The UHF-CNDO/2 study of tetra-atomic radicals containing silicon and phosphorus

The UHF-CNDO/2 calculations have been performed for several radicals containing C, Si or P. The equilibrium geometries found by the minimization of the total energies and calculated spin densities are compared with results from ESR experiments and INDO calculations. The electronic structure of the radicals is discussed for their equilibrium geometries.     

Simultaneous determination of silicon and phosphorus in biological standard materials with on-line column flow-injection spectrophotometry

Summary A simultaneous determination of silicon and phosphorus in biological standard materials with on-line column flow-injection spectrophotometry (FIA) is described. Biological materials are ashed, fused with a lithium carbonate-boric acid mixture, and dissolved in a hydrochloric acid solution. Interfering cations are removed by a simple cation-exchange column filtration. The acid effluent is evaporated to dryness, fused with a small amount of sodium carbonate for depolymerization, taken up in dilute EDTA solution, and analyzed for silica and phosphorus by FIA. For the simultaneous determination of these elements, TSK-gel SAX was used, and the eluent was 0.085 mol/l NaCl/0.01 mol/l NH₃/0.001 mol/l EDTA. Several standard reference materials [bovine liver (NBS), chlorella and pepperbush (NIES)] were analyzed for both elements. The results of phosphorus determination for bovine liver are in satisfactory agreement with the NBS certificated value. ICP measurements were applied to analyses of chlorella and pepperbush for silica and phosphorus. The agreement of the analytical results between FIA and ICP is satisfactory. Silica in bovine liver was determined in the present study for the first time.

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Simultanbestimmung von Silicium und Phosphor in biologischen Standardmaterialien mit Hilfe von On-line Fließinjektions-Spektralphotometrie

     

Simultaneous determination of arsenic,phosphorus, and silicon

Summary A simple, rapid, accurate and reliable method for the simultaneous determination of arsenic, phosphorus and silicon in the presence of each other is reported. The method involves the selective solvent extraction of phosphomolybdic acid by isobutyl acetate, the differential formation of phospho and arsenomolybdic acid when perchloric acid is added before the addition of ammonium molybdate, and the selective destruction of phospho and arsenomolybdic acid complexes in the presence of silicomolybdic acid. Silicon, phosphorus and arsenic were determined as their heteropoly blues.

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Zusammenfassung Eine einfache, rasche und verläßliche Methode zur gleichzeitigen Bestimmung von Arsen, Phosphor und Silicium nebeneinander wurde beschrieben. Phosphormolybdänsäure wird selektiv mit Isobutylacetat extrahiert. Setzt man vor der Zugabe von Ammoniummolybdat Perchlorsäure zu, so erfolgt die Bildung von Phospho- bzw. Arsenomolybdänsäure in differenter Weise. Diese beiden Säuren sind in Gegenwart von Silicomolybdänsäure selektiv zerstörbar. Silicium, Phosphor und Arsen werden auf der Grundlage der blauen Farbreaktion ihrer Heteropolysäure bestimmt.

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Résumé On communique une méthode simple, rapide, précise et sûre pour le dosage simultané de l'arsenic, du phosphore et du silicium en présence les uns des autres. La méthode met en jeu l'extraction par solvant sélectif de l'acide phosphomolybdique par l'acétate d'isobutyle, la formation différentielle de l'acide phospho et arsénomolybdique quand l'addition de l'acide perchlorique précède celle du molybdate d'ammonium, et la destruction sélective des complexes acides phospho et arsénomolybdiques en présence d'acide silicomolybdique. On a dosé le silicium, le phosphore et l'arsenic sous forme d'hétéropolycomplexes bleus.

     

dπ-pπ interaction in bonds of silicon with nitrogen and phosphorus

Conclusions The stretching vibration frequencies of the Si-H bond in substituted silanes containing an Si-N bond depend both on the inductive effect of the substituents and the d-p, p,- and , -conjugation effects.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2609–2611, November, 1970.     

Simultaneous determination of silicon and phosphorus in soil and plants by reversed-phase ion-pair chromatography

A reversed-phase ion-pair high-performance liquid chromatographic method, using tetrabutylammonium bromide (TBABr) as ion-pair reagent, has been developed for the simultaneous analysis of silicon (Si) and phosphorus (P) as heteropoly acids in soil and plant samples. The effect of the concentrations of ion-pair reagent, acetate buffer and organic modifier as well as the pH of buffer on separation was made clear. The reaction conditions and stability of heteropoly acids were investigated. Furthermore, the phenomenon occurred in the optimized process was also further researched. The separation was performed on a reversed-phase C(18) column within 11 min with 40:60 (v/v) 0.1M acetate buffer (pH 3.9)-acetonitrile (ACN) containing 0.8 mM TBABr as a mobile phase. The linear ranges of the peak area calibration curves for Si and P were 0.08-50 mg/L and 0.40-50 mg/L, respectively. The detection limits calculated at S/N=3 were 0.0057 mg/L and 0.0280 mg/L for Si and P, respectively. The method was successfully applied to the analysis of soluble and total contents of Si and P in soil and plant samples.     

Application of total selective solvent extraction of germanium,phosphorus and silicon to the simultaneous determination of arsenic,germanium, phosphorus and silicon

A simple rapid, accurate, and reliable method of simultaneous determination of arsenic, germanium, phosphorus, and silicon is reported. The method involves first, the determination of germanium as its phenlfluorone complex and its selective extraction with isoamyl alcohol. Phosphorus is next determined as its heteropoly blue after selective extraction of phosphomolybdic acid by isobutyl acetate at pH 1.0-0.8 and its direct reduction in this solvent. Silicon is then determined after its extraction as silicomolybdic acid by isooctyl alcohol at pH < 0.4 and direct reduction in the solvent phase. Finally, arsenic is determined in the remaining aqueous phase after reduction to its heteropoly blue.     

On the determination of phosphorus depth profile in phosphorus-doped silicon

The depth profile of phosphorus concentration in phosphorus-doped silicon was shown to be measureable with an accuracy of 1–3% by the use of liquid scintillation counting after neutron irradiation. Both the amount of Si and P are determined by neutron activation analysis followed by liquid scintillation counting for 1–5 hours after the end of irradiation and 5–10 days after irradiation, respectively. Concentrations as low as 10 ppm and thicknesses of 20 nm can be determined.     

Colorimetric determination of silicon in the presence of phosphorus

An accurate and rehable colorimetric method of silicon determination in the presence of phosphorus is reported The method involves the selective extraction of phosphomolybdate with ethyl acetate and determination of the aqueous phase after reduction to molybdenum blue lsoamyl acetate extracts phosphomolybdate to a lesser degree than ethyl acetate     

Thermal properties and combustion behaviors of a novel UV-curable flame retarded coating containing silicon and phosphorus

A silicon-based acrylate (SHEA) was synthesized via the reaction between 2-hydroxylethyl acrylate and dimethyldichlorosilane, and characterized by Fourier transform infrared (FTIR), ¹H NMR spectroscopy and ²⁹Si NMR spectroscopy. The SHEA was blended with phosphorus-containing tri(acryloyloxyethyl) phosphate (TAEP) at different ratios to obtain a series of UV-curable flame retarded resins. The final unsaturation conversion of the SHEA films was determined by FTIR. Their combustion behaviors were examined by microscale combustion calorimetry (MCC). The thermal degradations of TAEP/SHEA composites were characterized using thermogravimetric analysis/infrared spectrometry (TG–IR). The MCC results present that the addition of TAEP into SHEA was able to decrease the HRR, HRC, T_max and THC. Among the TAEP/SHEA resins, Si1 (TAEP:SHEA is 1:1) owns the highest initial decomposition temperature and leaves the most char residue at 800 °C. The change of chemical structure during the thermal degradation process was monitored by real-time FTIR analysis to study the condensed-phase flame retarded mechanism.     

Analogies between silicon and phosphorus stereochemistry—II : Influence of the attacking anion upon the stereochemistry of nucleophilic displacement at tetrahedral phosphorus

The stereochemistry of reactions of cyclic halogenophosphates with a representative series of p-substituted aryloxides emphasizes the relative influence of the attacking anion. For a given leaving group, the stereochemistry depends essentially upon the electronic character of the p-substituent and the ion-pair dissociation of the nucleophile. Both stereochemical and kinetic data rule out a cation-assisted mechanism to explain retention at phosphorus. Meanwhile, a comparison between S_N2(P) and S_N2(Si) suggests similar mechanisms in the two series. Retention and/or inversion are the consequence of two competing reactions of similar energies. The stereochemistry is determined by the factors which affect the approach of the nucleophile to give two initial intermediates of different geometries.     

Synthesis and characterization of cyclotriphosphazenes containing silicon as single solid-state precursors for the formation of silicon/phosphorus nanostructured materials

The synthesis and characterization of new organosilicon derivatives of N(3)P(3)Cl(6), N(3)P(3)[NH(CH(2))(3)Si(OEt)(3)](6) (1), N(3)P(3)[NH(CH(2))(3)Si(OEt)(3)](3)[NCH(3)(CH(2))(3)CN](3) (2), and N(3)P(3)[NH(CH(2))(3)Si(OEt)(3)](3)[HOC(6)H(4)(CH(2))CN](3) (3) are reported. Pyrolysis of 1, 2, and 3 in air and at several temperatures results in nanostructured materials whose composition and morphology depend on the temperature of pyrolysis and the substituents of the phosphazenes ring. The products stem from the reaction of SiO(2) with P(2)O(5), leading to either crystalline Si(5)(PO(4))(6)O, SiP(2)O(7) or an amorphous phase as the glass Si(5)(PO(4))(6)O/3SiO(2).2P(2)O(5), depending on the temperature and nature of the trimer precursors. From 1 at 800 degrees C, core-shell microspheres of SiO(2) coated with Si(5)(PO(4))(6)O are obtained, while in other cases, mesoporous or dense structures are observed. Atomic force microscopy examination after deposition of the materials on monocrystalline silicon wafers evidences morphology strongly dependent on the precursors. Isolated islands of size approximately 9 nm are observed from 1, whereas dense nanostructures with a mean height of 13 nm are formed from 3. Brunauer-Emmett-Teller measurements show mesoporous materials with low surface areas. The proposed growth mechanism involves the formation of cross-linking structures and of vacancies by carbonization of the organic matter, where the silicon compounds nucleate. Thus, for the first time, unique silicon nanostructured materials are obtained from cyclic phosphazenes containing silicon.     

A radioreagent method for determination of traces of phosphorus in high-purity silicon

The present study explores the feasibility of the determination of phosphorus at the extreme trace levels in high-purity silicon by radioreagent method. After silicon dissolution with hydrofluoric and nitric acids and matrix volatilization, 12-molybdophosphoric acid (12-MPA) is formed by the addition of the radioreagent,⁹⁹MoO ₄ ^2– , in nitric acid medium and then extracted into isobutyl acetate. By plotting the phosphorus content against the radioactivity of⁹⁹Mo in the organic phase, a linear relationship persisting down to 5 ng is obtained. Special effort has been made to the elimination of the unreacted⁹⁹MoO ₄ ^2– reagent and the optimal control of phosphorus blank introduced through the multistage analytical procedure in order to ensure reliable determination of phosphorus at the ppb level.     

Synthesis of phosphorus (silicon,tin)-containing derivatives of mercaptoketenes and some of their properties

Some newS-phosphorylated,S-silylated, andS-stannylated derivatives of -mercaptoketones were obtained. The reactions of some of these compounds induced by the temperature and by molecular oxygen as well as the phosphorylation of the Si- and Sn-containing derivatives were studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 353–357, February, 1995.     

Analogies between silicon and phosphorus stereochemistry—I : Influence of the leaving group on the stereochemistry of nucleophilic displacement at phosphorus

Stereochemistry of cyclic halogenophosphates has been studied by adding aryloxides, in THF. All extra parameters being equal, the fluoro substituent which is of the more electronegative (and the more apicophilic) is displaced with the more predominant retention F>Cl≈Br. Such behaviour cannot be explained with the usual concepts of phosphorus stereochemistry and, in particular, the generally accepted view of apical attack giving the more stable P^V intermediate. By contrast, strong analogies with the stereochemistry observed at silicon are clearly evidenced. Like for silicon compounds, front-side attack could explain predominant retention, particularly in P-F bond cleavage. Trigonal bipyramidal intermediates with the entering group in equatorial position and the leaving group in apical position, or square-pyramidal geometries may be envisaged.     

Enhanced thermal properties and flame retardancy of unsaturated polyester‐based hybrid materials containing phosphorus and silicon

A phosphorus and silicon containing liquid monomer (9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide–vinyltrimethoxysilane (DOPO–VTS)) was synthesized by the reaction between DOPO and VTS. DOPO–VTS and methacryloxypropyltrimethoxylsilane were introduced into unsaturated polyester resin to prepare flame retardant UPR/SiO₂ (FR‐UPR/SiO₂) hybrid materials by sol–gel method and curing process. DOPO–VTS contributes excellent flame retardancy to UPR matrix, which was confirmed by the limiting oxygen index and microscale combustion calorimeter results. The thermogravimetric analysis (TGA) results indicate that the FR‐UPR/SiO₂ hybrid materials possess higher thermal stability and residual char yields than those of pure UPR at high temperature region. The thermal degradation of materials was investigated by TGA/infrared spectrometry (TG‐IR) and real‐time infrared spectrometry (RT‐IR), providing insight into the thermal degradation mechanism. Moreover, scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) were used to explore the morphologies and chemical components of the residual char. Copyright © 2013 John Wiley & Sons, Ltd.     

Helium-4 and neutron activation analysis for phosphorus in aluminium—silicon alloys

An instrumental determination of phosphorus in aluminium-silicon alloys by activation with 20-MeV helium-4 particles can be based on the ³¹P(α , n)^34m Cl reaction. A mixture of aluminium powder and disodium hydrogenphosphate is used as a standard. For concentrations ranging from 1.7 to 25 μg g^-1, the experimental standard deviation ranges from 1 to 24% with an average of 8%. The method was compared with thermal neutron activation analysis based on the ³¹P(n, γ)³²P reaction. ³²P was chemically separated by precipitation as ammonium molybdophosphate. This technique yielded results with a standard deviation between 0.3 and 7.5% with an average of 2%. The agreement between the two methods was satisfactory. The results were also compared with photometry and atomic absorption spectrometry.