57-12-5Relevant academic research and scientific papers
Dissociative electron attachment to C2N2 molecules at surface and in gas phase
Deng,Souda
, p. 1725 - 1730 (2002)
Strong thermionic emission of CN- ions was observed during heating of nitrogen ion-irradiated graphite. An activation energy of 5.0±0.2 eV for CN- emission was derived from its temperature dependence. Several possible mechanisms were
Entropy-Driven Proton-Transfer Reactions
Meot-Ner, Michael
, p. 6580 - 6585 (1991)
The reation between kinetics and thermochemistry in fat reactions is examined, including reactions with substantial entropy changes.Rate constants for such reactions, in the range of (0.02-3.0) * 10-9 cm2 s-1, were measured by pulsed high-pressure mass spectrometry.The following relations were observed: (1) The reaction efficiency in either direction is controlled uniquely and completely by the overall reaction free energy change.Specifically, the efficieny r is determined by the equilibrium constant according to r= K/(1+K). (2) The sum of reaction efficiencies in the forward (exergonic) and reverse (endergonic) directions is near unity (rf + rr = ca. 1).These relations are obseved in anionic and cationic systems, in reactions with ΔH0 up to 12 kcal/mol and with ΔS0 up to 15 cal/(mol K).Consistent with (1), reactions that are endothermic up to 7 kcal/mol can nevertheless proceed near the collision rate, when positive entropy changes make the reactions exergonic.The entropy canges are effective regardless of their stuctural origin.Relations analogous to (1) and (2) are also derived for reactions with multiple channels that proceed without significant barriers through a common intermediate.
Mechanistic diversity covering 15 orders of magnitude in rates: Cyanide exchange on [M(CN)4]2- (M = Ni, Pd, and Pt)
Monlien, Florence J.,Helm, Lothar,Abou-Hamdan, Amira,Merbach, Andre E.
, p. 1717 - 1727 (2002)
Kinetic studies of cyanide exchange on [M(CN)4]2- square-planar complexes (M = Pt, Pd, and Ni) were performed as a function of pH by 13C NMR. The [Pt(CN)4]2- complex has a purely second-order rate law, with CN- as acting as the nucleophile, with the following kinetic parameters: (k2Pt,CN)298 = 11 ± 1 s-1 mol-1 kg, ΔH2? Pt,CN = 25.1 ± 1 kJ mol-1, ΔS2? Pt,CN = -142 ± 4 J mol-1 K-1, and ΔV2? Pt,CN = -27 ± 2 cm3 mol-1. The Pd(II) metal center has the same behavior down to pH 6. The kinetic parameters are as follows: (k2Pd,CN)298 = 82 ± 2 s-1 mol-1 kg, ΔH2? Pd,CN = 23.5 ± 1 kJ mol-1, ΔS2? Pd,CN = -129 ± 5 J mol-1 K-1, and ΔV2? Pd,CN = -22 ± 2 cm3 mol-1. At low pH, the tetracyanopalladate is protonated (pKa Pd(4,H) = 3.0 ± 0.3) to form [Pd(CN)3HCN]-. The rate law of the cyanide exchange on the protonated complex is also purely second order, with (k2PdH,CN)298 = (4.5 ± 1.3) × 103 s-1 mol-1 kg. [Ni(CN)4]2- is involved in various equilibrium reactions, such as the formation of [Ni(CN)5]3-, [Ni(CN)3HCN]-, and [Ni(CN)2(HCN)2] complexes. Our 13C NMR measurements have allowed us to determine that the rate constant leading to the formation of [Ni(CN)5]3- is k2Ni(4),CN = (2.3 ± 0.1) × 106 s-1 mol-1 kg when the following activation parameters are used: ΔH2? Ni,CN = 21.6 ± 1 kJ mol-1, ΔS2? Ni,CN = -51 ± 7 J mol-1 K-1, and ΔV2? Ni,CN = -19 ± 2 cm3 mol-1. The rate constant of the back reaction is k-2Ni(4),CN = 14 × 106 s-1. The rate law pertaining to [Ni(CN)2(HCN)2] was found to be second order at pH 3.8, and the value of the rate constant is (k2 Ni(4,2H),CN,)298 = (63 ± 15) × 106 s-1 mol-1 kg when ΔH2? Ni(4,2H),CN = 47.3 ± 1 kJ mol-1, ΔS2? Ni(4,2H),CN = 63 ± 3 J mol-1 K-1, and ΔV2? Ni(4,2H),CN = -6 ± 1 cm3 mol-1. The cyanide-exchange rate constant on [M(CN)4]2- for Pt, Pd, and Ni increases in a 1:7:200 000 ratio. This trend is modified at low pH, and the palladium becomes 400 times more reactive than the platinum because of the formation of [Pd(CN)3HCN]-. For all cyanide exchanges on tetracyano complexes (A mechanism) and on their protonated forms (IIIa mechanisms), we have always observed a pure second-order rate law: first order for the complex and first order for CN-. The nucleophilic attack by HCN or solvation by H2O is at least nine or six orders of magnitude slower, respectively than is nucleophilic attack by CN- for Pt(II), Pd(II), and Ni(II), respectively.
Kinetic and thermodynamic studies on the cyanation reactions and base-on/base-off equilibria of alkyl-13-epicobalamins
Hamza, Mohamed S. A.,Zou, Xiang,Brown, Kenneth L.,Van Eldik, Rudi
, p. 2986 - 2991 (2003)
Ligand substitution equilibria of two different 13-epicobalamins (X-13-epiCbl, X = NCCH2 and CN-) with cyanide have been studied. It was found that CN- substitutes the 5,6- dimethylbenzimidazole (DMBz) moiety in the α-position to form X(CN)Cbl-13epi, which for X = NCCH2 in the presence of CN- subsequently gives (CN)2Cbl-13epi. The kinetics of the displacement of DMBz by CN- showed saturation behaviour at high cyanide concentration and the limiting rate constants are characterized by the activation parameters: X = NCCH2, ΔH≠ = 83 ± 1 kJ mol-1, ΔS≠ = +77 ± 4 J K-1 mol-1, ΔV≠ = +13.3 ± 1.0 cm3 mol-1; X = CN-, ΔH≠ = 106 ± 1 kJ mol-1, ΔS≠ = +82 ± 4 J K-1 mol-1 and ΔV≠ = +14.8 ± 0.5 cm3 mol-1. These parameters are interpreted in terms of a limiting D mechanism. The rate constants for the displacement of DMBz in the case of the 13-epicobalamins were found to be slower than those obtained in the case of the analogous alkylcobalamins, and consequently, the thermodynamic equilibrium constants for the 13-epicobalamins were found to be smaller than those obtained in the case of the alkylcobalmins. This clearly shows the effect of the epimerization of the e-side chain attached to the C-13 of the corrin ring on the rate and equilibrium constants for these ligand displacement reactions. The Royal Society of Chemistry 2003.
Carbon Monoxide Dehydrogenase Reduces Cyanate to Cyanide
Ciaccafava, Alexandre,Tombolelli, Daria,Domnik, Lilith,Jeoung, Jae-Hun,Dobbek, Holger,Mroginski, Maria-Andrea,Zebger, Ingo,Hildebrandt, Peter
, p. 7398 - 7401 (2017)
The biocatalytic function of carbon monoxide dehydrogenase (CODH) has a high environmental relevance owing to its ability to reduce CO2. Despite numerous studies on CODH over the past decades, its catalytic mechanism is not yet fully understood. In the present combined spectroscopic and theoretical study, we report first evidences for a cyanate (NCO?) to cyanide (CN?) reduction at the C-cluster. The adduct remains bound to the catalytic center to form the so-called CN?-inhibited state. Notably, this conversion does not occur in crystals of the Carboxydothermus hydrogenoformans CODH enzyme (CODHIICh), as indicated by the lack of the corresponding CN? stretching mode. The transformation of NCO?, which also acts as an inhibitor of the two-electron-reduced Cred2 state of CODH, could thus mimic CO2 turnover and open new perspectives for elucidation of the detailed catalytic mechanism of CODH.
Laser catalysis of acrylonitrile on copper surfaces
Cáceres,Tornero López,González Ure?a
, p. 349 - 355 (2000)
The electron emission and CN- yield produced by laser irradiation of acrylonitrile (ACN) adsorbed on a polycrystalline Cu surface have been investigated over the 930-953 cm-1 wavenumber range. Both emissions show a clear wavelength dependence with a ca. 20 cm-1 red shift with respect to the gas-phase ACN spectrum. The laser catalysis CN- yield is discussed in light with both substrate and adsorbate-mediated mechanisms, which seem to be controlling this (charge-transfer) surface reaction.
Synthesis, characterization and thermal behaviour of adducts 8-quinolinol with the photoproduct of octacyano-molybdate(IV) and -tungstate (IV) with ethylenediamine and triethylenetetramine
Ali,Ansari
, p. 1763 - 1774 (1996)
The photoproduct of octacyanomolybdate(IV) and -tungstate(IV) with ethylenediamine and triethylenetetramine give complexes of the type K3[Mo(O2)(O)(OH)(C9H7ON)]·3C9H7ON I, K2[W(O
Difluorocarbene-based cyanodifluoromethylation of alkenes induced by a dual-functional Cu-catalyst
Zhang, Min,Lin, Jin-Hong,Jin, Chuan-Ming,Xiao, Ji-Chang
, p. 2649 - 2652 (2021)
Although cyanofluoroalkylation has received increasing attention, a toxic cyanation reagent is usually required. Herein, a Cu-catalyzed difluorocarbene-based cyanodifluoromethylation of alkenes with BrCF2CO2Et/NH4HCO3under photocatalytic conditions is described. BrCF2CO2Et and NH4HCO3serve as a carbon source and a nitrogen source of the nitrile group, respectively, avoiding the use of a stoichiometric toxic cyanation reagent. The Cu-complex plays a dual role. It is not only a photocatalyst, but also a coupling catalyst for the formation of a C-CN bond.
Catalytic Polarographic Wave of Fe(II) in Neutral Thiocyanate Solutions at Dropping Mercury Electrode
Himeno, Sadayuki,Saito, Atsuyoshi
, p. 1715 - 1719 (1981)
The electrochemical behavior of Fe(II) in neutral thiocyanate solutions has been investigated at a dropping mercury electrode (DME).It was found that Fe(II) in neutral thiocyanate solutions gave a catalytic polarographic wave at potentials prior to the main Fe(II) reduction wave.The mechanism of the catalytic process involves the chemical reduction of thiocyanate ions with Fe(OH)2,aq at the electrode surface.Controlled potential electrolysis suggests that the reduction of thiocyanate ions proceeds with the formation of sulfide and cyanide ions.Sulfide ions produced at the electrode surface can react with Fe(II) diffusing to the electrode to form FeS.The discharge of this is responsible for the catalytic current, while cyanide ions have no essential role in the catalytic process.The effects of surface active substances and iodate ions on the catalytic wave are also discussed.
Rate constant and activation energy measurement for the reaction of atomic hydrogen with thiocyanate and azide in aqueous solution
Mezyk, Stephen P.,Bartels, David M.
, p. 11823 - 11827 (2005)
Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous solution have been determined using electron pulse radiolysis and electron paramagnetic resonance free induction decay attenuation measurements. Absolute values for SCN-, N3-, and HN3 were well-described over the temperature range of 9-81 °C by the equations log k5 = (12.03 ± 0.12) - [(21.05 ± 0.66 kJ mol-1)/2.303RT], log k10 = (12.75 ± 0.21) - [(18.43 ± 1.22 kJ mol-1)/2.303RT], and log k15 = (11.59 ± 0.12) - [(21.44 ± 0.69 kJ mol -1)/2.303RT], corresponding to room temperature (22 °C) rate constants of (2.07 ± 0.03) ± 108, (3.15 ± 0.08) × 109, and (6.31 ± 0.05) × 107 M -1 s-1 and activation energies for these chemicals of 21.05 ± 0.66, 18.4 ± 1.2, and 21.44 ± 0.69 kJ mol -1, respectively. The similarity of these three measured activation energies, taken together with the available information on reaction products, suggests a similar reaction mechanism, which is proposed to be an initial hydrogen atom adduct formation in these molecules, followed by single bond breakage.
