Transition Metal-Free Synthesis of meta-Bromo- and meta-Trifluoromethylanilines from Cyclopentanones by a Cascade Reaction

Anilines are key constituents in biologically active compounds and often obtained from transition metal-catalyzed coupling of an aryl halide with an amine. In this work, we report a transition metal-free method for the synthesis of meta-bromo- and meta-trifluoromethylanilines starting from 3-tribromomethylcyclopentanone or 3-(2-bromo-2-chloro-1,1,1-trifluoroethyl)cyclopentanone, respectively. The scope of the transformation is shown by application of primary, secondary and aromatic amines. The reaction proceeds in acceptable to high yields (20–81 %), and allows for the synthesis of anilines with substitution patterns otherwise difficult to access.     

The Physicochemical Behavior of Phytosterol Ethoxylates

In this work the physicochemical behavior of a series of phytosterol ethoxylates in water is presented. The influence of the length of the polyoxyethylene chain is studied. The surfactant solutions have been examined by means of birefringent microscopy, surface tension, self-diffusion 1H NMR, dynamic and static light scattering, and rheology. The surfactants with a hydrophilic chain of 10 oxyethylene units or more gave a micellar region. The CMC values were generally very low and a reverse relationship between the CMC value and the polyoxyethylene chain length was obtained. The time required to reach equilibrium surface tension was very long, more than 150 min. For the hydrophobic surfactants large lamellar regions appeared while for the more hydrophilic surfactants cubic and hexagonal structures were present which remained stable up to temperatures of 100 degrees C. In the micellar region prolate aggregates were formed which showed "ghostlike" behavior, consisting of cross-linked micelles with very fast relaxation times. Copyright 1999 Academic Press.     

Facilitated hydride binding in an Fe-Fe hydrogenase active-site biomimic revealed by X-ray absorption spectroscopy and DFT calculations

Iron-only hydrogenases are high-efficiency biocatalysts for the synthesis and cleavage of molecular hydrogen. Their active site is a diiron center, which carries CO and CN ligands. Remarkably, the two iron atoms likely are connected by a non-protein azadithiolate (adt = S-CH2-NH-CH2-S). To dwell on the role of the adt in H2 catalysis, a specific biomimetic diiron compound, 1 = [Fe2(mu-adt-CH2-Ph)(CO)4(PMe3)2], with unprecedented positive reduction potential, has been synthesized and crystallized previously. It comprises two protonation sites, the N-benzyl-adt nitrogen that can hold a proton (H) and the Fe-Fe bond that will formally carry a hydride (Hy). We investigated changes in the solution structure of 1 in its four different protonation states (1', [1H]+, [1HHy]2+, and [1Hy]+) by X-ray absorption spectroscopy at the iron K-edge. EXAFS reveals that already protonation at the adt nitrogen atom causes a change of the ligand geometry involving a significant lengthening of the Fe-Fe distance and CO and PMe3 repositioning, respectively, thereby facilitating the subsequent binding of a bridging hydride. Hydride binding clearly is discernible in the XANES spectra of [1HHy]2+ and [1Hy]+. DFT calculations are in excellent agreement with the experimentally derived structural parameters and provide complementary insights into the electronic structure of the four protonation states. In the iron-only hydrogenases, protonation of the putative adt ligand may cause the bridging CO to move to a terminal position, thereby preparing the active site for hydride binding en route to H2 formation.     

Phase behavior of cetyltrimethylammonium surfactants with oligo carboxylate counterions mixed with water and decanol: attraction between charged planes or spheres with oligomeric counterions

Cetyltrimethylammonium surfactants with a range of oligo carboxylate anions bearing 2, 3, or 4 negative charges have been synthesized, and their respective behaviors in binary mixtures with water and in ternary mixtures with added decanol have been investigated. In binary mixtures with water, all surfactants formed nearly spherical micelles at high water contents; however, the interactions between micelles varied strongly with the number of charges in the counterion. Micelles with divalent counterions were generally miscible with water, whereas micelles with tri- or tetravalent counterions demixed in one concentrated and one dilute phase. Addition of decanol resulted in all cases in the appearance of a lamellar phase, and all investigated oligo carboxylate anions (di-, tri-, and tetravalent) gave rise to a strong attraction between the lamellar planes, resulting in a limited swelling (up to 35-40 wt % water) of the lamellar phase in contact with excess water. These experiments confirm the theoretically predicted influence of aggregate geometry (spheres or planes) on the attraction between colloidal aggregates neutralized by multivalent counterions. Further addition of decanol resulted in the appearance of a second birefringent phase in equilibrium with the lamellar phase. SWAXS showed this phase to be lamellar and to display short-range order that disappeared upon heating. This phase is identified as a lamellar gel phase (Lbeta-phase).     

Ylide‐Functionalized Phosphines: Strong Donor Ligands for Homogeneous Catalysis

Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross‐coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron‐rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide‐functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations.     

Incorporation of platinum nanoparticles in ordered mesoporous carbon

Platinum nanoparticles were incorporated within the pore system of ordered mesoporous carbon (OMC) by impregnating the carbon with a water-in-oil (w/o) microemulsion containing dissolved platinum salt followed by reduction of the platinum ions in situ inside the carbon pore system. The procedure provides preparation of metallic nanoparticles from hydrophilic precursors inside the hydrophobic carbon support structure with simultaneous control of the maximum metal particle size. Electron tomography was used to verify the presence of platinum nanoparticles inside the carbon material.     

Hollow-fibre supported liquid membrane extraction for determination of fluoxetine and norfluoxetine concentration at ultra trace level in sewage samples

In this study, a method was developed for determining the concentration of the pharmaceutical fluoxetine and its metabolite, norfluoxetine, in sewage water samples. Sample preparation was performed by hollow-fibre supported liquid membrane (HF-SLM) extraction with final analysis using liquid chromatography with UV detection. Several parameters were studied including type of organic solvent, sample and acceptor pH, and salt and humic acid content. The optimised method allowed determination of the analyte at the ng/L level in sewage water. A linear plot gave a correlation coefficient better than 0.991 for both analytes and resulted in limits of detection in sewage water of 11 and 12 ng/L, for fluoxetine and norfluoxetine, respectively. The enrichment factor was over 1700 for both analytes in sewage water. The repeatability and reproducibility were better than 8% and 17%, respectively. The developed methodology was used to study daily variations of fluoxetine and norfluoxetine in municipal sewage streams. Norfluoxetine has been detected for the first time in sewage water and a preliminary analysis gave average concentrations of 150 and 225 ng/L for norfluoxetine and fluoxetine, respectively.     

Use of different types of mesoporous materials as tools for organic synthesis

Mesoporous materials have been investigated as auxiliary agents for organic synthesis comprising reactants with widely different solubility characteristics. The finely divided oxide material was immersed in an aqueous solution of a water-soluble reactant, potassium iodide, and the loaded particles were kept under stirring in the hydrophobic reactant, 4-tert-butylbenzyl bromide, or in a hydrocarbon solution of this reactant. The reaction proceeded well in alumina and silica of either bicontinuous cubic or hexagonal geometry. It was shown for silica that the particle size was an important parameter; the smaller the size the faster the reaction. Titania gave a much lower reaction rate than alumina and silica. It was found that the hexagonal mesoporous alumina could be reused either as a slurry or in a column procedure. Attempts were also made to use hydrophobic mesoporous materials, either mesoporous graphite or mesoporous oxide treated with chlorotrimethylsilane, in the reversed mode. The hydrophobic solid was then immersed in a solution of the hydrophobic reactant and subsequently dispersed in an aqueous solution of the water-soluble reactant. Two nucleophilic substitution reactions and one oxidation reaction were investigated but the yields were low in all cases.     

[4+3] Cycloaddition of Donor–Acceptor Cyclopropanes with Amphiphilic Benzodithioloimine as Surrogate for ortho‐Bisthioquinone

Donor–acceptor cyclopropanes were reacted with amphiphilic benzodithioloimine to give seven‐membered heterocycles with two sulfur atoms. Formally, this transformation can be regarded as a [4+3] cycloaddition reaction of the three‐membered ring and ortho‐bisthioquinone. The benzodithioloimine serves as a surrogate for this highly reactive diene. The structure of the products was confirmed by X‐ray crystallography. Broad signals in ¹³C NMR studies suggest that several conformers, slowly interconverting on the NMR timescale, are present at room temperature.