Bistable dependence of the efficiency of second harmonic generation on the total energy of femtosecond soliton pulses propagating in an optical fiber

Taking into account the effect of cubic nonlinearity on the process of second harmonic generation by soliton-like femtosecond pulses results in a hysteresis dependence of the generation efficiency, the pulse durations, and the mismatch of the wave numbers of the interacting waves on their total energy. Color solitons with earlier unknown shapes are formed at a high efficiency of the frequency conversion. Varying the phase mismatch makes it possible to “switch” the soliton duration and the conversion efficiency without a change in the total energy of the waves or the soliton shape. It is emphasized that the soliton corresponding to the middle branch of the hysteresis dependence is stable against small perturbations. It is significant that the soliton shape remains unchanged in the considered range of energies.     

Noncatalytic hydrophosphorylation and hydrothiophosphorylation of hydroxyaldehydes

Nucleophilic addition of secondary phosphone oxides and phosphine sulfides to 2-hydroxyacet-, 2-hydroxybenz-, and 3,4-dihydroxybenzaldehydes proceeds under mild conditions (48–50°C, THF) and allows tertiary phosphine oxides and phosphine sulfides with several hydroxyl groups to be prepared.     

Selective hydrogenation of the vinyl group of 1-vinylpyrroles

The hydrogenation of 1-vinylpyrroles over Raney nickel in ethanol at 50–90°C proceeds exclusively at the 1-vinyl group and leads to the formation of 1-ethylpyrroles in 80–90% yields. The IR and PMR spectra are presented.Translated from Khimiya Geterotsilicheskikh Soedinenii, No. 2, pp. 215–216, February, 1077.     

The radiation yields of radicals in solid organic substances containing heteroatoms

EPR has been used to measure the radiation yields of radicals (G_R) in various classes of organic compounds containing heteroatoms: dialkyl disulfides, diphenyl- and dibenzyl disulfide, alkyl derivatives of thiophene, thiophenecarboxylic acids, halogen derivatives of thiophene, and saturated heterocyclic compounds containing nitrogen, oxygen, and sulfur atoms. It has been shown that 1) G_R=0.2–1 per 100 eV in saturated disulfides and cyclic sulfides, while G_R=3–8 per 100 eV in the corresponding hydrocarbons, alcohols, oxides, and alkyleneimines; 2) the introduction of a sulfur atom into aromatic compounds does not alter the radiation stability; 3) disturbance of the conjugation of halogen atoms and of the carboxyl group with the thiophene ring leads to a decrease in the radiation stability. It is suggested that the increased stability of sulfur-containing compounds may be due to the excitation of the electrons in the S atom at the d-orbitals, which lie appreciably lower in the sulfur atom than in the atoms of oxygen, nitrogen, and carbon, and the subsequent dissipation of the excitation energy.     

Sulfur-containing polymer and carbon materials based on poly(vinyl chloride)

New sulfur-containing copolymers based on poly(vinyl chloride) have been prepared by the nucleophilic substitution of chlorine atoms by sulfur atoms using sodium tetra- and pentasulfides. It has been shown that these copolymers can be carbonized to produce sulfur-containing carbon materials with residual chlorine content about 2 wt %.     

Reaction of Red Phosphorus with Allylbenzene in Superbasic System KOH-DMSO

Abstract

Red phosphorus reacts with allylbenzene in the superbase system KOH-DMSO (130°C, 3 h, Ar) to give a mixture of bis(1-methyl-2-phenylethyl)phosphane (1), bis(1-methyl-2-phenylethyl)phosphane oxide (2), and 1-methyl-2-phenylethylphosphinic acid (3). Secondary phosphane oxide 2 and phosphinic acid 3 have been isolated from this mixture in 35% and 32% yield, respectively. Microwave activation of the reaction (200 W, 30 min) affords secondary phosphane 1 as the main product in 48% yield.

GRAPHICAL ABSTRACT      

Non-catalytic Addition of 1,2,4-Triazole to Nucleophilic and Electrophilic Alkenes

Non-catalytic addition of 1,2,4-triazole to vinyl ethers and esters occurs on heating (65-175°C, 4-20 h) to give Markovnikov adducts (yield 30-100%). Electron-deficient alkenes (acrylonitrile, acrylic acid, 4-phenyl-3-buten-2-one) react with 1,2,4-triazole (78-190°C, 4-20 h) to give anti-Markovnikov adducts in yields of 45-83%.     

Quantum-Chemical Study of the Profiles of Reactions that Form Pyrrole Anion N-Adducts with CS<Subscript>2</Subscript> and CO<Subscript>2</Subscript>

The profiles of reactions leading to pyrrole anion N-adducts with CO₂ and CS₂ have been studied by the ab initio (RHF/6-31+G*, MP2/6-31+G*) and density functional (B3LYP/6-31+G*) methods. Addition of the pyrrole anion to the carbon disulfide molecule is accompanied by the appearance of a minimum corresponding to a pre-reaction complex. The transformation of the complex to the N-pyrrolyldithiocarboxylate anion occurs via a low activation barrier, which is due to repolarization of the C=S bonds. The profile of the reaction leading to the pyrrole anion N-adduct with CO₂ does not contain any intermediate stationary points throughout the whole route from reagents to products.Original Russian Text Copyright © 2004 by V. B. Kobychev, N. M. Vitkovskaya, I. L. Zaitseva, and B. A. Trofimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 6, pp. 990–993, November–December, 2004.     

Isomorphous substitutions of rare earth elements for calcium in synthetic hydroxyapatites

Polycrystalline hydroxyapatites Ca(10-x)REE(x)(PO(4))(6)(OH)(2-x)O(x) were synthesized and studied by X-ray powder diffraction, infrared absorption, diffuse-reflectance spectroscopy, and thermogravimetry. The solubility limits x(max) of rare earth elements (REE) in Ca hydroxyapatites decreases with an increasing REE atomic number from x(max) = 2.00 for La, Pr, and Nd to x(max) = 0.20 for Yb at 1100 °C. Refinements of X-ray diffraction patterns by the Rietveld method show that REE atoms substitute for Ca preferentially at the Ca(2) sites of the apatite structure. The substitution decreases the Ca(2)-O(4) atomic distances in the calcium coordination polyhedra and increases the Ca(2)-O(1,2,3) distances. This observation shows that interatomic distances depend not only on radii of the ions involved in the substitution but also on their charges.     

One-pot assembly of 4-methylene-3-oxa-1-azabicyclo[3.1.0]hexanes from alkyl aryl(hetaryl) ketoximes, acetylene, and aliphatic ketones: a new three-component reaction

A new three-component reaction between alkyl aryl(hetaryl)ketoximes, acetylene, and aliphatic ketones in the superbasic systems KOH/DMSO and LiOH/CsF/DMSO (70-90 °C, initial acetylene pressure 13-15 atm, 5-60 min) affords novel 4-methylene-3-oxa-1-azabicyclo[3.1.0]hexanes in yields of up to 75%. Using KOH/DMSO, the side products of the reaction are O-vinylketoximes and 2-aryl(hetaryl)pyrroles, while with LiOH/CsF/DMSO, the reaction proves to be selective, only minor amounts of the corresponding alkyl aryl(hetaryl) ketones being detectable.