Kinetics and energetics of the criegee intermediate in the gas phase. II. The criegee intermediate in the photooxidation of formaldehyde,in alkyldioxy disproportionation and O + oxoalkane addition reactions

The gas-phase kinetics and energetics of the Criegee intermediate, deduced from studies of O₃-alkene systems, suggest that a hydroxy-substituted Criegee intermediate probably participates in the photooxidation of formaldehyde. In contradistinction, the existing evidence suggests that the Criegee intermediate and its isomers are probably not involved in alkyldioxy disproportionation reactions. In the case of O + oxoalkane addition reactions, the Criegee intermediate and its isomers are discussed in terms of a complex equilibrium: .     

Electron impact studies. CVII—Negative ion mass spectra of the oxime group. Monoximes derived from α-dicarbonyl systems

Specific losses of water are observed from the molecular anions of monoximes of α-diketones. Labelling studies, kinetic energy release values and the +E spectra of ions have been used to aid in the elucidation of the fragmentation pathways. It is proposed that the majority of ions have α-keto nitrile structures.     

Fragmentations of protonated acetophenones via intermediate ion–molecule complexes

Protonated acetophenones, substituted with a methoxymethyl group in the para and meta positions, have been generated by electron impact induced fragmentation of the correspondingly substituted 2-phenylpropan-2-ols. The metastable ions, formed in the second field-free region of a VG ZAb 2F mass spectrometer, react unimolecularly by elimination of CH₃OH, formation of CH₃CO⁺ and ions, loss of CH₃COOCH₃, and loss of CH₂O. The mechanisms of these fragmentations have been elucidated with the aid of deuterated analogues of the protonated acetophenones. It is shown that these reactions are initiated by an endothermic transfer of the proton at the carbonyl group of the protonated acetophenones to the benzene ring. A further migration of the proton to the ether O atom of the methoxymethyl side-chain leads eventually to the elimination of CH₃OH. Protolytic bond cleavages of either side-chain gives rise to the CH₃CO⁺ and ions. At low internal energies both these ions may be trapped by the aromatic neutral fragment in ion-molecule complexes. Reactions within these complexes result in the energetically favourable losses of CH₃COOCH₃ and CH₂O, respectively. With respect to these reactions, the protonated acetophenones behave analogously to the correspondingly substituted and protonated benzaldehydes.     

On the mechanism of isomerization in the esters of some α,β-unsaturated carboxylic acids—II

The effect of a phenyl group on the mechanisms of isomerization in the ionized methyl esters of simple α,β-unsaturated acids (methyl acrylate and related compounds) has been investigated with the aid of deuterium labelling as well as information from mass analysed ion kinetic energy spectra and first field free region metastable peak shapes. Substitution of a hydrogen atom of the O? CH₃ group by a phenyl group (benzyl acrylate and homologues) greatly enhances the rate of [ester] → [acid] isomerizations (loss of H₂O and COOH˙). It is inferred that this is due to an accelerating effect of the phenyl group on the first and the third steps (ring opening of the key intermediate ion which has the structure of the ionized enol form of γ-butyrolactone) of the reaction whose mechanism is basically the same as that in methyl acrylate. A phenyl group present at the α- or β-position of the vinylic double bond appears to suppress the [ester] → [acid] isomerization in some compounds by promoting other reactions or opening up a new reaction pathway, i.e. the loss of CH₂O from ionized methyl atropate for which mechanisms are proposed.     

Metastable decompositions of cyclopentanol ions and [C5H10O]+˙ ions with the oxygen on the first carbon

Ionized cyclopentanol and [C₅H₁₀O]+˙ ions with the oxygen on the first carbon lose methyl, ethylene, ethyl, ethane and water in their metastable decompositions. We show by collisionally activated decompositions of the products that the losses of ethyl form CH₃CH₂C?O⁺, the losses of ethylene form , and the losses of methyl probably yield . Deuterium labeling indicates that ethyl loss from ionized cyclopentanol occurs following α-cleavage of the ring, isomerization to the enol isomer of ionized n-pentanal and subsequent isomerization to the 3-pentanone ion.     

Thermal decomposition of cyclopentane and related compounds

Cyclopentane has been decomposed in comparative-rate single-pulse shock-tube experiments. The pyrolytic mechanism involves isomerization to 1-pentene and also a minor pathway leading to cyclopropane and ethylene. This is followed by the decomposition of 1-pentene and cyclopropane. The rate expressions over the temperature range of 1000°–1200° K are Details of the cyclopentane decomposition processes are considered, and it appears that if the trimethylene radical is an intermediate, then ΔH_f(trimethylene) ≤ 280 kJ/mol at 300°K.     

Involvement of Singlet Oxygen in the Solid‐State Photochemistry of P3HT

We studied the role that singlet oxygen plays in the solid‐state photochemistry of poly(3‐hexylthiophene) (P3HT). The photosensitized formation of singlet oxygen by solid‐state P3HT and its subsequent reactivity on the polymer were investigated. Using a fluorescent probe, it was found that singlet oxygen (¹O₂) could be produced by irradiation of P3HT by photosensitization, with no oxidation of the polymer. In addition, ¹O₂ was directly formed on P3HT via a chemical reaction, again with no oxidation of the polymer. These results give strong evidence that ¹O₂ is not the principal photo‐oxidative degradation intermediate of P3HT, which conflicts with previous reports.

     

Thermal decomposition of azoethane

The thermal decomposition of azoethane (AE) was studied by detailed product analysis in the temperature and pressure intervals 508–598 K and 2.7–13.3 kPa. Besides the hydrocarbon products, three characteristic and quantitatively important nitrogen-containing compounds were also determined: ethyl-2-butyldiimide, ethanal-diethylhydrazone, and tetraethyl-hydrazine. Apart from the predominant termination reactions of the ethyl radical with itself and with the μ₂ radical, the decomposition is characterized by a very short chain reaction. The measurements led to determination of the following rate constants and rate constant ratios: for the following reactions:      

Is the Reduction in Tracer Diffusivity under Nanoscopic Confinement Related to a Frustrated Segmental Mobility?

We developed an experimental method for the determination of the tracer diffusivity D_tr in ultrathin polymer films, and the changes in the segmental mobility of tracer molecules while they diffuse through matrices of different thickness and get adsorbed onto a target substrate. D_tr starts decreasing already at 120–150 nm and drops to 1% of its bulk value in films as thin as 7.5 nm. We discuss the results highlighting a strong decoupling between the reduction in mass transport at the nanoscale and the increase in the glass transition temperature determined via capacitive dilatometry together with a breakdown of the Stokes–Einstein relation between orientational and translational degrees of freedom.

     

Phenacyl esters of acetic acid derivatives and their application for the synthesis of 2‐oxo‐4‐phenyl‐5‐(phenylhydrazono)‐2,5‐dihydro‐furan‐3‐derivatives

Coupling of various substituted phenacyl acetates 1 and diazonium salts 3 was studied. If the phenacyl acetates were substituted by an electronaceptor group such as CN or COOEt 3‐substituted phenyl‐5‐(phenyl‐hydrazono)‐5H‐furan‐2‐ones 4 were formed. Also synthesis of aza and diaza analogs is described. The compounds were characterized using MS and NMR spectroscopy.     

Fluorsulfonylstickstoffverbindungen

The reactions of fluorosulfonylurea derivatives with phosphorus pentachloride in carbon tetrachloride leads to and . These compounds are easily fluroinated by arsenic trifluoride to the corresponding fluorosulfonyl derivatives. It was shown that PCl₅ is reliable for the fluorine-chlorine exchange. Isocyanate esterchlorides as well as carbonyl-fluoride derivatives react with compounds which have an active hydrogen atom. By this way were prepared: . By hydrolysis of , is probably formed as the first reaction product. The acid could be trapped with tetraphenylphosphoniumchloride as a well-cristalline salt. Fluorosulfonyl isocyanate reacts with aldehydes to the following compounds: FSO₂N ? CHCH₃, FSO₂N ? CHC₂H₅, FSO₂N ? CH? CH(CH₃)₂ and FSO₂N ? CHC₆H₅. The physical and chemical properties as well as IR and NMR spectra of the compounds are described and, in part, compared and discussed.     

Darstellung und Eigenschaften von Ti-substituierten N-Heterocyclen

Preparation and Properties of Ti-substituted N-Heterocycles The compounds (x = 2 to 6) have been prepared by transamination of Ti(NMe₂)₄ with the heterocyclic amines and have been characterised by elemental analyses and ¹H NMR and IR spectroscopy. The dependence on both x and n of the thermal decomposition has been studied for the series and . The results can be interpreted in terms of the steric strain of the R₂N and substituents. Apart from the piperidido groups none of the ligands exhibit protective group properties comparable to the R₂N groups.     

Towards the Construction of a Complete Cyclic Water Decomposition System,Design and Operation of an Oxygen Producing Half Cell

Oxygen is generated when aqueous solution of iron (III) tris(2,2′-bipyridyl), Fe(bipy), are brought in contact with catalytic amounts of powdered or colloidal RuO₂. The oxygen yield depends strongly on the pH, reaching a maximum between pH 7 and 8 where it corresponds to the stoichiometry of the reaction: The rate of the reaction is so fast that it occurs practically upon dissolution of Fe(bipy) in the aqueous phase. In acidic media (pH 4), no O₂ evolution is observed. Instead, Fe(bipy) is converted to an intermediate which in the presence of RuO₂ yields O₂ upon neutralization. The pH profile of the O₂ evolution occuring upon illumination of Ru(bipy) in the presence of the cobalt complex [Co(NH₃)₅Cl]²⁺ was also investigated. The surprisingly low energy losses (160 mV) in reaction (1) makes the construction of four quanta water splitting systems feasible.     

The kinetics and the mechanism of the thermal decomposition of bis(trifluoromethyl) trioxide. The influence of carbonmonoxide on its decomposition

The kinetics of the thermal decomposition of CF₃O₃CF₃ has been investigated in the pressure range of 15–599 torr at temperatures between 59.8 and 90.3°C and also in the presence of CO between 42 and 7°C. The reaction is homogeneous. In the absence of CO the only reaction products are CF₃O₂CF₃ and O₂. The rate of reaction is strictly proportional to the trioxide pressure, and is not affected by the total pressure, the presence of inert gases, and oxygen. The following mechanism explains the experimental results: In the presence of CO there appear CO₂, (CF₃OCO)₂, and CF₃O₂C(O)OCF₃ as products. With increasing temperature the amount of peroxicarbonate decreases, while the amounts of oxalate and CO₂ increase. The rate of decomposition of the trioxide above a limiting pressure of about 10 torr CO is strictly first order and independent of CO pressure, total pressure, and the pressure of the products. The addition of larger amounts of O₂ to the CO containing system chaqnges the course of the reaction.     

The kinetics of the thermal bromination of CF3I. Determination of the bond dissociation energy D(CF3−I)

The kinetics of the thermal bromination reaction have been studied in the range of 173–321°C. For the step we obtain where θ=2.303RT cal/mole. From the activation energy for reaction (11), we calculate that This is compared with previously published values of D(CF₃?I). The relevance of the result to published work on k_c for a combination of CF₃ radicals is discussed.     

Monodispersed Magnetic Polystyrene Beads with Excellent Colloidal Stability and Strong Magnetic Response

Monodispersed polystyrene beads incorporated with Fe₃O₄ nanoparticles are prepared via dispersion polymerization. The resultant magnetic beads present well‐defined composite structures, excellent colloidal stability, and strong magnetic response. The formation mechanism for the monodispersed composite beads, incorporated with preformed Fe₃O₄ nanocrystals, was investigated. The potential applications of the monodispersed magnetic beads in bacteria capturing were demonstrated. After being coated with anti‐Salmonella CSA‐1 antibody, the magnetic beads show capturing efficiencies of >99.4% in isolating Salmonella sp.

     

Ab initio studies of negative ion-molecule(s) clusters present in the atmosphere. II. OH−(H2O)n for n = 0, 2, 3, 4

Ab initio calculations are performed with 6–31G basis set to study the geometry and binding of the H₃O, H₅O, H₇O, and H₉O complexes. The H₃O complex is also investigated with the 6–31 G* basis set and MP 2 (Moller–Plesset perturbation theory of second order).     

Thermal decomposition of azoisopropane. I. Primary decomposition processes

The thermal decomposition of azoisopropane (AIP) was studied by detailed product analysis in the temperature and pressure intervals 498–563 K and 0.67–5.33 kPa. Besides the predominant termination and hydrogen-abstraction reaction of the 2-propyl radical, the decomposition is characterized by a very short chain process. The following rate constants were determined from the measurements for the following reactions: