Structure, activity and selectivity of V2O5-TiO2 catalysts for o-xylene conversion

The formation of needle shaped crystallites of V₆O₁₃ at low V concentrations on V₂O₅-anatase coated catalysts explains the low selectivity for phthalic anhydride during o-xylene oxidation. The (010) plane of V-oxide, most active for selective oxidation of o-xylene, is not accessible and the contact of this plane with the anatase faces promotes the anatase-rutile transformation and the incorporation and blocking of V⁴⁺ ions.

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V₆O₁₃ V , V₂O₅-, -. (010) , -, , - V⁺⁴.

     

Unconventional nucleotide analogues. 3. 4-(N1-pyrimidyl)-2-aminobutyric acids

Alkylation of 4-ethoxy-2-hydroxypyrimidines (10a, b), via their anions, provides a convenient procedure for preparing N₁-substituted derivatives. Reaction of 10a, b with t-butyl 4-bromo-2-benzyloxycarbamidobutyrate (17) gives good yields of the N₁-alkylated products 18a, b. The latter have been converted to uracil- (20a), thymine- (20b) and cytosine- (21) substituted -aminobutyric acids.     

New insight into solvent effects on the formal HOO. + HOO. reaction

The 2,2'-azobis(isobutyronitrile)(AIBN)-induced autoxidation of gamma-terpinene (TH) at 50 degrees C produces p-cymene and hydrogen peroxide in a radical-chain reaction having HOO* as one of the chain-carrying radicals. The kinetics of this reaction in cyclohexane and tert-butyl alcohol show that chain termination involves the formal HOO. + HOO. self-reaction over a wide range of gamma-terpinene, AIBN, and O2 concentrations. However, in acetonitrile this termination process is accompanied by termination via the cross-reaction of the terpinenyl radical, T., with the HOO. radical under conditions of relatively high [TH] (140-1000 mM) and low [O2] (2.0-5.5 mM). This is because the formal HOO. + HOO. reaction is comparatively slow in acetonitrile (2k approximately 8 x 10(7) M(-1) s(-1)), whereas, this reaction is almost diffusion-controlled in tert-butyl alcohol and cyclohexane, 2k approximately 6.5 x 10(8) and 1.3 x 10(9) M(-1) s(-1), respectively. Three mechanisms for the bimolecular self-reaction of HOO. radicals are considered: 1) a head-to-tail hydrogen-atom transfer from one radical to the other, 2) a head-to-head reaction to form an intermediate tetroxide, and 3) an electron-transfer between HOO. and its conjugate base, the superoxide radical anion, O2-.. The rate constant for reaction by mechanism (1) is shown to be dependent on the hydrogen bond (HB) accepting ability of the solvent; that by mechanism (2) is shown to be too slow for this process to be of any importance; and that by mechanism (3) is dependent on the pH of the solvent and its ability to support ionization. Mechanism (3) was found to be the main termination process in tert-butyl alcohol and acetonitrile. In the gas phase, the rate constant for the HOO. + HOO. reaction (mechanism (1)) is about 1.8 x 10(9) M(-1) s(-1) but in water at pH< or =2 where the ionization of HOO. is completely suppressed, this rate constant is only 8.6 x 10(5) M(-1) s(-1). The very large retarding effect of water on this reaction has not previously been explained. We find that it can be quantitatively accounted for by using Abraham's HB acceptor parameter, beta(2)(H), for water of 0.38 and an estimated HB donor parameter, alpha(2)(H), for HOO. of about 0.87. These Abraham parameters allow us to predict a rate constant for the HOO. + HOO. reaction in water at 25 degrees C of 1.2 x 10(6) M(-1) s(-1) in excellent agreement with experiment.     

INCREASED QUANTUM YIELD OF PHOTOREDUCTION OF DYES (A CATALYTIC EFFECT)

Abstract— While studying the photoreduction of some dyes (D) by reducing agents (R), it was observed that the quantum yield of the photoreduction increases considerably upon addition of a third substance (C), whereas it is very small when the dye is photoreduced by C alone (catalytic effect), (see Table 1).
The system thionine (D), allylthiourea (R), and azulene (C) was investigated in detail using both flash photolysis and continuous illumination. On photolysis, thionine is converted into its photo-reduced form, leucothionine. Azulene reacts with the basic form of the thionine triplet ³ TH ⁺ to produce the semithionine radical. In the system thionine and azulene, most of these radicals revert back to thionine. When ATU (˜ 10^2- M ) is added to thionine and azulene (3 × 10^-4 M ), the semithionine radicals are reduced to leucothionine; the quantum yield of this reduction is considerably higher than in the system thionine and allylthiourea. Flash experiments demonstrate that allylthiourea does not react with the semithionine radicals.
At very high ATU concentrations (≥ 10^-1 M ), however, the primary reaction is between thionine triplet and allylthiourea; under these conditions the quantum yield is not influenced by azulene (3 × 10^-4 M ).     

Über die Hypergolität von Silylhydrazinen

Zusammenfassung Das Zündverhalten von mehr als 20 organylsilylsubstituierten Hydrazinen mit conc. Salpetersäure, Fluor, flüssigem Sauerstoff, mit O₂ verdünntem gasförmigen Ozon und mit verflüssigtem O₃ wurde beobachtet und im Falle HNO₃ auch mit einer schnell-laufenden Kamera gemessen. Die wesentlichsten Resultate können aus Tab. 1 und den Abb. 1 bis 4 entnommen werden.

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The hypergolic behaviour of more than 20 organosilyl substituted hydrazines in contact with conc. HNO₃, with gaseous F₂, with liquid O₂, with liquid O₃ and with gaseous O₃ (diluted with O₂), was observed and, in the case of conc. HNO₃, was registered by a fastrunning camera. The most interesting results are to be seen in table 1 and in pictures 1 to 4.

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Mit 4 Abbildungen

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60. Mitt.:U. Wannagat undF. Höfler, Mh. Chem.97, 976 (1966).

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Zugleich 11. Mitt. über Silicium—Hydrazin-Verbindungen; 10. Mitt.:H. Bürger undF. Höfler, Mh. Chem.97, 984 (1966).

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Auszüge aus der DiplomarbeitF. Höfler, T. H. Graz 1964.     

Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part I. Interfacing

The coupling of liquid chromatography (l.c.) on narrow-bore columns to thin-layer chromatography (t.l.c.) is described. The effluent from a l.c. column can be deposited on a t.l.c. plate after a normal-phase or reversed-phase separation without serious loss of chromatographic information. Both silica and alkyl-modified silica plates can be used for storage. The interface is a fused silica capillary which connects the column outlet to the spray jet assembly of a Linomat applicator for t.l.c. The stored chromatogram can serve as starting point for a new separation, but also allows the use of detection principles which are normally not compatible with l.c. The chromatography of some polynuclear aromatic hydrocarbons is used to illustrate the possibilities of the combinations.     

Beiträge zur Chemie des Phosphors. 167 [1, 2]. Konstitutions- und Konfigurationsisomere von Pentaphosphan(7), P5H7

Contributions to the Chemistry of Phosphorus. 167. Constitutional and Configurational Isomers of Pentaphosphane(7), P₅H₇ Phosphane mixtures containing 10—15 P-% of pentaphosphane(7), P₅H₇, are obtained by thermolysis of diphosphane, P₂H₄, or as residue from distillation of crude diphosphane [3]. According to the complete analysis of the ³¹P{¹H}-NMR spectrum on the basis of selective population transfer experiments, P₅H₇ exists as a mixture of three diastereomers of n-P₅H₇ — 1a (erythro, erythro), 1b (erythro, threo), 1c (threo, threo) — and of the constitutional isomer 2-phosphinotetraphosphane 2 (iso-P₅H₇, largest relative isomeric abundance). The correlation between the diastereomers and the observed spin systems results from the preferred gauche orientation of neighboring free electron pairs, the dependence of ¹J(PP) on dihedral angles, and the ³J(PP) long range couplings. From the ³¹P-NMR data of the phosphane molecules P_nH_n+2 with n = 1—5 general relationships for the δ(³¹P) values and the ¹J(PP) coupling constants of chain-type phosphorus hydrides as a function of their structural parameters are derived.     

Investigation of alkaloid N-oxides by secondary-ion mass spectrometry

An advantage of theSIMS method for investigating alkaloid N-oxides has been shown. In the case of N-oxides of steroid, diterpene, tropane, and pyrrolizidine alkaloids, fragments including the oxygen of the N-oxide group are revealed. The protonation of N-oxide molecules in a glycerol matrix takes place mainly through the negatively polarized oxygen atom of the N-oxide function. On fragmentation, theMH ⁺ ions of N-oxides of monoester tropane and pyrrolizidine alkaloids tend to form fragmentary ions of the protonated forms of the aminoalcohols (A+). The energies of the metastable transitionsMH ⁺ A⁺ have been calculated for the Noxides of the pyrrolizidine alkaloids viridif lorine, trachelanthamine, and echinatine.Institute of the Chemistry of Plant Substances [IKhRV], Academy of Sciences of the Republic of Uzbekistan [AN RUz], Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 833–837, November-December, 1995. Original article submitted February 20, 1995.