Cyanation Research Articles

Covalent Cyanates and Fulminates

Covalent Cyanates and Fulminates

Kinetics of the OCN−and HOCN formation from the HNCO + H2O thermal reaction in interstellar ice analogs

Aims. We study in the laboratory the kinetics of the low-temperature OCN− and HOCN formation from the purely thermal reaction of solid HNCO and H2O. The cyanate ion OCN− is an intermediate in the isomerization process of isocyanic acid HNCO into cyanic acid HOCN in water ice.

Isocyanic acid in the atmosphere and its possible link to smoke-related health effects

We measured isocyanic acid (HNCO) in laboratory biomass fires at levels up to 600 parts per billion by volume (ppbv), demonstrating that it has a significant source from pyrolysis/combustion of biomass. We also measured HNCO at mixing ratios up to 200 pptv (parts-per-trillion by volume) in ambient air in urban Los Angeles, CA, and in Boulder, CO, during the recent 2010 Fourmile Canyon fire. Further, our measurements of aqueous solubility show that HNCO is highly soluble, as it dissociates at physiological pH. Exposure levels > 1 ppbv provide a direct source of isocyanic acid and cyanate ion (NCO(-)) to humans at levels that have recognized health effects: atherosclerosis, cataracts, and rheumatoid arthritis, through the mechanism of protein carbamylation. In addition to the wildland fire and urban sources, we observed HNCO in tobacco smoke, HNCO has been reported from the low-temperature combustion of coal, and as a by-product of urea-selective catalytic reduction (SCR) systems that are being phased-in to control on-road diesel NO(x) emissions in the United States and the European Union. Given the current levels of exposure in populations that burn biomass or use tobacco, the expected growth in biomass burning emissions with warmer, drier regional climates, and planned increase in diesel SCR controls, it is imperative that we understand the extent and effects of this HNCO exposure.

Bis(cyanato-κN)bis(5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine-κN3)zinc

In the title complex, [Zn(NCO)2(C7H8N4)2], the ZnII ion exhibits a distorted tetra­hedral coordination geometry. The coordination environment is formed by two 5,7-dimethyl-1,2,4-triazolo[1,5-a]pyrimidine (dmtp) ligands, coordinated through the N atom in position 3, and two cyanate anions inter­acting by their N atoms. Supra­molecular dimers are generated by stacking inter­actions between the pyrimidine rings of two ligands related by an inversion center [centroid–centroid distance = 3.5444 (18) Å].

Dissociation Rates of Urea in the Presence of NiOOH Catalyst: A DFT Analysis

Single molecule reactions have been studied between nickel oxyhydroxide, urea, and the hydroxide ion to understand the process of urea dissociation into ammonia, isocyanic acid, cyanate ion, carbon dioxide, and nitrogen. In the absence of hydroxide ions, nickel oxyhydroxide will catalyze urea to form ammonia and isocyanic acid with the rate-limiting step being the formation of ammonia with a rate constant of 1.5 × 10⁻⁶ s⁻¹. In the presence of hydroxide, the evolution of ammonia was also the rate-limiting step with a rate constant of 1.4 × 10⁻²⁶ s⁻¹. In addition, desorption of the cyanate ion presented an energy barrier of 6190 kJ mol⁻¹ suggesting that the cyanate ion cannot be separated from NiOOH unless further reactions occurred. Finally, elementary dissociation reactions with hydroxide ions deprotonating urea to produce nitrogen and carbon dioxide were analyzed. These elementary reactions were investigated along three paths differing in the order that protons were removed and the nitrogen atoms were rotated. The rate-limiting step was found to be the removal of carbon dioxide with a rate constant of 4.3 × 10⁻⁶⁵ s⁻¹. Therefore, the catalyst could be deactivated by the surface blockage caused by carbon dioxide adsorption.

Synthesis and Study of Mixed Ligand‐Metal Complexes of 1, 3, 7‐Trimethylxanthine and 1, 3‐Dimethyl‐7H‐purine‐2, 6‐dione with Some Other Ligands

This work presents synthesis and study of a new mixed ligand metal complexes of 1,3,7‐trimethylxanthine and 1,3‐dimethyl‐7H‐purine‐2,6‐dione with some other ligands like SCN and OCN ions to give the general formula [M(Tx)2(Tp) )2XY] where M=Co(II), Ni(II), Cu(II), Zn(II) and Cd(II), Tx=1,3,7‐trimethylxanthine, Tp= 1,3‐dimethyl‐7H‐purine‐2,6‐dione, X= SCN and Y= OCN. The resulting products were found to be solid which have been characterized using UV‐Visible and infrared spectroscopy. Elemental analyses were performed using C, H, N analysis and atomic absorption techniques. The magnetic susceptibility and the conductivity were also measured. The present results suggest that the 1,3,7‐trimethylxanthine and 1,3‐dimethyl‐7H‐purine‐2,6‐dione were coordinated with metal ions through the nitrogen atom. Thiocyanate ion was coordinated with metal ions through the sulfur atom and the cyanate ion was coordinated with metal ions through the oxygen atom.

ChemInform Abstract: Preparation and Reactions of Some Organo-Silicon Cyanates.

ChemInform Abstract: Preparation and Reactions of Some Organo-Silicon Cyanates.

Cadmium(II) thio- and selenocyanate complexes of 3,3′-bis(1,2,4-triazol-4-yl)-1,1′-biadamantane, a ligand designed with an `extended nanodiamond' aliphatic platform

In the structures of the Cd(II) pseudohalide coordination polymer poly[[diaquabis[mu(2)-3,3'-bis(1,2,4-triazol-4-yl)-1,1'-biadamantane-kappa(2)N(1):N(1')]cadmium(II)] dithiocyanate dihydrate], {[Cd(C(24)H(32)N(6))(2)(H(2)O)(2)](NCS)(2).2H(2)O}(n), (I), and the isomorphous selenocyanate analogue, {[Cd(C(24)H(32)N(6))(2)(H(2)O)(2)](NCSe)(2).2H(2)O}(n), (II), the Cd(II) cations occupy inversion centres and have octahedral CdN(4)O(2) environments, completed by four N atoms of the organic ligands [Cd-N = 2.316 (2) and 2.361 (2) A for (I), and 2.313 (3) and 2.372 (3) A for (II)] and two trans-coordinated aqua ligands [Cd-O = 2.3189 (15) A for (I) and 2.323 (2) A for (II)]. In each compound, the ligand displays a bidentate N(1):N(1')-bridging mode, connecting the metal centres at a distance of 14.66 A into two-dimensional nets of (4,4)-topology, while the uncoordinated thio(seleno)cyanate anions reside inside the net cavities. Hydrogen bonding between the water molecules, anions and 1,2,4-triazole N atoms supports the tight packing, with an interlayer distance of 6.09 A.

Carbamylation of N-terminal proline.

Protein carbamylation is of great concern both in vivo and in vitro. Here, we report the first structural characterization of a protein carbamylated at the N-terminal proline. The unexpected carbamylation of the α-amino group of the least reactive codified amino acid has been detected in high-resolution electron density maps of a new crystal form of the HIV-1 protease/saquinavir complex. The carbamyl group is found coplanar to the proline ring with a trans conformation. The reaction of N-terminal with cyanate ion derived from the chaotropic agent urea was confirmed by mass spectra analysis on protease single crystals. Implications of carbamylation process in vitro and in vivo are discussed.

Pseudohalide supported mononuclear trans-Ni II complexes of cationic and neutral dinitrogen heterocycles

Two mixed ligand complexes trans-[Ni(NCS) 4(PpzH) 2] ( 1) and trans-[Ni(NCO) 2(Imd) 4] ( 2) (where Ppz = piperazine; Imd = imidazole) were synthesized from one-pot reactions, and their crystal and molecular structures were determined. The reaction of NiCl 2·4H 2O with piperazine and KSCN in a 1:2:4 mole ratio in aqueous MeOH at room temperature under stirring condition affords 1. Whereas the reaction of NiCl 2·6H 2O with imidazole and NaOCN in a 1:4:2 mole ratio in aqueous MeOH at room temperature under stirring condition yields 2 quantitatively. The nickel ions are hexacoordinated by six nitrogen donor atoms of two different origin, thiocyanate and piperazinium ions in case of 1 and cyanate ion and neutral imidazole in case of 2, to form tetragonally elongated and quite regular octahedral arrangements. In 1, the average Ni–N ppz distance is 2.198 Å is longer than the average Ni–N thc distance at 2.070 Å, whereas, in case of 2, the average Ni–N imd distance at 2.112 Å and is close to the average Ni–N cyt distance at 2.107 Å. The reactions in other varying stoichiometries failed to provide the hitherto unknown complexes [Ni(NCS) 2(Ppz) 4] and [Ni(NCO) 4(ImdH) 2] confirming the ease of protonation on non-bonding of piperazine is more compared to that of imidazole.

Evalution of in vitro effect of flavonoids on human low-density lipoprotein carbamylation.

The non-enzymatic carbamylation of low density lipoprotein (LDL) is a naturally occurring chemical modification of apolipoprotein B as a result of condensation between lysine residues and cyanate derived from urea. Carbamylated LDL is poorly recognized by LDL receptors and initiates different processes that can be considered proatherogenic. Thus, LDL carbamylation may contribute to the increased risk of atherosclerosis in patients with kidney failure. The objective of this study was to investigate in vitro effects of flavonoids on LDL carbamylation. LDL was isolated from plasma using ultracentrifuge technique with a single step discontinuous gradient. Then, cyanate was added to LDL and LDL carbamylation level was estimated in absence and presence of flavonoids by a colorimetric method at 530 nm. The results of this study showed that a number of flavonoids including rutin, catechin, morin, myricetin, kaempferol, taxifolin, luteolin, naringin and quercetin decreased LDL carbamylation in a dose dependent manner. Also, it was demonstrated that these nutrients decreased electrophoretic mobility of carbamylated LDL. Based on the results obtained in this study, it is suggested that flavonoids are able to inhibit LDL carbamylation (probably by scavenging cyanate ions) and thus, may have a role in ameliorating atherosclerotic risk of patients with kidney failure.

Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) Mixed Ligand Complexes of Theophylline and Cyanate: Synthesis and Spectroscopic Characterization

New mixed ligand complexes were synthesized between theophylline and cyanate to give complexes with general formula [M(Tp)4Y2] where Tp= theophylline, Y= cyanate ion and M=Co(II), Ni(II),Cu(II), Zn(II) and Cd(II). The resulting products were found to be crystallined which have been characterized using UV-Visible spectroscopic properties and Infrared spectra. Elemental analyses were performed using (C, H, N) and atomic absorption technique. The magnetic susceptibility and the conductivity for the complexes were also measured. The present results suggested the octahedral configuration for the metal complexes.

On the Formation and Decomposition of the Melonate Ion in Cyanate and Thiocyanate Melts and the Crystal Structure of Potassium Melonate, K3[C6N7(NCN)3

AbstractThe synthesis of potassium melonate, K3[C6N7(NCN)3], by reaction of a potassium thiocyanate melt with the polymer melon [C6N7(NH)(NH2)]n is an established, though poorly understood, reaction. We have modified the original approach by using salt melts containing Na+ ions and/or cyanate ions to yield the respective melonate salts. These melonates, however, are not the final reaction products. We have identified them to decompose in cyanate melts to formtricyanomelaminates at higher temperatures and prolonged reaction times. This is the first selective decomposition reaction leading from heptazines to triazines. The progress of the reactions was studied by using thermal analysis, thus allowing the exact determination of reaction temperatures and weight losses. With the data at hand we are now able to gain better insight into the formation and properties of alkali melonates while establishing new synthetic routes to these compounds. We were able to isolate crystals of anhydrous potassium melonate directly from a thiocyanate melt. The structure of this compound was solved by single‐crystal X‐ray‐diffraction. The new reaction conditions involving cyanates on the one hand avoid the release of CS2 and are no longer highly corrosive to most metallic reaction vessels and on the other hand these reagents provide new, cheap, and convenient access to melonates and tricyanomelaminates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Synthesis, Crystal Structure, Thermal, Spectroscopic and Magnetic Properties of a 2D Grid‐like Copper(II) μ‐1,1 Isocyanato Coordination Polymer with Pyrazine Bridges

AbstractReaction of copper(II) cyanate with pyrazine leads to the formation of [Cu(NCO)2(pyrazine)]n (1), in which the Cu2+ cations are coordinated by two nitrogen atoms of the pyrazine ligands, as well as by four nitrogen atoms of the cyanate anions within a slightly distorted octahedral coordination. In the crystal structure the Cu2+ cations are connected by the pyrazine ligands into chains which are further linked by the cyanate anions through asymmetric μ‐1,1‐NCO coordination into layers. On heating compound 1 transforms quantitatively to copper(II) cyanate which decompose to elemental copper on further heating. No ligand deficent intermediates are observed. Magnetic measurements reval an antiferromagnetic ordering at lower temperatures mediated by the π‐system of the aromatic pyrazine ligand as well as net ferromagnetic interactions mediated by the μ‐1,1‐NCO bridging cyanato anions. A search in the Cambridge Crystal Structure Database shows that the terminal coordination mode in cyanato complexes as well as their azido and thiocyanato analogs is obviously energetically favored. In addition, a comparison of their symmetric and asymmetric end‐on (μ‐1,1) as well as end‐to‐end (μ‐1,3) bridging modes reveal interesting correlations.

Poly[bis(cyanato-κN)bis(μ-pyrazine-κ2N:N′)cobalt(II)

In the crystal structure of the title compound, [Co(NCO)2(C4H4N2)2]n, the Co(II) cation is coordinated by four N-bonded pyrazine ligands and two N-bonded cyanate anions in a slightly distorted octa­hedral geometry. The crystal structure consists of μ-N:N′ pyrazine-bridged cobalt cyanate chains; these are further linked by additional μ-N:N′-bridging pyrazine ligands into layers, which are stacked perpendicular to the crystallographic a axis. The C and O atoms in both crystallographic independent cyanate anions are disordered in two orientations and were refined using a split model with site occupation factor ratios of 0.75/0.25 and 0.7/0.3.

鉄シアノ錯体の湿式加熱分解と過酸化水素添加による分解挙動への影響

In this work, hydrothermal decomposition of [Fe(CN)6]3− in alkaline solution was conducted in a batch-type autoclave. The initial concentration of CN in [Fe(CN)6]3− in the sample solution was set to correspond to 1,000 mg CN/dm3. The experiments were conducted at temperatures of 403-443 K under O2 atmosphere at 0.1-4 MPa pressure. Hydrogen peroxide (H2O2) was used as an oxidation agent to enhance oxidative decomposition of [Fe (CN)6]3−. Moreover, the mechanism of this reaction was discussed.Results show that the rate of hydrothermal decomposition of [Fe (CN)6]3− is independent of O2 partial pressure. The rate is sufficiently described by first-order reaction Kinetics with respect to the [Fe(CN)6]3− concentration. The principal reaction products of cyanate (OCN−), formate (HCOO−), and ammonium (NH4+) ions were detected using ion chromatography. When H2O2 was added to [Fe(CN)6]3− solution, the decomposition rate of CN in [Fe(CN)6]3− at the initial stage of the reaction (0.5-2 h) was found to be 1.2-1.3 times higher than that without H2O2. The reaction products of HCOO−, carbonate (CO32−) and NH4+ ions were detected. Such different reaction products resulting from H2O2 addition suggest the formation of CO32−and N2 during oxidative decomposition of [Fe(CN)6]3− by H2O2.

Nanostructural materials; nanolayers and nanofibres

Layered double hydroxides (LDHs) are a class of synthetic two-dimensional nanostructured anionic clays whose structure can be described as nanolayered ordered material. In this work, we study the effect of inclusion of tetravalent cation (titanium) into the layers and the insertion of cyanate anions into the lamellar region on the formation of nanostructure. Co-Al LDH acts as a host and has interlayer spacing 0.79 nm in the case of cyanate anions as a guest. The IR-spectra confirmed the insertion of cyanate anions in the first time into the lamellar region of LDH structure. X-ray diffraction patterns of Co-Al-CNO LDH indicated layered structure and SEM images showed plate-like morphology. With the preparation of Co-Al-Ti LDH, X-ray diffraction patterns confirmed nanolayered structure while SEM images showed that the edges of layers became curved layers. In the preparation of Co-Ti LDH, SEM images showed nanofibrous and nanoneedles depending on the percentage of titanium. This study concludes that the inclusion of titanium into the layers directs nanolayers to be fibrous or needles structure.

Kinetics of a Collagen-Like Polypeptide Fragmentation after Mid-IR Free-Electron Laser Ablation

Tissue ablation with mid-infrared irradiation tuned to collagen vibrational modes results in minimal collateral damage. The hypothesis for this effect includes selective scission of protein molecules and excitation of surrounding water molecules, with the scission process currently favored. In this article, we describe the postablation infrared spectral decay kinetics in a model collagen-like peptide (Pro-Pro-Gly) 10. We find that the decay is exponential with different decay times for other, simpler dipeptides. Furthermore, we find that collagen-like polypeptides, such as (Pro-Pro-Gly) 10, show multiple decay times, indicating multiple scission locations and cross-linking to form longer chain molecules. In combination with data from high-resolution mass spectrometry, we interpret these products to result from the generation of reactive intermediates, such as free radicals, cyanate ions, and isocyanic acid, which can form cross-links and protein adducts. Our results lead to a more complete explanation of the reduced collateral damage resulting from infrared laser irradiation through a mechanism involving cross-linking in which collagen-like molecules form a network of cross-linked fibers.

Cyanation of adamantane and diamantane with acetonitrile and tetrabromomethane in the presence of Mo(CO)6

Cyanation of adamantane and diamantane with acetonitrile and tetrabromomethane in the presence of Mo(CO)6

Cis-Bis(2,2′-bipyridyl)dicyanatocobalt(II)

In the title complex, [Co(NCO)2(C10H8N2)2], the Co atom is coordinated by four N atoms from two 2,2′-bipyridyl ligands and two N atoms from two cyanate anions in a distorted octa­hedral geometry. The Co atom lies on a twofold rotation axis. The average Co—N bond length is 2.126 (7) Å. Weak inter­molecular C—H⋯O inter­actions lead to the formation of a three-dimensional network.