Exploring organic reactions using simple cyclodiphosphazanes

Phosphine-activated reactions of alkynes/alkenes/allenes as well as the Mitsunobu reaction involve a rich phosphorus chemistry. With the aid of simple cyclodiphosphazanes, characterization of many compounds analogous to the proposed intermediates in such reactions has been accomplished. Use of a cyclodiphosphazane in Pd-catalyzed N-arylation reactions is highlighted. Results on molecular non-stoichiometry in phosphorus compounds and on the use of chiral phosphorus systems are discussed. Synthesis of allenylphosphoramides involving a cyclodiphosphazane is also described. X-ray structures of the new compounds [(t-BuNH)(PhCH₂CH(CN)CH₂-)P(μ-N-t-Bu)₂P(NH-t-Bu)]⁺[HCO₃]⁻ (13), [(t-BuNH)P(μ-N-t-Bu)₂P(N-t-Bu)-C(CH₂)CH(C₆H₄-4-Me)-P(O)(OCH₂CMe₂CH₂O)] (18), [(i-PrNH)P(μ-N-t-Bu)₂P(N-i-Pr)-N(CO₂-i-Pr)-NH(CO₂-i-Pr)] (24), [(S)-(2-OH-1-C₁₀H₆-1′-C₁₀H₆-2′-O-P(O)(NH-t-Bu)₂] (36) and [(t-BuNH)(O)P(μ-N-t-Bu)₂P(O)(CHCCMe₂)] (40) are also reported.     

Copolymerization of propene and 1-hexene using metallocene amide compounds

Copolymerization of propene and 1-hexene has been carried out at 30°C in toluene under atmospheric pressure by using three isospecific metallocene amide compounds, rac-(EBI)Zr(NMe₂₎₂ (EBI = ethylenebis(1-indenyl), rac- 1 ), rac-(EBI)Zr(NC₄H₈₎₂ (rac- 2 ), and rac-Me₂Si(1-C₅H₂-2-Me-4-t-Bu)₂Zr(NMe₂₎₂ (rac- 3 ), in the presence of methylaluminoxane (MAO) or [Ph₃C][B(C₆F₅)₄]. The rate enhancements in the presence of 1-hexene were recorded as a function of the catalytic systems. The incorporation of 1-hexene decreases in the following order: rac- 2 /MAO > rac- 3 /Al(i-Bu)₃/[Ph₃C][B(C₆F₅)₄] > rac- 1 /MAO. All copolymers investigated in this study have a nearly random sequence distribution.     

Fluorometry of hydrogen peroxide using oxidative decomposition of folic acid

Hydrogen peroxide (H₂O₂) is one of the most important reactive oxygen species. In the present study, a fluorometry method for detecting H₂O₂ utilizing folic acid was evaluated. Folic acid was decomposed by H₂O₂ in the presence of Cu(II) into pterine-6-carboxylic acid, leading to strong fluorescence enhancement. In the absence of the metal ion, superoxide and H₂O₂ could not decompose folic acid. Also, H₂O₂ plus sodium hypochlorite (a source of singlet oxygen) could not induce fluorescence enhancement. These results demonstrate that H₂O₂ can be selectively detected using folic acid plus Cu(II). The limit of detection (LOD; at S/N=3) for H₂O₂ is 0.5 μM. This method based on the fluorescence enhancement of folic acid was applied in order to determine small amounts of H₂O₂ generated through the autooxidation of semicarbazide (generation rate: ∼0.01 μM min⁻¹), a carcinogenic compound.      

Tetrafluoroethylene telomerization using dibromohaloethanes as telogens

Carrier mediated telomerization (CMT) between C₂F₄ and bromochlorofluoroethanes has been evaluated in terms of product distributions arising from CMT and ‘normal’ telomerization. The effect of parameters like type of initiator and telogen, TFE pressure and temperature on the reaction has been studied. The peroxide initiated telomerization between dibromohaloethanes and C₂F₄ offers an easy synthetic route to α,ω-dibromo perfluoroalkanes Br(CF₂)_nBr with n = 2, 4, 6 and 8. The selectivity of the CMT products versus those from “normal” telomerization depends mainly on the choice of telogen and on its ability to act as ‘bromine donor’ in the radical telomerization. These perfluoroalkyl dibromides are useful intermediates for other derivatives, for example, perfluorinated mono- and diolefins, Br(CF₂)_nCHCH₂ and CH₂CH(CF₂)_nCHCH₂.     

Chemoselective glycosylations using sulfonium triflate activator systems

A novel chemoselective glycosylation sequence is described that employs the recently developed BSP/Tf₂O and DPS/Tf₂O reagent systems to activate thioglycosides. In the first glycosylation event a relatively armed thioglycoside is activated with the BSP/Tf₂O activator system and condensed with an acceptor thioglycoside to yield the thiodisaccharide, which is activated with the more potent DPS/Tf₂O activator in the next glycosylation event. Quenching of (N-piperidino)phenyl(S-thiophenyl)sulfide triflate, which is formed upon activation of the first thioglycoside, with triethyl phosphite is crucial for a productive glycosylation.     

Deprotonation of chloropyridines using lithium magnesates

4-Chloropyridine was deprotonated on treatment with 1/3 equiv of the highly coordinated magnesate Bu₃(TMP)MgLi₂ in THF at −10 °C, as evidenced by trapping with I₂. The use of Bu(TMP)₂MgLi in Et₂O allowed the reaction of 2-chloropyridine, giving the 3-functionalized derivative as the main product. Mixtures of 3- and 4-functionalized derivatives were obtained when 2,6-dichloropyridine was involved in the reaction. Performing the reaction on 3-chloropyridine with lithium magnesates in THF, either the 4,4′-dimer or the 4-iodo derivative was formed after quenching by I₂, the former using 1/3 equiv of Bu₂(TMP)MgLi and the latter using 1 equiv of (TMP)₃MgLi. Similar results were observed with 3,5-dichloropyridine, 2,5-dichloropyridine and 3-chloro-2-fluoropyridine. 1,2-Migration of the lithium arylmagnesate formed by deprotonation was proposed to justify the dimers formation.     

Nickel-cermet electrodes for high-temperature electrochemical devices made using nanomaterials

Characteristics of nickel-cermet anodes obtained from weakly aggregated NiO nanopowders made by wire electric blasting (NiO/WEB) were studied. Electrodes made of NiO/WEB nanopowders have low sheet resistance (<0.1 Ohm) and high electrochemical activity (R _η = 0.06–0.09 Ohm cm² at 850–900°C). Prolonged studies of symmetric cells of the (0.9H₂ + 0.1H₂O) Ni-SSZ + CeO₂/YSZ/CeO₂ + Ni-SSZ (0.9H₂ + 0.1H₂O) type at the temperature of 850°C showed that the electrodes preserve sufficiently high activity (R _η < 0.1 Ohm cm²) for 1000 h. Using a NiO-WEB powder allows not performing presynthesis of nickel-cermet and decreasing the anode baking temperature to 1200°C.     

Preparation of microlatex dispersions using oil-in-water microemulsions

The preparation of microlatex dispersions from microemulsions of a monomer (styrene, methylmethacrylate or vinyl acetate) is described. A simple method for preparing the microemulsion has been devised. This consists of forming a water-in-oil (w/o) emulsion using a low (HLB) surfactant (nonylphenol with 5, 6 or 7 moles ethylene oxide) and then titrating with an aqueous solution of a high HLB surfactant (nonylphenol with 15 or 16 moles ethylene oxide). A small amount of anionic surfactant (sodium lauryl sulphate, sodium dodecyl benzene sulphonate or dioctyl sulphosuccinate) was also incorporated to enhance the stability of the w/o emulsion and facilitate the inversion to an o/w microemulsion. The droplet-size distribution of the resulting microemulsion was determined using photon-correlation spectroscopy.Three different methods of polymerising the microemulsion were used. These were thermally induced polymerisation using potassium persulphate, azobis-2-methyl propamidinium dichloride (AMP-water-soluble initiators) or azobisisobutyronitrile (AIBN, an oil-soluble initiator). All these initiators required heating to 60°C, i.e. above the stability temperature of the microemulsion. In this case, the microlatices produced were fairly large (37–100 nm diameter) and had a broad particle-size distribution. The second polymerisation procedure was chemically induced using a redox system of hydrogen peroxide and ascorbic acid. This produced microlatices with small sizes (18–24 nm diameter) having a narrow-size distribution. The microlatex size was roughly two to three times the size of the microemulsion droplets. This showed that collision between two or three microemulsion droplets resulted in their coalescence during the polymerisation process. The third method of polymerisation was based on UV irradiation in conjunction with K₂S₂O₈, AMP or AIBN initiators. In this case, the microlatex size was also small (30–63 nm) with a narrow particle-size distribution.Microlatex particles were also prepared using a mixture of monomers (styrene plus methylmethacrylate) or mixture of monomers and a macromonomer, namely methoxy (polyethylene glycol)methacrylate. The latter was used to produce hairy particles, i.e. with grafted polyethylene oxide (PEO) chains.The stability of the microlatices was determined by adding electrolytes (NaCl, CaCl₂, Na₂SO₄ or MgSO₄) to determine the critical flocculation concentration (CFC). The nonionic latices were very stable giving no flocculation up to 6 mol dm^–3 NaCl or CaCl₂ and a CFC of 0.6 mol dm^–3 for Na₂SO₄ or MgSO₄. Charged latices were less stable than the nonionic ones. The critical flocculation temperatures (CFT) of all latices were determined as a function of electrolyte concentration. With the nonionic latices, CFC was higher than the -temperature for polyethylene oxide at the given electrolyte concentration. This indicated enhanced steric stabilisation as a result of the dense packing of the chains and hence an elastic contribution to the steric interaction. This was not the case with the charged latex, which showed CFT values lower than the -temperature. The hairy latices [i.e. those containing methoxy polyethylene glycol (PEG) methacrylate] were also less stable towards electrolyte (CFT was much lower than -temperature), indicating a low density of PEO layers.     

Capillary electrophoretic determination of ammonia using headspace single-drop microextraction

A new method involving headspace single-drop microextraction (SDME) and capillary electrophoresis (CE) is developed for the preconcentration and determination of ammonia (as dissolved NH₃ and ammonium ion). An aqueous microdrop (5 μL) containing 1 mmol/L H₃PO₄ and 0.5 mmol/L KH₂PO₄ (as internal standard) was used as the acceptor phase. Common experimental parameters (sample and acceptor phase pH, extraction temperature, extraction time) affecting the extraction efficiency were investigated. Proposed SDME-CE method provided about 14-fold enrichment in about 20 min. The calibration curve was linear for concentrations of NH₄⁺ in the range from 5 to 100 μmol/L (R² = 0.996). The LOD (S / N = 3) was estimated to be 1.5 μmol/L of NH₄⁺. Such detection sensitivity is high enough for ammonia determination in common environmental and biological samples. Finally, headspace SDME was applied to determine ammonia in human blood, seawater and milk samples with spiked recoveries in the range of 96-107%.     

The synthesis of complexes using precursor complexes with ferrocenyl carboxylate units as building blocks

Using ferrocenyl carboxylates as functional ligands, we synthesized a mononuclear complex [Zn(η²-OOCCHCHFc)₂(CH₃OH)₂] (1) and a binuclear complex [Cd(bafca)₂(H₂O)₂]₂ (2) (bafca⁻ = α-benzamido-β-ferrocenylacrylic carboxylate) as precursor complexes. Investigation on the substitution reaction of precursor complexes as building blocks in solution-state, four complexes [Zn(OOCCHCHFc)₂(bbbm)]_n (1a), {[Zn(OOCCHCHFc)(ntb)](CH₃OH)} (1b), [Cd(bafca)₂(2,2′-bpy)]₂ · 9H₂O (2a) and {[Cd(bafca)₂(bbbm)(CH₃OH)₂] · 6CH₃OH}_n (2b) were obtained (bbbm = 1,1-(1,4-Butanediyl)bis-1H-benzimidazole, ntb = N,N-bis(1H-benzimidazol-2-ylmethyl)-1H-Benzimidazole-2-methanamine and 2,2′-bpy = 2,2′-bipyridine). As anticipated, the structural integrity of precursor complexes can be maintained in these four complexes. It indicates that we can synthesize the desired complexes with the destination structures by using precursor complexes as building blocks and choosing appropriate auxiliary ligands. In addition, the electrochemical properties of all complexes were investigated, and it can be seen from the results that half-wave potentials of these complexes are slightly higher than that of the corresponding ligand.     

Polymerization of methyl methacrylate using a metallocene catalyst system

Methyl methacrylate was polymerized with Cp₂YCl(THF) or IVB group metallocene compounds (i.e., Cp₂ZrCl₂ and Cp₂HfCl₂, etc.), in the presence of a Lewis acid like Zn(C₂H₅)₂. The Lewis acid was complexed with methyl methacrylate, which avoided the metallocene compounds being poisoned with a functional group. A living polymerization was promoted through the use of metallocene/MAO/Zn(C₂H₅)₂, which gave tactic poly(methyl methacrylate) with a high molecular weight. The polymer yield increases with polymerization time, which indicates that the propagation rate is zero in order in the concentration of the monomer. The polymer yield increases also with the concentration of Cp₂YCl(THF), which indicates the yttrocene to be the real catalyst. When the polymerization temperature exceeds room temperature, the poly(methyl methacrylate) cannot be synthesized by the Cp₂YCl(THF) catalyst. When the reaction temperature reachs −60 °C, the poly(methyl methacrylate) is high syndiotatic and molecular weight by the Cp₂YCl(THF)/MAO catalyst system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1184–1194, 2000     

Study on cationic polymerization of isobutylene using electrochemical method

The cationic polymerization of isobutylene (IB) initiated by H₂O/TiCl₄ was carried out in a mixture of methylene dichloride and n-hexane at −60 °C in the presence of a variety of external electron pair donors (EDs), such as triethylamine (TEA), N,N-dimethyl acetamide (DMA) and pyridine (Py). The effects of ED concentration ([ED]), H₂O concentration ([H₂O]) on conductance and capacitance in H₂O/TiCl₄/ED/CH₂Cl₂ reaction system were investigated. The effects of [ED], [H₂O], solven polarity and polymerization time on monomer conversion, molecular weight (MW), molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) were also investigated. Conductance decreased while capacitance increased with increases in both [ED] and electron donicity of ED. Conductance and capacitance increased with [H₂O] when [H₂O] was more than [Py]. Both unpaired and paired ions existed as propagating species or chain carriers in the presence of relatively low [ED] and polymers with bimodal molecular weight distribution (peak a and b) were obtained. The peak a with high molecular weight was induced by propagation via unpaired ions while peak b with low molecular weight was induced by propagation via paired ions. The propagation via paired ions could be achieved and polymers with unimodal molecular weight distribution could be produced when sufficient amounts of external ED was introduced to polymerization system.     

Background elimination in three-dimensional spectroscopy using the intensian method

The method to eliminate background in the case of quantitative multidimensional spectroscopy, chromatography or any analytical 3-dimensional technique is shown. The 3-dimensional signal is required to be proportional to the concentration of determined substance and the additivity of signals should be obeyed. Eliminated background is assumed to be a low-order polynomial of two variables. The intensian method [1] is a generalization of the Beer-Lambert law, where a certain determinant called intensian replaces absorption and absorptivity. In practice there will be no need to use determinants, since usually they are replaced by expressions of few terms. Some details on the practical use of the method are given.Index of used symbols x, y UV, IR, GC, NMR or other scale. - A (x, y) intensity (absorption) of the 3-dimensional band of interest. - a (x, y) standard intensity (absorption) of the 3-dimensional band of interest. - B(x, y) intensity (absorption) of 3-dimensional background. - S(tx, y) intensity (absorption) of 3-dimensional multicomponent spectrum. - f (x, y) auxiliary function:f (x, y) =A (x, y), B(x, y), a(x, y), S(x, y). - (x _i, Yi) selected point,i positive integer number. - f(xi, yi) value off (x, y) in point (xi, yi). - S _i value ofS(x, y) in point (x _i, y_i). - b pathlength, measurement coefficient,c concentration. - , , , real numbers. - ij, _ij real coefficients of power expansions. - x ⁱy^j monomial of degree (i +j). - F(·) linear functional acting on 3-dimensional spectral functions. - J^3-dim(·) 3-dimensional intensian acting on 3-dimensional spectral functions. - J _n ^3-dim (·) 3-dimensionaln-points intensian. - d _i ith intensian coefficient, cofactor of expansion of J _n ^3-dim (f(x, y)) according to its first row (eq. (10)). - (.) absolute error. - r _i,, R random variables: eqs. (13) and (14). - G(.) (normal) distribution function. - z ordinate axis. - a - f , h abreviations for some arguments. - d _ijk,D _mnp abreviations defined in eq. (22).     

The metal complexes using organic ligands with photo-excited high-spin states

In this work, 4-pyridyl-phenylanthracene-iminonitroxide radical 2 was synthesized, which can make the coordination to metal ions. It was confirmed by the time-resolved ESR experiments that 2 has a photo-excited quartet (S = 3/2) high-spin state. Cu(II)(hfac)₂(2)₂ and Mn(II)(hfac)₂(2)₂ were synthesized by using 2 as a ligand. Their magnetic properties on the ground states were analyzed by three-spincluster model S₁ − S_M − S₂ (S₁ = S₂ = S_M = 1/2 for Cu(II)(hfac)₂(2)₂ and S₁ = S₂ = 1/2, S_M = 5/2 for Mn(II)(hfac)₂(2)₂). The exchange interactions (J/k_B) between 2 and the metal ions were very weak (J/k_Bs were ferromagnetic for Cu(II)(hfac)₂(2)₂ and antiferromagnetic for Mn(II)(hfac)₂(2)₂). The molecular orbital calculations of 2 have suggested the strong interaction between the paramagnetic center of the metal ions and the photo-excited quartet high-spin state.     

Synthesis of lead magnesium niobate and La-modified lead magnesium niobate using different Mg precursors

Summary In the present study, the effect of the partial replacement of Pb²⁺ by La³⁺ in the lead magnesium niobate Pb(Mg_1/3Nb_2/3)O₃ (PMN) perovskite structure was examined, taking into account the Mg-source. Pure lead magnesium niobate (PMN) and lanthanum-modified lead magnesium niobate (PLMN) having composition (Pb_1-xLa_x) (Mg_1+x/3Nb_2-x/3)O₃ with x=0.2 were elaborated. The phase formation was investigated by DTA/TG methods correlated with X-ray diffraction, performed on materials obtained in non-isothermal conditions. The diffraction data for the ceramics obtained by isothermal treatments emphasized the influence of the lanthanum on the crystal structure, inducing the doubling of the unit cell parameter. SEM investigations pointed out the lanthanum inhibitor effect on the grain growth process, leading to an uniform grain distribution.     

Preconcentration of trace metals from salt solutions using thiuram disulphide as collector

Traces of Fe, Co, Ni, Cu, Zn, Cd and Pb in salt solutions (e.g. KCl, Ca(NO₃)₂, A1₂(SO₄)₃, Cr₂(SO₄)₃, (NH₄)₂SO₄) are determined by flame AAS after preconcentration with thiuram disulphide (TDS) as collector precipitate. The preconcentration recovery is mainly influenced by pH, TDS amount and its aging in the sample solution. Conditions of an optimal preconcentration procedure were elaborated. Detection limits vary from 0.5 ng/ml (for Cd) to 8.3 ng/ml (for Pb) and the relative standard deviation is 2 to 6 %. The accuracy of the results was checked by differential pulse anodic stripping voltammetry and by electrothermal AAS.     

Synthesis and structural characterization of a new layered gallium phosphate using triethylenetetramine as structure-directing agent

A new layered gallium phosphate Ga₁₀(PO₄)₂(HPO₄)₁₂(OH)₅2.5N₄C₆H₂₀4.5H₂O was hydrothermally synthesized at 180 °C for 3 days by using triethylenetetramine (teta) as structure-directing agent. Its structure was determined by single-crystal X-ray diffraction with a triclinic cell in the space group P-1 (n^o 2) with a=8.4718(1) Å, b=18.5915(1) Å, c=24.1994(3) Å, α=110.538(1)°, β=93.656(1)°, γ=93.549(1)° and V=3547.45(6) Å³. It consists of [Ga₁₀(PO₄)₂(HPO₄)₁₂(OH)₅]⁵⁻ macroanionic sheets composed of infinite chains of GaO₄(OH)₂ octahedra connected via corner-sharing to PO₄ and GaO₄ tetrahedra. They contain four-, seven- and nine-membered rings. The inorganic layers are held together through hydrogen bond between the terminal PO bondings, the water molecules and the terminal ammonium groups of the intercalated teta molecules.     

Preparation of CO_2 selective composite membranes using Pebax/CuBTC/PEG-ran-PPG ternary system

Three phase Pebax~? MH 1657/PEG-ran-PPG/CuBTC(polymer/liquid/solid) was successfully deposited as a selective layer on a porous Polysulfone(PSF) support. In fact, the beneficial properties of PEG(high selectivity) with those of PPG(high permeability, amorphous) have been combined with superior properties of mixed matrix membrane(MMMs). The membranes were characterized by DSC, TGA and SEM, while CuBTC was characterized by CO_2 and CH_4adsorption test. Statistically based experimental design(central composite design, CCD) was applied to analyze and optimize the effect of PEG-ran-PPG(10–50 wt%) and CuBTC(0–20 wt%) mass contents on the CO_2 permeance and CO_2/CH_4 ideal selectivity. Based on the regression coefficients of the obtained models, the CO_2 permeance was notably influenced by PEG-ran-PPG,while CuBTC has the most significant effect on the CO_2/CH_4 ideal selectivity. Under the optimum conditions(PEG-ran-PPG: 32.76 wt% and CuBTC: 20 wt%), nearly 620% increase in the CO_2 permeance and43% enhancement in the CO_2/CH_4 ideal selectivity was observed compared to the neat Pebax. The effect of pressure(3, 9 and 15 bar) on the pure and mixed gas separation performance of the composite membranes was also investigated. The high solubility of CO_2 in the membranes resulted in the enhancement of CO_2 permeability with increase in gas pressure.     

Asymmetric hydroesterification of styrene using catalysts with planar-chiral ferrocene oxazoline ligands

Chiral P,N-ferrocene ligands, 1-diphenylphosphino-1′-[(S)-4-isopropyl-2.5-oxazolinyl]-2′-(S_p)-(trimethylsilyl)-ferrocene and its diastereomer, and 1-diphenylphosphino-1′-[(S)-4-isopropyl-2.5-oxazolinyl]-2′(S_p)-(diphenylphosphino)-ferrocene and its diastereomer were used in the palladium-catalyzed asymmetric hydroesterification of styrene. The role of these ligands, which contain central, axial, and planar chirality, on the stereochemical outcome was investigated. A significant effect of using CuCl₂ as a co-catalyst on the reaction was observed. Excellent regioselectivity (b/n >99:1) with low ee (28%) was obtained in the presence of CuCl₂; moderate enantioselectivity (64% ee) but low regioselectivity (b/n, 40/60) was obtained in the absence of CuCl₂.