Utilisation of 1,3-dialkylimidazolium-2-carboxylates as CO2-carriers in the presence of Na and K: application in the synthesis of carboxylates, monomethylcarbonate anions and halogen-free ionic liquids

1,3-Dialkylimidazolium-2-carboxylate compounds have recently been fully characterised. Here we describe the utilisation of 1,3-dimethyl (1a) and 1-butyl-3-methyl-imidazolium-2-carboxylate (1b) in a carboxylation reaction with transfer of the CO₂ moiety to benzoylacetone and methanol for the synthesis, in high yield, of benzoylacetate and monoalkylcarbonate anions, respectively. Conversely, when compounds 1a and b are reacted with carbonylic substrates lacking C-H active bonds, a product resulting from nucleophilic attack of the 1,3-dialkylimidazol-2-ylidene species on the carbonyl moiety is obtained. The reported reactions can find applications in organic synthesis and in the synthesis of halogen-free ionic liquids.     

Ternary and tetrahedral symmetry in hybrid fluorides, fluoride carbonates and carbonates

Tren amine cations and carbonate anions adopt a ternary symmetry while tetra amine cations are tetrahedral. The symmetry of these constitutive ions influences strongly the nature of the solids which crystallise from solutions. Large fluorinated aluminate polyanions with tetrahedral symmetry appear in the presence of tren amine, while infinite chains of AlF₆ octahedra are observed with tetra amine and that noncentrosymmetric structures are frequently encountered in rare earth fluoride carbonates.     

One-Pot Formation of Carbonates from the Reactions of Carbonyl Compounds with Samarium Diiodide and Methyl Chloroformate

Treatment of carbonyl compounds with SmI₂ and methyl chloroformate in the presence of molecular sieves provides the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry obtained by this procedure is different from that of conventional pinacolic couplings.     

Effect of the rare earth in the perovskite-type mixed oxides AMnO3 (A=Y, La, Pr, Sm, Dy) as catalysts in methanol oxidation

The effect of the rare earth in the perovskite-type mixed oxides AMnO₃ (A=Y, La, Pr, Sm, Dy) on catalytic properties in methanol oxidation was investigated in this work. The perovskites were prepared by reactive grinding in order to enhance the specific surface area in comparison with other classical synthesis procedures. These catalysts were characterized by N₂ adsorption, X-ray diffraction, H₂ temperature-programmed reduction (TPR-H₂), O₂-, CH₃OH- and CO₂-temperature-programmed desorption (TPD). The activity of the five catalysts under study in the methanol oxidation reaction was evaluated. The behaviour of the α-O₂ from the surface of the perovskite was strongly related to the nature of the A-site cation and particularly to its electronegativity but also to its density. Concerning the β-O₂ from the bulk, the rare earth only induces an indirect effect notably due to structural modifications. As suggested in a previous study, the activity in methanol oxidation was directly linked with the surface oxygen density. Under an excess of α-oxygen, the reaction intermediate was found to be a monodentate carbonate that decomposes into CO₂. The stability of monodentate carbonates was also found to be related to the electronegativity of the rare earth during both CH₃OH- and CO₂-temperature-programmed desorption. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate that induces a consumption of anion vacancies in spite of the production of CO₂. Nevertheless, the accumulation of these carbonates leads to a decrease in the oxidation rate since their desorption requires high temperatures.     

Isotope Geochemical Studies on Carbonates of Quaternary Glacio-Lacustrine Lake Sediments as indicators of Paleoenvironment

Selected silty “summer” and argillaceous “winter” layers of profiles of the rhythmically bedded glacio-lacustrine ice-marginal lake sediment of the Dehlitz-Leipzig varved clay (Leipziger Tieflandsbucht, Central Germany) have been examined for isotope composition (¹⁸O/¹⁶O, ¹³C/¹²C) of carbonate and organic fraction. In addition, mineralogical and grain size compositions were determined. The results show 1) a change in source of carbonate sediment (provenance) through time; 2) the oxygen isotope ratios differed between the “summer” and “winter” layers of varves couplets due to different rates of sedimentation; 3) anoxic events occurred in the lake; 4) carbon isotope ratios suggest organics in lake sediments which were derived from land and the primary productivity was low in the lake itself. In the study of cold-climatic lake sediments, isotope investigations can efficiently be used as additional paleosedimentological and facies indicators.     

18O/16O and 13C/12C Fractionation During the Reaction of Carbonates with Phosphoric Acid: Effects of Cationic Substitution and Reaction Temperature

Abstract

The factors for ¹⁸O/¹⁶O fractionation between carbonates and CO₂ gas produced by the dissolution of the carbonates in phosphoric acid (sealed vessel method) have been investigated as a function of reaction temperature (20–90°C) and cationic substitution in the solid. Synthetic CaCO₃, Ca_0.75 Mn_0.25 CO₃, MnCO₃, BaCO₃ and SrCO₃ powders, and a natural kutnahorite sample were used as solids. The δ¹⁸O values of the gaseous CO₂ liberated by the reaction with phosphoric acid decrease with increasing temperature and seem to be a linear function of T(°K)^?2. The slopes are specific for different carbonates. No temperature-depended ¹³C/¹²C fractionation seems to exist.     

Ab initio vibrational spectra and dielectric properties of carbonates: magnesite, calcite and dolomite

The equilibrium geometry, the Raman and IR vibrational spectra at the Γ point, TO–LO splitting, IR intensities, Born and dielectric tensors of magnesite MgCO₃, dolomite MgCa(CO₃)₂ and calcite CaCO₃ have been calculated with the periodic ab initio program CRYSTAL, by using an all-electron gaussian type basis set and the B3LYP hamiltonian. LO (longitudinal-optical) modes are computed by correcting the dynamical matrix through Born charges and high frequency dielectric tensors obtained from well localized Wannier functions and a saw-tooth computational scheme. The mean absolute difference between calculated and experimental frequencies (IR TO and LO and RAMAN) is as small as 6.9 cm⁻¹ for magnesite, 7.7 cm⁻¹ for dolomite and 8.5 cm⁻¹ for calcite. Calculated IR intensities are in semiquantitative agreement with experiment. The modes of the three compounds are compared through graphical animation available on the CRYSTAL web-site.     

Basische Carbonate des Dysprosiums: Dy2O2(CO3) und Dy(OH)(CO3)

Basic Carbonates of Dysprosium: Dy₂O₂(CO₃) and Dy(OH)(CO₃) Single crystals of the basic carbonates Dy₂O₂(CO₃) and Dy(OH)(CO₃) are obtained via hydrothermal synthesis from a mixture of DyCl₃ · 6 H₂O and K₂CO₃ and Cs₂CO₃, respectively, as well as CO₂ and H₂O in a steel autoclave at 480 and 400 °C, respectively. The crystal structures are isotypic with those of II‐Nd₂O₂(CO₃) and B–Nd(OH)(CO₃), respectively; Dy₂O₂(CO₃): hexagonal, P6₃/mmc, Z = 2; a = 386.9(2), c = 1516.3(3) pm; Dy(OH) · (CO₃): hexagonal, P‐6, Z = 18; a = 1201.0(1), c = 971.8(9) pm.     

Er2(CO3)2(C2O4)(H2O)2 — Synthese,Kristallstruktur und thermischer Abbau eines Carbonat‐Oxalat‐Hydrates des Erbiums

Er₂(CO₃)₂(C₂O₄)(H₂O)₂ — Synthesis, Crystal Structure and the Thermal Decomposition of a Carbonate‐Oxalate‐Hydrate of Erbium The hydrothermal reaction of an equimolar ratio of Er₂O₃ with the aminoacid L‐cysteine in evacuated glass ampoules in H₂O at 130 °C gave transparent, pink crystals of the formula Er₂(CO₃)₂(C₂O₄)(H₂O)₂. It crystallises in the monoclinic space group Cm (Z = 2, a = 777.3(2) pm, b = 1492.0(3) pm, c = 473.09(8) pm, b = 90.12(9)°). The thermal decomposition of Er₂(CO₃)₂(C₂O₄)(H₂O)₂ was investigated.     

Palladium Catalyzed Additions to Allylic Hydroxy Phosphonates: Applications in the Enantioselective Synthesis of Enterolactone and Turmerone

Reaction of nonracemic allylic hydroxy phosphonates, prepared by the asymmetric phosphonylation of unsaturated aldehydes, with methyl chloroformate in pyridine yields the corresponding carbonates. The carbonates are excellent substrates for the palladium-catalyzed addition of nucleophiles. Addition of the nucleophile is highly regioselective, resulting in n -substituted vinyl phosphonates. The reaction of the allylic carbonates with aryl stannanes and malonates has been investigated. Progress in the application of these reactions to the synthesis of turmerone and enterolactone is reported.