Transformations of formaldehyde and glycolaldehyde during the hydroformylation of formaldehyde in the presence of rhodium catalysts

Hydroformylation of formaldehyde to give glycolaldehyde (GA) in the presence of RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, or the RhCl₃ + PPh₃ system inN,N-dimethylacetamide was studied. The hydroformylation is accompanied by the Cannizzaro-Tishchenko reaction, condensation of CH₂O with GA to give C₃-C₁₆ polyoxyaldehydes (POA), and dimerization of GA. The formation of POA, which probably occurs through coordination of GA with a Rh atom, predominates among the side reactions. The optimum conditions for hydroformylation of CH₂O were found to be: RhCl₃ + PPh₃ as the catalyst,T 383 K, 12MPa, [H₂O] 1.8 mol L^–1, [Rh] 2.5 · 10^–3 g-at. L^–1, and [CH₂O] 0.03 g L^–1. At a substrate conversion of 62–67 %, the selectivity of GA formation reaches 96 %, and the yield is 60–65 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 75–78, January, 1995.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

The outersphere complex of EuCl2+ in a mixed system of methanol and water of 1.0M (H, Na) (Cl, ClO4)

The stability constans, ₁, of each monochloride complex of Eu(III) have been determined in the methanol and water mixed system with 1.0 mol·dm^–3 ionic strength using a solvent extraction technique. The values of ₁ increase with an increase in the mole fraction of methanol (X _S ) in the mixed solvent system when 0X _S 0.40. The, distance of Eu³⁺–Cl^– in the mixed solvent system was calculated using the Born-type equation and the Gibbs' free energy derived from ₁. Calculation of the Eu³⁺–Cl^– distance and the preferential solvation, of Eu³⁺ by water proposed the variation of the outersphere complex of EuCl²⁺ as follows: (1) [Eu(H₂O)₉]³⁺Cl^–, [Eu(H₂O)₈]³⁺Cl^– and [Eu(H₂O)₇(CH₃OH)³⁺Cl^– inX _S0.014, (2) [Eu(H₂O)₈]^3–Cl^– and [Eu(H₂O)₇(CH₃OH)]³⁺Cl^– in 0.014<X _S <0.25 and (3) [Eu(H₂O)₇(CH₃OH)]^3–Cl^– and [Eu(H₂O)₆(CH₃OH)[₂ ³⁺Cl^– in 0.25<X _S 0.40.     

Kinetics of acid and base catalysed hydrolysis ofcis-α- andcis-β2-[Co(trien)(aniline)Cl]2+ cations

Summary The rate of hydrolysis of the title cations obey the rate law:-d ln[Complex]/dt=k_obs=k₀+k₁[OH^–] in the range: 1pH3. The rate and activation parameters for acid and base hydrolysis (k₀ and k₁ paths respectively) are reported in the 40–60 °C range.     

Rapid radiochemical separation and determination of chlorine,bromine and iodine in water samples using ion exchange

On the basis of tracer experiments, a simple and rapid radiochemical separation method for simultaneous determination of I^–, Br^– and Cl^– in one aliquot of a water sample (only 2–4 ml) has been developed. The method is based on short irradiation of the water sample and separation of the halogens using sequential ion exchange columns filled with Dowex 1×8, 100–200 mesh anionic resin prepared in I^–/I₂, Br^–/Br₂ and Cl^– form. After washing the columns with an appropriate volume of 2% NaCl solution, the resins were transferred to vials and activities of the isolated radionuclides¹²⁸I,⁸²Br and³⁸Cl measured together with standards in a well type or on a coaxial Ge detector connected to a Canberra 90 multichannel analyzer. Besides high chemical yields, from the -spectra of the isolated radionuclides, it is evident that high decontamination fac-The paper was presented at the MTAA-8, Vienna, September 1991.     

Zinc(II)cysteine and zinc(II)cystine systems: Selection of species from potentiometric data

Summary The formation constants of species formed in the systems H⁺-Zn²⁺-cysteine and H⁺-Zn²⁺-cystine have been determined in aqueous solution at 37° and I = 0.15 mot dm^–3 (NaClO₄), using the pH-metric method. The existence of the following species [ZnL], [ZnL₂], [ZnL₂H] and [Zn₂L₃] (2.3 pH 7.7) was proved for the Zn²⁺-cysteine system, whereas for the Zn²⁺-cystine [Zn₂L] (5.3 pH 6.4) was the only species found. In the Zn²⁺-cystine system the pH range was severely restricted because of precipitation occurring at pH > 6.4. A new experimental and numerical approach was employed in order to implement the possibility of rigorously selecting the species present in each system. The results have been compared with data previously reported on the same systems, considering in particular the different sets of species found in the various works.     

Aqueous Uranyl Complexes 1. Raman Spectroscopic Study of the Hydrolysis of Uranyl(VI) in Solutions of Trifluoromethanesulfonic Acid and/or Tetramethylammonium Hydroxide at 25°C and 0.1 MPa

Raman spectra have been used to identify and characterize aqueous hydroxouranyl(VI) complexes from 0.0038 to 0.647M at pH from 0.24 to 14.96 adjusted witheither HCF₃SO₃ and/or (CH₃)₄NOH under ambient conditions. In acidic media(0.24 pH 5.63), the existence of four species UO²⁺ ₂,(UO₂)₂(OH)³⁺,(UO₂)₂(OH)²⁺ ₂, and (UO₂)₃(OH)⁺ ₅ was confirmed. At high uranium concentrations(U 0.1M) and in strongly acidic solutions (pH 1.94), one additional weakband was observed at 883±1 cm^–1. This band was assumed torepresent thespecies UO²⁺ ₂ with a reduced hydration number.In neutral and basic solutions(5.63 pH 14.96), five complexes were postulated: (UO₂)₃(OH)^– ₇,(UO₂)₃(OH)^2– ₈,(UO₂)₃(OH)^4– ₁₀,(UO₂)₃(OH)^5– ₁₁, andUO₂(OH)^2– ₄, based on theassigned symmetrical stretching frequencies of the UO₂ group in each complex.(UO₂)₃(OH)^– ₇ is the dominant species over mostof the pH range (4.53–12.78).The stability ranges of the other trinuclear species are:(UO₂)₃(OH)^2– ₈ (10.97 pH 13.83), (UO₂)₃(OH)^4– ₁₀ (10.97 pH 13.85) and (UO₂)₃(OH)^5– ₁₁(12.53 pH 14.10), which were identified for the first time. Finally, the monomericuranate anion OU₂(OH)^2– ₄ dominates in highly basic solution (12.48 pH 14.96). The linear correlation between the symmetrical vibrational frequency v ₁of the linear O = U = O entity and the average number of hydroxide ligandscoordinated to each uranium atom in a given species has been reaffirmed andexpanded: The v ₁ correlation was also used to predict the vibration frequencies of theundetected monomers UO₂(OH)⁺, UO₂(OH)^o ₂,UO₂(OH)^– ₃ at 848±2, 826±2, and804±2 cm^±1, respectively. Characteristic band areas for eachuranyl hydrolyzedspecies were determined by Raman spectra decomposition and their hydrolysisquotients log Q, were calculated. Structures of the four triuranylspecies are proposed.     

An Asymmetric Edge-Sharing Bioctahedral Complex: (η2-DAniF)MoIII(μ-DAniF)2(μ-O,Cl)MoVCl2 (DAniF=N,N′-di-p-anisylformamidinate)

A novel asymmetric, edge-sharing bioctahedral complex with formamidinato ligands ( ²-DAniF)Mo(-DAniF)₂(-O,Cl)MoCl₂, 1, (DAniF=N,N-di-p-anisylformamidinate) has been isolated as a byproduct from the preparation of the dimolybdenum(II,III) compound Mo₂(DAniF)₃Cl₂. An X-ray crystallographic study shows that the structure consists of edge-sharing bioctahedra, with the shared edge defined by the vector joining the: -O and -Cl ligands. Compound 1 is best formulated as a mixed-valent Mo^IIIMo^V compound, the Mo(V) ion being that with the two terminal Cl^– ligands. The cyclic voltammogram of 1 shows a reversible reduction at –0.472 V and a reversible oxidation at 1.028 V vs. the Ag/AgCl reference electrode, while the absorption spectrum of 1 reveals an intense low energy absorption at 523 nm ( _max=12 500) which is attributed to an intervalence charge transfer transition. Crystallographic data for 1 are as follows: a=13.387(1) Å, b=15.500(2) Å, c=21.855(2) Å, =98.786(2)°, V=4481.8(8) ų, P2₁/c, R1 (wR2)=0.082 (0.177).     

Ionization gauge sensitivities of N2, O2, N2O, NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^–1 Pap1.3·10^–3Pa. Nitrogen was used as a calibration standard.     

Salt effects on the protonation of ortho-phosphate between 10 and 50°C in aqueous solution. A complex formation model

Protonation constants of o-phosphate were studied potentiometrically, using the (H⁺)-glass electrode in aqueous NaCl, KCl and tetraethylammonium iodide solutions, at 0IIM and 10T50°C. The differences found in the protonation constants for different salt solutions are explained by a complex formation model. The formation of the species MPO ₄ ^2– , MHPO ₄ ^– , MH₂PO ₄ ⁰ , M₂PO ₄ ^– and M₂HPO ₄ ⁰ (M=Na⁺, K⁺) is hypothesized. In mixed NaCl-KCl solutions, it is possible to find the mixed metal species NaKPO ₄ ^– and NaKHPO ₄ ⁰ . Ionic strength and temperature dependence parameters are reported for all species. The relevance of Na⁺ and K⁺ complexes is discussed in connection with speciation problems of natural fluids, such as marine water and urine.     

Measurements of relative thick target yields for PIGE analysis on light elements in the proton energy interval 2.4–4.2 MeV

In order to extend the energy range of the systematic investigation on relative thick target yields performed by ANTTILA et al² for 1E_p2.4 MeV bombarding energies, gamma spectra and yield data are presented for elements Z=3–9, 11–17, 19–21 in the energy range 2.4E_p4.2 MeV and the results are discussed from the point of view of PIGE analysis.     

Electroconductivity of Potassium Orthophosphate Modified by Four-Charged Cations

Solid solutions based on K₃PO₄ in systems K_{3 – 4x} E" _x PO₄ (E" = Si, Ti, Ge, Zr, Sn, Hf, Ce) are synthesized. The crystal structure, thermal behavior, and electroconduction of the synthesized solutions is studied. The narrowest single-phase regions take place in the systems where E" = Si, Ge (x 0.025), and the widest, in the system with Zr (x 0.125, at 700°C). Introducing Ti or Sn additives (x 0.05) and minimum quantities of Zr, Hf, or Ce (x = 0.025) into potassium orthophosphate leads to stabilization of highly-conductive -modification of K₃PO₄ at room temperature. Maximum values of potassium-cation conduction in all the systems studied correspond to regions of single-phase solid solutions based on K₃PO₄. The maximum electroconductivity (0.005 S cm^–1 at 300°C, 0.1 S cm^–1 at 700°C) and the smallest activation energies (32–35 kJ mol^–1) take place in the systems with Zr and Hf.     

Determination of Iron in Tap and Waste Water Using Liquid–Liquid Extraction in a Flow-Injection System

A flow-injection procedure for the determination of iron(III) in water is described. The procedure is based on the formation of an ion pair between the tetraphenylarsonium (Ph₄As⁺) (TPA) or tetrabutylammonium (But₄N⁺) (TBA) cations and the tetrathiocyanatoferrate(III) complex (TTF). This ion pair is extracted with chloroform, and the absorbance of the organic phase is measured at 503nm (for Ph₄As⁺) or 475nm (for But₄N⁺). Iron concentrations higher than 0.9×10^–6molL^–1 (50µgL^–1) can be detected in the first case, with a relative standard deviation of 1.9% (n=12), a linear application rangeof between 1.34 and 54.0×10^–6molL^–1 (75–3015µgL^–1), and a sampling frequency of 30h^–1. For the ion pair with But₄N⁺, the detection limit is 0.52×10^–6molL^–1 (29µgL^–1), with a relative standard deviation of 1.6% and a linear application range between 0.73 and 54.0×10^–6molL^–1. Under the proposed working conditions, only Pd(IV), Cu(II) and Bi(III) interfere. With the application of the merging zones technique, considerable amounts of organic reagent can be saved. The TBA method was applied to the analysis of iron(III) in tap and industrial waste waters.     

Perchlorate-selective membrane electrode based on a new complex of uranil

A potentiometric ion-selective electrode based on new compound, as a carrier, has been successfully developed for detection of perchlorate anion in aqueous solution. Within the perchlorate ion concentration range 1.0×10^–6 to 1.0 mol L^–1 the electrode had a linear response with a Nernstian slope of 60.6±1.0 mV per decade . The limit of detection as determined from the intersection of the extrapolated linear segments of the calibration plot was 8.0×10^–7 mol L^–1. The proposed electrode has fairly a good discriminating ability towards ClO₄^– ion in comparison to other anions. The sensor has a response time of 10 s and can be used for at least 2 months without substantial divergence in potential. It was successfully applied to direct determination of perchlorate in urine and water.     

Synthetic and kinetic studies on copper(II), nickel(II) and cobalt(III) complexes of 1,4,7,10,13-pentaazacyclohexadecane ([16]aneN5)

Summary The pentadentate macrocycle 1,4,7,10,13-penta-azacyclo-hexadecane [16]aneN₅=(3)=L} has been prepared and a variety of copper(II), nickel(II) and cobalt(III) complexes of the ligand characterised. The copper complex [CuL](ClO₄)₂, on the basis of its d-d spectrum, appears to be square pyramidal, while [NiL(H₂O)](ClO₄)₂ is octahedral. The copper(II) and nickel(II) complexes dissociate readily in acidic solution and these reactions have been studied kinetically. For the copper(II) complex, rate=k_H[complex][H⁺]² with k_H =4.8 dm⁶ mol^–2s^–1 at 25 °C and I=1.0 mol dm^–3 (NaClO₄) with H=43 kJ mol^–1 and S ₂₉₈ =–89 JK^–1 mol^–1. Dissociation rates of the copper(II) complexes increase with ring size in the order: [15]aneN₅ < [16]aneN₅ < [17]aneN₅. For the dissociation of the nickel(II) complex, rate=k_H[Complex][H⁺] with k_H=9.4×10^–3 dm³mol^–1 s^–1 at 25 °C and I =1.0 mol dm^–3 (NaClO₄) with H=71 kJ mol^–1 and S ₂₉₈ =–47 JK^–1mol^–1.The cobalt(III) complexes, [CoLCl](ClO₄)₂, [CoL(H₂O)]-(ClO₄)₃, [CoL(NO₂)](ClO₄)₂, [CoL(DMF)](ClO₄)₃ (DMF=dimethylformamide) and [CoL(O₂CH)](ClO₄)₂ have been characterised. The chloropentamine [CoCl([16]aneN₅)]²⁺ undergoes rapid base hydrolysis with k_OH=1.1× 10⁵dm³ mol^–1s^–1 at 25°C and I=0.1 mol dm^–3 (H=73 kJ mol^–1 and S ₂₉₈ =98 JK^–1 mol^–1). Rapid base hydrolysis of [CoL(NO₂)]²⁺ is also observed and the origins of these effects are considered in detail.     

Influence of magnetic dilution on the spin transition in the complex of iron(II) nitrate with 4-amino-1,2,4-triazole

Influence of magnetic dilution with Zn^II ions on the spin transition in the iron nitrate complex of 4-amino-1,2,4-triazole (AT) was studied by magnetochemistry, Mössbauer spectroscopy, and IR spectroscopy. In studies of the properties of solid phases of Fe _x Zn _1–x (AT)₃(NO₃)₂ (0.01x0.8), it was demonstrated that magnetic dilution results in a lowered spin transition temperature and an increased share of the high-spin form of the iron(II) complex.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 145–151, November–December, 1993.Translated by L. Chernomorskaya     

2,3-Dihydroxypyridine Loaded Amberlite XAD-2 (AXAD-2-DHP): Preparation, Sorption–Desorption Equilibria with Metal Ions, and Applications in Quantitative Metal Ion Enrichment from Water, Milk and Vitamin Samples

2,3-Dihydroxypyridine loaded (via –N=N–linker) Amberlite XAD-2 (AXAD-2-DHP) was prepared and characterized by elemental analyses, TGA and FT-IR spectra. It (1g packed in a column of 1cm diameter; surface area 135.5m²g^–1) was found to be an effective solid phase sorbent for enriching Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺ at pH 3.5 to 7.0 using flow rates between 1.0–5.0mLmin^–1. For desorption (recovery 97.0–99.8%) of the metal ions, 8 to 10mL of 2.0molL^–1 HCl or 1.5molL^–1 HNO₃ at a flow rate of between 2.0 and 4.0mLmin^–1 were found most suitable. The t_1/2 (time for 50% sorption) is between 2 and 10min when a 50mL solution (containing a total amount of metal of 2mg) was equilibrated with 0.5g of resin. Sorption of all metal ions except Pb²⁺ follows the Langmuir model, whereas for Pb the data fits with the Freundlich model. The sorption capacity is between 60.7 (for Cd) and 406.7 (for Cu) µmolg^–1. The resin can withstand an acid concentration of 6molL^–1 and can be reused for thirty cycles of sorption–desorption. The preconcentration factor varies between 100 and 300. For Cd, Ni and Cu the sorption capacity of 2,3-dihydroxypyridine loaded cellulose is lower than that of the present resin. The tolerance limits of electrolytes, humic acid, complexing agents, Ca²⁺ and Mg²⁺ in the enrichment of all metal ions are reported. The limits of detection are 3.88, 5.37, 8.72, 13.88, 4.71, 1.24, 0.59 and 0.30µgL^–1 for Zn²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Cd²⁺, Cu²⁺, Fe³⁺ and Co²⁺, respectively. The calibration curves for flame AAS determination were linear in the ranges 0.018–1.0, 0.067–5.0, 0.2–5.0, 0.9–20, 0.028–2.0, 0.077–5.0, 0.19–10 and 0.1–3.5µgmL^–1, respectively. All the eight metal ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples have been quantitatively enriched with Amberlite XAD-2-DHP and determined by flame atomic absorption spectrometry.     

Photometric detection of cyclodextrins in liquid chromatography by using iodine generated electrochemically in-situ

A method has been developed for photometric detection of cyclodextrins (CD) in liquid chromatography using iodine (I₂) generated electrochemically in-situ. Iodide ion in the mobile phase was electrochemically oxidized to I₂ which was subsequently reacted with I^–, in an electrochemical flow cell, forming I₃^–. The absorbance of I₃^– was found to be greatly enhanced when CD were present in the mobile phase. The absorbance enhancement was caused by the change in the mole fraction of I₃^–, because of the inclusion reaction of I₃^– with CD. On the basis of this phenomenon, CD were detected by means of a photodiode-array UV–visible detector positioned downstream of the electrochemical flow cell. The signals were found to be linearly dependent on CD concentration. Because the formation constants of I₃^– with CD decrease in the order -CD>-CD>-CD, -CD was most detectable by the method. Detection limits were 1.0 mol L^–1 for -CD, 65 mol L^–1 for monoG1--CD, 100 mol L^–1 for -CD, and 200 mol L^–1 for -CD.     

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

Summary The aquation ofcis-[Co(en)₂(NH₂Et)O₂CR]²⁺ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05[OH^–]_T 0.35 mol dm^–3 range (I=0.5 mol dm^–3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co–O bond heterolysis. A substantially large positive value for the activation entropy supports SN₁CB mechanism for base hydrolysis.     

Dry etching characteristics of III–V semiconductors in microwave BCl3 discharges

Electron cyclotron resonance (ECR) BCl₃ discharges with additional rf biasing of the sample position have been used to etch a variety of III–V semiconductors. GaAs and Al_xGa_1–xAs (x = 0–1) etch at equal rates in BCl₃ or BCl₃/Ar discharges, whereas SF₆ addition produces high selectivities for etching GaAs over AlGaAs. These selectivities are in excess of 600 for dc biases of –150 V, and fall to 6 for biases of –300 V. If the dc biases are kept to – 100 V, there is no measurable degradation of the optical properties of the GaAs and AlGaAs. The AlF₃ formed on the AlGaAs surface during exposure to BCl₃/SF₆ plasmas can be removed by sequential rinsing in dilute NH₄OH and water. In-based materials (InP, InAs, InSb, InGaAs) etch at slow rates with relatively rough morphologies in BCl₃ plasmas.