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31.
文中报道两种新的含茂钛低钛物Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_4CH-O)-O-]n-H(Ⅰ)与Cp_2Ti(Cl)-O-[-Ti(Cp)(O_2CCH_2CH)-O-]_u-H(Ⅰ)的制备并用元素分析和光谱(IR,1~H NMR,MS)对它们进行了鉴定。 相似文献
32.
Nishi K. Bhardwaj Viet Hoang Vinh Dang Kien L. Nguyen 《Colloids and surfaces. A, Physicochemical and engineering aspects》2006,290(1-3):222-228
A wide range of kraft pulps from radiata pine produced by low-temperature kraft pulping in flow-through reactors was assessed for carboxyl and hexenuronic acid (HexA) contents using the conductometric titrations and UV spectrophotometer, respectively. The Kappa number of pulps varied from 20.8 to 84.7 when using a cooking liquor of 1 M effective alkali as Na2O, 25% sulfidity, and cooking time of 100–250 min. The experimental results showed that the carboxyl groups (including HexA) and HexA groups dissolved and their residual values in the pulp samples correlate linearly with Kappa number and pulp yield. The dissolving rate of all carboxyl groups is much faster than the loss of HexA. The HexA/lignin ratio decreased non-linearly with Kappa number. 相似文献
33.
Ajay K. Bose Maghar S. Manhas Suhas Pednekar Subhendu N. Ganguly Hoang Dang William He Arun Mandadi 《Tetrahedron letters》2005,46(11):1901-1903
An important stage in process development is kilo scale preparation of the target compound. For this reason, a procedure involving water-based biphasic reaction media has been developed for conducting some exothermic reactions on a large scale. This protocol is illustrated by the energy-efficient and rapid preparation of dihydropyrimidinones by a solvent-free, green chemistry procedure applied to the Biginelli reaction using p-toluenesulfonic acid as catalyst. 相似文献
34.
Levitus M Zepeda G Dang H Godinez C Khuong TA Schmieder K Garcia-Garibay MA 《The Journal of organic chemistry》2001,66(9):3188-3195
Crystals of 1,4-bis(2-hydroxy-2-methyl-3-butynyl)-2-fluorobenzene 4 have a rich packing structure with four distinct molecules in the unit cell. A complex hydrogen bonding network results in the formation of cofacial trimers, cofacial dimers, and monomers within the same unit cell. Given a remarkable opportunity to investigate the effect of aggregation on the photophysics of 1,4-diethynylbenzenes, we analyzed the absorption, diffuse reflectance, and emission spectra of compound 4 in solutions and in crystals. Diffuse reflectance and fluorescence excitation revealed a red-shifted absorption that is absent in dilute solution but becomes observable at high concentrations and low temperatures. The fluorescence emission in the solid state is dual with components assigned to monomers and aggregates. The excitation and emission assigned to the monomer are nearly identical in crystals and dilute solutions. The absorption and emission bands assigned to aggregates are broad and red-shifted by 60--80 nm. As expected for a sample with absorbers and emitters with different energies and incomplete equilibration, efficient monomer-to-aggregate energy transfer was observed by a proper selection of excitation wavelengths. The fluorescence quantum yield of 4 in solution is relatively low (Phi(F) = 0.15) and the singlet lifetime short (tau(F) = 3.8 ns). A lower limit for the triplet yield of Phi(T) = 0.64 was determined indirectly in solution by (1)O(2) sensitization, and a relatively strong and long-lived phosphorescence was observed in low-temperature glasses and in crystals at 77 K. 相似文献
35.
Shengfei Jin Hang T. Dang Graham C. Haug Viet D. Nguyen Hadi D. Arman Oleg V. Larionov 《Chemical science》2020,11(34):9101
Construction of C–C bonds at the α-carbon is a challenging but synthetically indispensable approach to α-branched carbonyl motifs that are widely represented among drugs, natural products, and synthetic intermediates. Here, we describe a simple approach to generation of boron enolates in the absence of strong bases that allows for introduction of both α-alkyl and α-aryl groups in a reaction of readily accessible 1,2-dicarbonyls and organoboranes. Obviation of unselective, strongly basic and nucleophilic reagents permits carrying out the reaction in the presence of electrophiles that intercept the intermediate boron enolates, resulting in two new α-C–C bonds in a tricomponent process.α-Branched carboxylic acids and other carbonyls are readily accessed by a metal- and base-free deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls via boron enolates, resulting in a tricomponent coupling with unconventional electrophiles. 相似文献
36.
Ren Yan-Wei Dang Li-Long Li Jun Gao Wei-wei Zhang Feng-Xing 《Journal of Structural Chemistry》2005,46(2):352-357
A novel one-dimensional (1D) chain coordination polymer [Mn2(2,2′-dipha)2(phen)]n has been synthesized by hydrothermal reaction, and characterized by elemental analysis, IR spectroscopy, TGA, and X-ray diffraction. Orange crystals crystallized in the monoclinic system, space group C2/c with a = 19.393(7) Å, b = 19.183(7) Å, c = 19.729(7) Å, β = 90.826(6)°, V = 7338(5) Å3, Z = 8. In the crystal structure, one manganese atom is six-coordinated with four carboxylate oxygen atoms from one pentadentate 2,2′-dipha ligand and two tetradentate 2,2′-dipha ligands, and with two nitrogen atoms of one phen ligand, giving a slightly distorted octahedral geometry. The other manganese atom is five-coordinated with five oxygen atoms from two tetradentate 2,2′-dipha ligands and two pentadentate 2,2′-dipha ligands and has a trigonal bipyramidal environment. The TGA curve shows that the compound is stable below 310°. 相似文献
37.
Anna V. Gulevskaya Shee Van Dang Alexander F. Pozharskii 《Journal of heterocyclic chemistry》2005,42(3):413-419
Synthesis of some condensed pyrrolo‐, thieno‐, furo‐, pyrido‐ and pyranopteridines as well as isomeric pyrrolo‐ and thienopyrimido[4,5‐c]pyridazines from alkynyl derivatives of 6,8‐dimethylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐dione and 1,3‐dimethyllumazine is represented. 相似文献
38.
Le Ngoc Xuyen Hoang Dang Lanh Ho Si Thoang J. V?lter 《Reaction Kinetics and Catalysis Letters》1989,39(2):293-298
Pt–Ni/-Al2O3 catalysts have been prepared and studied in n-hexane dehydrocyclization. The selectivity for benzene and toluene, a chain lengthening product formation was improved by Ni and correlated with its content.
Pt–Ni/-Al2O3 -. Ni . Ni , .相似文献
39.
Hoang Dang Lanh G. Lietz Ho Si Thoang J. Völter 《Reaction Kinetics and Catalysis Letters》1982,21(4):429-432
The conversion of n-hexane was studied on a Pt-Sn/Al2O3 catalyst, a PtSn alloy and on the corresponding Pt catalysts. The results indicate the same catalytic effect of tin in supported and unsupported catalysts. It is concluded that the role of tin is connected with alloy formation.
- Pt-Sn/Al2O3, PtSn Pt-. . , .相似文献
40.