Calix[2]furano[2]pyrrole and related compounds as the neutral carrier in silver ion-selective electrode

The performance of calix[2]furano[2]pyrrole and related compounds used as neutral carriers for silver selective polymeric membrane electrode was investigated. The silver ion-selective electrode based on calix[2]furano[2]pyrroles gave a good Nernstian response of 57.1 mV per decade for silver ion in the activity range 1×10⁻⁶ to 1×10⁻² M. The present silver ion-selective electrode displayed very good selectivity for Ag⁺ ion against alkali and alkaline earth metal ions, NH₄⁺, and H⁺. In particular, the present Ag⁺-selective electrode exhibited very low responses towards Hg²⁺ and Pb²⁺ ions. The potentiometric selectivity coefficients of the silver ion-selective electrode exhibited a strong dependence on the solution pH. In particular, the response of the electrode to the Hg²⁺ activity was greatly diminished at pH 2.5 compared to that at pH 5.0. Overall, the performance of the present silver ion-selective electrode based on the ionophore, calix[2]furano[2]pyrrole, is very comparable to that of the electrode prepared with the commercially available neutral carrier in terms of slope, linear range, and detection limits.     

Silver alkoxide and amino N-heterocyclic carbenes; syntheses and crystal structures

Silver(I) complexes of heterobidentate ligands that incorporate one or two N-heterocyclic carbene moieties coupled with an alcohol or amine group have been made by direct deprotonation of ligands of the form [HOCR¹R²CH₂(1-HC{NCHCHNR})][X], H₂L¹X (X = Br, I), [H₂NR¹CHR²CHR²(1-HC{NCHCHNR})][Br]₂ H₃L²X₂ (X = Cl, Br), and [H₂N{CH₂CH₂(1-HC[NCHCHNMes])}₂][X]₃ H₄L³X₃ (X = Cl, Br). Silver(I) oxide is sufficiently basic to deprotonate both the imidazolium and the alcohol functional groups of all but one of the L¹ ligand precursors, to afford rare examples of silver alkoxide complexes [Ag(L¹)], stabilised by the soft donor carbene. Another complex of L¹ is characterised as the carbene alcohol adduct [Ag(HL¹)₂I]. The analogous reactions of silver(I) oxide with the amino imidazolium precursors afford silver amino-carbenes [Ag(HL²)Br] with the potentially bidentate L² ligand, and [Ag(HL³)X] (X = Cl, Br) with the potentially tridentate L³ ligand. A single crystal X-ray diffraction study of the latter complex confirms that the neutral amine of the potentially tridentate L³ ligand is unco-ordinated; instead the structure contains discrete chains of T-shaped silver bis(carbene) halide moieties that bridge to form a zig-zag 2-connected polymer. Protonolysis of two of the silver alkoxide and amino adducts, [Ag(L^1a)] and [Ag(HL^2a)Br], affords imidazolium complexes salts [H₂L^1a][AgCl₂] and [Ag(H₂L^2a)Br][AgBr₂] that retain the Ag(I) centre as complex counterions. The single crystal X-ray structures of these salts have been determined and show the silver(I) cations are now incorporated into ladders or chains as silver(I) halo-anions, and a silver amine dative bond is present in the latter complex.     

Metal Assisted Synthesis of Cationic Sulfidobismuth Cubanes in Ionic Liquids

Bi₂S₃ was dissolved in the presence of either AuCl/PtCl₂ or AgCl in the ionic liquids [BMIm]Cl ⋅ xAlCl₃ (BMIm=1-n-butyl-3-methylimidazolium; x=4–4.3) through annealing the mixtures at 180 or 200 °C. Upon cooling to room temperature, orange, air-sensitive crystals of [BMIm](Bi₄S₄)[AlCl₄]₅ ( 1 ) or Ag(Bi₇S₈)[S(AlCl₃)₃]₂[AlCl₄]₂ ( 2 ) precipitated, respectively. 1 did not form in the absence of AuCl/PtCl₂, suggesting an essential role of the metal cations. X-ray diffraction on single-crystals of 1 revealed a monoclinic crystal structure that contains (Bi₄S₄)⁴⁺ heterocubanes and [AlCl₄]⁻ tetrahedra as well as [BMIm]⁺ cations. The intercalation of the ionic liquid was confirmed via solid state NMR spectroscopy, revealing unusual coupling behavior. The crystal structure of 2 consists of (Bi₇S₈)⁵⁺ spiro-dicubanes, [S(AlCl₃)₃]²⁻ tetrahedra triples, isolated [AlCl₄]⁻ tetrahedra, and heavily disordered silver(I) cations. No cation ordering took place in 2 upon slow cooling to 100 K.     

Synthesis of Novel Greener Functionalized Ionic Liquids Containing Appended Hydroxyl

Novel “greener” functionalized ionic liquids have been prepared by the reaction of 1,2‐epoxy propane and dilute sulfuric acid with [EMIm]Br or [BMIm]Br formed by alkyl bromide (RBr) and 1‐methylimidazole. This kind of ionic liquid could be possibly used as green solvent and catalyst, especially as phase‐transfer catalyst in organic chemistry (e.g., the synthesis of ethoxybenzene). Their chemical structures were characterized by ¹H NMR, ¹³C NMR, and IR.     

Voltammetric sensors based on gel composites containing carbon nanotubes and an ionic liquid

Possibilities of using electrode coatings based on a gel of carboxylated multiwall carbon nanotubes (MWCNTs) in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIm]PF₆) for the creation of a voltammetric sensor with electrocatalytic properties with respect to the pharmacological group of catecholamines—levodopa, methyldopa, and carbidopa—are considered. Using cyclic voltammetry, it was found that a glassy carbon electrode coated with a thin layer of an MWCNT–[BMIm]PF₆ gel or an MWCNT–[BMIm]PF₆–Nafion gel-composite induced a decrease in overvoltage (~60 mV), improved the reversibility of the redox reaction, and increased oxidation currents of the studied substances in comparison with an unmodified glassy carbon electrode. The concentration dependence of the analytical signal was linear in the ranges of 1–250, 2–350, and 5–400 mM for carbidopa, levodopa, and methyldopa, respectively. In the determination of the specified substances in diluted urine samples and tableted drugs, the accuracy index was 98–102% and the relative standard deviation, 0.3–5% (n = 5, P = 0.95).     

A Cryptate Reference Electrode for Ionic Liquids

The cryptate electrode (Ag/Ag⁺222), prepared by immersing silver wire in a solution of silver(I) salt and the cryptand 222 (4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) in ionic liquids have been studied. The potential of the electrode is stabilized by the equilibrium of the Ag⁺ ion complexation by the cryptand, similarly to the potential stabilization by the ionic product of slightly soluble salts, used in aqueous electrodes of the second kind. The Ag/Ag⁺222 cryptate electrode (concentration of the cryptate was much higher than the silver(I) cation concentration, [222]>[Ag⁺]) may be used as a reference electrode in room temperature ionic liquids. The potential of the Ag/Ag⁺222 electrode is less sensitive to the presence of impurities, such as halides or water, in comparison to the Ag/Ag⁺ electrode. After anodic or cathodic polarization, the potential of the Ag/Ag⁺222 electrode comes back to the initial open circuit potential quickly. Preparation of the Ag/Ag⁺222 reference electrode is very easy: a silver wire is immersed in a solution of Ag⁺ salt and cryptand 222 (both available commercially) in the ionic liquid under study.     

Low Temperature Activation of Tellurium and Resource-Efficient Synthesis of AuTe2 and Ag2Te in Ionic Liquids

The low temperature syntheses of AuTe₂ and Ag₂Te starting from the elements were investigated in the ionic liquids (ILs) [BMIm]X and [P₆₆₆₁₄]Z ([BMIm]⁺=1-butyl-3-methylimidazolium; X = Cl, [HSO₄]⁻, [P₆₆₆₁₄]⁺ = trihexyltetradecylphosphonium; Z = Cl⁻, Br⁻, dicyanamide [DCA]⁻, bis(trifluoromethylsulfonyl)imide [NTf₂]⁻, decanoate [dec]⁻, acetate [OAc]⁻, bis(2,4,4-trimethylpentyl)phosphinate [BTMP]⁻). Powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy revealed that [P₆₆₆₁₄]Cl is the most promising candidate for the single phase synthesis of AuTe₂ at 200 °C. Ag₂Te was obtained using the same ILs by reducing the temperature in the flask to 60 °C. Even at room temperature, quantitative yield was achieved by using either 2 mol % of [P₆₆₆₁₄]Cl in dichloromethane or a planetary ball mill. Diffusion experiments, ³¹P and ¹²⁵Te-NMR, and mass spectroscopy revealed one of the reaction mechanisms at 60 °C. Catalytic amounts of alkylphosphanes in commercial [P₆₆₆₁₄]Cl activate tellurium and form soluble phosphane tellurides, which react on the metal surface to solid telluride and the initial phosphane. In addition, a convenient method for the purification of [P₆₆₆₁₄]Cl was developed.     

Supramolecular Ionic‐Liquid Gels with High Ionic Conductivity

Supramolecular ionogels were prepared by the gelation of room‐temperature ionic liquid 1‐butyl‐3‐methylimidazolium tetrafluoroborate ([BMIm][BF₄]) with (S,S)‐bis(leucinol)oxalamide. Remarkably, the ionic conductivity of solutions and ionogels with low gelator concentrations is higher than that of neat [BMIm][BF₄]. On the basis of molecular dynamics simulations and quantum mechanical calculations, the origin of this phenomenon is attributed to the higher affinity of gelator molecules towards [BF₄]^? ions, which reduces the electrostatic attraction between [BMIm]⁺ and [BF₄]^? and thus increases their mobility. With increasing gelator concentration, the ionic conductivity decreases due to the formation of a denser gelator matrix, which hinders the pathways for ionic transport. However, even for very dense ionogels, this decrease is less than one order of magnitude relative to neat [BMIm][BF₄], and thus they can be classified as highly conductive materials with strong potential for application as functional electrolytes.     

Synthesis of Silver Complexes in DMSO–HX and DMSO–HX–Ketone Systems

Comparative analysis of the oxidizing and complexing properties of the DMSO–HX (X = Cl, Br, I) and DMSO–HX–ketone (X = Br, I; the ketone is acetone, acetylacetone, or acetophenone) systems toward silver was performed. The reaction products are AgX (X = Cl, Br, I), [Me₃S⁺]Ag _n X^– _m (n= 1, 2; m= 2, 3; X = Br, I) and [Me₂S⁺CH₂COR]AgX^– ₂(R = Me, Ph; X = Br, I). The composition of the obtained complexes depends on both the DMSO : HX ratio and the nature of HX, as well as on the methods used to isolate solid products from the solution. It was noted that the formation of the [Me₂S⁺CH₂COMe]AgBr^– ₂complex in the Ag⁰–DMSO–HBr–acetylacetone system occurs with cleavage of the acetylacetone C–C bond and follows a specific reaction course. The optimum conditions for production of the silver compounds in the title systems are determined.     

Cyanidosilicates—Synthesis and Structure

Starting from fluoridosilicate precursors in neat cyanotrimethylsilane, Me₃Si?CN, a series of different ammonium salts [R₃NMe]⁺ (R=Et, ⁿPr, ⁿBu) with the novel [SiF(CN)₅]^2? and [Si(CN)₆]^2? dianions was synthesized in facile, temperature controlled F^?/CN^? exchange reactions. Utilizing decomposable, non‐innocent cations, such as [R₃NH]⁺, it was possible to generate metal salts of the type M₂[Si(CN)₆] (M⁺=Li⁺, K⁺) via neutralization reactions with the corresponding metal hydroxides. The ionic liquid [BMIm]₂[Si(CN)₆] (m.p.=72 °C, BMIm=1‐butyl‐3‐methylimidazolium) was obtained by a salt metathesis reaction. All the synthesized salts could be isolated in good yields and were fully characterized.     

The Intermetalloid Clusters [Ni2Bi12]4+ and [Rh2Bi12]4+ – Ionothermal Synthesis,Crystal Structures,and Chemical Bonding

The intermetalloid clusters [M₂Bi₁₂]⁴⁺ (M = Ni, Rh) were synthesized as halogenido‐aluminates in Lewis‐acidic ionic liquids. The reaction of bismuth and NiCl₂ in [BMIm]Cl · 5AlCl₃ (BMIm = 1‐butyl‐3‐methylimidazolium) at 180 °C yielded black, triclinic (P1 ) crystals of [Ni₂Bi₁₂][AlCl₄]₃[Al₂Cl₇]. Black, monoclinic (P2₁/m) crystals of [Rh₂Bi₁₂][AlBr₄]₄ precipitated after dissolving the cluster salt Bi_12–xRhX_13–x (X = Cl, Br; 0 < x < 1) in [BMIm]Br·4.1AlBr₃ at 140 °C. In the cationic cluster [Ni₂Bi₁₂]⁴⁺, the nickel atoms center two base‐sharing square antiprisms of bismuth atoms (symmetry close to D_4h). The valence‐electron‐poorer rhodium‐containing cluster is a distorted variant of this motif: the terminating Bi₄ rings are folded to bicyclic “butterflies“ and the central square splits into two dumbbells (symmetry close to D_2h). DFT‐based calculations and real‐space bonding analyses place the intermetalloid units between a triple‐decker complex and a conjoined Wade‐Mingos cluster.     

Ionic Liquid in Synthesis: A Phase Transfer Reagent and a Redox Mediating Medium

Ionic liquids (ILs) with chloride anion or bromide anion were attempted as a phase transfer reagent to depolymerize MX₂ (M = Pt, Pd; X = Br, Cl) in chloroform for reaction with 2,2′‐bipyridine (= bpy) to give the (bpy)MX₂ product. Supersonic irradiation of equiv‐molar bpy, PdX₂, and IL in CHCl₃ produced almost quantitative precipitate of (bpy)PdX₂ in a short time at ambient temperature, where IL is either [BEIm]Br or [BMIm]Br. That is, ILs and sono‐techniques assisted greatly on the synthesis of (bpy)PdX₂. For preparation of (bpy)PtX₂, nonetheless, free bpy always remained in mixture even after a long time of supersonic treatment. The system of equiv‐molar bpy, PtBr₂, and IL in CHCl₃, produced yellow (bpy)PtBr₂ and orange (bpy)PtBr₄, both being characterized with ¹H NMR and ¹⁹⁵Pt NMR in d₆‐Me₂SO as well as with single crystal X‐ray diffraction. Overall for PtX₂ reactions with halide anions in highly polar environments attributable to ILs, the redox pathway becomes important in that Pt(II) transforms to Pt(IV) to yield (bpy)PtBr₂ and (bpy)PtBr₄.     

Chemical fixation of CO2 with highly efficient ZnCl2/[BMIm]Br catalyst system

The chemical fixation of CO₂ with mono-substituted terminal epoxides or cyclohexene oxide to form cyclic carbonates under the ZnCl₂/[BMIm]Br catalyst system without using additional organic solvents was achieved in excellent selectivity (>98%) and TOF (5410 h⁻¹) and the catalyst could be used six times almost without losing its catalytic activity and selectivity. Besides, the pure cis-cyclic carbonate of cyclohexene oxide was obtained in this catalyst system.     

Synthesis,acid hydrolysis,and Visible spectra of some bromopentakis(alkylamine)cobalt(III) complexes

Complexes of the [Co(RNH₂)₅Br]²⁺ type with R = Me, Et, n-Pr and n-Bu have been synthesized. The acid hydrolysis of these complexes have been studied in aqueous solution except for the butylamine complex, in which case the acid hydrolysis has been done in diocane-water medium because the complex is only slightly soluble in water. The acid hydrolysis of these complexes follow a pseudo-first-order reaction rate law and an S_N2 mechanism with an octahedral wedge transition state has been assigned. The visible spectra of these complexes, together with [Co(NH₃)₅Br]²⁺, have been recorded and the overlapped bands have been resolved into Gaussian curves by least squares. Values of crystal field parameters Dq(RNH₂), Dq(Br) and Dt in the complexes have been determined with a method originally devised by Wentworth and Piper. The calculated results agree well with those reported by other workers and a linear relationship previously observed by Mitzner et al. between Dq(RNH₂) and ΔH° of proton ionization of RNH₃⁺ ions is also found.     

Effect of a copolymer poly(4-styrenesufonic acid-co-maleic acid) sodium salt on aggregation behavior of surface active ionic liquid 1-tetradecyl-3-methylimidazolium bromide and structurally similar conventional surfactant tetradecyltrimethylammonium bromide in aqueous media

The complex formation of anionic copolymer poly(4-styrenesufonic acid-co-maleic acid) sodium salt (PSSA-co-MA) with surfactant tetradecyltrimethylammonium bromide (TTAB) and surface active ionic liquid (SAIL) 1-tetradecyl-3-methylimidazolium bromide ([C₁₄mim][Br]) has been studied in aqueous media by utilizing various techniques such as tensiometry, conductometry and fluorimetry. Conductometric and tensiometric curve of all the investigated systems demonstrate four break points corresponding to four transition states. All the thermodynamic and surface properties of surfactant-polyelectrolyte systems have been determined by conductance and surface tension measurements respectively. The value of cmc decreases with increasing the concentration of polyelectrolyte for studied systems. But it has been observed that, the lowering in cmc values is more in [C₁₄mim][Br]-PSSA-co-MA system than TTAB-PSSA-co-MA system, although the differences in cmc are not much significant. The lowering in cmc of [C₁₄mim][Br]-PSSA-co-MA system shows that ionic attractions between cationic head group [C₁₄mim]⁺ and anionic parts (SO₃^? and COOH), are stronger than those in TTA⁺ and anionic parts (SO₃^? and COOH). The results indicated that the [C₁₄mim][Br]-PSSA-co-MA complexes are comparatively more surface active than TTAB-PSSA-co-MA complexes. The fluorescence probe behaviour also confirms cmc value and provides aggregation number (N_agg). Finally all the findings of [C₁₄mim][Br] and TTAB have been compared.     

Electrochemical activation and dehalogenation of freons in low-temperature ionic liquids

The effect of various factors (the nature of the medium and the electrode material, the electronic structure of the Freons, etc.) on the electrochemical activation and dehalogenation of a series of Freons [F113 (CF₂ClCFCl₂), F13B1 (CF₃Br), F114B2 (CF₂BrCF₂Br), and F113B2 (CFClBrCF₂Br)] in various low-temperature ionic liquids (LTIL) [1-butyl-3-methylimidazolium, 1-butyl-1-methylpyrrolidinium, and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imides and 1-butyl-3-methylimidazolium hexafluorophosphate, tetrafluoroborate, and trifluoroacetate] at various electrodes (glassy carbon, Pt, Ag) was studied. It was established in particular that the investigated processes are affected substantially by the electrical conductivity and viscosity of the medium. With decrease of the latter the peak potential in the cyclic voltammetry of the electrochemical reduction of the Freons is shifted toward less negative values while the current increases. It was found that a silver cathode has a specific effect on the electrochemical activation of the Freons in the LTILs, and this may be due to the formation of complexes Ag⋯Hal⋯R_f between the Freons and silver atoms on the electrode surface, in which cleavage of the C—Hal bond is facilitated. Such processes are compared with the processes realized in the traditional solvent dimethylformamide. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 2, pp. 67–74, March–April, 2007.     

A Green Method for the Synthesis of Cyclopenta[b]chromen‐1(9H)‐one Derivatives in Ionic Liquids

A series of cyclopenta[b]chromen‐1(9H)‐one derivatives is prepared in high yields by a one‐pot reaction of substituted salicylaldehydes and cyclopentane‐1,3‐dione in ionic liquids of [BMIm]Br, the procedure is very mild and environmentally benign.     

Efficient Microscale Preparation of Isotopically Enriched 1‐[79Br]Bromo‐2‐Fluoroethylene, [79Br]BrHC˭CHF

Abstract

An efficient preparation of 1‐[⁷⁹Br]bromo‐2‐fluoroethylene, [⁷⁹Br]BrHC?CHF, was carried out by a three‐step procedure: (a) natural 1‐bromo‐2‐fluoroethylene, BrHC?CHF, was iodinated to 1‐fluoro‐2‐iodoethylene, FHC?CHI; (b) 1‐fluoro‐2‐iodoethylene was ⁷⁹Br₂‐brominated to 1,2‐di[⁷⁹Br]bromo‐1‐fluoro‐2‐iodoethane, [⁷⁹Br]BrFCHCH[⁷⁹Br]BrI; and (c) 1,2‐di[⁷⁹Br]bromo‐1‐fluoro‐2‐iodoethane was dehalogenated to 1‐[⁷⁹Br]bromo‐2‐fluoroethylene, [⁷⁹Br]BrHC?CHF. The yield of isolated product, on a 2‐mmol scale, was 62% with respect to ⁷⁹Br₂.     

Electrochemical characterization of common catalysts and initiators for atom transfer radical polymerization in [BMIm][OTf]

The redox properties of some largely employed ATRP initiators and copper catalysts (Cu/L/X⁻) were investigated in 1-butyl-3-methylimidazolium trifluoromethanesulfonate (L = amine ligand, X = Br or Cl). Both Cu(II) and Cu(I) complexes are stable in the IL and, as required by ATRP, X⁻ stabilizes more Cu(II) than Cu(I). The activation rate constants of initiators by [Cu^ITPMA]⁺ were measured and a good correlation between k_act and the C-X bond dissociation free energy (BDFE) was observed. Overall, the results indicated that [BMIm][OTf] behaves much like organic solvents; the reported data launch the bases for a useful database to select the appropriate catalyst/initiator couple for ATRP in ILs.