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971.
972.
《Journal of organometallic chemistry》2007,692(25):5633-5645
Triorganotin(IV) chlorides containing one LCN chelating ligand were hydrolyzed with an excess of sodium hydroxide. The composition of the products is strongly dependent on the nature of the organic groups bound to the tin atom. Di(n-butyl)tin, dimethyltin as well as the diphenyl derivative exhibits an equilibrium between hydroxide and stannoxane forms (oxide), whereas alkyltin species react spontaneously and reversibly with carbon dioxide present in the air to form carbonate species. On the other hand, diphenyl derivatives display virtually no reaction with CO2 towards carbonates, while the di-t-butyl-substituted tin derivative is stable under the same experimental condition and remains as a tin hydroxide. In the case of the dimethyltin derivative, a methyl group migration was observed with displacement of one LCN chelating ligand during the reaction on the air. The coordination geometry of the tin central atom(s) of all studied compounds can be described as trigonal bipyramidal with a dative bonded dimethylamino group occupying one coordination site. The catalytic activity of these compounds in transesterification reactions is generally lower compared to the systems reported in the literature, with the exception of the transesterification of ethyl acetate by cyclohexanol which displays a remarkable activity. 相似文献
973.
Yunhui Zhai Xijun Chang Yuemei Cui Ning Lian Shoujun Lai Hong Zhen Qun He 《Mikrochimica acta》2006,154(3-4):253-259
A rapid, selective method that utilize 4-(2-Pyridylazo)-resorcinol (PAR)-modified nanometer SiO2 (nanometer SiO2–PAR) as a new solid-phase extractant for preconcentration of trace mercury (II) has been developed. The adsorption property
of nanometer SiO2–PAR for metal ions was studied by selectively extracting different metal ions from aqueous solutions. The results revealed
an excellent affinity of the nanometer SiO2–PAR for mercury (II) in presence of interfering metal ions at pH 4. The main parameters of solid-phase extraction such as
shaking time, elution and sample dilution effect were studied. The extractant shows rapid kinetic sorption, and the adsorption
equilibrium of mercury (II) on nanometer SiO2–PAR was achieved in less than 2 min. The adsorbed mercury (II) was easily eluted by 4 mL of 6 mol L−1 HCl. The maximum preconcentration factor was 50. The maximum static adsorption capacity was 276 μmol g−1 at pH 4. The detection limit (3σ) was 0.43 μg L−1 for cold vapor atomic absorption spectrometry (CVAAS), and the relative standard deviation of the eight replicate determinations
was 2.4% for the determination of 2.0 μg of Hg(II) in 100 mL water sample. The method was applied to the determination of
trace mercury (II) in sample solutions with satisfactory results. 相似文献
974.
HUA Er-BingCoordination Chemistry Institute State Key Laboratory of Coordination Chemistry Nanjing University Nanjing Jiangsu ChinaYANG Pin LI Qing-Shan YANG Bin-ShengInstitute of Molecular Science Shanxi University Taiyuan Shanxi China 《中国化学》1996,14(4):297-302
The effect of Cu2+ on the triple-stranded helical structure of poly(A:2I) was studied by means of circular dichroism spectral method with the help of ultraviolet spectral and ethidium bromide fluorescence probe methods. It was found that Cu2+ destabilizes the structure of the triple helix poly(A:2I) and induces its structural transformations, meanwhile, the transformations can be partially reversed by a higher NaCl concentration. The structural transformations may be expressed by the following scheme: poly(A:2I) - poly(A:I) + poly(I)- poly(A) + 2poly(I) 相似文献
975.
In our former investigations, the phenomenon high temperature corrosion (HTC) was described exemplarily on selected materialcoating combinations for blades of stationary gas turbines, mainly in the temperature region of up to 750° C. To answer the question, in which manner higher gas inlet and/or higher material surface temperature would influence the HTC behaviour, a special analytical technique—the integral layer profile analysis—was introduced to ameliorate concentration profile methods. By examining IN 738 LC specimens with CoCrAlY plasma spray coating, stressed by hot gas at 900° C, the limits of this system are shown by explaining the corrosion mechanism; the method is also used for other systems, e.g. U 520 with NiCrAlY coating at 750° C. 相似文献
976.
S. N. Tandura S. P. Kolesnikov M. P. Egorov K. S. Nosov O. M. Nefedov 《Russian Chemical Bulletin》1997,46(3):602-604
Assignment of all of the signals in the1H and13C NMR spectra of 1,1-dichloro-2,3,4,5-tetraphenyl-l-germacyclopenta-2,4-diene has been carried out using two-dimensional NMR
spectroscopy.
Translated fromIzvestiya Akademii Nauk Seriya Khimicheskaya, No. 3, pp. 623–625, March, 1997. 相似文献
977.
茂锆载体催化剂下的乙烯/辛烯共聚及聚合物的^13C NMR研究 总被引:3,自引:0,他引:3
茂锆载体催化剂下的乙烯/辛烯共聚及聚合物的~(13)CNMR研究刘胜生,于广谦,黄葆同(中国科学院长春应用化学研究所长春130022)关键词茂锆载体催化剂,共聚,序列分布,~(13)CNMR由于茂锆催化剂具有高活性,单一活性中心等特点[1,2],并且能... 相似文献
978.
V. N. Odinokov G. Yu. Ishmuratov R. Ya. Kharisov E. P. Serebryakov G. A. Tolstikov 《Russian Chemical Bulletin》1993,42(1):100-101
A novel path toS-(+)-hydroprene (1) starting from the technical gradeS-(+)-dihydromyrcene (2, e.e. 50%) is proposed. The latter was selectively transformed intoS-3,7-dimethyloctanal (5) in three steps including hydroalumination. The reactions of5 with allyl- or methallylmagnesium chloride followed, respectively, either by oxygenation in the presence of PdCl2/CuCl or by ozonolysis, affordS,E-6,10-dimethyl-3-undecen-2-one (7) which was treated with ethoxyethynylmagnesium bromide to give the title juvenile hormone analogue in 23% overall yield.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No 1, pp. 110–112, January, 1993. 相似文献
979.
The crosslinking Diels-Alder reaction between styrene-furfuryl methacrylate copolymer samples (poly(ST-co-FM)) and bismaleimide (BM) at 25 °C in chloroform was studied by following the decay in UV absorbance of the maleimide (MI) group at 320 nm. Reaction conditions were changed by using copolymers with different mole fraction of FM, FFM, and by employing different initial molar ratios of reactants (furan group within FM and MI group within BM). Second order kinetics were obeyed. 13C NMR spectra showed that, even when all reactants had been converted to an insoluble crosslinked network, unreacted MI groups remained, presumably in the form of singly reacted pendant BM molecules. The fractions of MI groups remaining unreacted were found to be 0.49, 0.34 and 0.22 for FM:MI mole ratios in the initial mixture of 2, 1 and 0.5 respectively, when using a copolymer of FFM=0.1354. An attempt was also made to follow the kinetics of network formation by 13C NMR spectroscopy, using the peak areas for reacted and unreacted MI and FM groups, but many of the findings were subject to some uncertainty for reasons, which are discussed. However, because the peak areas were considered reliable for unreacted MI groups, the rate constant, k, was evaluated, thereby. Overall using UV and NMR the values of k lay within the interval (0.8-3.6) × 10−5 dm3 mol−1 s−1. 相似文献
980.
Atsushi TatamiMasayuki Inoue Hisatoshi UeharaMasahiro Hirama 《Tetrahedron letters》2003,44(28):5229-5233
A concise route to the HIJKLM-ring fragment 10 of ciguatoxin (CTX) and 51-hydroxyCTX3C was developed in which oxiranyl anion addition and intramolecular carbonyl olefination were utilized as key transformations. The present procedure requires only 23 steps from the I-ring 5, while 35 steps were employed in a previous synthesis of the corresponding right wing 11 of CTX3C. The high efficiency of the present synthesis ensures a supply of 10 for total synthesis and biomedical applications. 相似文献