Ammoxidation of ethane on oxide catalysts

Ammoxidation of ethane on chromium- and scandium-molybdenum oxide catalysts has been studied. The rate-determining step of acetonitrile formation is shown to be C–H bond breaking in n-paraffins.

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- . , C–H -.

     

Ammoxidation of methylpyrazine over phosphorus-modified vanadium-titanium catalysts

Vanadium-titanium catalysts modified with phosphorus additives (1-15 wt.% of P₂O₅) have been studied in methylpyrazine ammoxidation. Introduction of high amounts of the additive (≥ 10 wt.% of P₂O₅) results in a decrease in activity and selectivity of the catalysts due to formation of low active phase - a ternary compound with the component ratio V : P : Ti ≈ 1 : 1 : 1 with only one type of slightly distorted tetrahedral vanadium (5+) bound via oxygen to phosphorus (5+). The nature of the active sites of the samples modified with 1-5 wt.% of P₂O₅, similarly to that in the V-Ti-O catalyst, was found to include the V⁵⁺ cations strongly bound with TiO₂ and located in the significantly distorted octahedral oxygen environment. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ammoxidation of 3-picoline to nicotinonitrile using silica-supported VCrO catalysts

A series of vanadium–chromium oxide (VCrO) catalysts supported on silica was prepared by wetness impregnation method with different Cr/V molar ratios from 0.2 to 1.0. These catalysts were characterized by XRD, TG, temperature-programmed desorption of ammonia (NH₃-TPD), X-ray photoelectron spectra (XPS), and Raman spectroscopy, and their catalytic activity was evaluated in the ammoxidation of 3-picoline (3-PIC) to nicotinonitrile (NN). The results of XRD, TG, Raman, and XPS confirmed that the active components on the silica surface were mainly amorphous V₂O₅ and CrVO₄. The results of NH₃-TPD showed that acidity of the catalysts decreased with the increase of Cr/V ratio. Catalytic results revealed that acidity of the catalysts was closely related to the catalytic performance. Low acidity gave low conversion of 3-PIC and high NN selectivity. Furthermore, the conversion of 3-PIC increased with rise in reaction temperature, and the selectivity of NN was slightly influenced by the 3-PIC conversion. Therefore, among the catalysts (Cr/V ratio was 0.2, 0.4, 0.6) tested, Cr/V-0.6 catalyst retained the lowest acidity and exhibited the highest selectivity and yield of NN in the ammoxidation of 3-PIC.     

Ammoxidation of methylpyrazine over vanadium-titanium catalysts modified by alkali additives

Vanadium-titanium catalysts modified with sodium or potassium additives (1-15 wt.% of Me₂O) have been studied in methylpyrazine ammoxidation. Introduction of the additives results in a decrease in the activity and selectivity of the catalysts due to formation of low-active phase - bronzes (MeV₆O₁₅) and vanadates (α-NaVO₃, KVO₃ and K₃V₅O₁₄). The active sites of the modified samples, similar to those in the V-Ti-O catalyst, are found to be V⁵⁺ cations strongly bound to TiO₂ and located in a significantly distorted octahedral oxygen environment. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ammoxidation of pyridinecarbinols on V-Mo oxide catalyst

The ammoxidation of pyridinemethanols over V-Mo oxide gave cyanopyridines and the selectivity towards the formation of respective aldehydes changes with the isomeric carbinols. A reaction mechanism is suggested for the formation of nitriles.

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V-Mo . . .

     

Ammoxidation of cyclohexanol to adiponitrile on vanadium oxide

The reaction pathway of ammoxidation of cyclohexanol to adiponitrile (ADN) on vanadium pentoxide catalyst has been investigated. ADN was produced directly via adipic acid obtained from oxidation of cyclohexanone. The main end-products were carbon dioxide and benzene.

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() V₂O₅. , . .

     

Molecular and electronic structure of halogen-substituted phosphaalkenes

Peculiarities of the molecular and electronic structure of P- and C-halogen-substituted phosphaalkenes have been considered on the basis of results of X-ray diffraction studies and quantumchemical calculations. Introduction of an electronegative halogen atom is shown to have an insignificant effect on the intramolecular bond angle distribution, whereas the influence on the P=C bond length is noticeable. Thus, in P-substituted phosphaalkenes it substantially increases the polarization of the P=C bond (which causes its noticeable shortening). In C-substituted phosphaalkenes the effect of halogen atoms is less pronounced: decreasing the P=C bond polarization leads only to its slight elongation. In addition, a considerable elongation of the phosphorus-halogen bond in comparison with three-coordination phosphorus compounds is a peculiarity of the molecular structure of P-halogen-substituted phosphaalkenes.     

Mesomorphic properties of achiral halogen-substituted banana-shaped compounds

Three banana-shaped achiral compounds, derivatives of 4,6-dichloro-1,3-phenylene bis-[4-(4-n-octyloxyphenyliminomethyl) benzoate], were synthesized by varying the substituent (X = H, F and Cl). Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray analysis. The compound with X = H exhibited an enantiomeric nematic phase. The compounds with X = F and Cl formed a nematic phase on heating, while on cooling they formed a nematic phase at high temperature and a smectic A phase at a lower temperature (monotropic). A schematic representation of the mesophase structures for the compound with X = F is also illustrated.     

Photochemistry and photophysics of halogen-substituted dibenzothiophene oxides

Dibenzothiophene-5-oxide (DBTO) cleanly produces dibenzothiophene (DBT) on direct photolysis, but with very low quantum yield. A proposed mechanism involves scission of the S-O bond which is coupled to an intersystem crossing step, thus producing the sulfide and O((3)P) via a unimolecular pathway. To test this hypothesis, heavy atom substituted DBTOs were prepared and photolyzed. Iodo-, bromo-, and chloro-substituted DBTOs show higher quantum yields for deoxygenation than does the parent molecule, in the order consistent with an intersystem crossing-related heavy atom effect. 2-Iododibenzothiophene also undergoes photochemical deiodination. Phosphorescence data are consistent with heavy-atom assisted intersystem crossing.     

多组分Mo-Bi-Fe-O催化剂上丙烯氨氧化研究进展

综述了多组分Mo_Bi_Fe_O催化剂上丙烯氨氧化研究进展 ,包括反应机理、催化剂设计、晶格氧迁移、活性位模型与协同效应四个方面     

Mesomorphic properties of achiral halogen-substituted banana-shaped compounds

Three banana-shaped achiral compounds, derivatives of 4,6-dichloro-1,3-phenylene bis-[4-(4- n -octyloxyphenyliminomethyl) benzoate], were synthesized by varying the substituent ( X =H, F and Cl). Their mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, and X-ray analysis. The compound with X = H exhibited an enantiomeric nematic phase. The compounds with X = F and Cl formed a nematic phase on heating, while on cooling they formed a nematic phase at high temperature and a smectic A phase at a lower temperature (monotropic). A schematic representation of the mesophase structures for the compound with X = F is also illustrated.     

Oxidative synthesis of benzamides from toluenes and DMF

An interesting oxidative procedure for the synthesis of benzamides has been developed through the cleavage of sp³ CH bond of methyl arenes with N-substituted formamides. Various benzamides were prepared in low to moderate yields. Even though the yields are moderate in general, this new synthetic procedure provides another option for benzamide synthesis.     

Potential barriers of internal rotation in halogen-substituted ethanes

A simple model is proposed for calculating torsional vibrational frequencies and torsion potentials in ethane-type molecules. The model is based on internuclear coulomb electrostatic interactions of the end atoms in molecular groups undergoing rotations. The effective charges on the nuclei are considered to be the model parameters. The results of calculations show that the model can reliably reproduce the frequencies of torsional vibrations for rotational conformers and that the effective charges are transferable among halogen-substituted ethanes, both symmetrical and asymmetrical.Orenburg Pedagogical Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 39–43, January–February, 1993.     

Pd-catalyzed alkylation of halogen-substituted steroids with organozinc compounds

A general procedure has been developed for the introduction of hydrophobic alkyl groups into positions 6, 3, and 17 of steroid molecules via palladium-catalyzed Negishi reaction of halogen-substituted steroids with benzyl- and alkylzinc halides.     

Toluene dioxygenase mediated oxidation of halogen-substituted benzoate esters

A series of ortho-, meta-, and para- halogen-substituted methyl benzoate esters was subjected to enzymatic dihydroxylation via the whole-cell fermentation with E. coli JM109 (pDTG601A). Only ortho-substituted benzoates were metabolized. Methyl 2-fluorobenzoate yielded one diol regioselectively whereas methyl 2-chloro-, methyl 2-bromo- and methyl 2-iodobenzoates each yielded a mixture of regioisomers. Absolute stereochemistry was determined for all new metabolites. Computational analysis of these results and a possible rationale for the regioselectivity of the enzymatic dihydroxylation is advanced.