Accurate quantification and transformation of arsenic compounds during wet ashing with nitric acid and microwave assisted heating

Arsenous acid, dimethylarsinic acid (DMA), methylarsonic acid (MA), arsenic acid, arsenobetaine bromide (AB), trimethylarsine oxide (TMAO), arsenocholine iodide (AC), and tetramethylarsonium iodide (TETRA) were heated in a microwave autoclave with nitric acid to 100-300 degrees C. The arsenic compounds in the digests were separated with anion- and cation-exchange chromatography and determined with an inductively coupled plasma mass spectrometer as arsenic-specific detector. Arsenous acid was completely oxidized to arsenic acid at 100 degrees C. For a complete oxidation of MA and DMA to arsenic acid temperatures > 220 degrees C and > 280 degrees C were necessary. AB decomposed to arsenic acid via TMAO. Complete conversion was only obtained after heating the sample for 90 min to 300 degrees C. For a complete conversion of TMAO similar harsh conditions were necessary. AC was already substantially degraded to TMAO, TETRA and two unknown compounds at 100 degrees C. The unknown arsenic compounds were found only in the digests up to 160 degrees C. Quantitative conversion of AC to arsenic acid went also via TMAO. At temperatures above 220 degrees C TETRA started to convert to TMAO, which then was further converted to arsenic acid. To investigate whether the results obtained for the arsenic standards are transferable to real samples, the certified reference material DORM-2 was also heated in nitric acid with variable digestion temperatures and times. For an almost complete conversion of the AB present in DORM-2 90 min at 300 degrees C were necessary. Total organic carbon (TOC) was less < 0.2% when DORM-2 was heated at temperatures > or = 260 degrees C for 60 min. UV photo-oxidation of DORM-2 was investigated as an alternative sample decomposition. Only 6% of AB was converted to arsenic acid when DORM-2 was irradiated for 2 h at 1000 W. In contrast to microwave heating substantial amounts of MA were observed as degradation product.     

Treatment of radioactive waste phenol with Fenton's oxidation

A new procedure was developed for the waste treatment of radioactive phenol on a laboratory scale. Waste phenol was dissolved in water (2% as phenol), and ferrous ion (10 mg/l as Fe2+) was added. Hydrogen peroxide (6% as H2O2) was added separately in three steps, 20, 30, and 50% of the volume, in order to avoid rapid reaction. The solution was heated at 80-90 degrees C for several hours in a beaker covered with a watch glass till the color of the solution changes from red purple to pale yellow. Then, the solution was neutralized with sodium hydroxide and heated for 1 h to decompose excess hydrogen peroxide. When the procedure is carried out with four 2 l beakers on a hot plate, 100 ml of phenol (1,200 ml of the aqueous solution saturated with phenol) can be oxidized simultaneously.     

Nanostructured pure gamma-Fe2O3 via forced precipitation in an organic solvent

Pure maghemite, gamma-Fe(2)O(3), was prepared as ultra fine particles in the nanometer-sized range via the forced precipitation method in an organic solvent. The precipitation of iron(III) ions, from iron(III) chloride in 2-propanol led selectively to highly dispersed particles of ferrihydrite, which upon treatment with temperatures higher than 200 degrees C under dynamic vacuum resulted in high-surface-area particles of gamma-Fe(2)O(3). Precipitation in water also led to ferrihydrite, but the final product, after heating at 300 degrees C, contained a mixture of gamma-Fe(2)O(3) and alpha-Fe(2)O(3) (hematite). The precipitation from iron(III) nitrate in water resulted in goethite which was converted to hematite upon heating. On the other hand, the final product in 2-propanol was a mixture of maghemite and hematite. The products were characterized by FTIR, TGA, XRD, and gas sorption analysis. Nitrogen gas adsorption studies for the pure gamma-Fe(2)O(3) samples revealed mesoporous particles with high surface areas in the range of 70-120 m(2) g(-1) after heat treatment at 300 degrees C. The gamma-Fe(2)O(3) particles retained their gamma-phase as well as their mesoporous structure at relatively high temperatures, as high as 400 degrees C.     

Intramolecular cyclization of phenol derivatives with CC double bond in a side chain

Intramolecular cyclization of phenol derivatives with CC double bond on a side chain was examined using copper and silver catalyst. For example, 2-allylphenol (1a) was converted to 2,3-dihydro-2-methylbenzofuran (2a) in 70% yield using Cu(OTf)₂ or in 90% yield using AgClO₄. This catalysis was applied to cyclization of 2-allylphenol derivatives, 2-(3-butenyl)phenol, benzoic acids with CC double bond, 2-allyl-N-tosylaniline, and 2-(3-butenyloxy)phenol. Furthermore, allyl phenyl ether was converted to 2a via Claisen rearrangement and cyclization.     

Resistance changes due to thermal coalescence in colloidal au/organic linker molecule multilayer films

A decrease in the resistance of colloidal Au multilayer films was observed upon heating. These multilayer Au films were fabricated by a layer-by-layer approach, using Au colloids and a bifunctional linker molecule, 1,6 hexanedithiol (HD) on polymer substrates. The resistance of the film prior to heating was 1 MOmega. The films were heated at three different temperatures, 120, 160, and 180 degrees C. After heating for 12 h, the resistance decreased by 6 orders of magnitude to about 50 Omega. This decrease in resistance was faster at higher temperatures. X-ray photoelectron spectroscopy (XPS) of the unheated films revealed two S 2p peaks corresponding to the Au-S thiolate peak and an oxidized S peak. Upon heating, the relative intensity of the oxidized S peak increased and that of the Au-S peak decreased, indicating an oxidation and desorption of the linker molecules. Scanning electron microscope (SEM) images of the heated films depict coalescence of the spherical Au particles into irregular shapes. The resistance decrease is believed to be due to the desorption of the linker molecule and subsequent coalescence of the Au particles. This method paves a way for controlling the resistance of electrodes on flexible polymer substrates.     

Selective measurement of chromium(VI) by fluorescence quenching of ruthenium

The oxidative deterioration of polyunsaturated fatty acids (PUFAs) in culinary oils and fats during episodes of heating associated with normal usage (80-300 degrees C, 20-40 min) has been monitored by Fourier transform infrared spectroscopy (FTIR). The thermal oxidation of PUFAs is a free radical chain reaction, in which hydroperoxides are generally recognized as the primary major products. Hydroperoxides of PUFAs are easily decomposed into a very complex mixture of secondary products with the decrease in unsaturation. The oxidative advance of PUFAs during heating was studied by the determination of unsaturation percentage at different temperatures and heating times. Oils frequently used in food frying such as olive oil, sunflower oil, corn oil and seeds oil (sunflower, safflower and canola seed) were studied. The results show there is a decrease in unsaturation starting at 150 degrees C and becoming more pronounced at temperatures around 250 degrees C. The following variations were found in the unsaturation percentage, expressed as methyl linoleate, between the original sample and the sample heated at 300 degrees C for 40 min: olive oil (19-6%), sunflower oil (29-12%), corn oil (28-18%) and seeds oil (23-11%). This variation in unsaturation grade provides evidence of the transformation of essential PUFAs and subsequent decrease in the oils' nutritional value. The internal standard method is suitably precise when the n-valeronitrile is used as standard as shown by the 1-2% relative standard deviation (R.S.D.) found for seven replicates.     

Photochemistry of N-isopropoxy-substituted 2(1H)-pyridone and 4-p-tolylthiazole-2(3H)-thione: alkoxyl-radical release (spin-trapping,EPR, and transient spectroscopy) and its significance in the photooxidative induction of DNA strand breaks

UVA-irradiation of the photo-Fenton reagents N-isopropoxypyridone 2b and N-isopropoxythiazole-2(3H)-thione 3b releases radicals which induce strand breaks. Transient spectroscopy establishes N-O bond scission [Phi(N)(-)(O) = (75 +/- 8)% for 2b and (65 +/- 7)% 3b] as the dominating primary photochemical process to afford the DNA-damaging radicals. Product studies and laser-flash experiments reveal that the thiazolethione 3b leads primarily to the disulfide 5, from which through C-S bond breakage, the bithiazyl 6, the thiazole 7, and the isothiocyanate 8 are derived. Upon irradiation of pyridone 2b (300 nm) in aqueous media, a mixture of isopropoxyl and 2-hydroxyprop-2-yl radicals is formed, as confirmed by trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and EPR spectroscopy. In contrast, the photolysis of the thiazolethione 3b (350 nm) affords exclusively the DMPO adducts of the isopropoxyl radicals. Control experiments disclose that the thiazolethione-derived photoproduct disulfide 5, or the intermediary thiyl radicals B, scavenge the carbon-centered 2-hydroxyprop-2-yl radicals, which are generated from the isopropoxyl radicals by hydrogen shift. With supercoiled pBR 322 DNA in a 60:40 mixture of H(2)O-MeCN, the pyridone 2b and the thiazolethione 3b display moderate strand-break activity (17% open-circular DNA for 2b and 12% for 3b). In pure water, however, the pyridone 2b photoinduces substantially more DNA cleavage (32% open-circular DNA), which is attributed to the peroxyl radicals generated from the 2-hydroxyprop-2-yl radicals by oxygen trapping. The lower strand-break activity of the thiazolethione 3b derives presumably from isopropoxyl radicals, because only these are detected in the photolysis of this photo-Fenton reagent.     

A new high-temperature multinuclear-magnetic-resonance probe and the self-diffusion of light and heavy water in sub- and supercritical conditions

A high-resolution nuclear-magnetic-resonance probe (500 MHz for 1H) has been developed for multinuclear pulsed-field-gradient spin-echo diffusion measurements at high temperatures up to 400 degrees C. The convection effect on the self-diffusion measurement is minimized by achieving the homogeneous temperature distributions of +/-1 and +/-2 degrees C, respectively, at 250 and 400 degrees C. The high temperature homogeneity is attained by using the solid-state heating system composed of a ceramic (AlN) with high thermal conductivity comparable with that of metal aluminium. The self-diffusion coefficients D for light (1H2O) and heavy (2H2O) water are distinguishably measured at subcritical temperatures of 30-350 degrees C with intervals of 10-25 degrees C on the liquid-vapor coexisting curve and at a supercritical temperature of 400 degrees C as a function of water density between 0.071 and 0.251 gcm3. The D value obtained for 1H2O is 10%-20% smaller than those previously reported because of the absence of the convection effect. At 400 degrees C, the D value for 1H2O is increased by a factor of 3.7 as the water density is reduced from 0.251 to 0.071 gcm3. The isotope ratio D(1H2O)D(2H2O) decreases from 1.23 to approximately 1.0 as the temperature increases from 30 to 400 degrees C. The linear hydrodynamic relationship between the self-diffusion coefficient divided by the temperature and the inverse viscosity does not hold. The effective hydrodynamic radius of water is not constant but increases with the temperature elevation in subcritical water.     

Atomic layer deposition of tungsten(III) oxide thin films from W2(NMe2)6 and water: precursor-based control of oxidation state in the thin film material

The atomic layer deposition of W2O3 films was demonstrated employing W2(NMe2)6 and water as precursors with substrate temperatures between 140 and 240 degrees C. At 180 degrees C, surface saturative growth was achieved with W2(NMe2)6 vapor pulse lengths of >/=2 s. The growth rate was about 1.4 A/cycle at substrate temperatures between 140 and 200 degrees C. Growth rates of 1.60 and 2.10 A/cycle were observed at 220 and 240 degrees C, respectively. In a series of films deposited at 180 degrees C, the film thicknesses varied linearly with the number of deposition cycles. Time-of-flight elastic recoil analyses demonstrated stoichiometric W2O3 films, with carbon, hydrogen, and nitrogen levels between 6.3 and 8.6, 11.9 and 14.2, and 4.6 and 5.0 at. %, respectively, at substrate temperatures of 160, 180, and 200 degrees C. The as-deposited films were amorphous. Atomic force microscopy showed root-mean-square surface roughnesses of 0.7 and 0.9 nm for films deposited at 180 and 200 degrees C, respectively. The resistivity of a film grown at 180 degrees C was 8500 microhm cm.     

Collisions of slow polyatomic ions with surfaces: dissociation and chemical reactions of C2H2+*, C2H3+, C2H4+*, C2H5+, and their deuterated variants C2D2+* and C2D4+* on room-temperature and heated carbon surfaces

Interaction of C2Hn+ (n = 2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 degrees C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11-46 eV and an incident angle of 60 degrees with respect to the surface normal. The work is an extension of our earlier research on surface interactions of CHn+ (n = 3-5) ions. Mass spectra, translational energy distributions, and angular distributions of product ions were measured. Collisions with the HOPG surface heated to 600 degrees C showed only partial or substantial dissociation of the projectile ions; translational energy distributions of the product ions peaked at about 50% of the incident energy. Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and, in the case of radical cation projectiles C2H2+* and C2H4+*, chemical reactions with the hydrocarbons on the surface. These reactions were (i) H-atom transfer to the projectile, formation of protonated projectiles, and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C3H3+. The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy. Angular distributions of reaction products showed peaking at subspecular angles close to 68 degrees (heated surfaces) and 72 degrees (room-temperature surfaces). The absolute survival probability at the incident angle of 60 degrees was about 0.1% for C2H2+*, close to 1% for C2H4+* and C2H5+, and about 3-6% for C2H3+.     

Photoreactions of quinine in aqueous citric acid solution. part 2, some end-products

A novel spiro-compound derived from 2',4'-b1s-(1,3-dicarboxy-2-hydroxyprop-2-y1) -1',4'-dihydroquinine has been identified as a major end-product of the irradiation of quinine in aqueous citric acid solution. 7'-(1,3-Dicarboxy-2-hydroxyprop-2-yl)deoxyquinine and products arising from the cleavage of quinine at C-9 were also detected in the reaction mixture.     

Absorption in the visible region of YSZ implanted with Ag ions

Ag ions were implanted into YSZ (yttrium-stabilized (cubic) zirconia) single crystals in two different energy regimes: kiloelectron volt and megaelectron volt. Optical absorption spectra were measured in the visible region at each stage in the annealing process of the sample. Depth profiles of Ag for the samples implanted at the energy of 20 keV were measured by X-ray photoelectron spectroscopy (XPS). For the samples implanted with Ag at the low energy of 20 keV, one large absorption peak appeared in the wavelength ranging from 470 to 536 nm, depending on the dose of Ag ions. As the sample was heated to 1000 degrees C, the intensity of the absorption peak decreased gradually, but a small, broad peak remains even at the temperature of 1000 degrees C. For the samples implanted with 2.8x10(16) Ag ion cm(-2) at the high energy of 3 MeV, one broad absorption peak was observed at around 470 nm. As the sample was heated sequentially to high temperatures, the peak gradually decreased and almost disappeared at 400 degrees C. When the sample was further heated to even higher temperatures, the absorption peak at 514 nm reappeared at 1000 degrees C and grew with heating time.     

Thermal ring contraction of dibenz[b,f]azepin-5-yl radicals: new routes to pyrrolo[3,2,1-jk]carbazoles

Flash vacuum pyrolysis (FVP) of N-allyl- or N-benzyldibenz[b,f]azepine at temperatures from 750 to 950 degrees C gives pyrrolo[3,2,1-jk]carbazole as the major product. The mechanism of the ring contraction involves dibenzazepin-1-yl radical formation, followed by transannular attack and formation of a 2-(indol-1-yl)phenyl radical which cyclizes. The mechanism is supported by independent generation of 2-(indol-1-yl)phenyl radicals by two different methods, and the use of 1-(2-nitrophenyl)indole as a radical generator gives an optimized synthetic route to pyrrolo[3,2,1-jk]carbazole (54% overall yield in two steps from indole). The first substituted pyrrolo[3,2,1-jk]carbazoles have been synthesized by FVP methods and also by reactions of the parent compound with electrophiles, leading to a range of 4-substituted pyrrolocarbazoles.     

Doping gamma-Fe(2)O(3) nanoparticles with Mn(III) suppresses the transition to the alpha-Fe(2)O(3) structure

Here we report on a mixed oxide system, gamma-Fe2O3 nanoparticles doped with Mn(III), where the transition from the cubic to the more stable hexagonal alpha-Fe2O3 structure is suppressed. When amorphous Fe2O3 is heated at 300 degrees C for 3 h, ferrimagnetic gamma-Fe2O3 is observed as the sole product. On the other hand, when the temperature is raised to 500 degrees C, one observes only antiferromagnetic alpha-Fe2O3 as the product. However, upon doping with 8.5 wt % Mn(III), the amorphous nanoparticles crystallized to mainly the gamma-Fe2O3 matrix after heating at 500 degrees C for 3 h, and need to be heated to >650 degrees C for the complete transition to the alpha-Fe2O3 structure to take place.     

Structure of Reaction Products of 1,3,4,6-Tetracarbonyl Compounds with o-Aminothiophenol. Synthesis of 3-aryl-1-(1,3-benzothiazol-2-yl)-3-hydroxyprop-2-en-1-ones

Russian Journal of Organic Chemistry - 1,6-Diarylhexane-1,3,4,6-tetraones react with o-aminothiophenol forming 3-aryl-1-(1,3-benzothiazol-2-yl)-3-hydroxyprop-2-en-1-ones.     

Microwave-assisted combined Mitsunobu reaction-Claisen rearrangement and microwave-assisted phenol oxidation: rapid synthesis of 2,6-disubstituted-1,4-benzoquinone natural products

Microwave irradiation of a phenol, an allylic alcohol, di-isopropyl azodicarboxylate and triphenylphosphine at 220-240 °C for 30 min results in a combined Mitsunobu reaction and Claisen rearrangement to give the rearranged 2-allylphenol. Following the first detailed study of microwave-assisted phenol oxidation, rapid syntheses of the natural products primin and 2-methoxy-6-pentadecyl-1,4-benzoquinone (four reaction steps, total reaction time 1 h) were achieved using this combined Mitsunobu-Claisen strategy in combination with two further microwave-assisted steps (alkene hydrogenation and phenol oxidation).     

Synthesis and thermal decomposition of haloalkoxy-sym-triazines

Reaction of [2-methylthio-6-dialkylamino-sym-triazin-4-yl]trimethylammonium chlorides with ethylene chlorohydrin gave 2-methylthio-4-(2-chloroethoxy)-6-dialkylamino-sym-triazines, which are converted to 2-methylthio-3-(2-chloroethyl)-4-oxo-6-dialkylamino-3,4-dihydro-symtriazines when they are heated to 115–120°C and to the corresponding tetrahydrothiazolo-symtriazine derivatives when they are heated at 180–190°C.See [1] for communication II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1420–1423, October, 1977.     

Simultaneous determination of manganese and selenium in serum by electrothermal atomic absorption spectrometry

A method for determination of manganese and selenium in serum by simultaneous atomic absorption spectrometry (SIMAAS) is proposed. The samples (30 mul) were diluted (1+3) to 1.0% v/v HNO(3)+0.10% w/v Triton X-100 directly in the autosampler cups. A total of 20 mug Pd+10 mug Mg(NO(3))(2) was used as chemical modifier. The pyrolysis and atomization temperatures for the simultaneous heating program were 1200 and 2300 degrees C, respectively. The addition of an oxidant mixture (15% w/w H(2)O(2)+1.0% v/v HNO(3)) and the inclusion of a low temperature pyrolysis step (400 degrees C) attenuated the build-up of carbonaceous residues onto the integrated platform. An aliquot of 15 mul of the reference or sample solution was introduced into the graphite tube and heated at 80 degrees C; subsequently, 10 mul of oxidant mixture+10 mul of chemical modifier was introduced over that aliquot and the remaining heating program steps were executed. This strategy allowed at least 250 heating cycles for each THGA tube without analytical signal deterioration. The characteristic masses for manganese (6 pg) and selenium (46 pg) were estimated from the analytical curves. The detection limits were 6.5 pg (n=20, 3delta) for manganese and 50 pg (n=20, 3delta) for selenium. The reliability of the entire procedure was checked with the analysis of serum from Seronormtrade mark Trace Elements in Serum (Sero AS) and by addition and recovery tests (97+/-9% for manganese and 96+/-7% for selenium) using five serum samples.     

Dibenzo[b,h][1,4,7]thiadiazonines: examples of a novel ring system

Acetanilides 1a-e react with 1,1'-sulfinylbis(benzotriazole)/trimethylchlorosilane at 45-65 degrees C to form 1,2-di(benzotriazol-1-yl)-2-arylimino-1-ethanethiones 3a-e, while heating the same reagents at 110 degrees C results in dibenzo[b,h][1,4,7]thiadiazonines 5a,c,d, and 6. X-ray crystal structures are reported for three representative examples.     

A vibrational spectroscopic study of structure evolution of water dissolved in supercritical carbon dioxide under isobaric heating

A combination of Raman scattering spectroscopy and infrared absorption was applied to investigate the structural evolution of water dissolved in supercritical carbon dioxide under isobaric heating (T=40-340 degrees C, P=250 bar). Quantitative analysis of experimental spectra allowed us to determine that at relatively moderate temperatures water dissolved in CO(2)-rich phase exists only under monomeric form (solitary water surrounding by CO(2) molecules), but hydrogen-bonded species, namely, dimers, begin to appear upon heating. At the same time, the ratio of dimers to monomers concentration increases with further temperature increase and at temperatures close to the temperature of total miscibility of the mixture (T=366 degrees C, P=250 bar), water dimers only are present in the CO(2)-rich phase.