Complexation and Transport of Alkali and Alkaline Earth Metal Cations by p-tert-Butyldihomooxacalix[4]arene Tetraketone Derivatives

The binding properties of three p-tert-butyldihomooxacalix[4]arene tetraketone derivatives (tert-butyl 2b, adamantyl 2c and phenyl 2d) in the cone conformation and one derivative (methyl 2a) in a partial cone conformation, towards alkali and alkaline earth metal cations have been established by extraction studies of metal picrates from water into dichloromethane, stability constant measurements in methanol and acetonitrile, and by ¹H NMR spectrometry. Transport experiments of metal picrates through a dichloromethane membrane were also performed. The results are compared to those obtained with closely-related calix[n]arene derivatives (n = 4 and 5) and discussed in terms of the substituents, size and conformational effects. Methylketone 2a is a poor binder for all the cations studied, due to its partial cone conformation. Ketones 2b, 2c and 2d show high extraction and complexation levels for the alkali cations, with similar profiles and preference for K⁺ and Na⁺ (plateau selectivity). Towards alkaline earth cations, these ketones show a strong peak selectivity for Ba²⁺ in extraction, but a plateau selectivity for Ca²⁺, Sr²⁺ and Ba²⁺ in complexation. The nature of the substituent attached to the ketone function has some influence on their binding properties, with phenylketone 2d being a slightly weaker binder than ketones 2b and 2c. ¹H NMR titrations confirm the formation of 1:1 complexes between the ketones and the cations studied, also indicating that they should be located inside the cavity defined by the phenoxy and carbonyl oxygen atoms. Ketones 2b, 2c and 2d show transport rates that do not follow, in general, the same trends observed in extraction and complexation.     

The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations

The adsorption of uranium(VI) from aqueous solutions onto activated carbon has been studied using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined (contact time 240 min; pH 3.0+/-0.1; initial uranium concentration 100 mg/L; temperature 293.15 K). The experimental data were analyzed using sorption kinetic models (pseudo-first- and pseudo-second-order equations) to determine the equation that fits best our experimental results. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of activated carbon and experimental results showed this to be 28.30 mg/g. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model and that the sorption is physical in nature (the activation energy Ea=7.91 kJ/mol). Thermodynamic parameters (DeltaHads0=-50.53 kJ/mol, DeltaSads0=-98.76 J/mol K, DeltaGads(293.15 K)0=-21.61 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process.     

A Samarium "Soluble" Anode: A New Source of SmI(2) Reagent for Electrosynthetic Application

An electrochemical method to prepare solutions of samarium diiodide in THF is reported. The simple electrolysis of a samarium rod provides a rapid and straightforward in situ synthesis of SmI(2) . The electrogenerated complex catalyzes various C?C bond formations. The reagent is produced continuously and leads to efficient organic electrosynthesis with significantly smaller amounts of solvent than usually required.     

Chiral Chromium Salen@rGO as Multipurpose and Recyclable Heterogeneous Catalyst

The first immobilization of a pyrene-tagged chromium salen complex through π-π noncovalent interactions on reduced graphene oxide (rGO) is described. A very robust supported catalytic system is obtained to promote asymmetric catalysis in repeated cycles, without loss of activity or enantioselectivity. This specific behavior was demonstrated in two different catalytic reactions (up to ten reuses) promoted by chromium salen complexes, the cyclohexene oxide ring-opening reaction and the hetero-Diels-Alder cycloaddition between various aldehydes and Danishefsky's diene. Furthermore, the chiral chromium salen@rGO has been found to be compatible with a multi-substrate type use, in which the structure of the substrate involved is modified each time the catalyst is reused.     

Interaction between p-tetraphenyl tetrahomodioxacalix[4]arene amide derivatives and alkali and alkaline-earth metal cations

The binding properties of four amido derivatives of p-tetraphenyl tetrahomodioxacalix[4]arene towards alkali and alkaline-earth metal cations using UV-absorption spectrophotometry, ¹H NMR and ESI-mass spectrometry techniques are reported.     

Characterization of crude and calcined phosphates of Kef Essennoun (Djebel Onk,Algeria)

Journal of Thermal Analysis and Calorimetry - Rock phosphate is the fundamental component for the manufacture of phosphoric acid and phosphate fertilizers. The aim of this study is to predict how...     

Recoverable salen-based macrocyclic chiral complexes; catalysts for enantioselective Henry reactions

Cobalt and chromium complexes have been prepared from chiral calix–salen cyclic ligands. The corresponding tetrahydrosalen reduced forms have been used for copper salt complexation. These new chiral catalysts have been tested for their ability to promote asymmetric Henry reactions between various aldehydes and nitromethane under heterogeneous conditions. The best results were obtained by using tetrahydrosalen-based copper macrocycles, in terms of activity, selectivity, and stability during the recycling process. Ten consecutive runs could indeed be performed with the same catalyst batch to produce the target 1-(2-methoxy-phenyl)-2-nitro-ethanol with highly stable values in terms of yield and enantioselectivity (up to 94% ee).     

Well‐Defined Four‐Coordinate Iron(II) Complexes For Intramolecular Hydroamination of Primary Aliphatic Alkenylamines

Despite the growing interest in iron catalysis and hydroamination reactions, iron‐catalyzed hydroamination of unprotected primary aliphatic amines and unactivated alkenes has not been reported to date. Herein, a novel well‐defined four‐coordinate β‐diketiminatoiron(II) alkyl complex is shown to be an excellent precatalyst for the highly selective cyclohydroamination of primary aliphatic alkenylamines at mild temperatures (70–90 °C). Both empirical kinetic analyses and the reactivity of an isolated iron(II) amidoalkene dimer, [LFe(NHCH₂CPh₂CH₂CH?CH₂)]₂ favor a stepwise σ‐insertive mechanism that entails migratory insertion of the pendant alkene into an iron–amido bond associated with a rate‐determining aminolysis step.     

New Chiral Calixsalen Chromium Complexes: Recyclable Asymmetric Catalysts

A chiral N,N′‐bis(salicylidene)ethylenediamine (salen) polymer has been prepared by a condensation reaction between a thiophenedisalicyladehyde derivative and (S,S)‐cyclohexane‐1,2‐diamine. This polymeric compound was demonstrated to possess a cyclic structure with two to five repetitive units. The addition of chromium(II) salts led to the generation of a chiral catalyst that could be recovered as an insoluble powder. The performance of this new calixsalen‐type catalyst was examined in various transformations, particularly in its ability to promote nucleophilic epoxide ring opening under heterogeneous conditions. The target products were obtained in high yields and with improved selectivity compared with those obtained by using analogous linear polymers. The arrangement of the catalytic sites in the cyclic structure is probably more suitable for the necessary cooperative bimetallic pathway of this demanding reaction. The catalyst could be successfully recycled. This approach represents the first use of calixsalen complexes under heterogeneous catalytic conditions.