T:Toxic;7440-38-2Relevant articles and documents
Pnictogen-hydride activation by (silox)3Ta (silox = tBu3SiO); Attempts to circumvent the constraints of orbital symmetry in N2 activation
Hulley, Elliott B.,Bonanno, Jeffrey B.,Wolczanski, Peter T.,Cundari, Thomas R.,Lobkovsky, Emil B.
, p. 8524 - 8544 (2010/12/18)
Activation of N2 by (silox)3Ta (1, silox = tBu3SiO) to afford (silox)3Ta=N-N=Ta(silox) 3 (12-N2) does not occur despite ΔG°cald = -55.6 kcal/mol because of constraints of orbital symmetry, prompting efforts at an independent synthesis that included a study of REH2 activation (E = N, P, As). Oxidative addition of REH 2 to 1 afforded (silox)3HTaEHR (2-NHR, R = H, Me, nBu, C6H4-p-X (X = H, Me, NMe2); 2-PHR, R = H, Ph; 2-AsHR, R = H, Ph), which underwent 1,2-H2- elimination to form (silox)3Ta=NR (1=NR; R = H, Me, nBu, C6H4-p-X (X = H (X-ray), Me, NMe2, CF 3)), (silox)3Ta=PR (1=PR; R = H, Ph), and (silox) 3Ta=AsR (1=AsR; R = H, Ph). Kinetics revealed NH bond-breaking as critical, and As > N > P rates for (silox)3HTaEHPh (2-EHPh) were attributed to (1) ΔG°calc(N) calc(P) ～ ΔG°calc(As); (2) similar fractional reaction coordinates (RCs), but with RC shorter for N P～As. Calculations of the pnictidenes aided interpretation of UV-vis spectra. Addition of H2NNH2 or H2N-N(cNC2H3Me) to 1 afforded 1=NH, obviating these routes to 12-N2, and formation of (silox)3MeTaNHNH2 (4-NHNH2) and (silox) 3MeTaNH(-cNCHMeCH2) (4-NH(azir)) occurred upon exposure to (silox)3Ta=CH2 (1=CH2). Thermolyses of 4-NHNH2 and 4-NH(azir) yielded [(silox)2TaMe](μ- NαHNβ)(μ-NγHN δH)[Ta(silox)2] (5) and [(silox)3MeTa] (μ-η2-N,N: η1-C-NHNHCH2CH 2CH2)[Ta(κ-O,C-OSitBu2CMe 2CH2)(silox)2] (7, X-ray), respectively. (silox)3Ta=CPPh3 (1=CPPh3, X-ray) was a byproduct from Ph3PCH2 treatment of 1 to give 1=CH 2. Addition of Na(silox) to [(THF)2Cl3Ta] 2(μ-N2) led to [(silox)2ClTa](μ-N 2) (8-Cl), and via subsequent methylation, [(silox) 2MeTa]2(μ-N2) (8-Me); both dimers were thermally stable. Orbital symmetry requirements for N2 capture by 1 and pertinent calculations are given.
Synthesis of volatile inorganic hydrides by electrochemical method
Turygin,Tomilov,Berezkin, M. Yu.,Fedorov
, p. 1459 - 1478 (2011/02/28)
Published data and results of our investigations on the problem of electrochemical synthesis of arsenic, phosphorus, and germanium hydrides are generalized. The results of the developments of the physicochemical bases of arsine synthesis by electrochemical reduction of arsenic acid, phosphine by reduction of white phosphorus in organic solvents, and monogermane by reduction of germanate in basic conditions are reported. The current yield of hydrides is 95, 90, and 40%, respectively. The promising guidelines of the practical use of electrochemical methods of the synthesis of the hydrides in the manufacture of semiconductor materials for microelectronics, optics, and laser engineering are discussed. The development of an arsine generator attracts considerable interest, which can serve as a basis for an aggregative continuous apparatus used in complex flow charts of manufacture of semiconductor materials.
GASEOUS DIELECTRICS WITH LOW GLOBAL WARMING POTENTIALS
-
, (2010/12/31)
A dielectric gaseous compound which exhibits the following properties: a boiling point in the range between about ?20° C. to about ?273° C.; non-ozone depleting; a GWP less than about 22,200; chemical stability, as measured by a negative standard enthalpy of formation (dHf0); a toxicity level such that when the dielectric gas leaks, the effective diluted concentration does not exceed its PEL; and a dielectric strength greater than air.
Electrochemical reduction of As(III) in acid media
Smirnov,Turygin,Shalashova,Khudenko,Tomilov
, p. 25 - 29 (2008/10/09)
Measurements of the cathode potentials of different electrode materials in the galvanostatic electrolysis of As2O3 solutions in sulfuric acid indicate that the Pb cathode ensures the most stable negative potential, favorable for AsH3 formation. Preparative electrolyses confirm stability of the arsine yield in a series of experiments. The current efficiency for arsine on the Pb cathode is 60-70%. The byproduct of this process is As0, with a current efficiency of about 2%. We have designed and tested an electrolyzer with improved hydrodynamics, which makes it possible to avoid the formation of dead zones and to prevent the cathode chamber from being clogged.
Spectrophotometric determination of arsenic via nanogold formation in micellar medium
Pal, Anjali,Maji, Sanjoy Kumar
, p. 1178 - 1182 (2007/10/03)
Colloidal gold nanoparticles are formed in aqueous anionic micellar medium by the quantitative reduction of chloroauric acid (HAuCl4) by arsine (AsH3) gas produced from arsenic bearing sample water. The absorbance of the pink gold sol (λmax at 530 nm) is a measure of arsenic concentration present in the sample. Both, As(III) and As(V) either present individually or in mixture could be determined. The molar absorptivity is 6.1×103 lit mol-1 cm-1 and the Sandell sensitivity is 1.28×10-2 μg cm-2. The gold particles, as observed from the transmission electron microscopy analysis, are spherical in nature, the average size being 14±5 nm. The linear dynamic range (LDR) for the arsenic determination is 0-0.5 ppm (0-6.67×10 -6 M). The limit of detection (LOD) is 0.005 ppm. The 95% confidence limit for 0.2 ppm of arsenic is 0.207±0.007 ppm (for 10 replicates). The relative standard deviation (RSD) is 2+/Fe3+, Ca2+/Mg 2+, PO4-3, SiO3-2, NO3-, Cl-, SO4-2, humic acid, common herbicides/pesticides like 2,4-D, endosulfan, atrazine, etc. and can be applied for the determination of total arsenic concentration in real water samples. The results are in good agreement with the SDDC method. The toxic and volatile organic solvents used for silver diethyldithiocarbamate method could be avoided in this method and hence it is safer, much easier and more reproducible.
Electrochemical preparation of H2S and H2Se
Bastide, Stephane,Huegel, Paul,Levy-Clement, Claude,Hodes, Gary
, p. D35-D41 (2008/10/09)
H2S and H2Se have been electrolytically prepared by electrolysis in aqueous H2SO4 solutions of composite cathodes made of S or Se and graphite. The efficiencies depended strongly on the electrolyte composition, in particular on the acid concentration and presence of K+. Faradaic efficiencies of 80% were obtained in dilute (0.05 M) acid, and this increased to 100% with added K2SO4. The efficiencies dropped drastically in concentrated acid (>a few moles). H 2Te and AsH3 generation were also briefly studied for comparison. The mechanisms of hydride formation are discussed. Both the reaction of nascent hydrogen with the free element and direct reduction of the element are considered. The latter is believed to be the dominant mechanism.
Synthesis and TG/DTA study on two new metallo(VI)-arsenato(V) heteropolyacids containing vanadium(V)
Fodor,Ghizdavu,?uteu,Caraban
, p. 153 - 158 (2008/10/09)
An improved method for the synthesis of two heteropolyacids of the same type: H5[AsMo10V2O40]· 13H2O and H5[AsW10V2O40] ·16H2O was elaborated. Th
Etching AlAs with HF for epitaxial lift-off applications
Voncken,Schermer,Van Niftrik,Bauhuis,Mulder,Larsen,Peters,De Bruin,Klaassen,Kelly
, p. G347-G352 (2008/10/09)
The epitaxial lift-off process allows the separation of a thin layer of III/V material from the substrate by selective etching of an intermediate AlAs layer with HF In a theory proposed for this process, it was assumed that for every mole of AIAs dissolved three moles of H2 gas are formed. In order to verify this assumption the reaction mechanism and stoichiometry were investigated in the present work. The solid, solution and gaseous reaction products of the etch process have been examined by a number of techniques, It was found that aluminum fluoride is formed, both in the solid form as well as in solution. Furthermore, instead of H2 arsine (AsH3) is formed in the etch process. Some oxygen-related arsenic compounds like AsO, AsOH, and AsO2 have also been detected with gas chromatography/mass spectroscopy. The presence of oxygen in the etching environment accelerates the etching process, while a total absence of oxygen resulted in the process coming to a premature halt. It is argued that, in the absence of oxygen, the etching surface is stabilized, possibly by the sparingly soluble A1F3 or by solid arsenic.
Electrochemical preparation of arsenic and its compounds
Smetanin,Smirnov,Chernykh,Turygin,Khudenko,Fedorov,Tomilov
, p. 22 - 36 (2008/10/08)
Electrochemical processes are used to recover elemental arsenic from NaH2AsO3 solutions, oxidize As2O3 suspensions to arsenic acid, and reduce arsenic acid to arsine. The electrolysis conditions are optimized for obtaining elemental arsenic: 0.8-0.9 M NaH 2AsO3, 0.03-0.05 A/cm2, 20-25°C. The introduction of tetraalkylammonium salts containing C9-C12 substituents, e.g., trimethylcetylammonium bromide, is shown to stabilize the current efficiency in terms of As at a level of 45-50%. The current efficiency of copper cathodes attains 89% in 1-2 M H3AsO4 solutions at a current density of 0.2 A/cm2. In the electrosynthesis of arsenic acid, quantitative substance and current yields are achieved in 2-3 M HCl solutions. Low-waste processes are proposed for preparing arsenic, H 3AsO4, and As2O5 from As 2O3. The resulting arsenic is suitable for producing high-purity (99.9999%) material. The physicochemical processes underlying arsine generation are examined, and a bench-scale electrochemical arsine generator is described which can be used in the manufacturing of semiconductor materials.
Ba11KX7O2 (X = P, AS): Two novel zintl phases with infinite chains of oxygen centered Ba6 octahedra, isolated X3- and dimeric X24- anions
Lulei, Michael
, p. 1796 - 1802 (2008/10/09)
Reactions of BaX (X = P, As) with Ba, K and BaO in tantalum tubes at 900-1000°C yielded black, very air-and moisture-sensitive crystals of Ba11KP7O2 and isotypic Ba11KAs7O2 which were characterized by EDX and X-ray diffraction (orthorhombic, Fddd, Z = 8; a = 1069.9(1), b = 1514.3(2), c = 3164.6(4) pm and a = 1087.8(2), b = 1542.3(2), c = 3232.4(4) pm, respectively). The structure contains infinite zigzag chains, 1∞[Ba4Ba2/2O], of oxygen-centered, corner-sharing Ba6 octahedra along [100]. They are connected by linear strings built of alternating isolated X atoms and X2 dimers to form layers parallel to (001). While the isolated X atoms are surrounded by eight Ba forming a distorted cube, the X2 dimers center a Ba12 polyhedron which is comprised of a pair of face-sharing Ba square antiprisms. This results in a cube-antiprism-antiprism-cube sequence of face-sharing Ba polyhedra. Additional X atoms function as spacers between the layers and connect them along [001]. Two atom positions are statistically occupied by Ba and K, and the formula may be written as Ba2+11K+X3-5(X 2)4-O2-2 according to the Zintl-Klemm concept.
