Studies on catalytically active surface compounds, IX. Formation of O2? radicals on VCl4/SiO2 catalysts

The conditions for the formation of O ₂ ^– on VCl₄/SiO₂ catalysts have been investigated. It is shown that thermal vacuum treatment (TVT) of unhydrolyzed catalysts leads to partial hydrolysis of the surface vanadium complex caused by the silanol groups of the support. The ability of the catalysts to generate O ₂ ^– radicals was found to depend on the degree of hydrolysis caused by thermal vacuum treatment.

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O ₂ ^– VCl₄/SiO₂. , , . , O ₂ ^– , .

     

Studies on catalytically active surface compounds, X. Alkali metal induced slow tumbling of vanadyl complexes on the surface of aerosil

The effect of alkali metal admixtures (Li, Na, K, Rb, and Cs) on V/SiO₂ catalysts was studied by ESR spectroscopy. Alkali metals strongly change the VO²⁺ spectra. Reduction leads to spectra showing a slow rotational motion of VO²⁺ species on the support surface. The proposed explanation includes former structural models and the formation of salts of polyvanadium acid.

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(Li, Na, K, Rb Cs) V/SiO₂ . VO²⁺. , VO²⁺ . .

     

Studies on catalytically active surface compounds: XVIII. Photoreduction of oxidic vanadium clusters on aerosil and their chemisorptive properties

Photoreduction by CO of silica supported vanadia catalysts of different cluster size has been studied. It was found that the rates of photoreduction and the highest attainable degrees of reduction depend on the size of vanadia clusters. The chemisorptive properties of photoreduced catalysts toward but-1-ene and O₂ are studied and discussed in terms of the distribution of V³⁺ ions in partially reduced clusters.

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. , -1 O₂. V³+ .

     

The resonance raman effects of VCl4 and SnI4

Raman spectra of VCl₄ and SnI₄ in solution are obtained using the exciting lines of a HeNe and an Ar⁺ laser. The spectra show a pre-resonance Raman effect with an enhancement of the stretching vibrations for shorter wavelengths of excitation. The features of the intensity variation are discussed quantitatively in terms of the frequency factors given by Albrecht and Hutley.     

ESR investigation of the MgO?VCl4 system

The MgO–VCl₄ system was investigated by the ESR method. Reduction of VCl₄ by the MgO surface to V³⁺ and V²⁺ (partly) is postulated.

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MgO–VCl₄ , VCl₄ V⁺³ V⁺², MgO.

     

Catalytic hydrogenation of olefins with the VCl4?Mg?H2 system in tetrahydrofuran

The hydrogenation of olefins with the VCl₄–Mg–H₂ system in tetrahydrofuran was examined. The yield was found to depend on the Mg: VCl₄ mole ratio. The maximum yield of cyclohexene hydrogenation is achieved at C₆H₁₀/VCl₄=4. Addition of AlCl₃ or triphenylphosphine increases the yield of hydrogenation to a mole ratio C₆H₁₂/VCl₄=7.

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: VCl₄–Mg–H₂ . , Mg:VCl₄. C₆H₁₀/VCl₄=4. AlCl₃ C₆H₁₂/VCl₄=7.

     

Studies of reaction heats and structures of complexes formed between macro compounds and SbCl5 in CCl4

The heats of reactions between the acyclic and cyclic macro-compounds are determined. The values can be used as a measure of the donor abilities of the macro ligands. Formation of two types of complexes between the macro compounds and SbCl₅ is established. The acyclic macro-compounds form 1:1 complexes, whereas the macrocyclic compounds only 1:2 complexes.     

Condensation reaction of C4H4 with pyridine

C₄H₄⁺ reacts with pyridine (C₅H₅N) via the channels of proton transfer, charge transfer and condensation with H-elimination. The condensation reaction is of general interest in terms of basic chemistry and is the focus of the present study. By means of theoretical calculations and Fourier transform mass spectrometer experiments using deuterated pyridine and substituted pyridines, the structure of the product ion and the reaction pathways are investigated. From the experimental results we find that the H atom that is eliminated can originate from either pyridine or C₄H₄⁺. The experiments show that elimination of an H atom from C₄H₄⁺ is preferred and that there is an observable kinetic isotope effect. By replacing H atoms with methyl groups in ortho positions of pyridine, the experimental results also suggest possible steric blocking to the condensation. Based on the experimental observations and results of theoretical calculations of several possible structures of intermediates, transition states, and final product ions, a possible reaction scheme for the condensation-H-elimination is discussed.     

Novel solvent-free reaction of C60 with active methylene compounds in the presence of Na2CO3 under high-speed vibration milling

Inorganic base, Na₂CO₃, was utilized to replace organic base, DBU, in the Bingel reaction employing diethyl bromomalonate under the mechanochemical ‘high-speed vibration milling’ conditions to give the cyclopropanated C₆₀1 in high yield. In contrast, reactions of C₆₀ with diethyl malonate and ethyl acetoacetate in the presence of Na₂CO₃ under HSVM conditions afforded 1,4-bisadduct 2 and dihydrofuran-fused C₆₀ derivative 3, respectively.     

Studies on the active sites for dehydrocyclization reaction over Pt?Al2O3 catalysts

The work represents a search for direct evidence of the existence of low temperature and high temperature active sites over Pt–Al₂O₃ for dehydrocyclization reaction. It is suggested that the former consists of dispersed metallic Pt and the latter of super-dispersed metallic Pt or isolated atomic Pt and ionic Pt.

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- - Pt/Al₂O₃ . , Pt, Pt, Pt.

     

On the reaction of 2-amino-4-thiazoliniminium salts with active methylene compounds

Summary The easily available 2-amino-4-thiazoliniminium salts6 react with different types of active methylene compounds. Whereas 2-amino-4-cyanomethylene-4,5-dihydrothiazoles13 and14 are formed with malononitrile (11) or ethyl cyanoacetate (12) in the presence of bases, acetyl acetone (15) and ethyl acetic acetate (16) afford 2-amino-thiazolo[4,5-b]pyridines21 and22, resp. The structures of the new compounds13, 14, 21 and22 have been elucidated by means of analytical and spectroscopic methods and confirmed by some chemical reactions.

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Reaktion von 2-Amino-4-thiazoliniminium-Salzen mit aktivierten Methylenverbindungen

Zusammenfassung Durch Reaktion der einfach zugänglichen 2-Amino-4-thiazoliniminium-Salze6 mit Malonsäuredinitril (11) oder Cyanessigsäureethylester (12) in Gegenwart von Basen werden die 2-Amino-4-cyanmethylen-4,5-dihydrothiazole13 bzw.14 gebildet, während mit Acetylaceton (15) und Acetessigsäureethylester (16) auf analoge Weise die 2-Aminothiazolo[4,5-b]pyridine21 bzw.22 entstehen. Die Strukturen der neu dargestellten Verbindungen des Typs13, 14, 21 und22 wurden spektroskopisch abgesichert und durch einige Folgereaktionen bestätigt.

     

Higher energy bands in the electronic absorption spectra of CrO4, RuO4, OsO4, WS4, MoS4, WSe4 and MoSe4. A note on the assignment of the electronic spectra of closed shell tetroxo-, tetrathio- and tetraselenoanions

The electronic spectra of several closed shell tetroxo-, tetrathio- and tetraselenoanions have been remeasured and some more bands in the higher energy range were obtained. An assignment of the first three bands basing on empirical assumptions is proposed.     

Molecular beam chemiluminescence. VIII: Pressure dependence and kinetics of Sm + (N2O,O3, F2, Cl2) and Yb + (O3, F2, Cl2) reaction. Dissociation energies of the diatomic reaction products

The CL spectra of the title reactions and their pressure dependences have been studied over the 5 × 10^?6 ? 5 × 10^?3 torr range in a beam-gas experiment. In the Sm + N₂O, O₃ and Yb + O₃ reactions simple bimolecular formation of the short lived (radiative lifetime τ_R < 3 × 10^?6 s) MO* emitters dominates the entire pressure range. In the other systems Sm + (F₂, Cl₂), Yb + (F₂, Cl₂) the CL spectra are strongly pressure dependent, indicating extensive energy transfer from long-lived intermediates. Reaction mechanisms are suggested. The quantum yields Φ, obtained by calibrating relative quantum yields with Dickson and Zare's absolute value for Sm + N₂O [Chem. Phys. 7 (1975) 367], range from Φ = 2.3% (for Sm + F₂, the most efficient reaction) down to Φ = 0.005% for Yb + Cl₂. The following lower limit estimates were obtained for the product dissociation energies from the short wavelength CL cutoffs: D⁰₀(SmF) ? 121.3 ± 2.4 kcal/mole, D⁰₀(SmCl) ? ? 100 ± 3 kcal/mole, D⁰₀(YbO) ? 94.2 ± 1.5 kcal/moie, D⁰₀(YbF) ? 123.7 ± 2.3 kcal/mole.     

Formation mechanism and structure of compounds catalytically active in propylene dimerization and formed in Pd(acac)2?PR3?BF3OEt2 systems

The interaction between the components of catalytic Pd(acac)₂–PR₃–BF₃OEt₂ systems dimerizing propylene to linear hexenes with 59 % selectivity, has been studied by UV and¹H NMR spectroscopy methods. Formation mechanism of catalytically active [R₃P–Pd–H]⁺BF ₄ ^– compounds is suggested.

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, ¹ Pd(acac)₂–PR₃–BF₃OEt₂, 59%, [R₃P–Pd–H]⁺BF ₄ ^– .

     

Substitution and addition reactions of NF4BF4 with aromatic compounds

Benzene, toluene, and nitrobenzene interact rapidly with NF₄BF₄ in anhydrous HF to give, almost exclusively, fluorine substituted aromatic derivatives. Up to four hydrogens can be replaced in a rapid reaction, before a much slower addition reaction takes over. The direction of the substitution in C₆H₆, C₆H₅CH₃ and C₆H₅NO₂ and the lack of side chain fluorination in C₆H₅CH₃ support an electrophillic substituion mechanism. These rapid substitution reactions are followed by much slower fluorine addition reactions to give the corresponding cyclo-hexadienes and -hexenes. These addition reactions were also studied separately using tetra-, penta- and hexa- fluorobenzene as the starting materials. In these addition reactions, almost no hydrogen substitution occured. The addition of the first pair of fluorines always gave 1,4-cyclohexadienes in which CF₂ group was adjacent to hydrogen on the ring. The addition of the second pair of fluorines resulted in the formation of cyclohexenes. These reactions occured in high yield and offer a controlled, high yield path to dienes. All products were characterized spectroscopically and by comparison to literature data.     

Theoretical study on the reaction mechanism of CH4 with CaO

The reaction pathways and energetics for the reaction of methane with CaO are discussed on the singlet spin state potential energy surface at the B3LYP/6-311+G(2df,2p) and QCISD/6-311++G(3df,3pd)//B3LYP/6-311+G(2df,2p) levels of theory. The reaction of methane with CaO is proposed to proceed in the following reaction pathways: CaO + CH₄ → CaOCH₄ → [TS] → CaOH + CH₃, CaO + CH₄ → OCaCH₄ → [TS] → HOCaCH₃ → CaOH + CH₃ or [TS] → CaCH₃OH → Ca + CH₃OH, and OCaCH₄ → [TS] → HCaOCH₃ → CaOCH₃ + H or [TS] → CaCH₃OH → Ca + CH₃OH. The gas-phase methane–methanol conversion by CaO is suggested to proceed via two kinds of important reaction intermediates, HOCaCH₃ and HCaOCH₃, and the reaction pathway via the hydroxy intermediate (HOCaCH₃) is energetically more favorable than the other one via the methoxy intermediate (HCaOCH₃). The hydroxy intermediate HOCaCH₃ is predicted to be the energetically most preferred configuration in the reaction of CaO + CH₄. Meanwhile, these three product channels (CaOH + CH₃, CaOCH₃ + H and Ca + CH₃OH) are expected to compete with each other, and the formation of methyl radical is the most preferable pathway energetically. On the other hand, the intermediates HCaOCH₃ and HOCaCH₃ are predicted to be the energetically preferred configuration in the reaction of Ca + CH₃OH, which is precisely the reverse reaction of methane hydroxylation.     

Phase equilibria in systems based on Tl4SnSe3 and Tl4SnSe4 ternary compounds

Phase equilibria in the Tl₄SnSe₃-Tl (I), Tl₄SnSe₃-Sn (II), Tl₄SnSe₄-SnSe (III), Tl₄SnSe{ia4}-TlSe (IV), and Tl₄SnSe₃-Tl₄SnSe₄ (V) systems have been studied by differential thermal analysis and power X-ray diffraction. Systems I–V have been found to have eutectic interactions. In systems I and II, width regions of solid solutions based on the ternary compound Tl₄SnSe₃ are formed.     

Synthesis of the sulfones of leukotriene C4, D4, and E4

A simple one-step preparation of the sulfones of Leukotriene C₄, D₄ and E₄ has been developed by the direct oxidation of the parent compounds. An alternative synthesis of these sulfones has also been carried out by reduction of an acetylenic precursor.     

Magnetic behavior of tetrahedral Cr4+ compounds: Sr2CrO4, Ba2CrO4, and Ba3CrO5

The preparation of the compounds Sr₂CrO₄, Ba₂CrO₄, and Ba₃CrO₅ is described. The characterization of these three Cr⁴⁺ compounds by X-ray and magnetic susceptibility experiments has been conducted. The magnetic moments for Sr₂CrO₄, Ba₂CrO₄, and Ba₃CrO₅ were determined to be in good agreement with the calculated value expected for a tetrahedral Cr⁴⁺ ion. Weak antiferromagnetic ordering for all three compounds is indicated from the small paramagnetic Weiss constants determined from the susceptibility data in the temperature region 80–300 K. Distortions of the tetrahedra from ideality, as determined from the structural features, further cause a reduction in the magnetic moments from the theoretical values.