.80 was synthesized at 1223 K from the reaction of Sm and Te in a KBr flux. SmTe_1.80 crystallizes in a new structural type in the tetragonal space group P4/n with 20 formula units in a cell of dimensions at 153 K of a=9.7026(4), , . Both of these layered structures, which may be derived from the ZrSiS structure type, consist of double layers of [LnTe] polyhedra separated by planar Te nets that contain vacancies. In these nets the shortest Te-Te distances are 2.9194(5), 3.1204(5), and 3.3324(6) Å in CeTe_1.90 and 2.878(1), 2.9932(3), and 3.2114(7) Å in SmTe_1.80. Neither a simple delineation of the Te-Te bonding nor an assignment of individual formal oxidation states is possible in either of these compounds if one takes strict account of the Te-Te distances.     

Thermodynamic properties of lithium mica: Lepidolite

Calorimetric measurements were made on natural sample of lepidolite having the composition (K_0.80Na_0.05Ca_0.07Rb_0.16Cs_0.03)(Li_1.34Al_1.40Fe³⁺_0.01)[Si_3.25Al_0.75O₁₀]F_1.80(OH)_0.20 from Na-Li-type rare-element-rich pegmatites of East Sayany, Russia. High-temperature enthalpy increments were measured with a Tian-Calvet calorimeter at 444-972 K using the drop method. The resultant (T) equation in the interval T = 298.15-972 K was calculated:  = 316.10 + 228.12 × 10⁻³ T − 50.10 × 10⁵ T⁻² (J K⁻¹ mol⁻¹) [± 0.4%] and the value of (298.15 K) = 327.8 J K⁻¹ mol⁻¹ was obtained. The standard molar enthalpy of formation from the elements was determined by high-temperature drop solution calorimetry in molten lead borate at T = 973 K. The value of Δ_f(298.15 K) for lepidolite was found to be −6201 ± 18 kJ mol⁻¹. The thermodynamic properties of lepidolite of idealized composition KLi_1.5Al_1.5[Si₃AlO₁₀]F₂ were estimated based on the experimental data obtained.     

Heat capacity and standard molar enthalpy of formation of crystalline 2,6-dicarboxypyridine (C7H5NO4)

Low-temperature heat capacity C_p,m of 2,6-dicarboxypyridine (C₇H₅NO₄; CAS 499-83-2) was precisely measured in the temperature range from (80 to 378) K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were calculated in the range from (80 to 378) K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined, and , by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. The thermodynamic properties of the compound were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.     

Crystal growth, characterization and physical properties of PrNiSb3, NdNiSb3 and SmNiSb3

The crystal structures of three new intermetallic ternary compounds in the LnNiSb₃ (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb₃, NdNiSb₃ and SmNiSb₃ all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb₆ octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb₃), 4.6 K (NdNiSb₃), and 2.9 K (SmNiSb₃). Effective moments of 3.62 μ_B, 3.90 μ_B and 0.80 μ_B are found for PrNiSb₃, NdNiSb₃ and SmNiSb₃, respectively, and are consistent with Pr³⁺ (f ²), Nd³⁺ (f ³), and Sm³⁺ (f ⁴).     

Preparation, crystal structures, EPR and reflectance spectra of two new charge-transfer salts, [CpFeCpCH2N(CH3)3]4[XMo12O40] · nCH3CN (n = 0 for X = P or n = 1 for X = Ge)

Two new charge-transfer salts, [CpFeCpCH₂N(CH₃)₃]₄[PMo₁₂O₄₀] · CH₃CN (1) and [CpFeCpCH₂N(CH₃)₃]₄[GeMo₁₂O₄₀] (2), were synthesized by the traditional solution synthetic method and their structures were determined by single-crystal X-ray analysis. Salt 1 belongs to the triclinic space group P1, and salt 2 belongs to the triclinic space group . There exist the complex interactions of the cationic ferrocenyl donor and Keggin polyanion in the solid state. The solid state UV-Vis diffuse reflectance spectra indicate the presence of a charge-transfer band climbing from 450 nm to well beyond 900 nm for 1, a charge-transfer band from 460 to 850 nm with λ_max = 630 nm for 2.The EPR spectra of salts 1 and 2 at 77 K show a signal at g = 2.0048 and 1.9501, respectively, ascribed to the delocalization of one electron in reduced Keggin ion in salt 1 and the Mo^VI in [GeMo₁₂O₄₀]⁴⁻ is partly reduced to Mo^V owing to the charge-transfer transitions taking place between the ferrocenyl donors and the POM acceptors. The two compounds were also characterized by IR spectroscopy and cyclic voltammetry.