Über Chalkogenolate. 126. Untersuchungen über N-Cyanformamidinodithiocarbimidsäure 2. Thermisches Verhalten von Kalium-N-cyanformamidinodithiocarbimat in Lösung

On Chalcogenolates. 126. Studies on N-Cyanformamidino Dithiocarbimic Acid. 2. Thermal Behaviour of Potassium N-Cyanformamidino Dithiocarbimate in Solution The thermal treatment of K₂[S₂C?N? C(NH₂)?N? CN] in methanolic solution yields . The semi-hydrate has been isolated. It reacts with acid to form The reaction with H₃CI gives The compounds have been characterized by means of electron absorption, ¹H- and ¹³C-N.M.R., infrared, and mass spectra.     

Der Sättigungsdruck von NbCl4 und NbBr4

Vapour Pressure of NbCl₄ and NbBr₄ The vapour pressur of solid NbCl₄ has been determined spectralphotometrically near 600 K: . NbCl₄ is monomolecular in the gaseous state. In the same way the vapour pressure of NbBr₄ has been found: .     

Trägerfixierte Organometallkomplexe. VI. Charakterisierung und Reaktivität Polysiloxan-gebundener (Ether-phosphan)ruthenium(II)-Komplexe

Supported Organometallic Complexes. VI. Characterization und Reactivity of Polysiloxane-Bound (Ether-phosphane)ruthenium(II) Complexes The ligands PhP(R)CH₂D [R = (CH₃O)₃Si(CH₂)₃; D = CH₂OCH₃ ( 1b ); D = tetrahydrofuryl ( 1c ); D = 1,4-dioxanyl ( 1d )] have been used to synthesize (ether-phosphane)ruthenium(II) complexes, which have been copolymerized with Si(OEt)₄ to yield polysiloxane-bound complexes. The monomers cis,cis,trans-Cl₂Ru(CO)₂(P ～ O)₂ ( 3b ) and HRuCl(CO)(P ～ O)₃ ( 5b ) were treated with NaBH₄ to form cis,cis,trans-H₂Ru(CO)₂(P ～ O)₂ ( 4b ) and H₂Ru(CO)(P ～ O)₃ ( 6b ), respectively (P ～ O = η¹-P coordinated; = η²- coordinated). Addition of Si(OEt)₄ and water leads to a base catalyzed hydrolysis of the silicon alkoxy-functions and a precipitation of the immobilized counterparts 4b ′, 6b ′. The polysiloxane matrix resulting by this new sol gel route has been described under quantitative aspects by ²⁹Si CP-MAS NMR spectroscopy. 4b ′ reacts with carbon monoxide to form Ru(CO)₃(P ～ O)₂ ( 7b ′). Chelated polysiloxane-bound complexes Cl₂Ru( )₂ ( 9c ′, d ′) and Cl₂Ru( )(P ～ O)₂ ( 10b ′, c ′) have been synthesized by the reaction of 1b–c with Cl₂Ru(PPh₃)₃ ( 8 ) followed by a copolymerization with Si(OEt)₄. The polysiloxane-bound complexes 9c ′, d ′ and 10b ′, c ′ react with one equivalent of CO to give Cl₂Ru(CO)( )(P ～ O) ( 12b ′– d ′). Excess CO leads to the all-trans-complexes Cl₂Ru(CO)₂(P ～ O)₂ ( 14b ′– d ′), which are thermally isomerized to cis,cis,trans- 3b ′– d ′. The chemical shift anisotropy of ³¹P in crystalline Cl₂Ru( )₂ ( 9a , R = Ph, D = CH₂OCH₃) has been compared with polysiloxane-bound 9d ′ indicating a non-rigid behavior of the complexes in the matrix.     

Decomposition of the t-butoxy radical — I. Studies over the temperature range 402–443 K

By allowing the t-butoxy radical to decompose in the presence of nitric oxide, it has been possible to determine rate constants for decomposition by the measurements of the relative rates (2) and (3) Process (3) is clearly pressure dependent. The value of k₃(∞) has been determined in the presence of several inert gases (CF₄, SF₆, N₂, and Ar) and a value of k₃ interpolated for atmospheric conditions. The results may be compared with those for other relevant alkoxy radicals at room temperature. Extrapolated values for k₃ in the presence of CF₄ lead to the result      

Beiträge zur Chemie der Oxidhalogenide von Molybdän und Wolfram. V. Molybdänoxidtetrachlorid und Molybdänoxidtrichlorid

The formation enthalpies were ascertained from the solution enthalpies in 2 n NaOH resp. 2 n NaOH + 1% H₂O₂. The results of equilibrium measurements in the systems give the formation enthalpies and standard entropies: . The value of the standard entropy of the gaseous MoOCl₄ was estimated to be 91 (±3) cl. From the enthalpies and entropies of sublimation the values were obtained.     

A shock tube study of H + HNCO → NH2 + CO

The reaction of atomic hydrogen with isocyanic acid (HNCO) to produce the amidogen radical (NH₂) and carbon monoxide, has been studied in shock-heated mixtures of HNCO dilute in argon. Time-histories of the ground-state NH₂ radical were measured behind reflected shock waves using cw, narrowlinewidth laser absorption at 597 nm, and HNCO time-histories were measured using infrared emission from the fundamental v₂-band of HNCO near 5 μm. The second-order rate coefficient of reaction (2(a)) was determined to be: cm³ mol^?1 s^?1, where f and F define the lower and upper uncertainty limits, respectively. An upper limit on the rate coefficient of was determined to be:      

Rate data for O + OCS → SO + CO and SO + O3 → SO2 + O2 by a new time-resolved technique

Pulsed laser photolysis of O₃ in a large excess of N₂ has been used to generate O(³P) atoms in the presence of OCS. By observing chemiluminescence from the small fraction of electronically excited SO₂ formed in the reaction of SO with O₃, rate constants of (1.7 ± 0.2) × 10^?14 and (8.7 ± 1.6) × 10^?14 cm³/molecule sec have been determined at 296 ± 4 K for the reactions and In addition, it has been shown that any reaction between SO and OCS has a rate constant 10^?14 cm³/molecule sec.     

Über Chalkogenolate. 121. Untersuchungen über N-Cyanomonothiocarbimidsäure 1. Darstellung und Eigenschaften von Alkalimetall-N-cyanomonothiocarbimaten

On Chalcogenolates. 121. Studies on N-Cyanomonothiocarbimic Acid. 1. Synthesis and Properties of Alkali Metal N-Cyanomonothiocarbimates The hitherto unknown N-cyanomonothiocarbimates M₂[SOC?N? CN] · H₂O, where M = Na, K, Rb, Cs, have been prepared by reaction of the corresponding alkali metal salt of cyanamide with COS. N-Cyanomonothiocarbimates react with sulfur to form the ion, which gives with an acid and with CH₃I the methyl compound . The reaction of the latter compound with H₂O₂ yields . All compounds have been characterized by means of diverse methods.     

Chlorine-photosensitized reactions in the Cl2 + O2 + 1,1,1,2-C2H2Cl4 system

The gas-phase photochlorination (λ = 436 nm) of the 1,1,1,2-C₂H₂Cl₄ has been studied in the absence and the presence of oxygen at temperatures between 360 and 420°K. Activation energies have been estimated for the following reaction steps: The dissociation energy D(CCl₃CHCl? O₂) ± (24.8 ± 1.5) kcal/mole has also been estimated from the difference in activation energy of the direct and reverse reactions The mechanism is discussed and the rate parameters are compared to those obtained for a series of other chlorinated ethanes.     

BrNO—thermodynamic properties,the ultraviolet/vis spectrum,and the kinetics of its formation

The equilibrium has been studied between 275°and 363°K. Third-law calculations lead to ΔH°₂₉₈(1) = -11.50 ±0.17 kcal/mol, from which Absorption bands of BrNO in the ultraviolet with e (γ_max = 215 nm) = 1.84±0.17 × 10⁴ 1/mol·cm, and in the red with e (γ_max = 708 nm) = 7.7±1.9 1/mol·cm at 298°K have been investigated. The rate of formation of BrNO has also been measured between 275°and 363°K.     

Kinetics,mechanism, and endo selectivity of Diels–Alder reactions of alkylmonosubstituted ethenes with cyclohexa-1,3-diene in the gas phase

The reactions where Y = CH₃ (M), C₂H₅ (E), i? C₃H₇ (I), and t? C₄H₉ (T) have been studied between 488 and 606 K. The pressures of CHD ranged from 16 to 124 torr and those of YE from 57 to 625 torr. These reactions are homogeneous and first order with respect to each reagent. The rate constants (in L/mol·s) are given by The Arrhenius parameters are used as a test for a biradical mechanism and to discuss the endo selectivity of the reactions.     

H2S-promoted thermal isomerization of butene-2 CIS to butene-1 or butene-2 trans around 500°C

H₂S increases the thermal isomerization of butene-2 cis (B_c) to butene-1 (B₁) and butene-2 trans (B_t) around 500°C. This effect is interpreted on the basis of a free radical mechanism in which buten-2-yl and thiyl free radicals are the main chain carriers. B₁ formation is essentially explainedby the metathetical steps: whereas the free radical part of B_t formation results from the addition–elimination processes: . It is shown that the initiation step of pure B_c thermal reaction is essentially unimolecular: and that a new initiation step occurs in the presence of H₂S: . The rate constant ratio has been evaluated: and the best values of k₁ and k_1', consistent with this work and with thermochemical data, are . From thermochemical data of the literature and an “intrinsic value” of E_?3 ? 2 kcal/mol given by Benson, further values of rate constants may be proposed: is shown to be E₄ ? 3.5 ± 2 kcal/mol, of the same order as the activation energy of the corresponding metathetical step.     

Über Chalkogenolate. 82 [1]. N-Hydroxycarbamate und Ester der N-Hydroxycarbamidsäure und -carbimidsäure

On Chalcogenolates. 82. N-Hydroxy Carbamates and Esters of N-Hydroxy Carbamic Acid and Carbamic Acid The reaction between hydroxylammonium chloride, CO₂, and the corresponding hydroxide leads to N-hydroxy carbamates Esters of N-hydroxy carbamic acid have been prepared by reaction of N-hydroxy carbamates with alkyl bromide. – At room temperature the ethyl ester decomposes and forms the ester of N-hydroxy carbimic acid HO? N?C(OC₂H₅)₂. The prepared compounds have been characterized by different methods.     

Kinetics and mechanism of oxidation of l‐ascorbic acid by peroxomonophosphate in aqueous acid medium

The kinetics of oxidation of l ‐ascorbic acid (H₂A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation (1) where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: (2) Such pH dependence is somewhat different from that observed in the case of metal ion oxidants. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 41–16, 2013     

Iodostannate(II) mit kettenförmigen [SnI3]–‐Anionen – der Übergang von fünffach zu sechsfach koordinierten SnII‐Zentralatomen

Iodostannates(II) with Anionic [SnI₃]^– Chains – the Transition from Five to Six‐coordinated Sn^II The iodostannates (Me₄N) [SnI₃] ( 1 ), [Et₃N–(CH₂)₄–NEt₃] [SnI₃]₂ ( 2 ), [EtMe₂N–(CH₂)₂–NEtMe₂] [SnI₃]₂ ( 3 ), [Me₂HN–(CH₂)₂–NH–(CH₂)₂–NMe₂H] [SnI₃]₂ ( 4 ), [Et₃N–(CH₂)₆–NEt₃] [SnI₃]₂ ( 5 ) and [Pr₃N–(CH₂)₄–NPr₃]‐ [SnI₃]₂ · 2 DMF ( 6 ) with the same composition of the anionic [SnI₃]^– chains show differences in the coordination of the Sn^II central atoms. Whereas the Sn atoms in 1 and 2 are coordinated in an approximately regular octahedral fashion, in compounds 3 – 6 the continuous transition to coordination number five in (Pr₄N) [SnI₃] ( 7 ) or [Fe(dmf)₆] [SnI₃]₂ ( 8 ) can be observed. Together with the shortening of two or three Sn–I bonds, the bonds in trans position are elongated. Thus weak, long‐range Sn…I interactions complete the distorted octahedral environment of SnI₄ groups in 3 and 4 and SnI₃ groups in 5 and 6 . Obviously the shape, size and charge of the counterions and the related cation‐anion interactions are responsible for the variants in structure and distortion.     

Multilayer Assemblies Consisting of Tri‐Vanadium‐Substituted Heteropolyanions and Its Electrocatalytic Properties

We describe the controlled fabrication of ultrathin multilayer films consisting of tri‐vanadium‐ substituted heteropolytungstate anions (denoted as P₂W₁₅V₃) and a cationic polymer of quaternized poly (4‐vinylpyridine) partially complexed with osmium bis(2,2′‐bipyridine) (denoted as QPVP‐Os) on the 4‐aminobenzoic acid (4‐ABA) modified glassy carbon electrode (GCE) surface based on layer‐by‐layer assembly. Cyclic voltammetry and UV‐vis absorption spectrometry have been used to easily monitor the thickness and uniformity of thus‐formed multilayer films. The V‐centered redox reaction of P₂W₁₅V₃ in the multilayer films can effectively catalyze the reduction of BrO and NO . The resulting P₂W₁₅V₃/QPVP‐Os multilayer film modified electrode behaves as a much promising electrochemical sensor because of the low overpotential for the catalytic reduction of BrO and NO , and the catalytic oxidation of ascorbic acid.     

Oligomérisation anionique de l'ethylène. I. Etude cinétique

A kinetic study of ethylene oligomerization in hexane, in the presence of n-BuLi–TMEDA complexes, allowed us to suggest a new mechanism for anionic ethylene oligomerization. n-BuLi and n-Bu(CH₂CH₂)Li species have the same reactivity. The RLi–TMEDA complex in a 1-to-1 stoichiometry is the active species. The following kinetic equation has been established: It reflects the intervention of associated species (n-BuLi–TMEDA)₂ as well as the influence of the concentration of the complexing agent on the kinetics of oligomerization.     

The determination of the arrhenius parameters for the reaction Cl + C2F5I → ICl + C2F5 using a competitive method

The reactions have been studied competitively over the range of 28–182°C by photolysis of mixtures of Cl₂ + C₂F₅I+ CH₄. We obtain where θ = 2.303RT J/mol. The use of published data on reaction (2) leads to log (k₁cm³/mol sec) = (13.96 ± 0.2) ? (11,500 ± 2000)/θ.     

Kinetics of the reaction: 2C2H4 → C2H5 + C2H3· heat of formation of the vinyl radical

The initial rates of formation of the major products in the thermal reactions of ethylene at temperatures in the neighborhood of 800 K have been measured in the presence and absence of the additives neopentane and ethane. It has been shown that in the absence of the additive the main initiation process is (1) while in the presence of neopentane and ethane the following additional initiation processes occur: (2) From the ratios of the rates of formation of the major products in the presence and absence of the additive the ratios k_N/k₁ and k_E/k₁ were measured over the temperature range of 750–820 K. Taking values from the literature for k_N and k_E, the following value was obtained for k₁: Previous results using butene-1 as additive were rexamined and shown to be consistent with this measurement. From this measurement the following values were derived: ΔH_f(C₂H₃) = 63.4 ± 2 kcal/mol and D(C₂H₃? H) = 103 kcal/mol.     

Stable γ-distonic oxonium ions: R\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm O}\limits^ + $\end{document}HCHR′ĊH2CHR″ and their characteristic reaction

The γ-distonic radical ions R$ \mathop {\rm O}\limits^ + $CHR′CH₂?HR″ and their molecular ion counterparts R$ \mathop {\rm O}\limits^{{\rm + } \cdot } $CHR′CH₂CH₂R″ have been studied by isotopic labelling and collision-induced dissociation, applying a potential to the collision cell in order to separate activated from spontaneous decompositions. The stability of CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, C₂H₅$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?HCH₃, CH₃$ \mathop {\rm O}\limits^ + $HCH(CH₃)CH₂?H₂, CH₃$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃ and C₂H₅$ \mathop {\rm O}\limits^ + $HCH₂CH₂?HCH₃, has been demonstrated and their characteristic decomposition, alcohol loss, identified. For all these γ-distonic ions, the 1,4-H abstraction leading to their molecular ion counterpart exhibits a primary isotope effect.