Kinetics of the thermal decomposition of ferrocenyl azide: Character of ferrocenyl nitrene

The Arrhenius parameters for the thermal decomposition of ferrocenyl azide in isooctane are A = (5.1 ± 1.4) × 10¹² s^?1 and E_act = 113.1 ± 0.9 (kJ mol^?1) and the rate is relatively insensitive to solvent (isooctane, benzene, acetonitrile: 1:1.7:2.4). The results indicate a relatively nonpolar transition state which is considerably “tighter” than for a normal bond fission reaction. The Arrhenius parameters are comparable to those for aromatic azides and do not offer any support for anchimeric assistance by the iron atom. A kinetic scheme is presented which accounts for the observed products: Nitrogen, ferrocene, aminoferrocene, azoferrocene, and insoluble material. Rates of hydrogen abstraction by the intermediate ferrocenyl nitrene from cyclohexane, benzene, and acetonitrile are used to show that the nitrene is nucleophilic. © 1994 John Wiley & Sons, Inc.     

Formation of nitrene complexes of rhenium by the reaction of oxo derivatives of rhenium with phenyl isocyanate

Conclusions Phenyl isocyanate can be a source of nitrenes when it is oxidized by the oxo complexes of the transition metals. The nitrene fragment can be trapped by the complex of the transition metal.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2065–2066, September, 1971.     

Emission characteristics of phenyl isocyanate and parachlorophenyl isocyanate in polar media

The fluorescence and phosphorescence quantum yields (Φ_Γ and Φ_Π) and observed triplet decay time (τ_P) of phenyl isocyanate and its chloro derivative, parachlorophenyl isocyanate have been measured in the polar solvent ethanol. Kinetic parameters for the energy depletion process have been generated K_P the triplet-singlet transition probability is much more sensitive to Cl substitution than K_ISC the intersystem crossing rate.     

Application of thermokinetics in chemical process analysis,as illustrated by the reaction of phenyl isocyanate andn-Butanol

Shortening the time required for chemical process development from the first laboratory trial through technical and pilot plants to industrial installation is a long-standing aim. Knowledge of the reaction kinetics is of major importance for this purpose. The usefulness of thermokinetics in chemical process engineering is illustrated by reaction of phenyl isocyanate andn-butanol.

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Zusammenfassung Die Abkürzung der Verfahrensentwicklung vom ersten Laborversuch über Technikums- und Pilotanlagen bis zur großtechnischen Anlage ist ein seit langem erstrebtes Ziel. Dabei ist bekanntlich die Kenntnis der Reaktionskinetik von großer Bedeutung. Am Beispiel der Reaktion Phenylisocyanat undn-Butanol wird die Nützlichkeit der Thermokinetik in der chemischen Verfahrensentwicklung aufgezeigt.

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Kinetics and mechanism of the thermal decomposition of methyl isocyanate

The kinetics of gas-phase decomposition of methyl isocyanate have been investigated in the range of 427–548°C. Two decomposition routes are followed; the predominant one is a radical-chain process giving CO, H₂, and HCN as major products, which has an order of 1.5 and an Arrhenius equation given by log k(L^1/2/mol^1/2·s) = (13.12 ± 0.06) ? (56,450 ± 1670) cal/mol/2.303 RT. The minor route is the bimolecular formation of N,N′-dimethylcarbodiimide and CO₂, which from the low activation parameters E_a = 31.6 kcal, A = 10^5.30 L^1/2/mol^1/2·s, and the reaction order of 1.57 appears to be heterogeneous.     

Molecular organization of reactants in the kinetics and catalysis of liquid phase reactions: XII. Mechanism of the boron trifluoride-catalyzed Curtius thermal rearrangement of benzoyl azide into phenyl isocyanate

The kinetics of the thermal decomposition and rearrangement of benzoyl azide into phenyl isocyanate was studied in n-heptane in the presence of boron trifluoride etherate as the catalyst. The apparent activation energy of the noncatalytic reaction is 28.0 kcal/mol, and that of the catalytic reaction is 11.0 kcal/mol. The electronic structure and geometry of various complexes between benzoyl azide and BF₃ were studied using the PBE/TZ2P density functional method, and fragments of the potential energy surface were calculated for the catalytic rearrangement. Comparatively stable 1: 1 and 1: 2 complexes between the syn conformer of benzoyl azide and the catalyst can form in the system by coordination to the oxygen and nitrogen atoms of the acyl azide group. The heats of formation of these complexes are between ?1.7 and ?6.4 kcal/mol. The main consequence of the formation of these complexes is that the acyl azide group comes out of the benzene ring plane and thus becomes more reactive. The effective activation energies calculated for the catalytic rearrangement involving complexes of different compositions are 12–15 kcal/mol lower the effective activation energy of the noncatalytic reaction. Information has been obtained about the structure of the transition state of the catalytic reaction, in which a nitrogen molecule is abstracted from benzoyl azide with a synchronous rearrangement of other atoms, resulting in the formation of the ultimate product.     

Reaction of 1,2-borylphosphinoethene with phenyl isocyanate and the structure of the reaction products

The reaction of 1-butyl-1-dibutylboryl-2-phenyl-2-phenylphosphinoethene with phenyl isocyanate gave two structural isomers, which were identified as 1-aza-5-phosphonia-2-borata-3-cyclohexene and 2-aza-4-phosphonia-1-boratabicyclo-[3.1.0]hexane by³¹P NMR and IR spectroscopy and x-ray diffraction structural analysis. The reversibility of the interconversion of these isomers was demonstrated. The reversible migration of a butyl anion from a carbon atom to the boron atom during this process was found.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2393–2396, October, 1991.     

Catalysis in competing isocyanate reactions. I. Effect of organotin–tertiary amine catalysts on phenyl isocyanate and N-butanol reaction

An analytical method based on high performance liquid chromatography (HPLC) has been developed to investigate the competing isocyanate reactions under the influence of various catalysts. The kinetics of the model reaction between phenyl isocyanate and n-butanol was studied in acetonitrile at 50°C. Effects of various catalysts such as an organotin compound, dibutyltin dilaurate, and tertiary amines, 1,4-diazabicyclo-(2,2,2)octane,N,N′,N″-pentamethyldiprophylene triamine,N,N′N″-tris(3-dimethyl-aminopropyl)-3-hexahydrotriazine, and N,N,N′-trimethylaminoethyl-ethanolamine on the reaction rate and the formation of reaction products were investigated. The reactions were followed by determining the NCO disappearance using the standard di-n-butylamine back-titration method as well as measuring the formation of various reaction products using the HPLC method. The relative specificity of a catalyst in isocyanate reactions can thus be determined from the profile of the model reaction which depends upon the structure of the catalyst employed.     

Kinetic evidence for a tetrameric transition state in the asymmetric autocatalytic alkylation of pyrimidyl aldehydes

Experimental kinetic data coupled with kinetic modeling implicates a tetrameric transition state in the Soai autocatalytic alkylation of pyrimidyl aldehydes. The kinetic model accurately predicts both the reaction rate and the amplification in enantiomeric excess observed in reactions carried out under a wide range of conditions. These studies reveal the Soai reaction to be an example of true autocatalytic efficiency in a template-directed "minimal system" for self-replication.     

Dimethylsulphide as a nitrene trap in the photolysis of some phosphinic azides

When PhRP(O)N₃ (R = Ph or t-Bu) is photolysed in dimethylsulphide substantial amounts (22 – 32%) of PhRP(O)N:SMe₂ and PhRP(O)NHCH₂SMe are produced and rearrangement is less important than in benzene.     

Induced free-radical chain decomposition of dimethylacetamide hydroper oxide in dimethylacetamide as the medium

Conclusions The thermal gross decomposition of dimethylacetamide hydroperoxide (ROOH) in dimethylacetamide (RH) as the medium proceeds in harmony with the equation: W_p=k_ind [ROOH]₀ ^m/[RH]₀ ⁿ, where m=1.5–2; n=2–0.5. Alkyl radicals with a chain length of 195–3 units are mainly responsible for the induced decomposition. We determined the ratio between the molecular and radical directions of the decomposition and k_ind in the range 80–132°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 967–970, April, 1978.     

Semiempirical description of the C6H5N reactive intermediate in phenyl azide photolysis

The C₆H₅N intermediate generated by photolysis of phenyl azide in solution is studied by semiempirical computations separately parametrized for thermochemistry and spectra. We find that the intermediate which absorbs only weakly in the region 320–370 nm and which is trapped by amines is the bicyclic azirine singlet, as proposed by DeGraff, Gillespie and Sundberg. Other species such as azepinylidine, the distorted azallyl azacycloheptatetraene and pyridyl carbene seem less likely candidates, either because they would be expected to have a rich spectrum in the visible or because they are unstable relative to the azirine. The adduct formed during trapping by amines rearranges by a suprafacial [1, 3] sigmatropic shift, in contradiction to Woodward-Hoffman predictions. Details of the path are easily rationalized as due to specific orbital interactions.     

IR absorption intensities as a new spectral criterion for the activation of adsorbed molecules in heterogeneous acid catalysis

The criterion conventionally used to judge bond activation in molecules adsorbed on active sites of heterogeneous catalysts is the bathochromic shift of the corresponding IR absorption bands. The intensity of these bands, which characterizes bond polariability, can be used as an additional bond activation criterion. This new spectral criterion is particularly promising for acid and acid-base catalysis, in which the activation of adsorbed molecules is due to their polarization by active sites. Examples are provided here to illustrate the fruitfulness of the new approach. These examples include judging the strength of Brønsted acid sites from the intensity of the OH stretching band and an analysis of the dissociative adsorption and dehydrogenation of light paraffins on metal cation forms of zeolites and of proton transfer from Brønsted acid sites to adsorbed paraffin molecules.     

A unique autocatalytic process and evidence for a concerted-stepwise mechanism transition in the dissociative electron-transfer reduction of aryl thiocyanates

Electrochemical reduction of p-methyl-, p-methoxy-, and 3,5-dinitrophenyl thiocyanates as well as p-methyl- and p-methoxyphenyl disulfides was investigated in acetonitrile at an inert electrode. This series of compounds reveals a striking change in the reductive cleavage mechanism of the S-CN bond in thiocyanates as a function of the substituent on the aryl ring of the aryl thiocyanate. With nitro substituents, a stepwise mechanism, with an anion radical as the intermediate, takes place. When electron-donating groups (methyl and methoxy) are present, voltammetric as well as convolution analyses provide clear evidence for a transition between the concerted and stepwise mechanisms based on the magnitude of the transfer coefficient alpha. Moreover, a very interesting autocatalytic process is involved during the electrochemical reduction of these compounds. This process involves a nucleophilic substitution reaction on the initial aryl thiocyanate by the electrochemically generated arenethiolate ion. As a result of this unusual process, the electrochemical characteristics (peak potential and peak width) of the investigated series are concentration dependent.