- Photochemistry of HNCO in Solid Xe: Channels of UV Photolysis and Creation of H2NCO Radicals
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Photolysis of HNCO at wavelengths between 266 and 193 nm is studied in solid Xe with FTIR and laser-induced fluorescence methods. The channels HNCO → H + NCO (a) and HNCO → NH + CO (b) are operative in a Xe matrix. Channel b produces both isolated fragments and NH?CO complexes as characterized by the CO absorption. The MP2/6-311++G(3df,3pd) calculations are presented for the NH-CO complexes and compared with the experimental data. Photolysis of NCO produces mainly NO + C. A part of the carbon atoms form C2 after which C2- is created in a photoinduced charge transfer reaction. For comparison, in solid Kr, photolysis of HNCO produces additionally HOCN but this channel is absent in a Xe matrix. Upon annealing of the partially photolyzed matrix at 50 K, hydrogen atoms are mobilized and a radical H2NCO is formed by a reaction of a hydrogen atom with a HNCO molecule. Four IR absorptions of H2NCO are observed and they agree well with the MP2/6-311++G(3df,3pd) calculations. The assignment is supported by experiments with DNCO. The threshold for the photodecomposition of H2NCO is between 365 and 405 nm.
- Pettersson, Mika,Khriachtchev, Leonid,Jolkkonen, Santtu,R?s?nen, Markku
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- Reactivity of HNCO with NH3 at low temperature monitored by FTIR spectroscopy: Formation of NH4+OCN-
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The reactivity of isocyanic acid (HNCO) with solid ammonia (NH3) was first studied at 10 K, using FTIR spectroscopy. The ammonium isocyanate (NH4+OCN-) is formed from a reaction between HNCO and NH3. Vibrational band assignments for NH4+OCN- have been given. On the other hand, when HNCO is adsorbed on amorphous NH3 film, the reaction does not occur. Warming up of this sample at 90 K induces the NH4+OCN- formation. Quantum calculations showed that the solvation of NH3 directly bonded to HNCO by at least three NH3 molecules plays a major role in the NH4+OCN- formation process and confirmed the spontaneous character of this reaction.
- Raunier, Sebastien,Chiavassa, Thierry,Marinelli,Allouche,Aycard
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- Photodecomposition of N-hydroxyurea in argon matrices. FTIR and theoretical studies
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The photochemistry of N-hydroxyurea in solid argon has been investigated by FTIR and ab initio calculations. The irradiation of the NH2CONHOH/Ar matrices with the full output of the Xe arc lamp leads to the formation of the HNCO-NH2OH and N2-H2O-CO complexes. For the isocyanic acid-hydroxylamine complex, the spectra prove the existence of the hydrogen bonded structure with the NH group of HNCO attached to the oxygen atom of the NH2OH molecule. Two structures were identified for the nitrogen-water-carbon monoxide complex. In the first one, water is hydrogen bonded to the carbon atom and interacts with the nitrogen atom through van der Waals forces. In the second structure, water serves as a proton donor toward the nitrogen and carbon atoms of N2 and CO molecules, respectively. The identification of the products is confirmed by deuterium substitution and by MP2 calculations of the structure and vibrational spectra of the identified complexes.
- Saldyka, Magdalena
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- Simultaneous derivatization and trapping of volatile products from aqueous photolysis of thiamethoxam insecticide.
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An aqueous photolysis study was conducted with radiolabeled thiamethoxam, 4H-1,3,5-oxadiazin-2-imine, 3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro, to establish the relevance of aqueous photolysis as a transformation process for (14)C-[thiazolyl]-thiamethoxam. (14)C-[thiazolyl]-thiamethoxam was applied to sterile sodium acetate pH 5 buffer solution at a dose rate of approximately 10 ppm. The resulting samples were incubated for up to 30 days at 25 degrees C under irradiated and nonirradiated conditions. The irradiated samples were exposed to a 12-hour-on and 12-hour-off light cycle. Volatile fractions accounted for up to an average of 56.76% of the total dose for the irradiated incubations and a mixture of carbonyl sulfide (COS) and isocyanic acid (CONH). Verification of these components was accomplished by trapping with cyclohexylamine and formation of the thiocarbamate and the isocyanic acid derivatives. A similar method of trapping thiocarbamate metabolites was reported (Chen and Casida, 1978) where filter paper saturated with isobutylamine in methanol was arranged to trap (14)COS and (14)CO(2) under a positive flow of O(2) at 25 degrees C. Mass spectroscopy of the derivatized components confirmed the presence of carbonyl sulfide as the cyclohexylamine thiocarbamate and of isocyanic acid as its cyclohexylamine derivative. Evidence from this study indicates that thiamethoxam degrades significantly under photolytic conditions.
- Schwartz,Sparrow,Heard,Thede
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- The formation and hydrolysis of isocyanic acid during the reaction of NO, CO, and H2 mixtures on supported platinum, palladium, and rhodium
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The extent to which isocyanic acid (HNCO) is formed during the reaction of NO/CO/H2 mixtures over silica-supported Pt, Rh, and Pd was studied with the subsequent hydrolysis of HNCO on oxide systems placed downstream. HNCO formation was a characteristic feature of the NO + CO + H2 reaction over silica-supported Pt, Rh, and Pd. Platinum produced the largest quantity in two stages, i.e., from H2 and then using NH3 being formed as a coproduct. With Pd, HNCO arose largely from NH3 alone because H2 was totally removed by reaction with NO at low temperature. Rhodium gave rise to the least HNCO. Formation was confined to a narrow temperature area due to the coincident consumption of H2 and NO, which precluded NH3 reaction with CO and NO. Hydrolysis of HNCO to NH3 and CO2 was appreciable on SiO2 alone and faster when a metal was present. Other oxide systems gave complete hydrolysis to the limit of the water present and total reaction with even small excesses of water. The possible presence of HNCO in vehicle exhaust was not an issue since the presence of a vast excess of steam and an active washcoat in three-way converters would ensure complete hydrolysis. However, the latter process might contribute to ammonia emissions at moderate temperatures under conditions where CO is still present.
- Cant,Chambers,Angove
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- An experimental and theoretical study of the HNCO+ ion
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The dissociations of energy-selected HNCO+ ions have been examined at ionisation energies up to 40 eV using photoelectron-photoion coincidence spectroscopy. The slow metastable dissociation to HCO+ is shown to occur from initial population of low vibrational levels within the doublet states corresponding to the third photoelectron band. Rate constants for the dissociation from several levels have been measured and the existence of an optical emission is predicted. High level calculations identify the third band in the photoelectron spectrum as an overlay of almost degenerate states arising from ionisation of the in-plane and out-of-plane bonding π-orbitals. The calculations suggest that at energies between 15.5 and 16 eV, the dominant pathway for dissociation involves slow internal conversion to the ground doublet state without surface crossing, followed by intersystem crossing to the quartet surface. At energies over 16 eV, two mechanisms are possible; intersystem crossing from the second excited doublet state to the lowest quartet surface in a cis-bent configuration, or internal conversion to the first excited doublet state via a surface crossing in the same region, followed by a second nonradiative transition to the doublet ground state and intersystem crossing to the quartet surface. In each case, the initial step is expected to be slow, consistent with the existence of an optical emission, and H-atom transfer occurs on the quartet surface via a 'loose' transition state leading to the direct formation of HCO+ and N(4S(u)). (C) 2000 Published by Elsevier Science B.V.
- Wilsey,Thomas,Eland
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- Initial state resolved electronic spectroscopy of HNCO: Stimulated Raman preparation of initial states and laser induced fluorescence detection of photofragments
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Stimulated Raman excitation (SRE) efficiently prepares excited vibrational levels in the ground electronic state of isocyanic acid, HNCO. Photofragment yield spectroscopy measures the electronic absorption spectrum out of initially selected states by monitoring laser induced fluorescence (LIF) of either NCO (X 2II) or NH (a 1Δ) photofragments. Near threshold, the N-H bond fission is predissociative, and there is well-resolved rotational and vibrational structure in the NCO yield spectra that allows assignment of Ka, rotational quantum numbers to previously unidentified vibrational and rotational levels in the ν1 N-H stretch and ν3 N-C-O symmetric stretch fundamentals in the ground electronic state of HNCO. The widths of NCO yield resonances depend on the initial vibrational state, illustrating one way in which initial vibrational state selection influences dissociation dynamics. Initial excitation of unperturbed ν1 (N-H stretch) states leads to diffuse NCO yield spectra compared to excitation of mixed vibrational levels. The higher energy dissociation channel that produces NH (a 1Δ) has coarser structure near its threshold, consistent with a more rapid dissociation, but the resonance widths still depend on the initially selected vibrational state.
- Brown, Steven S.,Berghout, H. Laine,Crim, F. Fleming
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- Internal Energy Distribution of the NCO Fragment from Near-Threshold Photolysis of Isocyanic Acid, HNCO
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We report the first measurement of the vibrational- and rotational-state distributions in the NCO fragment resulting from photolysis of HNCO.Recent studies have drawn conclusions about the photochemistry of HNCO and the vibrational distribution in the NCO fragment from observations of the kinetic energy distribution of the H atom produced in this photolysis; however, there has been no direct observation of the NCO fragment itself.We use laser-induced fluorescence to detect the nascent NCO photoproducts and spectral simulations to extract vibrational-state populations.The rotational distributions, where we can measure them, show little excitation, and the vibrational energy preferentially appears in the bending mode.The vibrational-state distribution results directly from the excited-state geometry of the HNCO parent, in which the NCO group is bent.The dissociation proceeds from this bent NCO group to a linear NCO fragment, strongly exciting the bending mode.We find about 65percent of the total energy in relative translation of the fragments, while 30percent goes into vibration and 5percent into rotation of NCO.
- Brown, Steven S.,Berghout, H. Laine,Crim, F. Fleming
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- Kinetic Study of the Thermal Decomposition of Isocyanic Acid in Shock Waves
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Thermal decomposition of isocyanic acid HNCO diluted to less than 2.0 molpercent in argon was studied behind incident shock waves over the temperature range 2100-2500 K.The decomposition course was followed by monitoring the light absorption of HNCO and NH(3Σ-) at 206 and 336 nm, respectively.It is confirmed that the primary step of the decomposition is a bimolecular process HNCO+Ar->NH(3Σ-)+CO+Ar, ΔH00=337 kJ*mol-1, with the low pressure limit rate constants k=E17.23+/-0.36 exp-1/RT>cm3*mol-1*s-1.The singlet-to-triplet crossing po int is estimated on the basis of the RRKM low-pressure-limit rate constant calculations.The overall decomposition mechanism is suggested and its validity is confirmed by computer simulation of the time-concentration profiles of NH(3Σ-) at varying temperature.
- Kajimoto, Okitsugu,Kondo, Osamu,Okada, Kazuo,Fujikane, Jiro,Fueno, Takayuki
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- Photodissociation Studies of HNCO: Heat of Formation and Product Branching Ratios
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The heat of formation (ΔHf(298 K)) of HNCO is determined to be -24.9+0.7-2.8 kcal/mol (based on ΔHf(NH) = 85.2 kcal/mol).This value is obtained by measuring the threshold for the production of NH(a1Δ) and by determining the energy contents of the NH fragment and the CO cofragment produced by photolysis of HNCO at wavelengths near the threshold.Saturated laser-induced fluorescence is used to determine the internal state distribution of NH(a1Δ), and multiphoton ionization is used to measure the internal state distribution of CO.An upper limit for the branching ratio of NCO/NH production from photodissociation of HNCO at 193 nm is determined from an analysis of kinetic experiments to be 0.10.To clarify the mechanism of photodissociation, HNCO fluorescence-excitation and NH(a1Δ) action spectra are also measured.They imply that two excited states of HNCO are present where only one had previously been considered.
- Spiglanin, Thomas A.,Perry, Robert A.,Chandler, David W.
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- The H-NCO bond energy and ΔH0f (NCO) from photoionization mass spectrometric studies of HNCO and NCO
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A photoionization mass spectrometric study of HNCO yields the ionization potential (I.P.) (HNCO)=11.595+/-0.005 eV and the appearance potential (A.P.) (NCO+/HNCO)16.532+/-0.011 eV at 0 K.A similar study of NCO (generated by F+HNCO) gives I.P. (NCO)=11.759+/-0.006 eV.These observations lead to D0 (H-NCO)110.1+/-0.3 kcal/mol.Additional analysis enables one to infer 28.4+/-0.5 kcal/molΔH0 (NCO)32.8+/-0.7 kcal/mol.The implication of these results for kinetic modeling of the processes for reduction of NOx is discussed.
- Ruscic, B.,Berkowitz, J.
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- Molecular Structure of Isocyanic Acid, HNCO, the Imide of Carbon Dioxide
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Isocyanic acid, HNCO, the imide of carbon dioxide, was prepared by reaction of stearic acid and potassium cyanate (KOCN) at 60 °C in a sealed, thoroughly dried reactor. Interestingly, its crystal structure, solved by X-ray single crystal diffraction at 12
- Evers, Jürgen,Krumm, Burkhard,Axthammer, Quirin J.,Martens, J?rn,Blaha, Peter,Steemann, Franz Xaver,Reith, Thomas,Mayer, Peter,Klap?tke, Thomas M.
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- Photofragment imaging of HNCO decomposition: Angular anisotropy and correlated distributions
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Photodissociation of jet-cooled isocyanic acid has been examined by photofragment ion imaging of H(D) from H(D)NCO and CO from HNCO, and by laser induced fluorescence (LIF) of NH(a 1Δ) from HNCO. Only modest recoil anisotropy is observed in the H+NCO channel at 243.1 nm (β=-0.13±0.05), while the D+NCO channel at approximately the same wavelength reveals no anisotropy (β=0.00±0.05), confirming that the dissociation of H(D)NCO from the opening of the H(D) channel proceeds via vibrational predissociation on the S0(1A′) surface. In contrast, substantial anisotropy (β=-0.66±0.08) is observed in the NH(a 1Δ)+CO channel at 230.1 nm, but this value can correspond to dissociation on either S0 or S1. The photolysis region between 243 and 230 nm thus appears important in providing clues to the dissociation mechanism and the competition between different potential energy surfaces. At 217.6 nm, product state distributions exhibit clear dynamical biases. CO is produced in both v=0 and v=1, while NH(a 1Δ) distributions correlated with different rovibrational levels of CO, although different in shape, are always cold, consistent with the global NH distribution measured by LIF. The NH distributions indicate dissociation on S1(1A″), and can be described by Franck-Condon mapping of transition state wave functions in the HNC bending coordinate without additional torque, implying little anisotropy in the potential along that coordinate. On the other hand, a larger torque is manifest in the CO rotational distribution. Although at 217.6 nm the dissociation is likely to be dominated by decomposition on S1, competition with radiationless decay is still manifest. From analysis .of the CO photofragment velocity distribution at 230.1 nm, the NH(a 1Δ)+CO dissociation threshold is determined at 42 765 ±25 cm-1.
- Sanov,Droz-Georget,Zyrianov,Reisler
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- Competitive photodissociation channels in jet-cooled HNCO: Thermochemistry and near-threshold predissociation
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The photoinitiated unimolecular decomposition of jet-cooled HNCO has been studied following S1(1A″)←S0(1A′) excitation near the thresholds of the spin-allowed dissociation channels: (1) H (2S)+NCO(X 2∏) and (2) NH(a 1Δ)+CO(X 1∑+), which are separated by 4470 cm-1. Photofragment yield spectra of NCO(X 2∏) and NH (a 1Δ) were obtained in selected regions in the 260-220 nm photolysis range. The NCO(X 2∏)yield rises abruptly at 38 380 cm-1 and the spectrum exhibits structures as narrow as 0.8 cm-1 near the threshold. The linewidths increase only slowly with photolysis energy. The jet-cooled absorption spectrum near the channel (1) threshold [D0(H+NCO)] was obtained using two-photon excitation via the S1 state, terminating in a fluorescent product. The absorption spectrum is similar to the NCO yield spectrum, and its intensity does not diminish noticeably above D0(H+NCO), indicating that dissociation near threshold is slow. The NCO product near threshold is cold, as is typical of a barrierless reaction. NH (a 1Δ) products appear first at 42 840 cm-1, but their yield is initially very small, as evidenced also by the insignificant decrease in the NCO yield in the threshold region of channel (2). The NH (a 1Δ) yield increases faster at higher photolysis energies and the linewidths increase as well. At the channel (2) threshold, the NH (a 1Δ) product is generated only in the lowest rotational level, J=2, and rotational excitation increases with photolysis energy. We propose that in the range 260-230 nm, HNCO (S1) undergoes radiationless decay terminating in S0/T1 followed by unimolecular reaction. Decompositions via channels (1) and (2) proceed without significant exit channel barriers. At wavelengths shorter than 230 nm, the participation of an additional, direct pathway cannot be ruled out. The jet-cooled photofragment yield spectra allow the determination, with good accuracy, of thermochemical values relevant to HNCO decomposition. The following heats of formation are recommended: ΔHf0(HNCO) = -27.8±0.4 kcal/mol, and ΔHf0(NCO)=30.3±0.4 kcal/mol. These results are in excellent agreement with recent determinations using different experimental techniques.
- Zyrianov,Droz-Georget,Sanov,Reisler
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- Isomerization and intermolecular solute-solvent interactions of ethyl isocyanate: Ultrafast infrared vibrational echoes and linear vibrational spectroscopy
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The dynamics of ethyl isocyanate (EIC) in the solvent, 2-methylpentane (2MP), are investigated by examining the temperature dependences of the isocyanate (N=C=O) antisymmetric stretching mode's absorption spectrum and ultrafast infrared vibrational echo decay. By combining the spectral data and the vibrational echo data, an interesting picture of the EIC dynamics emerges. As such, electronic structure calculations of the isolated molecule show that trans and gauche forms should be stable, while the cis conformation is a saddle point on the potential surface.
- Levinger, Nancy E.,Davis, Paul H.,Behera, Pradipta Kumar,Myers,Stromberg, Christopher,Fayer
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- Photochemistry of O3/HNCO mixtures
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Pulsed photolysis of gaseous O3/HNCO mixtures at 249 nm produces emission from the NH A3Π → X3Σ- transition near 336 nm. The data suggest that the excited NH is produced by the reaction O(1D) + HNCO →
- Ongstad,Liu,Coombe
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- Aminohydroxymethylene (H2N-C¨-OH), the Simplest Aminooxycarbene
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We generated and isolated hitherto unreported aminohydroxymethylene (1, aminohydroxycarbene) in solid Ar via pyrolysis of oxalic acid monoamide (2). Astrochemically relevant carbene 1 is persistent under cryogenic conditions and only decomposes to HNCO +
- Bernhardt, Bastian,Ruth, Marcel,Reisenauer, Hans Peter,Schreiner, Peter R.
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p. 7023 - 7028
(2021/09/02)
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- Nitrosation of Cyanamide: Preparation and Properties of the Elusive E- and Z-N'-Cyanodiazohydroxides
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Nitrosation of cyanamide leads to unstable E/Z-cyanodiazohydroxides that easily deprotonate to E/Z-cyanodiazotates. Pursuing observations of E. Drechsel 145 years ago, the structure and reactivity of those products was determined, mainly in aqueous solution. Depending on the pH, three different thermal decomposition pathways give either N2O + HCN or N2 + HNCO. They were evaluated experimentally and by quantum mechanical calculations.
- Guethner, Thomas,Huber, Evi,Sans, Juergen,Thalhammer, Franz
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supporting information
(2020/04/29)
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- Trapping of Br?nsted acids with a phosphorus-centered biradicaloid - synthesis of hydrogen pseudohalide addition products
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The trapping of classical hydrogen pseudohalides (HX, X = pseudohalogen = CN, N3, NCO, NCS, and PCO) utilizing a phosphorus-centered cyclic biradicaloid, [P(μ-NTer)]2, is reported. These formal Br?nsted acids were generatedin situas gases and passed over the trapping reagent, the biradicaloid [P(μ-NTer)]2, leading to the formation of the addition product [HP(μ-NTer)2PX] (successful for X = CN, N3, and NCO). In addition to this direct addition reaction, a two-step procedure was also applied because we failed in isolating HPCO and HNCS addition products. This two-step process comprises the generation and isolation of the highly reactive [HP(μ-NTer)2PX]+cation as a [B(C6F5)4]?salt, followed by salt metathesis with salts such as [cat]X (cat = PPh4,n-Bu3NMe), which also gives the desired [HP(μ-NTer)2PX] product, with the exception of the reaction with the PCO?salt. In this case, proton migration was observed, finally affording the formation of a [3.1.1]-hetero-propellane-type cage compound, an OC(H)P isomer of a HPCO adduct. All discussed species were fully characterized.
- Beer, Henrik,Bl?sing, Kevin,Bresien, Jonas,Chojetzki, Lukas,Schulz, Axel,Stoer, Philip,Villinger, Alexander
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supporting information
p. 13655 - 13662
(2020/10/27)
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- A Facile Synthesis of Pd–C3N4@Titanate Nanotube Catalyst: Highly Efficient in Mizoroki–Heck, Suzuki–Miyaura C–C Couplings
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Abstract: A Pd–C3N4@titanate nanotube (Pd–C3N4@TNT) catalyst workable in water medium, robust against leaching and agglomeration was prepared in a facile synthetic procedure using quite common chemicals such as TiO2 powder, urea and palladium acetate. The Pd–C3N4@TNT catalyst has been characterized by BET surface area and pore size distribution, X-ray diffraction, solid-state 13C NMR spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. The Pd–C3N4@TNT is a green catalyst for the Miziroki–Heck and Suzuki–Miyaura C–C coupling reactions in water medium with high efficiency (??99% product yields) due to atomic level immobilization of Pd in C3N4 networked titanate nanotubes. Pd–C3N4@TNT is robust against leaching and agglomeration due to stable and furthermore it is recyclable and usable at least for five repeated cycles. The use of water as solvent, absence of leaching and agglomeration, recyclability and reusability ascertains the greenness of Pd–C3N4@TNT) catalyst and process. Graphic Abstract: Novel Pd–C3N4@titanate nanotube catalyst prepared from bulk TiO2 and urea by simple hydrothermal and thermal pyrolysis followed by immobilization of Pd is active and selective for Mizoroki–Heck, Suzuki–Miyaura C–C couplings in water medium.[Figure not available: see fulltext.].
- Velpula, Venkata Ramana Kumar,Ketike, Thirupathaiah,Paleti, Gidyonu,Kamaraju, Seetha Rama Rao,Burri, David Raju
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- Contrasting Photolytic and Thermal Decomposition of Phenyl Azidoformate: The Curtius Rearrangement Versus Intramolecular C-H Amination
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The decomposition of phenyl azidoformate, PhOC(O)N3, was studied by combining matrix isolation spectroscopy and quantum chemical calculations. Upon UV laser photolysis (193 and 266 nm), the azide isolated in cryogenic noble gas matrices (Ne and Ar, 2.8 K) decomposes into N2 and a novel oxycarbonylnitrene PhOC(O)N, which was identified by matrix-isolation IR spectroscopy (with 15N labeling) and EPR spectroscopy (|D/hc| = 1.620 cm-1 and |E/hc| = 0.024 cm-1). Subsequent visible-light irradiation (532 nm) causes rearrangement of the nitrene into phenoxy isocyanate PhONCO with complex secondary fragmentation (PhO· + ·NCO) and radical recombination species in matrices. The observation of PhONCO provides solid evidence for the Curtius rearrangement of phenyl azidoformate. In sharp contrast, flash vacuum pyrolysis (FVP) of PhOC(O)N3 at 550 K yields N2 and exclusively the intramolecular C-H amination product 3H-benzooxazol-2-one. FVP at higher temperature (700 K) leads to further dissociation into CO2, HNCO, and ring-contraction products. To account for the very different photolytic and thermal decomposition products, the underlying mechanisms for the Curtius rearrangement (concerted and stepwise) of PhOC(O)N3 and the intramolecular C-H amination of the nitrene in both singlet and triplet states are discussed with the aid of quantum chemical calculations using the B3LYP, CBS-QB3, and CASPT2 methods.
- Wan, Huabin,Xu, Jian,Liu, Qian,Li, Hongmin,Lu, Yan,Abe, Manabu,Zeng, Xiaoqing
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p. 8604 - 8613
(2017/11/24)
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- Thermal behavior, decomposition mechanism and thermal safety of 5,7-diamino-4,6-dinitrobenzenfuroxan (CL-14)
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Thermal decomposition kinetics and mechanism of the high-energetic material 5,7-diamino-4,6-dinitrobenzenfuroxan (CL-14) were determined by differential scanning calorimetry (DSC), rapid scanning Fourier transform infrared spectroscopy, and simultaneous thermogravimetric and DSC analyses, coupled with FT-IR and mass spectroscopy. To evaluate the thermal safety of 5,7-diamino-4,6-dinitrobenzenfuroxan (CL-14), its specific heat capacity (Cp) was measured by DSC, and thermal conductivity (λ) was estimated. Kinetic parameters and heat of exothermic decomposition reaction of CL-14 were obtained by analysis of DSC curves. Kinetic parameters used to evaluate the thermal safety of CL-14, such as self-accelerating decomposition temperature (TSADT), critical temperature of thermal explosion (Tb) and impact sensitivity (H50), were obtained. Results showed that for CL-14, TSADT?=?282.0?°C and Tb?=?307.9?°C, whereas H50?=?39.79?cm, revealing that CL-14 had better thermal safety and heat resistance than HMX, RDX and GNTO.
- Fu, Xiao-Long,Fan, Xue-Zhong,Wang, Bo-Zhou,Huo, Huan,Li, Ji-Zhen,Hu, Rong-Zu
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p. 993 - 1001
(2016/07/06)
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- Product channels in the 193-nm photodissociation of HCNO (fulminic acid)
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IR diode laser spectroscopy was used to detect the products of HCNO (fulminic acid) photolysis at 193 nm. Six product channels are energetically possible at this photolysis wavelength: O + HCN, H + NCO/CNO, CN + OH, CO + NH, NO + CH and HNCO. In some experiments, isotopically labeled 15N18O, C2D6 or C6H12 reagents were included into the photolysis mixture in order to suppress and/or redirect possible secondary reactions. HCN, OC18O, 15N15NO, CO, DCN and HNCO molecules were detected upon laser photolysis of HCNO/reagents/buffer gas mixtures. Analysis of the yields of product molecules leads to the following photolysis quantum yields: φ1a (O + HCN) = 0.38 ± 0.04, φ1b (H + (NCO)) = 0.07 ± 0.02, φ1c (CN + OH) = 0.24 ± 0.03, φ1d (CO + NH(a1Δ)) 1e (HNCO) = 0.02 ± 0.01 and φ1f (CH + NO) = 0.21 ± 0.1, respectively.
- Feng, Wenhui,Hershberger, John F.
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- Effects of o -methoxy groups on the properties and thermal stability of renewable high-temperature cyanate ester resins
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Renewable phenols derived from biomass sources often contain methoxy groups that alter the properties of derivative polymers. To evaluate the impact of o-methoxy groups on the performance characteristics of cyanate ester resins, three bisphenols derived from the renewable phenol creosol were deoxygenated by conversion to ditriflates followed by palladium-catalyzed elimination and hydrolysis of the methoxy groups. The deoxygenated bisphenols were then converted to the following cyanate ester resins: bis(4-cyanato-2-methylphenyl)methane (16), 4,4′-(ethane-1,1′-diyl)bis(1-cyanato-3-methylbenzene) (17), and 4,4′-(propane-1,1′-diyl)bis(1-cyanato-3-methylbenzene) (18). The physical properties, cure chemistry, and thermal stability of these resins were evaluated and compared to those of cyanate esters derived from the oxygenated bisphenols. 16 and 18 had melting points 37 and >95 °C lower, respectively, than the oxygenated versions, while 17 had a melting point 14 °C higher. The Tgs of thermosets generated from the deoxygenated resins ranged from 267 to 283 °C, up to 30 °C higher than the oxygenated resins, while the onset of thermal degradation was 50-80 °C higher. The deoxygenated resins also exhibited water uptakes up to 43% lower and wet Tgs up to 37 °C higher than the oxygenated resins. TGA-FTIR of thermoset networks derived from 16-18 revealed a different decomposition mechanism compared to the oxygenated resins. Instead of a low-temperature pathway that resulted in the evolution of phenolic compounds, 16-18 had significantly higher char yields and decomposed via evolution of small molecules including isocyanic acid, CH4, CO2, and NH3.
- Harvey, Benjamin G.,Guenthner, Andrew J.,Lai, William W.,Meylemans, Heather A.,Davis, Matthew C.,Cambrea, Lee R.,Reams, Josiah T.,Lamison, Kevin R.
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p. 3173 - 3179
(2015/06/08)
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- Experimental and theoretical understanding of the gas phase oxidation of atmospheric amides with OH radicals: Kinetics, products, and mechanisms
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Atmospheric amides have primary and secondary sources and are present in ambient air at low pptv levels. To better assess the fate of amides in the atmosphere, the room temperature (298 ± 3 K) rate coefficients of five different amides with OH radicals were determined in a 1 m3 smog chamber using online proton-transfer-reaction mass spectrometry (PTR-MS). Formamide, the simplest amide, has a rate coefficient of (4.44 ± 0.46) × 10-12 cm3 molec-1 s-1 against OH, translating to an atmospheric lifetime of ~1 day. N-methylformamide, N-methylacetamide and propanamide, alkyl versions of formamide, have rate coefficients of (10.1 ± 0.6) × 10-12, (5.42 ± 0.19) × 10-12, and (1.78 ± 0.43) × 10-12 cm3 molec-1 s-1, respectively. Acetamide was also investigated, but due to its slow oxidation kinetics, we report a range of (0.4-1.1) × 10-12 cm3 molec-1 s-1 for its rate coefficient with OH radicals. Oxidation products were monitored and quantified and their time traces were fitted using a simple kinetic box model. To further probe the mechanism, ab initio calculations are used to identify the initial radical products of the amide reactions with OH. Our results indicate that N-H abstractions are negligible in all cases, in contrast to what is predicted by structure-activity relationships. Instead, the reactions proceed via C-H abstraction from alkyl groups and from formyl C(O)-H bonds when available. The latter process leads to radicals that can readily react with O2 to form isocyanates, explaining the detection of toxic compounds such as isocyanic acid (HNCO) and methyl isocyanate (CH3NCO). These contaminants of significant interest are primary oxidation products in the photochemical oxidation of formamide and N-methylformamide, respectively.
- Borduas, Nadine,Da Silva, Gabriel,Murphy, Jennifer G.,Abbatt, Jonathan P.D.
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p. 4298 - 4308
(2015/05/27)
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- Quantification of the 248 nm photolysis products of HCNO (fulminic Acid)
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IR diode laser spectroscopy was used to detect the products of HCNO (fulminic acid) photolysis at 248 nm. Five product channels are energetically possible at this photolysis wavelength: O + HCN, H + (NCO), CN + OH, CO + NH, and HNCO. In some experiments, isotopically labeled 18O2, 15N18O and C2D6 reagents were included into the photolysis mixture in order to suppress and/or isotopically label possible secondary reactions. HCN, OC18O, C18O, NCO, DCN, and NH molecules were detected upon laser photolysis of HCNO/reagents/buffer gas mixtures. Analysis of the yields of product molecules leads to the following photolysis quantum yields: 1a (O + HCN) = 0.39 ± 0.07, 1b (H + (NCO)) = 0.21 ± 0.04, 1c (CN + OH) = 0.16 ± 0.04, 1d (CN + NH(a1Δ)) = 0.19 0.03, and 1e (HNCO) = 0.05 ± 0.02, respectively. The uncertainties include both random errors (1σ) and consideration of major sources of systematic error. In conjunction with the photolysis experiment, the H + HCNO reaction was investigated. Experimental data demonstrate that this reaction is very slow and does not contribute significantly to the secondary chemistry.
- Feng, Wenhui,Hershberger, John F.
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p. 829 - 837
(2014/03/21)
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- Catalytic urea hydrolysis in the selective catalytic reduction of NO x: Catalyst screening and kinetics on anatase TiO2 and ZrO2
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The catalytic hydrolysis of urea was investigated under conditions relevant for the selective catalytic reduction of NOx (urea-SCR). The hydrolysis activities of the tested catalysts coated on cordierite monoliths were in the order ZrO2 > TiO2 > Al2O 3 > H-ZSM-5 > SiO2. A comparison with isocyanic acid (HNCO) hydrolysis on the same catalysts showed that urea decomposition was much slower than HNCO hydrolysis; hence, catalytic urea thermolysis into NH 3 and HNCO is likely to be the rate-determining step in urea decomposition. Interestingly, a different order of catalyst activities was found in water-free experiments on urea thermolysis: TiO2 > H-ZSM-5 ≈ Al2O3 > ZrO2 > SiO2. The widely accepted reaction pathway for urea decomposition, namely urea thermolysis followed by HNCO hydrolysis, seems to be valid on all the tested catalysts except ZrO2: The high urea hydrolysis activity of the ZrO2 catalyst compared to its low urea thermolysis activity suggested a different reaction pathway, in which water directly attacks adsorbed urea rather than adsorbed HNCO.
- Bernhard, Andreas M.,Peitz, Daniel,Elsener, Martin,Schildhauer, Tilman,Kroecher, Oliver
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p. 942 - 951
(2013/04/24)
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- Photochemistry of 1-allyl-4-aryltetrazolones in solution; Structural effects on photoproduct selectivity
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The photochemistry of tetrazolones derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol was investigated in solution with the aim of assessing the effect of solvent and of structural constraints imposed by bulky allylic moieties on photoproduct selectivity and stability. Photolysis of tetrazolones derived from nerol and cyclohex-2-enol afforded the corresponding pyrimidinones as major products through a pathway that appears to be similar to that proposed for other 1-allyl-4-phenyl-1,4-dihydro-5H-tetrazol-5-ones derived from acyclic and unhindered allylic alcohols previously investigated but photolysis of the tetrazolone derived from the bulkier 3-methylcyclohex-2-enol 4c leads to formation of a benzimidazolone, indicating that, in this case, cyclization of the biradical formed upon extrusion of N2 involves the phenyl substituent and not the allylic moiety. Theoretical calculations (DFT(B3LYP)/3-21G*) were conducted to support the interpretation of the experimental results and mechanistic proposals. Laser flash photolysis experiments were conducted with the aim of clarifying the nature of the intermediate involved in the primary photocleavage process.
- Ismael, Amin,Serpa, Carlos,Cristiano, M. Lurdes S.
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p. 272 - 283
(2013/08/24)
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- Formyl azide: Properties and solid-state structure
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The simplest acyl azide, HC(O)N3, has been prepared as the neat substance and characterized by IR and Raman spectroscopy and low-temperature X-ray crystallography (see solid-state structure; C white, H gray, N blue, O red). Photolysis of the azide in CO-doped solid noble-gas matrices furnished the first experimental proof of the elusive parent acyl isocyanate HC(O)NCO.
- Zeng, Xiaoqing,Bernhardt, Eduard,Beckers, Helmut,Banert, Klaus,Hagedorn, Manfred,Liu, Hailiang
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supporting information
p. 3503 - 3506
(2013/04/24)
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- Fascinating diazirinone: A violet gas
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Diazirinone (cyclic N2CO) recently identified in solid noble gas matrices and in the gas phase by infrared spectroscopy, has now been trapped at -196°C as a neat brownish-yellow solid, and characterized by low-temperature IR and Raman spectroscopy. Evaporation of the solid yields violet gaseous N2CO, which is surprisingly stable in a clean quartz cell. Its decay at room temperature in the dark follows a second-order rate law (k2 = 4.9 × 10-2 L mol-1 s-1) with a half-life of 30 h at an initial pressure of 5 mbar. The visible absorption spectrum of the gas reveals a structured band with the 0-0 transition at 567 nm (17651 cm-1), and its assignment has been made with the aid of theoretical calculations. Cyclic diazirinone that is isolated in solid Ar at 16 K decomposes upon visible light irradiation to yield N2 and CO, but after being exposed to ArF excimer laser irradiation (193 nm) the N=N bond is cleaved and the open-chain isomers NOCN, ONCN, and ONNC are formed. Diazirinone (cyclic N2CO) has been prepared in a neat form as a violet gas. It has a half-life of 30 h at an initial pressure of 5 mbar in a clean quartz container at room temperature, and the substance has been characterized by IR, Raman, and UV/Vis spectroscopy. Copyright
- Zeng, Xiaoqing,Beckers, Helmut,Willner, Helge,Stanton, John F.
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p. 3403 - 3409
(2012/11/06)
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- Experimental and theoretical studies on the synthesis, spectroscopic data, and reactions of formyl azide
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Small is beautiful: spectroscopic proof or any other indication for the existence of formyl azide (HC(O)N3) has until now been lacking. Although it liberates dinitrogen much more rapidly than homologous acyl azides, it has been prepared for the first time by four different methods (see scheme). Copyright
- Banert, Klaus,Berndt, Christian,Hagedorn, Manfred,Liu, Hailiang,Anacker, Tony,Friedrich, Joachim,Rauhut, Guntram
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supporting information; experimental part
p. 4718 - 4721
(2012/06/30)
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- Eugenol and its methyl ether in the synthesis of 3-methyl derivatives of 3,4-dihydroisoquinoline
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3-Methyl derivatives of 1-substituted 3,4-dihydroisoquinoline were obtained proceeding from eugenol and its methyl ether. The propylene oxide in a three-component reaction with veratrol and ethyl cycnoacetate provided the reaction products in a low yield. The isoeugenol in a linear synthesis also gives a low yield of the target compounds.
- Shklyaev, Yu. V.,Smolyak,Gorbunov
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scheme or table
p. 239 - 244
(2011/05/03)
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- Methods And Devices For Preparing Biuret And Cyanuric Acid
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Provided are methods and devices for preparing biuret and cyanuric acid by thermal decomposition of urea. Specifically, a product of thermal decomposition is cooled to precipitate a crystal and the precipitated crystal is dissolved using an alkali aqueous solution and cooled to obtain biuret having high purity. Furthermore, the cyanuric acid that is one of byproducts by the thermal decomposition of urea is effectively recovered with high purity.
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Page/Page column 4-5
(2008/06/13)
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- Determination of the rate constant and product channels for the radical-radical reaction NCO(X 2Π) + C2H5(X 2A″) at 293 K
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The rate constant and product branching ratios for the reaction of the cyanato radical, NCO(X 2Π), with the ethyl radical, C 2H5(X 2A″), have been measured over the pressure range of 0.28 to 0.59 kPa and at a temperature of 293 ± 2 K. The total rate constant, k1, increased with pressure, P(kPa), described by k1 = (1.25 ± 0.16) × 10-10 + (4.22 ± 0.35) × 10-10 P cm3 molecule-1 s-1. Three product channels were observed that were not pressure dependent: (1a) HNCO + C2H4, k1a = (1.1 ± 0.16) × 10-10, (1b) HONC + C2H4, k1b = (2.9 ± 1.3) × 10-11, (1c) HCN + C 2H4O, k1c = (8.7 ± 1.5) × 10 -13, with units cm3 molecule-1 s-1 and uncertainties of one-standard deviation in the scatter of the data. The pressure dependence was attributed to a forth channel, (1d), forming recombination products C2H5NCO and/or C2H 5OCN, with pressure dependence: (1d) k1d = (0.090 ± 1.3) × 10-11 + (3.91 ± 0.27) × 10-10 P cm3 molecule-1 s-1. The radicals were generated by the 248 nm photolysis of ClNCO in an excess of C2H 6. Quantitative infrared time-resolved absorption spectrophotometry was used to follow the temporal dependence of the reactants and the appearance of the products. Five species were monitored, HCl, NCO, HCN, HNCO, and C 2H4, providing a detailed picture of the chemistry occurring in the system. Other rate constants were also measured: ClNCO + C 2H5, k10 = (2.3 ± 1.2) × 10 -13, NCO + C2H6, k2 = (1.6 ± 0.11) × 10-14, NCO + C4H10, k4 = (5.3 ± 0.51) × 10-13, with units cm3 molecule-1 s-1 and uncertainties of one-standard deviation in the scatter of the data. the Owner Societies.
- Glen Macdonald
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p. 4301 - 4314
(2008/09/19)
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- Selective catalytic reduction of NO2 with urea in nanocrystalline NaY zeolite
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In this study, the selective catalytic reduction (SCR) of NO2 with urea in nanocrystalline NaY zeolite was investigated with in situ transmission Fourier transform infrared (FTIR) spectroscopy and solid-state nuclear magnetic resonance spectroscopy. At T=473 K, the reaction rate for urea-SCR of NO2 in nanocrystalline NaY zeolite was significantly greater than that in commercial NaY zeolite with a larger crystal size. In addition, a dramatic decrease in the concentration of undesirable surface species, including biuret and cyanuric acid, was observed in nanocrystalline NaY compared with commercial NaY after urea-SCR of NO2 at T=473 K. The increased reactivity for urea-SCR of NO2 was attributed to silanol groups and extra-framework aluminum species located on the external surface of nanocrystalline NaY. Specifically, NOx storage as nitrate and nitrite on the internal zeolite surface was coupled to reactive deNOx sites on the external surface. Isotopic labeling combined with IR analysis suggest that NN bond formation involved both an N-atom originating from NO2 and an N-atom originating from urea. This is the first clear example demonstrating that the increased external surface area (up to ~40% of total surface area) of nanocrystalline zeolites can be used as a reactive surface with unique active sites for catalysis.
- Li, Gonghu,Jones, Conrad A.,Grassian, Vicki H.,Larsen, Sarah C.
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p. 401 - 413
(2008/10/09)
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- The catalytic chemistry of HCN + NO2 over Na- and Ba-Y,FAU: An in situ FTIR and TPD/TPR study
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The adsorption of HCN and the reaction of HCN with NO2 over Na-, and Ba-Y,FAU zeolite catalysts were investigated using in situ FTIR and TPD/ TPR spectroscopies. Both catalysts adsorb HCN molecularly at room temperature, and the strength of ads
- Szanyi, János,Kwak, Ja Hun,Peden, Charles H. F.
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p. 1481 - 1490
(2007/10/03)
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- Process for making dialkyl carbonates
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A process for the production of dialkyl carbonates from the reaction of alcohol, for example C1-C3 alcohols, with urea is disclosed wherein the water and ammonium carbamates impurities in the feed are removed in a prereactor. The water is reacted with urea in the feed to produce ammonium carbamate which is decomposed along with the ammonium carbamates originally in the feed to ammonia and carbon dioxide. In addition some of the urea is reacted with the alcohol in the first reactor to produce alkyl carbamate which is a precursor to dialkyl carbonate. Dialkyl carbonates are produced in the second reaction zone. The undesired by-product N-alkyl alkyl carbamates are continuously distilled off from the second reaction zone along with ammonia, alcohol and dialkyl carbonates under the steady state reactor operation. N-alkyl alkyl carbamates can be converted to heterocyclic compounds in a third reaction zone to remove as solids from the system.
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Page/Page column 10
(2008/06/13)
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- The formation of isocyanic acid during the reaction of NH3 with NO and excess CO over silica-supported platinum, palladium, and rhodium
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The reaction between NH3 and NO in excess CO over silica-supported platinum, palladium, and rhodium has been investigated for temperatures from 100 to 450°C. As found previously for the corresponding reactions of H2/NO/CO mixtures, isocyanic acid (HNCO) is produced with each catalyst. With Pd/SiO2, the peak yield when NH3 is used is 46% based on the total nitrogen converted and 55% based on the hydrogen taken from NH3, with the remaining hydrogen converted to water. The reaction over Pt/SiO2 requires a somewhat higher temperature and is more efficient with a maximum HNCO yield of 70% based on nitrogen and 95% on hydrogen. The near-absence of water as a product correlates with the high activity of platinum for the production of HNCO from H 2O/NO/CO mixtures, which in turn is driven by activity for the water-gas shift reaction. The peak yield of HNCO from NH3/NO/CO mixtures is much lower with Rh/SiO2 (10% based on nitrogen), and, unlike the yield of the platinum and the palladium catalysts, it is less than that observed during the H2 + NO + CO reaction (30%). In experiments using 15NO and 14NH3, the 15N content of N2, HNCO, and the end nitrogen of N2O are similar, consistent with dissociation of both nitric oxide and ammonia to form a single surface pool of nitrogen atoms. However, neither dissociation is rapidly reversible, since there is little exchange of 14N from ammonia into unreacted 15NO, and significant formation of 15NH 3 is confined to Pt/SiO2 at temperatures where it could be formed by hydrolysis of product H15NCO. It is concluded that HNCO is formed by the rapid pick-up of surface hydrogen atoms by metal-bound NCO groups existing in equilibrium with N atoms and surrounding CO molecules. The trends in product distribution and in activity between the three metals can be rationalised in terms of competition between NO and CO for surface sites with CO favoured on Pt, NO favoured on Rh, and Pd exhibiting intermediate characteristics.
- Cant, Noel W.,Chambers, Dean C.,Liu, Irene O.Y.
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p. 201 - 212
(2008/10/09)
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- IMPROVING THE MELAMINE YIELD OF CATALYTIC MELAMINE PRODUCTION PROCESSES
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The process to increase the melamine yield and improving the dust separation in the melamine production from urea in fluidized-bed catalytic processes comprises transferring the process gas of the fluid-bed reactor, which contains besides melamine non-converted isocyanic acid, melam, melem and other higher molecular nitrogen compounds, into a filter-reactor which consists of one or more ring-reactors filled with catalysts, in which the not yet converted isocyanic acid is converted to melamine, the higher molecular nitrogen compounds, especially melam and melem, are also re-converted to melamine by reaction with the ammonia in the process gas, and the catalyst fines still present in the process gas of the fluidized-bed reactor are removed.
- -
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Page/Page column 7-8
(2008/06/13)
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- Kinetics of the homogeneous, unimolecular elimination reactions of ethyl oxamate, ethyl N,N-dimethyloxamate and ethyl oxanilate in the gas phase
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The gas-phase elimination kinetics of the title compounds were determined over the temperature range 350-430°C and pressure range 35-240 Torr (1 Torr = 133.3 Pa). The reactions, which were carried out in a static reactor system, seasoned with allyl bromide and in the presence of a free radical inhibitor, are homogeneous, unimolecular and obey a first-order rate law. The temperature dependences of the overall rate coefficients are given by the following Arrhenius equations: for ethyl oxamate, log [k1 (s-1)] = (13.28±0.20)-(203.7±2.5)kJ mol-1 (2.303RT) -1, for ethyl N,N-dimethyloxamate, log [k1(s -1)] = (13.06±0.34)-(206.8±4.4)kJ mol -1(2.303RT)-1, and for ethyl oxanilate, log [k1 (s-1)] = (13.86±0.12)-(207.4±1.5)kJ mol -1(2.303RT)-1. The overall rates, the partial rates and the kinetic and thermodynamic parameters of these eliminations are presented and discussed. These reactions appear to proceed through moderately polar cyclic transition states. Copyright
- Chacin, Esker V.,Tosta, Maria,Herize, Armando,Dominguez, Rosa M.,Alvarado, Ysaias,Chuchani, Gabriel
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p. 539 - 545
(2007/10/03)
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- Nitrogen-containing compounds as a reductant for the selective catalytic reduction of NO
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When acrylonitrile and other nitrogen-containing compounds are passed over Cu- and H-ZSM-5, they can act as efficient reductants in the selective catalytic reduction of NO by forming NH3 and carbonaceous deposits through hydrolysis.
- Nanba, Tetsuya,Masukawa, Shouichi,Uchisawa, Junko,Obuchi, Akira
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p. 924 - 925
(2007/10/03)
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- Infrared spectrum of solid isocyanic acid (HNCO): Vibrational assignments and integrated band intensities
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Characterization of infrared spectra thin films of solid HNCO condensed from the gas phase was reported. It was characterized in terms of integrated band intensities, vibrational frequencies and mode assignments. Reaction of Isocyanic acid with water (Hs
- Lowenthal,Khanna,Moore, Marla H.
-
-
- Synthesis, properties and dimerization study of isocyanic acid
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Isocyanic acid was prepared in pure form by reaction of KOCN or NaOCN with stearic or oxalic acid in good yield. Identification, characterization and investigation of the thermal stability of HNCO and evidence for a possible existence of "dicyanic acid" h
- Fischer, Gerd,Geith, Janna,Klap?tke, Thomas M.,Krumm, Burkhard
-
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- Product analysis of selective catalytic reduction of NO2 with C2H4 over H-ferrierite
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The reaction paths for the selective reduction of NO2 with C2H4 over H-ferrierite were studied by focusing on the formation and reaction of the by-products. Nitroethylene (NE), HCN, and HNCO were detected as nitrogen-containing by-products in C2H4-SCR-NO2. NE was converted to HNCO, HCN, NH3, HCHO, CO, and CO2 in the absence of NOx. HNCO had a high reactivity for hydrolysis and was fully decomposed into NH3 and CO2 above 200°C. HNCO hydrolysis followed by the reaction of NH3 with NOx to form N2 was a very feasible pathway. HCN was mostly hydrolyzed to NH3 and CO at high temperatures and partly oxidized to HNCO in the presence of NO2. N2 and N2O were formed by the reactions of NH3 with NO, and NH3 with NO2. The latter reaction was much faster. Two reaction pathways were observed for N2 formation, i.e. the direct reaction between NE and NO2, and NE decomposition followed by the formation and hydrolysis of HNCO. The second pathway resulted in the formation of NH3, which further reacted with NOx to form N2.
- Nanba,Obuchi,Sugiura,Kouno,Uchisawa,Kushiyama
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-
- Formation of HCNO and HCN in the 193 nm photolysis of H2CCO in the presence of NO
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NO-reburning is one of the main strategies for removing NOx from the combustion of fossil fuels. The products derived from the ArF laser photolysis of H2CCO in the presence of a large excess of NO at 298 K and 3.5 mbar in He bath gas were studied in a tubular flow reactor using time-resolved MS. HCNO and HCN were the major reaction products observed in the presence of NO. The observed yields, HCNO = 0.18 and HCN = 0.04 were attributed to the contributions of the reactions CH2 + NO → HCNO + H, CH2 + NO → HCN + OH, and HCCO + NO → HCNO + CO (HCCO + NO → HCN + CO2), which confirmed results of earlier FTIR end-product analyses. The efficient production of HCNO by the reactions CH2 + NO → products and HCCO + NO → products should be taken into account in improved NOx-reburn models.
- Temps,Eshchenko,Koecher,Kerst
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p. 181 - 187
(2008/10/08)
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- Photochemistry of HNCO in solid xenon: Photoinduced and thermally activated formation of HXeNCO
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The preparation and characterization of a novel rare-gas-containing compound HXeNCO in solid Xe is described. HXeNCO is formed in two ways. Photolysis of HNCO at 193 nm in solid Xe directly produces HXeNCO providing the first experimental evidence of direct photoinduced formation of a HXY-type rare-gas compound (X = Xe, Kr; Y is an electronegative fragment), which can be attributed to relatively high photostability of HXeNCO. This finding particularly shows that the HXY compounds can be intermediates in the photolysis of HY in the presence of X. The amount of HXeNCO produced initially in photolysis of HNCO remains small because HXeNCO decomposes under irradiation. More efficient production of HXeNCO is achieved in the thermal reaction H+Xe+NCO→HXeNCO after photolysis of HNCO. HXeNCO has two strong IR absorptions: the asymmetric NCO stretch at 2148.3 cm-1 and the Xe-H stretch at 1788.1 cm-1. The assignment is supported by the deuteration experiments and the ab initio calculations. HXeNCO decomposes at 405 nm irradiation producing HNCO and (H+NCO).
- Pettersson, Mika,Khriachtchev, Leonid,Lundell, Jan,Jolkkonen, Santtu,Rasanen, Markku
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p. 3579 - 3583
(2007/10/03)
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- Pyrolysis nozzles coupled to a microwave spectrometer with stark modulation for the detection of transients species in a supersonic expansion
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Two types of pyrolysis nozzles have been constructed and coupled to a new Stark modulated microwave spectrometer. The nozzles were tested on their ability to generate rotationally cooled transient species through a supersonic expansion. The transients species vinylamine, thioketene and ketene were generated and detected using nozzle temperatures ranging from 400-800°C. Pyrolysis temperatures were generally lower than those used in normal flow pyrolysis experiments and rotational temperatures of ca. 10 K were achieved. A preliminary investigation of the jet nozzle pyrolysis of 3-methyl-4-hydroxyiminoisoxaline-5-one was carried out and showed a different distribution of CHNO pyrolysis products to that observed in previous low pressure studies. by Oldenbourg Wissenschaftsverlag, Muenchen.
- McNaughton, Don,Evans, Corey J.
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p. 1313 - 1327
(2007/10/03)
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- Temperature dependence of the product branching ratio of the CN + O2 reaction
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The reaction of CN radicals with O2 was studied using infrared diode laser absorption spectroscopy. CO and CO2 products were detected directly, while the yield of NCO products was inferred by measuring the N2O yield upon addition of excess NO. Experiments and kinetic modeling calculations were performed to examine the extent of secondary chemistry in this system. The following branching ratios of the CN + O2 reaction at 296 K were determined: ?(N+CO2) = 0.02 ± 0.01 and ?(CO+NO) = 0.22 ± 0.02. The branching ratio into the CO + NO channel has a strong negative temperature dependence over the range 239-643 K.
- Rim, Kwang Taeg,Hershberger, John F.
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p. 3721 - 3725
(2007/10/03)
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- Pyrolysis, photolysis and mass spectra of pyran and thiopyran derivatives
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Pyrolysis and photolysis of 2-amino-3,5-dicyano-6-phenyl-4H-pyran (1) afford HNCO, acrylonitrile, cinnamonitrile and 2-hydroxy-3,5-dicyano-6-phenylpyridine. Pyrolysis of 2-carboxyimino-3,5-dicyano-6-phenyl-4H-pyran (2) gives HCN, acrylonitrile, cinnamonitrile and 2-hydroxy-3,5-dicyano-6-phenylpyridine. Furthermore both pyrolysis and photolysis of 2,6-diamino-3,5-dicyanothiopyran (3) gives rise to HNCS, acrylonitrile and 6-amino-3,5-dicyano-6-mercaptopyridine. Moreover, comparative studies of pyrolysis, photolysis and mass spectra of 2,6-diamino-3,5-dicyano-4-arylthiopyran derivatives 4a-c revealed similar results as HNCS, cinnamonitrile derivatives and pyridinethione derivatives. The mass spectral fragmentation patterns of these compounds were recorded and studied to determine the homolysis fission involved in the rearrangements. Partial similarity of products obtained from pyrolysis and photolysis, and the mechanistic implications of these data are discussed.
- Atalla,Hussein,Badr
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p. 163 - 170
(2007/10/03)
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- Kinetics of the reactions of NCO radicals with NO and NH3
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The rate constants for the reaction of NCO (X2∏) radicals with NO and NH3 were measured at 20 Torr total pressure in temperature ranges of 290-1098 K and 295-882 K, respectively, using C1NCO excimer laser photolysis for NCO radical formation in combination with laser-induced fluorescence detection of NCO. In the temperature range investigated the NCO + NO reaction exhibits a negative temperature dependence which is described by the following three parameter Arrhenius equation: (Equation Presented) with E0 in units of kJ/mol. For the NCO + NH3 reaction the measurements exhibit a positive temperature dependence over the temperature range investigated with a slight upwards curvature. A modified three parameters Arrhenius fit provides a good description of the experimental data: (Equation Presented) with E0 in units of kJ/mol. In addition, the rate constant of the NCO + NH3 reaction was found to be pressure independent in the range 10-193 Torr at 295 K. VCH Verlagsgesellschaft mbH, 1997.
- Becker,Kurtenbach,Schmidt,Wiesen
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p. 128 - 133
(2007/10/03)
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- Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride, FXe(N3), and Xenon Isocyanate Fluoride, FXe(NCO)
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The reaction behavior of xenon difluoride, XeF2, toward HN3, NaN3, and NaOCN was investigated in H2O, aHF (anhydrous HF), and SO2ClF solution. The analysis of the final reaction products (XeF2 + HN3 (NaN3) in H2O → HF, N2, N2O, Xe; XeF2 + HN3 in aHF → N2, Xe, N2F2; XeF2 + HOCN (NaOCN) in H2O → HF, N2, N2O, NH3, CO2, Xe) indicated the intermediate formation of FXe(N3) and FXe(NCO) and revealed different reaction mechanisms for both compounds. Both intermediates, FXe(N3) and FXe(NCO), were studied on the basis of ab initio computations at HF and correlated MP2 levels using a quasirelativistic LANL2DZ pseudopotential for Xe. Both were shown to possess stable minima at HF and MP2 levels (no imaginary frequencies) with the following structural parameters (MP2/LANL2DZ). FXe(N3): Cs; d(F-Xe) = 2.051, d(Xe-N1) = 2.318, d(N1-N2) = 1.241, d(N2-N3) = 1.180 ?; s; d(F-Xe) = 2.024, d(Xe-N) = 2.206, d(N-C) = 1.194, d(C-N) = 1.231 ?; -1.
- Schulz, Axel,Klap?tke, Thomas M.
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p. 1929 - 1933
(2008/10/09)
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- Heterocumulenes, 9. Ethenedione oxime: Photochemical generation and matrix-spectroscopic identification
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The title compound 2, a very close derivative of the still elusive ethenedione (1), was generated by photocleavage of the three different precursor molecules 7-9 in an argon matrix at 10 K. The structure elucidation of monoxime 2 is based on the comparison of the experimental and calculated IR spectrum. VCH Verlagsgesellschaft mbH, 1996.
- Maier, Guenther,Reisenauer, Hans Peter,Roether, Bernd,Eckwert, Juergen
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p. 303 - 306
(2007/10/03)
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- Formation of HNCO during Catalytic Reduction of NOx with Olefins over Cu/ZSM-5
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Gaseous cyanic acid (HNCO) is formed in the temperature range 513-666 K during the selective catalytic reduction of NOx with olefins (ethene, propene) over Cu/ZSM-5 under dry conditions, whereas with ammonia no HNCO is observed in the presence of water in
- Radtke, Frank,Koeppel, Rene A.,Baiker, Alfons
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p. 427 - 428
(2007/10/02)
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