Oxidation Of CH3CN Research Articles

Experimental and kinetic modeling study of oxidation of acetonitrile

Oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. The experiments were conducted at atmospheric pressure in the temperature range 1150–1450 K, varying the excess air ratio from slightly fuel-lean to very lean. Oxidation of CH3CN was slow below 1300 K. Nitric oxide, hydrogen cyanide and nitrous oxide were detected as important products. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. The rate coefficients for the reactions of CH3CN and CH2CN with O2 were calculated from ab initio theory. Modeling predictions were in satisfactory agreement with experiments. Calculations were sensitive to thermal dissociation of CH3CN and to the branching fraction for CH3CN + OH to CH2CN + H2O and HOCN + CH3, respectively. More work is desirable for these steps, as well as for reactions of CH2CN and HCCN.

On the appearance of nitrite anion in [PdX(OAc)L2] and [Pd(X)(C^N)L] syntheses (X = OAc or NO2): photocrystallographic identification of metastable Pd(η1-ONO)(C^N)PPh3

Pd3(OAc)5NO2, an impurity in “Pd(OAc)2” {formally Pd3(OAc)6}, emerges as a serious issue in the synthesis of pure PdII complexes derived from Pd(OAc)2, for example in our C–H activation precatalyst, Pd(OAc)2(pip)2 (pip = piperidine). A previous proposal that nitrite anion can be formed by oxidation of CH3CN by metallic Pd and air, leading to cyclo(ortho)palladated complexes containing nitrite anion, e.g. Pd(NO2)(C^N)L (C^N = papaverine; L = CH3CN or DMSO) can be explained by Pd3(OAc)5NO2 acting as the nitrite source. Finally, photocrystallographic metastable linkage isomerisation and complete conversion to an oxygen-bound nitrito complex Pd(η1-ONO)(C^N)PPh3 has been observed.

Influence of Alkali Metal Cation (Li(I), Na(I), K(I)) on the Construction of Chiral and Achiral Heterometallic Coordination Polymers

A series of chiral and achiral lanthanide-alkali coordination polymers, [LnM(INA)3(OAc)] where [M = Li, Ln = Eu (1); M = Li, Ln = Tb (2); M = Na, Ln = Eu (3); M = Na, Ln = Tb (4); INA = isonicotinate; OAc = acetate] and [TbK(INA)2(OAc)2] (5), have been solvothermally synthesized and structurally characterized. The acetate groups were in situ obtained from oxidation of CH3CN during the reaction. Structures with remarkably different connectivities are formed when Li(I), Na(I), and K(I) were introduced into the system. Compounds 1–4 are isostructural three-dimensional (3D) coordination polymers and built up by right-/left-handed Ln-O-M chiral helicals and INA linkers possessing a 3,3,4,7T2 topology. Compound 5 is a 3D pillared coordination polymer constructed from two-dimensional (2D) Tb–O–K layers with INA as connectivities possessing an alb-4,8-P21/c topology. Circular dichroism (CD) measurements confirmed that the resulting crystals of 1, 3, and 4 were racemic mixtures. The photoluminescent properties of ...

Variable Scan Rate Cyclic Voltammetry and Theoretical Studies on Tocopherol (Vitamin E) Model Compounds

Variable scan rate (0.1-500 V s(-1)) cyclic voltammetry experiments were performed on a series of model tocopherol (vitamin E) compounds with differing degrees of methyl substitution around the aromatic (phenolic) ring. alpha-Tocopherol, with a fully methylated aromatic ring, produced stable phenoxonium cations upon oxidation in CH3CN, and was modeled via an ECE mechanism (where "E" represents an electron transfer and "C" a chemical step). Compounds with less methyl substitution around the aromatic ring were more reactive following oxidation, and formed additional oxidation products (hemiketals and p-quinones), and were modeled according to a more complicated ECECC mechanism. The equilibrium and rate constants associated with the chemical steps were estimated by digital simulations of the variable scan rate data over a range of temperatures ( T = 253-313 K) in acetonitrile containing 0.5 M Bu4NPF6 as the supporting electrolyte. The relative lifetimes of the phenoxonium cations of tocol and the tocopherols were compared with theoretical results obtained from molecular orbital calculations.

Titanium dioxide photosensitised oxidation of α,β-dihydroxybenzyl derivatives in CH 3CN

The TiO 2-photosensitised oxidation in CH 3CN of a series of 1-(X-phenyl)-1,2-ethanediols ( 1) and of 2-(X-phenyl)-1,2-propanediols ( 2) gives the corresponding benzaldehyde and acetophenone, respectively, accompanied by formaldehyde, whereas a series of symmetrically X-ring-substituted 1,2-diphenyl-1,2-ethanediols ( 3) yields the corresponding benzaldehyde (substrate/product molar ratio = 0.5). The adsorption constant values (2400–3900 M −1) are significantly higher than those of benzylic alcohols and can be explained by assuming that the TiO 2 surface adsorption occurs through both OH groups (chelation effect). The relative rates, determined for each series from competitive kinetic experiments, remained nearly constant when the oxidation potential increased, instead of decreasing as observed in homogeneous phase. This behaviour has been attributed to the preferential adsorption of the OH groups, that increases their oxidizability until they favourably compete, as regards electron abstraction, with the aromatic site. The reaction rate thereby becomes much less sensitive to the ring substituent effect. Based on the comparison of true quantum yield values (obtained in the photo-oxidation in the presence of colloidal TiO 2) of ring unsubstituted 1 and 2, the deprotonation pathway of the cation radical was excluded. Analogous to what happens with 2-aminoalcohol radical cations, the most probable path is a heterolytic, concerted and base-catalysed (by basic sites at the TiO 2 surface) C α–C β fragmentation that produces a radical and a final product (carbonyl compound).

Synthesis, Structure, and Properties of Low-Spin Manganese(III)−Poly(pyrazolyl)borate Complexes

The manganese(III)-bis[poly(pyrazolyl)borate] complexes, Mn(pzb)2SbF6, where pzb- = tetrakis(pyrazolyl)borate (pzTp) (1), hydrotris(pyrazolyl)borate (Tp) (2), or hydrotris(3,5-dimethylpyrazolyl)borate (Tp*) (3), have been synthesized by oxidation of the corresponding Mn(pzb)2 compounds with NOSbF6. The Mn(III) complexes are low-spin in solution and the solid state (microeff = 2.9-3.8 microB). X-ray crystallography confirms their uncommon low-spin character. The close conformity of mean Mn-N distances of 1.974(4), 1.984(5), and 1.996(4) A in 1, 2, and 3, respectively, indicates absence of the characteristic Jahn-Teller distortion of a high-spin d4 center. N-Mn-N bite angles of slightly less than 90 degrees within the facially coordinated pzb- ligands produce a small trigonal distortion and effective D3d symmetry in 1 and 2. These angles increase to 90.0(4)degrees in 3, yielding an almost perfectly octahedral disposition of N donors in Mn(Tp*)2+. Examination of structural data from 23 metal-bis(pzb) complexes reveals systematic changes within the metal-(pyrazolyl)borate framework as the ligand is changed from pzTp to Tp to Tp*. These deformations consist of significant increases in M-N-N, N-B-N, and N-N-B angles and a minimal increase in Mn-N distance as a consequence of the steric demands of the 3-methyl groups. Less effective overlap of pyrazole lone pairs with metal atom orbitals resulting from the M-N-N angular displacement is suggested to contribute to the lower ligand field strength of Tp* complexes. Mn(pzb)2+ complexes undergo electrochemical reduction and oxidation in CH3CN. The electrochemical rate constant (ks,h) for reduction of t2g4 Mn(pzb)2+ to t2g3eg2 Mn(pzb)2 (a coupled electron-transfer and spin-crossover reaction) is 1-2 orders of magnitude smaller than that for oxidation of t2g4 Mn(pzb)2+ to t2g3 Mn(pzb)22+. ks,h values decrease as Tp* > pzTp > Tp for the Mn(pzb)2+/0 electrode reactions, which contrasts with the behavior of the comparable Fe(pzb)2+/0 and Co(pzb)2+/0 couples.

Infrared Spectroscopic Study of Acetonitrile on SnO2-Based Thick Film and its Characteristics as a Gas Sensor

The SnO2/Al2O3/Pd and SnO2/Al2O3/Nb2O5/SiO2 thick film sensors were fabricated by screen printing and dipping methods, and their sensing characteristics to CH3CN gas were investigated. The oxidation products of CH3CN on the thick film were analyzed by FT-IR using a heatable gas cell. For the SnO2/Al2O3/Pd thick film, metallic Pd played a great role as a co-catalyst for the oxidation of CH3CN. The IR results showed that the products formed by oxidation of CH3CN at 300°C on the SnO2/Al2O3/Nb2O5 thick film without SiO2 were mainly CO2, H2O, and NH3, while on the SnO2/Al2O3/Nb2O5/SiO2 thick film products such as CO2, H2O, N2O, HNO3, and HNO2 were observed. The thick film devices containing SiO2 showed high selectivity and negative sensitivity to CH3CN due to the presence of nitrogen compounds produced by oxidation of CH3CN. The optimum amount of Nb2O5 and operating temperature were 1.0 wt% and 300°C, respectively.

Synthesis, Structure, and Properties of 1,1‘-Diamino- and 1,1‘-Diazidoferrocene

We report an improved synthesis of 1,1‘-diaminoferrocene, employing the reduction of 1,1‘-diazidoferrocene with H2−Pd/C, along with extensive characterization data for both compounds. Diaminoferrocene undergoes a reversible 1e- oxidation in CH3CN at a potential of −602 mV vs Fc0/+, one of the most negative redox potentials for a ferrocene derivative. The chemical reversibility of this process was confirmed by isolation of the stable, 17-electron [Fc(NH2)2]+ cation as PF6-, OTf-, and TCNE- salts. In the solid state, diaminoferrocene exists in two conformations: one with the NH2 groups eclipsed, and the other with the NH2 groups offset by one-fifth turn around the Cp−Fe−Cp axis. Diazidoferrocene, on the other hand, exhibits only the fully eclipsed conformation in the solid state. The Fe−Cp(centroid) vectors in the diazidoferrocene molecules are roughly aligned with the crystallographic c-axis, and the molecules form layers perpendicular to this axis. The compound is thermally unstable at elevated temperatu...

Acetonitrile sensing characteristics and infrared study of SnO 2-based gas sensors

SnO 2/Al 2O 3/Nb 2O 5/SiO 2 thick-film sensors were fabricated by screen-printing and dipping, and their sensing characteristics to CH 3CN gas were investigated. The oxidation products of CH 3CN on the thick film were analyzed by Fourier transform infrared spectroscopy (FTIR) using a heatable gas cell. The IR results showed that the products formed by oxidation of CH 3CN at 300°C on the SnO 2/Al 2O 3/Nb 2O 5 thick film without SiO 2 were mainly CO 2, H 2O, and NH 3, while on the SnO 2/Al 2O 3/Nb 2O 5/SiO 2 thick film products such as CO 2, H 2O, N 2O, HNO 3, and HNO 2 were observed. The thick-film devices containing SiO 2 showed high selectivity and negative sensitivity to CH 3CN due to the presence of nitrogen compounds produced by oxidation of CH 3CN. The optimum amount of Nb 2O 5 and the optimum operating temperature were 1.0 wt.% and 300°C, respectively.

Infrared spectroscopic study and characteristics of SnO2-based thick film for CH3CN detection

The SnO2/Al2O3/Nb2O5/ISiO2 thick film devices were fabricated by screen printing and dipping methods, and their sensing characteristics to CH3CN gas was investigated. The oxidation products of CH3CN on the thick film were analyzed by FT-IR using a heatable gas cell. The IR results showed that the products formed by oxidation of CH3CN at 300 ‡C on the SnO2/Al2/Nb2O5 thick film without SiO2 were mainly CO2, H2O, and NH3, while on the SnO2/Al2O3/Nb2O5/SiO2 thick film products such as CO2, H2O, N2O, HNO3, and HNO2 were observed. The thick film devices containing SiO2 showed high selectivity and negative sensitivity to CH3CN due to the presence of nitrogen compounds produced by oxidation of CH3CN. Optimum amount of Nb2O5 and operating temperature were 1. 0 wt% and 300 ‡C, respectively.

Cationic iroporphyrins as catalyst in comparative oxidation of hydrocarbons: homogeneous and supported on inorganic matrices systems

Cationic ironporphyrins in solution and supported on imidazole propyl gel (IPG) and silica gel (SG) as catalyst in cyclohexane hydroxylation using iodosylarene as oxygen donor were studied. FeTM4PyP 5+, 1 as homogeneous catalyst for cyclohexane hydroxylation, in acetonitrile (CH 3CN) and ultrasound stirring, gives cyclohexanol (C-ol) yields of 20%. The FeTM2PyP 5+, 2 as catalyst for cyclohexene oxidation in CH 3CN and ultrasound stirring is a very efficient system, giving 93% of total yield, with an epoxide:alcohol:ketone selectivity of 77:12:11. The supported systems, 1-IPG and 1-SG are particularly efficient in dichloromethane (CH 2Cl 2), giving C-ol yields of 37% and 53%, respectively. These systems consist of polar hemin in isolated sites, which selectively catalyze cyclohexane oxidation in apolar solvent. They represent good cytochrome P-450 model systems. In the same way, the active site of P-450 consists of a polar protohemin in a hydrophobic pocket, promoting selective cyclohexane oxidation. These rigid cationic 1-IPG, 1-SG, 2-IPG, 2-SG, 3-IPG and 3-SG systems can catalyze with very small amounts of ironporphyrins, which correspond to about 30–80 times fewer numbers than the hemin in P-450 catalytic site.

Poly( N-hydroxypyrrole) and poly(3-phenyl- N-hydroxypyrrole): synthesis, conductivity, spectral properties and oxidation

N-Hydroxypyrrole and 3-phenyl- N-hydroxypyrrole were oxidized by (Bu tO 2) in the presence of light to give the transient pyrrolyl-1-oxyl (nitroxide) radicals which were observed by EPR spectroscopy. The corresponding poly( N-hydroxypyrroles) were prepared by chemical oxidation with ferric salts, or, in the case of N-hydroxypyrrole only, by electrochemical oxidation in CH 3CN at + 1.2 V versus SCE. The latter polymer had a considerably higher electronic conductivity than the chemically produced polymers (10 −4 cf. 10 −10 S cm −1), but much lower conductivity than polypyrrole prepared via the same route. It is not clear from the FT-IR spectra of these polymers whether the hydroxyl group survived intact, or whether it was converted back to the amine. Microanalyses showed that the electropolymerized materials had the expected formulation, but chemical polymerization with FeCl 3 led to the introduction of one O per monomer unit in the case of pyrrole, and two and three O atoms, respectively, for FeCl 3- and Fe(NO 3) 3-polymerized N-hydroxypyrroles. The EPR spectrum of each polymer consisted of a single featureless band at g = 2.003. The poly( N-hydroxypyrroles) were further oxidized by PbO 2 and m-chloroperbenzoic acid (MCPBA) to give polymer containing a strong band at 1720 cm −1 which may be due either to a ketone group (e.g. pyrrolidone) or possibly an oxoammonium (>N +O) species. Microanalyses showed that while electropolymerized polypyrrole had been oxidized by one O atom per monomer, the chemically prepared polymers (FeCl 3) had been oxidized up to the same level as the ferric nitrate-prepared polymers (i.e. from two to three O per pyrrole unit). These oxidized polymers were effectively insulators.

Anodic and cathodic electrochemical ‘ring-opening’ polymerization of styrene sulphide in organic media

Poly(styrene sulphide) (PStS) films or soluble polymers were obtained by ring-opening electropolymerization of styrene sulphide (StS) submitted to either a cathodic or an anodic polarization on different metallic electrodes (Pt, Fe, Ni, Al). Linear PStS chains were formed in both cases, and they were made up of about 280 and 170 monomer units respectively. The films obtained by oxidation in CH 3CN on Pt were transparent, plastic and amorphous, whereas those formed by reduction on Fe, Ni or Pt were powdered and amorphous. The conductivity of these films ranged between 10 −10 and 10 −11 S cm −1. Their structure was characterized by infra-red, nuclear magnetic resonance and X-ray photoelectron spectroscopy, gel permeation chromatography and X-ray diffraction. Only soluble polymers were synthesized by reduction of StS in dimethylsulphoxide and dimethylformamide.

Electrochemical studies of dinuclear molybdenum(V) complexes with EDTA in aprotic solvents

The electrochemical behaviour of the dinuclear complexes [Mo 2O 4- n S n (edta)] 2− ( n = 0–2) was investigated in various aprotic solvents, acetonitrile (CH 3CN), dimethyl sulphoxide (DMSO), N,N-di-methylformamide (DMF) and N,N-dimethylacetamide (DMA). These complexes undergo quasi-reversible one-electron reduction and quasi-reversible one-electron oxidation in CH 3CN. This behaviour is quite different from that in aqueous media. The formal potentials for the reduction of these complexes, as well as the formal potentials for the oxidation of these complexes, shift in the positive direction with an increase in the number of bridging sulphides. The electrochemical behaviour of these complexes in DMF and DMA is similar to that in CH 3CN. The only exception is the oxidation processes of [Mo 2O 4edta)] 2−. in which an irreversible and nearly two-electron transfer occurs in DMF or DMA. The complexes of [Mo 2O 4− n S n edta)] 2− ( n = 0–2) also undergo quasi-reversible one-electron reduction in DMSO. However, anomalies were observed for the oxidation process in this solvent.

Structural and electrochemical studies on trithia macrocyclic complexes of palladium

The single crystal X-ray structure of [Pd( 1) 2](PF 6) 2 ( 1 = 1,4,7-trithiacyclononane) shows a crystallographically centrosymmetric cation with a distorted octahedral stereochemistry about the Pd II centre with PdS eq 2.332(3) and 2.311(3) Å for the equatorial thia donors, and PdS ax 2.952(4) Å for the two apically coordinated donors. The crystals have space group C2/ C, with a 17.879(8), b 15.627(13), c 11.476(8) Å, β 125.92(4)° and Z = 4. Least squares refinement gave R = 0.0565 for 1153 unique observed reflections measured by counter diffracometry using Mo- K α radiation. This green complex undergoes a chemically reversible, one-electron oxidation in CH 3CN, E pa = +0.65V, E pc = +0.56 V vs. Fc/Fc +, Δ E p = 84 mV. Oxidation of [Pd( 1) 2](PF 6) 2 by controlled potential electrolysis at +0.7 V affords an orange, ESR active product which may be tentatively assigned to the corresponding palladium(III) species. These results are contrasted with data for the related homoleptic thia complexes [Pd( L)] 2+ ( L = 1,4,8,11-tetrathiacyclotetradecane ( 2), 1,4,7,10,13,16-hexathiacyclooctadecane ( 3)). The syntheses of the complexes cis-[Pd( 1)Cl 2], cis-[Pt( 1)Cl 2], cis-[Pd( 1)(PPh 3) 2](PF 6) 2 and cis-[Pt( 1)(PPh 3) 2](PF 6) 2 are also described.

Oxidation of CH 3CN over silver: formation of surface compounds

The oxidation of CH 3CN over silver particles was examined between 200 and 300°C. The kinetic data exhibit an unusually abrupt change in activity between 270 and 300°C which is attributed to the oxidation/decomposition of surface AgCN and possibly AgOCN.