Ionic liquids are not always green: hydrolysis of 1-butyl-3-methylimidazolium hexafluorophosphate

1-Butyl-3-methylimidazolium fluoride hydrate has been identified crystallographically as a decomposition product created during purification of the hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate. This highlights the need to treat ionic liquids much as one would any other research chemical with potentially hazardous properties, unknown toxicity and/or stability, particularly when searching for 'green solvents'.

Facile in situ synthesis of nanofluids based on ionic liquids and copper oxide clusters and nanoparticles

Two stable nanofluids comprising of mixed valent copper(_I,_II) oxide clusters (<1 nm) suspended in 1-butyl-3-methylimidazolium acetate, [C(₄)mim][OAc], and copper(_II) oxide nanoparticles (<50 nm) suspended in trioctyl(dodecyl) phosphonium acetate, [P-₈₈₈₁₂][OAc], were synthesised in a facile one-pot reaction from solutions of copper(_II) acetate hydrate in the corresponding ionic liquids. Formation of the nanostructures was studied using ¹³C NMR spectroscopy and differential scanning calorimetry (DSC). From a solution of Cu(OAc)₂ in 1-ethyl-3-methylimidazolium acetate, [C₂mim][OAc], crystals were obtained that revealed the structure of [C₂mim][Cu₃(OAc)₅(OH)₂(H₂O)]center dot H₂O, indicating the formation of copper hydroxo-clusters in the course of the reaction. Synthesised nanostructures were studied using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Physical properties of the prepared IL-nanofluids were examined using IR and UV-VIS spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and densitometry. 

THE EFFECT OF POWER ULTRASOUND ON THE OXIDATIVE DISSOLUTION OF RUO2.XH2O BY BROMATE IONS

The effects of continuous sonication and presonication on the kinetics of oxidative dissolution of ruthenium dioxide hydrate by bromate ions under acidic conditions are reported. Compared with unsonicated and presonicated dispersions the overall rate of dissolution of continuously sonicated dispersions is significantly greater due to a reduction in the average particle size and, hence, an increase in the specific surface area. Powder dispersions subjected to continuous ultrasound and presonication exhibit an initial induction period in their corrosion kinetics; the length of this induction period increases with increasing presonication. This corrosion feature is retained in the dissolution kinetics of powder samples which have been subjected to pre-ultrasound, but which are then stirred during the dissolution process. It is believed that this apparent permanent change in the nature of the powder particles is due to the ultrasound induced formation of a very thin layer of a largely unreactive form of ruthenium dioxide (possibly due to partial dehydration) on the surface of the powder particles. A kinetic scheme, based on this model, is used to account for the observed kinetics of dissolution of RuO2 . xH2O which have been subjected to both continuous sonication and presonication.

Synthesis of caffeic acid and p-hydroxybenzoic acid molecularly imprinted polymers and their application for the selective extraction of polyphenols from olive mill waste waters

Using caffeic acid and p-hydroxybenzoic acid as templates, two molecularly imprinted polymers (MIPs) were prepared that were used for isolation of polyphenols from olive mill waste water samples (OMWWs) without previous pre-treatment. For the preparation of the caffeic acid MIPs 4-vinylpyridine, allylurea, allylaniline and methacrylic acid were tested as functional monomers, ethylene glycol dimethylacrylate (EDMA), pentaerythritol trimethylacrylate (PETRA) and divinylbenzene 80 (DVB80) as cross-linkers and tetrahydrofuran as porogen. For p-hydroxybenzoic acid 4-vinylpyridine, allylurea and allylaniline were tested as functional monomers, EDMA and PETRA as cross-linkers and acetonitrile as porogen. The performance of the synthesized polymers was evaluated against seven structurally related compounds by means of polymer-based HPLC. The two polymers that presented the most interesting properties were further evaluated by batch rebinding and from the derived isotherms their capacity and binding strength were determined. Using solid-phase extraction (SPE), their ability to recognize and bind the template molecule from an aqueous solution as well as the pH dependence of the binding strength were explored. After establishing the best SPE protocol, an aqueous model mixture of compounds and a raw OMWWs sample were loaded on the two best polymers. The result of the consecutive use of the two polymers on the same sample was explored. It was concluded that acidic conditions favour the recognition abilities of both polymers and that they can be used for a quick and efficient isolation of the polyphenol fraction directly from raw OMWW.

The phase diagram of water at negative pressures: Virtual ices

The phase diagram of water at negative pressures as obtained from computer simulations for two models of water, TIP4P/2005 and TIP5P is presented. Several solid structures with lower densities than ice Ih, so-called virtual ices, were considered as possible candidates to occupy the negative pressure region of the phase diagram of water. In particular the empty hydrate structures sI, sII, and sH and another, recently proposed, low-density ice structure. The relative stabilities of these structures at 0 K was determined using empirical water potentials and density functional theory calculations. By performing free energy calculations and Gibbs-Duhem integration the phase diagram of TIP4P/2005 was determined at negative pressures. The empty hydrates sII and sH appear to be the stable solid phases of water at negative pressures. The phase boundary between ice Ih and sII clathrate occurs at moderate negative pressures, while at large negative pressures sH becomes the most stable phase. This behavior is in reasonable agreement with what is observed in density functional theory calculations.

Chemoenzymatic synthesis of monocyclic arene oxides and arene hydrates from substituted benzene substrates

Enantiopure cis-dihydrodiol bacterial metabolites of substituted benzene substrates were used as precursors, in a chemoenzymatic synthesis of the corresponding benzene oxides and of a substituted oxepine, via dihydrobenzene oxide intermediates. A rapid total racemization of the substituted benzene 2,3-oxides was found to have occurred, via their oxepine valence tautomers, in accord with predictions and theoretical calculations. Reduction of a substituted arene oxide to yield a racemic arene hydrate was observed. Arene hydrates have also been synthesised, in enantiopure form, from the corresponding dihydroarene oxide or trans-bromoacetate precursors. Biotransformation of one arene hydrate enantiomer resulted in a toluene-dioxygenase catalysed cis-dihydroxylation to yield a benzene cis-triol metabolite.

Degradable Polymer Networks and Star Polymers Based on Mixtures of Two Cleavable Dimethacrylate Crosslinkers: Synthesis, Characterization, and Degradation

Mixtures of two cleavable dimethacrylate crosslinkers, the hydrolyzable di(methacryloyloxy-1-ethoxy)methane (DMOEM) and the thermolyzable 1,1-ethylene-diol dimethacrylate (EDDMA), were used for the preparation of neat crosslinker polymer networks, randomly crosslinked polymer networks of methyl methacrylate (MMA), and star polymers of MMA, using group transfer polymerization in tetrahydrofuran (THF). All star polymers and randomly crosslinked polymer networks containing mixtures of the hydrolyzable DMOEM and the thermolyzable EDDMA crosslinkers gave THF-soluble final products when subjected to sequential thermolysis and hydrolysis, in this order. When applying sequential hydrolysis and thermolysis, only the star polymers with an EDDMA crosslinker content equal to or higher than 50% gave THF-soluble final products.

Thermolyzable polymer networks and star polymers containing a novel, compact, degradable acylal-based dimethacrylate cross-linker: Synthesis, characterization, and thermolysis

A compact, cleavable acylal dimethacrylate cross-linker, 1,1-ethylenediol dimethacrylate (EDDMA), was synthesized from the anhydrous iron(III) chloride-catalyzed reaction between methacrylic anhydride and acetaldehyde. The ability of EDDMA to act as cross-linker was demonstrated by using it for the preparation of one neat cross-linker network, four star polymers of methyl methacrylate (MMA), and four randomly cross-linked MMA polymer networks using group transfer polymerization (GTP). For comparison, the corresponding polymer structures based on the commercially available ethylene glycol dimethacrylate (EGDMA) cross-linker (isomer of EDDMA) were also prepared via GTR The number of arms of the EDDMA-based star polymers was lower than that of the corresponding EGDMA polymers, whereas the degrees of swelling in tetrahydrofuran of the EDDMA-based MMA networks were higher than those of their EGDMA-based counterparts. Although none of the EDDMA-containing polymers could be cleanly hydrolyzed under basic or acidic conditions, they could be thermolyzed at 200 degrees C within 1 day giving lower molecular weight products.

Synthesis and characterization of amphiphilic star copolymers of 2-(dimethylamino) ethyl methacrylate and methyl methacrylate: Effects of architecture and composition

Six amphiphilic star copolymers comprising hydrophilic units of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and hydrophobic units of methyl methacrylate (MMA) were prepared by the sequential group transfer polymerization (GTP) of the two comonomers and ethylene glycol dimethacrylate (EGDMA) cross-linker. Four star-block copolymers of different compositions, one miktoarm star, and one statistical copolymer star were synthesized. The molecular weights (MWs) and MW distributions of all the star copolymers and their linear homopolymer and copolymer precursors were characterized by gel permeation chromatography (GPC), while the compositions of the stars were determined by proton nuclear magnetic resonance (H-1 NMR) spectroscopy. Tetrahydrofuran (THF) solutions of all the star copolymers were characterized by static light scattering to determine the absolute weight-average MW ((M) over bar (w)) and the number of arms of the stars. The R, of the stars ranged between 359,000 and 565,000 g mol(-1), while their number of arms ranged between 39 and 120. The star copolymers were soluble in acidic water at pH 4 giving transparent or slightly opaque solutions, with the exception of the very hydrophobic DMAEMA(10)-b-MMA(30)-star, which gave a very opaque solution. Only the random copolymer star was completely dispersed in neutral water, giving a very opaque solution. The effective pKs of the copolymer stars were determined by hydrogen ion titration and were found to be in the range 6.5-7.6. The pHs of precipitation of the star copolymer solutions/dispersions were found to be between 8.8-10.1, except for the most hydrophobic DMA-EMA(10)-b-MMA(30)-Star, which gave a very opaque solution over the whole pH range. (c) 2006 Elsevier Ltd. All rights reserved.

Synthesis and characterization of star polymers and cross-linked star polymer model networks with cores based on an asymmetric, hydrolyzable dimethacrylate cross-linker

A hydrolyzable dimethacrylate cross-linker, 2-methyl-2,4-pentanediol dimethacrylate (MPDMA), was synhesized by the reaction of 2-methyl-2,4-pentanediol and methacryloyl chloride in the presence of triethylamine. This cross-linker was used to prepare a neat cross-linker network and three cross-linked star polymer model networks (CSPMNs) of methyl methacrylate (MMA), as well as star-shaped polymers of MMA, by group transfer polymerization (GTP). Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions (MWDs) of the linear polymer precursors, and demonstrated the increase in molecular weight (MW) on each successive addition of cross-linker or monomer. Characterization of the star polymers by static light scattering (SLS) in THF showed that star polymers with MPDMA cores bear a relatively small number of arms, between 7 and 35. All star polymers and polymer networks containing the MPDMA cross-linker were hydrolyzed at room temperature in neat trifluoroacetic acid to yield lower-MW products.

Synthesis and characterization of polymer networks and star polymers containing a novel, hydrolyzable acetal-based dimethacrylate cross-linker

An acid-labile dimethaerylate acetal cross-linker,di(methacryloyloxy-l-ethoxy)methane(DMOEM), was synthesized by the reaction of 2-hydroxyethyl methacrylate and paraformaldehyde using p-toluenesulfonic acid and toluene as catalyst and solvent, respectively. Group transfer polymerization was employed to use this cross-linker in the preparation of nine hydrolyzable polymer structures: one neat cross-linker network, one randomly cross-linked network of methyl methacrylate (MMA), and seven star-shaped polymers of MMA. Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions of the linear polymer precursors to the stars and demonstrated the increase in molecular weight upon the addition of cross-linker for the formation of star-shaped polymers. Characterization of the star polymers in THF using static light scattering and GPC showed that the molecular weights and the number of arms of each star polymer increased with an increase in the molar ratio of cross-linker to initiator and with a decrease in the molar ratio of monomer to initiator. The star polymers with DMOEM cores bore a smaller number of arms than those cross-linked with the non-hydrolyzable commercial cross-linker ethylene glycol dimethacrylate due to the bulkier structure of DMOEM. All DMOEM-containing polymer networks and star polymers were completely hydrolyzed within 48 h using hydrochloric acid in THF.

Synthesis and characterization of star polymers and cross-linked star polymer model networks containing a novel, silicon-based, hydrolyzable cross-linker

An acid-labile dimethacrylate cross-linker, dimethyldi(methacryloyloxy-l-ethoxy)silane (DMDMAES), was synthesized by the reaction of 2-hydroxyethyl methacrylate (HEMA) and dichlorodimethylsilane in the presence of triethylamine. Group transfer polymerization (GTP) was employed to use this cross-linker in the preparation of six hydrolyzable polymer structures: one neat cross-linker network, one randomly cross-linked network of methyl methacrylate (MMA), two star-shaped polymers of MMA, and two cross-linked star polymer model networks (CSPMNs) of MMA. A nonhydrolyzable CSPMN of MMA, based on a stable cross-linker, was also synthesized. Gel permeation chromatography (GPC) in tetrahydrofuran (THF) confirmed the narrow molecular weight distributions (MWDs) of the linear polymer precursors and demonstrated the increase in molecular weight (MW) upon each successive addition of cross-linker or monomer. Characterization by static light scattering (SLS) and GPC showed that star polymers with DMDMAES cores bear a relatively small number of arms, around 7. All star polymers and polymer networks were hydrolyzed using hydrochloric acid in THF. While the MWs of the products from the hydrolysis of the star polymers, the neat cross-linker network, and the randomly cross-linked network were as expected, those from the CSPMNs were of a much higher than expected MW, indicating extensive star-star coupling.

Group 6 carbene complexes derived from lithiated azoles and the crystal structure of a molybdenum thiazolinylidene complex

Fischer-type (alkoxy)azolyl carbene complexes and Ofele-Lappert-type azolylinylidene complexes were synthesised by reaction of 1-phenylpyrazol-3 -yllithium, 4-methylthiazol-2-yllithium, benzothiazol-2-yllithium, 1-methylimidazol-2-yllithium with M(CO)(5)L (L = CO, THF or Cl-; M = Cr, Mo or W) and subsequent alkylation with CF3SO3CH3. The alkylation of Fischer-type carbene complexes containing an azolyl as the organic substituent proceeded via ring opening of tetrahydrofuran. When the alkylation is carried out in THF, the carbocation CH3O(CH2)(4)(+) acts as an electrophile. Protonation rather than alkylation of coordinated imidazolyl furnished cyclic imine complexes. Changing the donor atom of a coordinated thiazole from N to C by deprotonation and alkylation afforded a carbene complex. (C) 1999 Elsevier Science S.A. All rights reserved.

Preparation of Aqueous Core/Polymer Shell Microcapsules by Internal Phase Separation

Aqueous core/polymer shell microcapsules with mommuclear and polynuclear core morphologies have been formed by internal phase separation from water-in-oil emulsions. The water-in-oil emulsions were prepared with the shell polymer dissolved in the aqueous phase by adding a low boiling point cosolvent. Subsequent removal of this cosolvent (by evaporation) leads to phase separation of the polymer and, if the spreading conditions are correct, formation of a polymer shell encapsulating the aqueous core. Poly(tetrahydrofuran) (PTHF) shell/aqueous core microcapsules, with a single (mononuclear) core, have been prepared, but the low T-g (-84 degreesC) of PTHF makes characterization of the particles more difficult. Poly(methyl methacrylate) and poly(isobutyl methacrylate) have higher T-g values (105 and 55 degreesC, respectively) and can be dissolved in water at sufficiently high acetone concentrations, but evaporation of the acetone from the emulsion droplets in these cases mostly resulted in polynuclear capsules, that is, having cores with many very small water droplets contained within the polymer matrix. Microcapsules with fewer, larger aqueous droplets in the core could be produced by reducing the rate of evaporation of the acetone. A possible mechanism for the formation of these polynuclear cores is suggested. These microcapsules were prepared dispersed in an oil-continuous phase. They could, however, be successfully transferred to a water-continuous phase, using a simple centrifugation technique. In this way, microcapsules with aqueous cores, dispersed in an aqueous medium, could be made. It would appear that a real challenge with the water-core systems, compared to the previous oil-core systems, is to obtain the correct order of magnitude of the three interfacial tensions, between the polymer, the aqueous phase, and the continuous oil phase; these control the spreading conditions necessary to produce shells rather than "acorns".