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21.
Aleksandra Gasperowicz Wodzimierz askawski 《Journal of polymer science. Part A, Polymer chemistry》1976,14(12):2875-2886
The grafting of styrene onto low molecular weight polybutadienes and butadiene–styrene co-polymers was studied. A mathematical method was used for the design of experiments and for the determination of the optimum grafting conditions with respect to the conversion of styrene and the efficiency of grafting. The reaction parameters were temperature (65–105°C), time (2–10 hr), concentration of the initiator, polymer to monomer ratio (10/90–90/10) and dilution by solvent (toluene). The optimum grafting conditions were chosen under which 50–60 wt-% of styrene was grafted onto backbone polymer at a high conversion of the monomer. It was found that the reactions producing graft copolymer prevailed over the styrene homopolymerization when the temperatures employed were lower (65–85°C), and the reaction time (8–10 hr), backbone polymer/monomer ratio, and the dilution by solvent were higher. The efficiency, density, and degree of grafting were found to increase with the increase in the molecular weight of the backbone polymer. The efficiencies and densities of grafting onto low molecular weight polybutedienes were higher than those of grafting onto low molecular weight butadiene–styrene copolymers. Grafting efficiencies and grafting densities were in the ranges 37.8–61.6 wt % and 0.06–0.26, respectively, in the studied range of number-average molecular weights (M?n = 2400–6000). 相似文献
22.
Dagmara Jacewicz Agnieszka Łapińska Aleksandra Dąbrowska Lech Chmurzyński 《Transition Metal Chemistry》2006,31(1):111-117
The kinetics of the reaction between gaseous CO2 and the cis-[Cr(phen)2(OH2)2]3+ ion leading to the formation of the carbonato complex ion, have been studied over the pH and temperature ranges: 3 < pH <
6 and 5 < T < 25 °C, respectively, at a constant ionic strength of 1 m (NaClO4). Investigations were carried out using the stopped-flow spectrophotometry technique in the UV–Vis range: 340–700 nm. The
major reactant species in the pH range studied was cis-[Cr(phen)2(OH)(OH2)]2+ ion, which underwent reaction with CO2 to form cis-[Cr(phen)2(OH2)(HCO3)]2+ ion. Subsequently, slower ring closure of the latter species to form the bidentate carbonato chelate was observed. The possible
mechanism has been discussed and the activation parameters ΔH† and ΔS† were also determined for the reaction studied. 相似文献
23.
The debenzylation of N-benzylimidazo[1,2-a]benzimidazoles with sodium in liquid ammonia was studied. The debenzylation of the 2-phenyl-substituted derivative is accompanied by hydrogenation of the outer imidazole ring to give 2-phenyl-2,3-dihydro-1H-imidazo[1,2-a]benzimidazole, the alkylation of which in alkaline media and neutral media, respectively, gives the 1-methyl derivative and the 9-methyl derivative. The 1-methyl derivative was subjected to quaternization and bromination; the latter proceeds in the condensed benzene ring. Debenzylation of the 2-methyl derivative of imidazo[1,2-a]benzimidazole is not accompanied by hydrogenation but gives 2-methyl-1(9)H-imidazo[1,2-a]benzimidazole.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 791–796, June, 1973. 相似文献
24.
The influence of various reclamation agents (montmorillonite, peat, activated sludge microbocenosis) on the stability of dispersions of the colloidal fraction of meadow chernozem soil is studied. It is established that biocolloids possess the strongest coagulating action in the aforementioned series of reclamation agents. It is shown that, in the process of microorganism growth involving glucose or polypeptides as a carbon source, exopolymers are synthesized that caused the coagulation of soil dispersions. Upon the growth of microorganisms on polypeptides (alkaligeneous metabolism), precipitates are formed that are denser and less peptized by water than those grown on glucose (acidogeneous metabolism). The addition of montmorillonite and peat intensifies the aggregation processes in soil-microbe heterodispersions. The inverse relationship between the content of an organic substance in a colloidal system and the stability of aggregates of soil colloids is revealed. 相似文献
25.
Snezana S.?MiticEmail author Gordana Z.?Miletic Aleksandra N.?Pavlovic Snezana B.?Tosic 《Monatshefte für Chemie / Chemical Monthly》2004,135(8):927-936
Summary. A new selective, sensitive, and simple kinetic method is developed for the determination of trace amounts of chromium (VI). The method is based on the catalytic effect of Cr(VI) on the reaction of sodium pyrogallol-5-sulphonate (PS) with hydrogen peroxide. The reaction is followed spectrophotometrically by tracing the oxidation product at 437nm within 1min after addition of H2O2. The optimum reaction conditions are PS (1.32·10–3mol·dm–3), H2O2 (0.32mol·dm–3), HClO4 (2.6·10–3mol·dm–3) at 25°C. Following this procedure, chromium (VI) can be determined with a linear calibration graph up to 0.25ng·cm–3 and a detection limit of 0.024ng·cm–3, based on the 3 criterion. The interference effect of several species was also investigated and it was found that the most common cations and anions do not interfere with the determination. The developed procedure was successfully applied to the determination of Cr(VI) and total Cr in river waters and total Cr in herbal samples. 相似文献
26.
Borisova I. V. Nechaev M. S. Khrustalev V. N. Zemlyanskii N. N. Ustynyuk Yu. A. 《Russian Chemical Bulletin》2002,51(5):721-753
The review surveys the data on the reactions of phosphorus and arsenic ylides with compounds containing E=X bonds (E = C, Si, Ge, or Sn; X = C or S), cyclic oligomers (R2ES)n (n = 2 or 3), and heavier analogs of carbenes. These reactions give rise to two new classes of heteroorganic betaines containing the (+)E15—C—E14—X(–) (I) and (+)E15—C—E14(–) (II) (E15 = P or As; E14 = Si, Ge, or Sn; X = C or S) structural fragments. Procedures for the synthesis of these compounds, their reactivities, the X-ray diffraction structures, and the electronic structures established by high-level quantum-chemical calculations are considered in detail. The carbon analogs of betaines of type I, viz., compounds bearing the (+)P—C—C—X(–) fragment (III), are also discussed. The latter were long considered as possible intermediates in the reactions of compounds containing the polar C=X bond (X = C, O, S, NR, etc.) with phosphorus ylides (classical Wittig and Corey—Chaykovsky reactions and related processes). 相似文献
27.
Aleksandra Drzewiecka Krystyna Stepniak Anna Barcicka Anna E. Koziol 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(8):m346-m348
The asymmetric unit in the title compound, {[Cd2(C4H4O6)(SO4)(H2O)5]·3H2O}n, is composed of two cadmium cations, one (R,R)‐tartrate and one sulfate anion, five aqua ligands and three solvent water molecules. One of the cadmium ions is coordinated in an octahedral environment, whereas the second is surrounded by seven O atoms in a pentagonal–bipyramidal geometry. Both types of coordination polyhedra form two sets of perpendicular non‐intersecting polymeric chains. CdO6 octahedra share two corners, while CdO7 units are joined by a bridging carboxylate group. An extensive hydrogen‐bond pattern involving all of the OH groups contributes to the stabilization of the structure. 相似文献
28.
L. G. Voskressensky S. V. Akbulatov T. N. Borisova A. V. Kleimenov A. V. Varlamov 《Russian Chemical Bulletin》2007,56(11):2323-2329
A reaction of substituted hexahydroazepino[4,3-b]-and-[3,4-b]indoles with activated alkynes was studied. A one-step method for the synthesis of isomeric hexahydroazonino[5,6-b]indoles different by positions of the double bond in the azonine ring was developed.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2244–2250, November, 2007. 相似文献
29.
Nesković OM Veljković MV Velicković SR Petkovska LT Perić-Grujić AA 《Rapid communications in mass spectrometry : RCM》2003,17(3):212-214
Ionization energies of hypervalent Li(2)F, Li(2)Cl and Na(2)Cl molecules detected by surface ionization electron impact neutralization mass spectrometry are reported. The ionization energies were 3.78 +/- 0.2 eV for Li(2)F, 4.93 +/- 0.2 eV for Li(2)Cl, and 4.21 +/- 0.2 eV for Na(2)Cl. The ionization energies (IE) agree with theoretical ionization energies calculated by ab initio methods, supporting the theoretical prediction that Li(2)F has a hyperlithiated configuration in which the odd electron delocalizes over the two lithiums and with photoionization measurement. The first ionization energy of Na(2)Cl was experimentally confirmed earlier and for Li(2)Cl as well.8 We have developed and used this new approach for the problem--in the present work ions were first formed by surface ionization, followed by electron attachment (neutralization). 相似文献
30.
Frontera A Saczewski F Gdaniec M Dziemidowicz-Borys E Kurland A Deyà PM Quiñonero D Garau C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6560-6567
Several structures of pi complexes of isocyanuric acid and of several thio derivatives with anions have been computed by using high level ab initio calculations. The nature of the complexes has been studied by means of the method of molecular interaction potential with polarization (MIPp) and Bader's theory of atoms-in-molecules. These molecules form favorable complexes with anions and can be used as binding units for building receptors for the molecular recognition of anions. In several cases, the anion-pi interaction has been demonstrated experimentally by means of X-ray crystallography. 相似文献