Effect of medium acidity on the efficiency of oxidation of 2,4,6-trinitrotoluene to 2,4,6-trinitrobenzoic acid

An effect of boric acid additives on oxidation of 2,4,6-trinitrotoluene (TNT) to 2,4,6-trinitrobenzoic acid (TNBA) with chromic anhydride in concentrated (96—100%) H₂SO₄ has been studied. In the presence of tetrahydrosulfatoboric acid HB(HSO₄)₄ formed in situ (up to 5 mol.%) or added as a preliminary prepared solution (up to 1 mol. %), TNT is selectively oxidized to TNBA in the yields up to 95—99%. The mechanism including formation of TNT dication as a key step of its oxidation at the methyl group has been suggested.     

Rheological properties of sulfur-containing hyperbranched polycarbosilanes and related magnetic compositions

Russian Chemical Bulletin - The rheological properties of hyperbranched polycarbosilanes with butyl and decyl terminal groups and their sulfur-containing analogs were compared. The use of various...     

Relaxation and equilibrium properties of dilute aqueous solutions of alcohols

Regularities of equilibrium state establishment in dilute aqueous solutions of alcohols and the concentration and temperature dependences of the contraction, which is one of the simplest and important thermodynamic characteristics of solutions, were considered. The equilibrium state in aqueous solutions of the alcohols is established for days and even weeks after preparation. Such a slow relaxation process is directly related to the formation of the microheterogeneous state of the system and peculiarities of its time evolution. The character of the temperature and concentration dependences of the contraction is satisfactorily explained on the basis of the simplest virial equation of state assuming that its parameters are determined by the averaged potentials of intermolecular interaction. The physical nature of peculiar points of aqueous solutions of alcohols, i.e., intersection points of the contraction curves or points in the vicinity of which the intensity of molecular light scattering anomalously increases, was considered. The appearance of peculiar points depends on orientational correlations in water. The possibility of existence of peculiar points in other binary solutions is also discussed.     

Random Features of the Fatigue Limit

The classical fatigue limit is often an important characteristic in fatigue design regarding metallic material. The limit is usually obtained from a staircase test in combination with some assumption about the statistical distribution of the limit. This distribution can be of a normal, log-normal or of extreme value type and no particular physical argument gives favor to any specific distribution. This leads to a certain ambiguity in the evaluation of test results which forces the designer to introduce large safety factors. In order to find a physically based statistical distribution for use in staircase tests to determine the fatigue limit we present here a random model for the fatigue limit based on the following assumptions; (i) The square root area model according to Murakami and co-workers is valid, (ii) the randomness in the fatigue limit is induced by the randomness of the maximum defect size, (iii) the random maximum defect size has an extreme value distribution of Gumbel type. This leads to the fatigue limit distribution based on Gumbel (FLG), which is recommended to replace the normal distribution in the evaluation of staircase fatigue tests in case of hard materials. It turns out that the skewness of the resulting distribution depends on the coefficient of variation; with a normal-like non-skewed distribution at the coefficient of variation of five percent.     

Synthesis,properties, and antibacterial activity of a new nitric oxide donor — a nitrosyl iron complex with 5-phenyl-1H-1,2,4-triazole-3-thiol

Russian Chemical Bulletin - A new binuclear μ-NSC-type nitrosyl iron complex [Fe2(SR)2(NO)4] (R is 5-phenyl-1H-1,2,4-triazole-3-thiolyl) was synthesized. The composition and structure of the...     

Analysis of Spontaneous Electrochemical Oscillations by the Wavelet Transformation Method

A new way of analyzing current oscillations that accompany anodic metal dissolution is presented. A wavelet transformation is used for separation and spectral analysis of singular courses—elementary components of electrochemical oscillation recordings. A method of obtaining oscillation energy distribution analogous to the spectral power density function is presented. It is shown that the chaotic component (Shil'nikov chaos) can be separated from the deterministic component of the described process.     

Nonlinearity of the Automorphism Groups of Some Free Algebras

We prove that the groups of tame automorphisms of a free Lie algebra (free associative algebra, absolutely free algebra, algebra of polynomials) of rank at least four over a field of characteristic zero admit no faithful representation by matrices over any field.     

Asymptotic aspects of Schreier graphs and Hanoi Towers groups

We present relations between growth, growth of diameters and the rate of vanishing of the spectral gap in Schreier graphs of automaton groups. In particular, we introduce a series of examples, called Hanoi Towers groups since they model the well known Hanoi Towers Problem, that illustrate some of the possible types of behavior. To cite this article: R. Grigorchuk, Z. ?unik´, C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Di-μ-hydroxo complexes of palladium(II) with α-diimines

The binuclear hydroxo α-diiminate palladium complexes [Pd2(R′N=CR-CR=NR′)2(μ-OH)2][ClO4]2 (R=H, R′= C6H4Me-o or C6H4Me-p; R=Me, R′=Ph, C6H4Me-o or C6H4Me-p) have been prepared by reacting the corresponding chloro complexes with AgClO4 in Me2CO–H2O. The hydroxo complexes react with the protic electrophiles ethanoic acid, acetylacetone and8-hydroxoquinoline to give the corresponding acetylacetonate, acetate and 8-hydroxiquinolinate complexes. This revised version was published online in June 2006 with corrections to the Cover Date.     

Lefschetz pencil structures for 2-calibrated manifolds

We prove that for closed 2-calibrated manifolds there always exist Lefschetz pencil structures. This generalizes similar results for symplectic and contact manifolds. To cite this article: A. Ibort, D. Marti´nez Torres, C. R. Acad. Sci. Paris, Ser. I 339 (2004).