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1.
A. Pizzi 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):739-764
The kinetic behavior of copper–chromium–arsenic (CCA) wood preservatives in their reaction with wood, lignin, cellulose, and their respective simple model compounds, guaiacol and D(+)-glucose, has been elucidated. Copper chromatesVI/lignin guaiacyl units and chromiumIII arsenates/lignin guaiacyl units, which are stable and insoluble complexes formed during the reaction, have been characterized. No copper arsenates were formed during the reactions (which were carried out using a CCA of type C). The sequence, nature, and combined effect of the reactions of CCA with wood, lignin, and cellulose are similar to that already described for the “CrO3 alone,”1 Cu/Cr2, and Cr/As3 systems. Rate constants, energies of activation, and Arrhenius equations have been obtained and reported. The distribution of CrVI, CrIII, Asv, and Cu2+ in CCA-C-treated wood has been calculated. The results obtained have allowed meaningful comparisons of several commercial CCA formulations. 相似文献
2.
The chemistry and kinetic behavior of Cu-Cr-As/B wood preservatives. I. Fixation of chromium on wood
A. Pizzi 《Journal of polymer science. Part A, Polymer chemistry》1981,19(12):3093-3121
The kinetic behavior of CrO3 in its reaction with wood has been elucidated. Various reactions take place between CrO3 and the lignin and cellulose in wood. CrO3 reacts with cellulose in a two-step reaction: the first step is an adsorption of CrVI onto the cellulose to form CrVI/cellulose activated complexes. The second step is a CrVI → CrIII reduction taking place on the cellulose surface. The CrIII formed is only physically adsorbed to the cellulose or very weakly bound as small amounts of CrIII can be released into the reaction medium. The CrVI adsorbed by cellulose appears mainly to be reduced to CrIII. The reaction of CrVI with lignin has been shown to be the composition of the three successive reaction of Cr2O72?, HCrO4?, and CrO42? with the guaiacyl units of lignin. Insoluble and stable CrVI/lignin complexes in which chromium maintains its hexavalent oxidation state are formed. Rate constants and energies of activation for all the reactions have been determined. The fixation of CrO3-derived compounds on wood has been explained as the combination of the various reactions investigated. The results indicate that 60% of Cr is fixed irreversibly to the lignin of wood as CrVI and 40% is weakly bound, probably just precipitated, on the cellulose surface as CrIII of which small amounts can be released in a water medium. The complex CrVI and CrIII species forming complexes with the guaiacyl units have been identified. 相似文献
3.
A. Pizzi 《Journal of polymer science. Part A, Polymer chemistry》1982,20(3):725-738
The kinetic behavior of a Cr/As system in its reaction with wood is described, as are its reactions with lignin and carbohydrates of wood for CrVI alone. ChromiumIII arsenate complexes with the guaiacyl units of lignin, as well as the usual chromic acid/guaiacyl unit complexes already characterized, was formed. The interference of As concentration on the various zones of fixation of chromium are identified. Complexes between guaiacol and chromium arsenates indicate that in this Cr/As system CrIII can also be linked to the guaiacyl units of lignin when in the form of CrAsO4·6H2O contrary to what obtained with systems not containing As. An initial increase in the rate of reduction CrVI → CrIII by the carbohydrates fraction in wood is ascribed to the catalytic effect of the arsenic. The percentages of chromium fixed onto lignin and cellulose of wood compare well with experimental values. 相似文献
4.
Dalma Gyepesov Vratislav Langer 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(2):111-113
The structure analysis of so‐called 9CaO·4CrO3·Cr2O3 proved it to be the title compound, decacalcium hexakis[chromate(V)] chromate(VI), with the simultaneous presence of unusual chromium oxidation states. The structure determination was carried out on a crystal that had inversion twinning. The CrVIO4 tetrahedron is situated on a threefold axis and is disordered over two possible orientations that share three O atoms, while the CrVO4 tetrahedra are in general positions and are ordered. The charge is balanced by Ca2+ cations, one of which is located on a threefold axis. The Ca2+ ions are coordinated by six, seven or eight O atoms. The compound is a significant phase in the CaO–CrOx system and its formation reduces the refractoriness of calcium‐rich compositions in an oxidizing atmosphere. 相似文献
5.
CrOx/SiO2催化剂上丙烷在CO2气氛中脱氢反应的研究 总被引:2,自引:0,他引:2
采用XRD、UV-vis DRS、ESR和微分吸附量热等技术,考察了铬担载量分别为2.5、5和10wt%的CrOx/SiO2催化剂的结构、表面性质和氧化还原性能。结果表明,催化剂表面上存在多种Cr的氧化态和聚集形式。随着Cr担载量从2.5wt%到10wt%的逐渐增大,催化剂表面占主导地位的Cr物种由CrO3单体转为多聚CrO3和Cr2O3晶相。在CO2气氛中催化剂对丙烷转化率和丙烯选择性的大小顺序为2.5wt%CrOx/SiO2>5wt%CrOx/SiO2>10wt%CrOx/SiO2,反应过程中的原位ESR和UV-visDRS测定结果表明,催化剂表面的反应活性中心为Cr5+,Cr5+可由催化剂预处理过程中Cr3+的氧化及丙烷反应过程中CrO3单体的还原产生,在反应中CO2可使Cr3+重新氧化为Cr5+. 相似文献
6.
Investigation of the chemical modifications of beech wood lignin during heat treatment 总被引:3,自引:0,他引:3
Nicolas Brosse Roland El Hage Mounir Chaouch Mathieu Pétrissans Stéphane Dumarçay Philippe Gérardin 《Polymer Degradation and Stability》2010,95(9):1721-1528
Holocellulose, Klason lignin and milled wood lignin (MWL) of beech wood were extracted before and after heat treatment and analysed using CP MAS 13C NMR, 13C NMR, 31P NMR and size exclusion chromatography (SEC). Experimental results showed that the thermal treatment degrades hemicelluloses and affects lignin polymer through depolymerisation due mainly to cleavage of β-aryl-ether linkages and recondensation reactions. The spectroscopic analysis of MWL demonstrated that these recondensation reactions involved mainly guaiacyl units through formation of 5,5′-biphenolic and diarylmethane structures.Analysis of molecular weight distribution of MWL by SEC indicated that average molecular weights of heat treated milled wood lignin were lower than those of native milled wood lignin. 相似文献
7.
《Helvetica chimica acta》1969,52(1):291-300
Dilute solutions ( < 1· 10?4M ) of CrO4K2 in concentrated sulfuric acid, were investigated spectrophotometrically. Spectral, kinetic and equilibrium studies confirm the instability of CrVI species and their conversion to CrV complexes, as proposed by MISHRA & SYMONS . Reaction mechanisms are proposed. 相似文献
8.
Summary The kinetics of oxidation of l-ascorbic acid (H2A) by CrVI with and without added CuII conforms to the stoichiometry represented by the equation: 2CrVI + 3H2A 2CrIII + 3A + 6H+ where A is dehydroascorbic acid. The mode of the electron transfer from H2A to CrVI is suggested to involve oxidative decomposition of an intermediate complex. Catalysis by CuII is indicated via complexation of the catalyst and substrate. The inhibitory effects of Cl–, NO
f3
p–
and SO
f4
p2–
ions indirectly support complexation between CrVI and H2A. 相似文献
9.
The electrochemical behavior of chromate and dichromate, ions in molten NaNO3-KNO3 at 250°C has been studied by single-sweep voltammetry and cyclic voltammetry. The anodic dimerization of CrO42- ions has been shown to proceed in three steps, the reaction: CrO42-→CrO4ad?+e? being rate-determining. The cathodic reduction of Cr2O72- ions includes the coupled acid-base reactions; it forms solid chromium oxide Cr2O3 and the soluble chromate and chromite ions. 相似文献
10.
Removal of chromate from aqueous solution by reduction with nanoscale Fe–Al layered double hydroxide
Leila Alidokht Shahin Oustan Alireza Khataee Mohammadreza Neyshabouri Adel Reyhanitabar 《Research on Chemical Intermediates》2018,44(4):2319-2331
Nanoscale layered double hydroxides of FeII and AlIII (Fe–Al LDH) have been applied for removal of chromate (CrVI) from aqueous solution. Given the reaction stoichiometry, CrVI was completely reduced to CrIII and coprecipitated with FeIII and AlIII oxyhydroxides. The extent of CrVI removal decreased with increasing initial pH and decreasing molar ratio of CrVI/structural FeII in the LDH. The chromate reduction rate at different initial concentrations of CrVI was well described by the pseudo-second-order model with reaction rate constant ranging from 197.4 to 13.53 (mmol min)?1. Initial pH and substitution of various amounts of FeIII in the LDH structure had little effect on the reaction rate. Backtransformation of CrIII to CrVI by birnessite Mn oxide (δ-MnO2) after 40 days of reaction was less than 1% of the initial Cr (as CrIII solid), indicating high stability of the final reaction products and high efficiency of nanoscale Fe–Al LDHs for removal of chromate from aqueous solution. 相似文献
11.
N. E. Fouad 《Journal of Thermal Analysis and Calorimetry》2000,60(2):541-547
The thermal behaviour of CrO3 on heating up to 600°C in dynamic atmospheres of air, N2 and H2 was examined by thermogravimetry (TG), differential thermal analysis (DTA), IR spectroscopy and diffuse reflectance spectroscopy
(DRS). The results revealed three major thermal events, depending to different extents on the surrounding atmosphere: (i)
melting of CrO3 near 215°C (independent of the atmosphere), (ii) decomposition into Cr2(CrO4)3 at 340–360°C (insignificantly dependent), and (iii) decomposition of the chromate into Cr2O3 at 415–490°C (significantly dependent). The decomposition CrO3 → Cr2(CrO4)3 is largely thermal and involves exothermic deoxygenation and polymerization reactions, whereas the decomposition Cr2(CrO4)3 → Cr2O3 involves endothermic reductive deoxygenation reactions in air (or N2) which are greatly accelerated and rendered exothermic in the presence of H2. TG measurements as a function of heating rate (2–50°C min−1) demonstrated the acceleratory role of H2, which extended to the formation of Cr(II) species. This could sustain a mechanism whereby H2 molecules are considered to chemisorb dissociatively, and then spillover to induce the reduction. DTA measurements as a function
of the heating rate (2–50°C min−1) helped in the derivation of non-isothermal kinetic parameters strongly supportive of the mechanism envisaged.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
12.
The detection ot As+5, BO3-3. Cu+2, Cr+3, Cr+6, Zn+2, and F- in treated wood with Pyrocatechol Violet is described.Es wird eine Method vorgeschlagen zum Nachweis von As+5, BO3-3, Cu+2, Cr+3, Cr+3, Zn+2 and F- in imprägniertem Holz unter Verwendung von Pyrocatechol Violet. 相似文献
13.
T. P. Maniecki P. Mierczyński W. Maniukiewicz W. K. Jóźwiak 《Kinetics and Catalysis》2011,52(6):835-842
The influence of addition of silver and copper on the reduction behavior of binary oxide CrAl3O6 was investigated. The formation of copper chromite CuCr2O4 and silver chromate Ag2CrO4 during calcinations process was observed. The intermediate phase CrO was detected when copper and silver-copper systems were
reduced at temperatures above 500°C. This intermediate is formed from Cr2O3, which is yielded by the initial reduction of Cr2O42− species. 相似文献
14.
Tarafder M. Tofazzal H. Ali Manaf A. Wee D. Juan Azahari Kasbollah Silong Sidik Crouse Karen A. 《Transition Metal Chemistry》2000,25(4):456-460
Several new complexes of a tridentate ONS Schiff base derived from the condensation of S-benzyldithiocarbazate with salicylaldehyde have been characterised by elemental analyses, molar conductivity measurements
and by i.r. and electronic spectra. The Schiff base (HONSH) behaves as a dinegatively charged ligand coordinating through
the thiolo sulphur, the azomethine nitrogen and the hydroxyl oxygen. It forms mono-ligand complexes: [M(ONS)X], [M=NiII, CuII, CrIII, SbIII, ZnII, ZrIV or UVI with X = H2O, Cl]. The ligand produced a bis-chelated complex of composition [Th(ONS)2] with ThIV. Square-planar structures are proposed for the NiII and CuII complexes. Antimicrobial tests indicate that the Schiff base and five of the metal complexes of CuII, NiII, UVI, ZnII and SbIII are strongly active against bacteria. NiII and SbIII complexes were the most effective against Pseudomonas aeruginosa (gram negative), while the CuII complex proved to be best against Bacillus cereus (gram positive bacteria). Antifungal activities were also noted with the Schiff base and the UVI complex. These compounds showed positive results against Candida albicans fungi, however, none of them were effective against Aspergillus ochraceous fungi. The Schiff base and its zinc and antimony complexes are strongly active against leukemic cells (CD50 = 2.3–4.3 μg cm−3) while the copper, uranium and thorium complexes are moderately active (CD50 = 6.9–9.5 μg cm−3). The nickel, zirconium and chromium complexes were found to be inactive.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
15.
A. Dominic Fortes Ian G. Wood Matthias J. Gutmann 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(4):324-329
Hexaaquamagnesium(II) sulfate pentahydrate, [Mg(H2O)6]SO4·5H2O, and hexaaquamagnesium(II) chromate(II) pentahydrate, [Mg(H2O)6][CrO4]·5H2O, are isomorphous, being composed of hexaaquamagnesium(II) octahedra, [Mg(H2O)6]2+, and sulfate (chromate) tetrahedral oxyanions, SO42− (CrO42−), linked by hydrogen bonds. There are two symmetry‐inequivalent centrosymmetric octahedra: M1 at (0, 0, 0) donates hydrogen bonds directly to the tetrahedral oxyanion, T1, at (0.405, 0.320, 0.201), whereas the M2 octahedron at (0, 0, ) is linked to the oxyanion via five interstitial water molecules. Substitution of CrVI for SVI leads to a substantial expansion of T1, since the Cr—O bond is approximately 12% longer than the S—O bond. This expansion is propagated through the hydrogen‐bonded framework to produce a 3.3% increase in unit‐cell volume; the greatest part of this chemically induced strain is manifested along the b* direction. The hydrogen bonds in the chromate compound mitigate ∼20% of the expected strain due to the larger oxyanion, becoming shorter (i.e. stronger) and more linear than in the sulfate analogue. The bifurcated hydrogen bond donated by one of the interstitial water molecules is significantly more symmetrical in the chromate analogue. 相似文献
16.
On the Chemical Transport of Cr2O3 with Cl2 and with HgCl2 — Experiments and Model Calculations The migration of Cr2O3 in a temperature gradient (1 000°C → 900°C) in the presence of low concentrations of chlorine and water (from the wall of silica ampoules) is a result from the endothermic reactions (1) Cr2O3,s + H2Og + 3 Cl2,g = 2 CrO2Cl2,g + 2 HClg (2) Cr2O3,s + 1/2 O2,g + 2 Cl2,g = 2 CrO2Cl2,g With higher concentrations of chlorine, the transport reaction is (3) Cr2O3,s + 5/2 Cl2,g = 3/2 CrO2Cl2,g + 1/2 CrCl4,g The gas phase of the transport system Cr2O3/Cl2 can be reduced step by step by adding small amounts of chromium, so that CrCl3 and finally also CrCl2 become more important. Further, at a lower ratio n°(Cl)/n°(Cr) three transport reactions have to be taken into consideration; with the participation of CrOCl2,g (5). (4) Cr2O3,s + 9/2 CrCl4,g = 3/2 CrO2Cl2,g + 5 CrCl3,g (5) Cr2O3,s + 3 CrCl4,g = 3 CrOCl2,g + 2 CrCl3,g (6) Cr2O3,s + H2,g + 4 HClg = 2 CrCl2,g + 3 H2Og The reactions (1), (2) and (6) become possible through the cooperation of two transport agents at a time. The migration of Cr2O3 with HgCl2 can also be described with reactions (1) – (3). The decomposition of HgCl2 Produces the small chlorine pressure for the transport reaction. The oxidation potential of the transport agent HgCl2 is too low for the oxidation of CrIII to CrVI. 相似文献
17.
María Inés Frascaroli Juan Manuel Salas-Peregrin Luis F. Sala Sandra Signorella 《Polyhedron》2009,28(6):1049-1056
The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by CrVI in acid medium yields CrIII, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over CrVI is used. The redox reaction takes place through the combination of CrVI → CrIV → CrII and CrVI → CrIV → CrIII pathways. Intermediacy of free radicals and CrII in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO22+ formed by reaction of CrII with O2. Intermediate oxo-CrV–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO4, intermediate CrV rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate CrV bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with CrVI distinguishes this derivative from glucose, which is oxidized to gluconic acid. 相似文献
18.
B.L. Chamberland M.P. Herrero-Fernandez T.A. Hewston 《Journal of solid state chemistry》1985,59(1):111-115
The preparation of the compounds Sr2CrO4, Ba2CrO4, and Ba3CrO5 is described. The characterization of these three Cr4+ compounds by X-ray and magnetic susceptibility experiments has been conducted. The magnetic moments for Sr2CrO4, Ba2CrO4, and Ba3CrO5 were determined to be in good agreement with the calculated value expected for a tetrahedral Cr4+ ion. Weak antiferromagnetic ordering for all three compounds is indicated from the small paramagnetic Weiss constants determined from the susceptibility data in the temperature region 80–300 K. Distortions of the tetrahedra from ideality, as determined from the structural features, further cause a reduction in the magnetic moments from the theoretical values. 相似文献
19.
The reaction of CrO2Cl2 with 2, 2′‐bipyridyl or 1, 10‐phenanthroline (diimine) in CCl4 or anhydrous CH3CO2H solution, produces orange‐brown diamagnetic [CrO2Cl2(diimine)]. The X‐ray structure of [CrO2Cl2(2, 2′‐bipy)] shows a six‐coordinate central chromium(VI) atom with cis‐dioxo groups trans to the diimine. In contrast, the diimines react with CrO3 in CH3CO2H / conc. aqueous HCl to form bright red paramagnetic CrV complexes, [CrOCl3(diimine)]. The X‐ray structure of [CrOCl3(2, 2′‐bipy)] shows a six‐coordinate central chromium atom with mer‐chlorines and the diimine trans to O/Cl. The addition of [2, 2‐bipyH2]Cl2 to a solution of CrO3 in CH3CO2H saturated with HCl gas, produces the CrV anion [2, 2′‐bipyH2][CrOCl4]Cl, which loses HCl on heating in vacuo to form [CrOCl3(2, 2′‐bipy)]. IR, UV/Vis, and 1H NMR spectra (CrVI only) are reported for the new complexes. Attempts to extend these routes to oxygen donor ligands, including ethers and phosphine oxides, were unsuccessful. The diimine complexes are the first structurally autheticated adducts of chromium(VI) and (V) oxide‐chlorides with neutral ligands. 相似文献
20.
Juan C. Gonzlez Silvia I. García Sebastin Bellú Ana María Atria Juan Manuel Salas Pelegrín Antal Rockenbauer Lazlo Korecz Sandra Signorella Luis F. Sala 《Polyhedron》2009,28(13):2719-2729
Selective oxidation of galacturonic residues of oligo and polyuronic acids by CrVI affords CO2/HCO2H, oxidized uronic acid, and CrIII as final redox products. Kinetic studies show that the redox reaction proceeds through a mechanism combining CrVI → CrIV → CrII and CrVI → CrIV → CrIII pathways. The mechanism is supported by the observation of free radicals, CrO22+ and CrV as reaction intermediates. The EPR spectra show that five- and six coordinated oxo-CrV intermediates are formed. Penta-coordinated oxo-CrV species are present at any [H+], whereas hexa-coordinated ones are only observed at pH <1. At low pH CrV predominating species are coordinated by carboxylate groups and Oring (giso = 1.9783/5). At pH 7.5, the predominating ones are those coordinated by alcoholate groups of the ligand (giso = 1.9800). Polygal can reduce CrVI and efficiently trap CrIII. This behaviour represents an interesting model for the study of biomaterials, which possess a high proportion of polygal, in order to remove chromium from polluted waters. 相似文献