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141.
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
142.
Quantum-chemical calculations were performed on the mechanisms of reaction of NCN with NO and NS. Possible mechanisms were classified according to four pathways yielding products in the following four possible groups: N2O/N2S + CN, N2 + NCO/NCS, N2 + CNO/CNS, and CNN + NO/NS, labeled in order from p1/p1s to p4/p4s. The local structures, transition structures, and potential-energy surfaces with respect to the reaction coordinates are calculated, and the barriers are compared. In the NCN + NO reaction, out of several adduct structures, only the nitroso adduct NCNNO lies lower in energy than the reactants, by 21.89 kcal/mol; that adduct undergoes rapid transformation into the products, in agreement with experimental observation. For the NS counterpart, both thionitroso NCNNS and thiazyl NCNSN adducts have energies much lower than those of the reactants, by 43 and 29 kcal/mol, respectively, and a five-membered-ring NCNNS (having an energy lower than those of the reactants by 36 kcal/mol) acts as a bridge in connecting these two adducts. The net energy barriers leading to product channels other than p4s are negative for the NS reaction, whereas those for the NO analogue are all positive. The channel leading to p1 (N2O + CN) has the lowest energy (3.81 kcal/mol), whereas the channels leading to p2 (N2 + NCO) and p2s (N2 + NCS) are the most exothermic (100.94 and 107.38 kcal/mol, respectively). 相似文献
143.
Heekyoung Choi Sojeong Heo Seonae Lee Ka Young Kim Jong Hyeon Lim Sung Ho Jung Shim Sung Lee Hiroyuki Miyake Jin Yong Lee Jong Hwa Jung 《Chemical science》2020,11(3):721
We report kinetically controlled chiral supramolecular polymerization based on ligand–metal complex with a 3 : 2 (L : Ag+) stoichiometry accompanying a helical inversion in water. A new family of bipyridine-based ligands (d-L1, l-L1, d-L2, and d-L3) possessing hydrazine and d- or l-alanine moieties at the alkyl chain groups has been designed and synthesized. Interestingly, upon addition of AgNO3 (0.5–1.3 equiv.) to the d-L1 solution, it generated the aggregate I composed of the d-L1AgNO3 complex (d-L1 : Ag+ = 1 : 1) as the kinetic product with a spherical structure. Then, aggregate I (nanoparticle) was transformed into the aggregate II (supramolecular polymer) based on the (d-L1)3Ag2(NO3)2 complex as the thermodynamic product with a fiber structure, which led to the helical inversion from the left-handed (M-type) to the right-handed (P-type) helicity accompanying CD amplification. In contrast, the spherical aggregate I (nanoparticle) composed of the d-L1AgNO3 complex with the left-handed (M-type) helicity formed in the presence of 2.0 equiv. of AgNO3 and was not additionally changed, which indicated that it was the thermodynamic product. The chiral supramolecular polymer based on (d-L1)3Ag2(NO3)2 was produced via a nucleation–elongation mechanism with a cooperative pathway. In thermodynamic study, the standard ΔG° and ΔHe values for the aggregates I and II were calculated using the van''t Hoff plot. The enhanced ΔG° value of the aggregate II compared to that of the formation of aggregate I confirms that aggregate II was thermodynamically more stable. In the kinetic study, the influence of concentration of AgNO3 confirmed the initial formation of the aggregate I (nanoparticle), which then evolved to the aggregate II (supramolecular polymer). Thus, the concentration of the (d-L1)3Ag2(NO3)2 complex in the initial state plays a critical role in generating aggregate II (supramolecular polymer). In particular, NO3− acts as a critical linker and accelerator in the transformation from the aggregate I to the aggregate II. This is the first example of a system for a kinetically controlled chiral supramolecular polymer that is formed via multiple steps with coordination structural change.The nanoparticles were transformed into the supramolecular polymer as the thermodynamic product, involving a helical inversion from left-handed to right-handed helicity. 相似文献
144.
The Zimmermann reaction for the determination of 17-ketosteroids was tested under both room-temperature and steam-distillation reaction conditions. meta-Nitroaniline was isolated from the residue of the steam distillation by ether extraction and thin-layer chromatography. Conclusive identification was by infrared spectroscopy. In contrast, m-nitroaniline was not formed under room-temperature reaction conditions, even when allowed to react for 24 hr. Similar results were also obtained for the reaction between acetone and m-dinitrobenzene under alkaline conditions. In conclusion, the results indicate that m-nitroaniline formation cannot account for the conversion of structure I to structure II under room-temperature reaction conditions as investigated herein. 相似文献
145.
J. Ho L. Zhu E. K. Parks S. J. Riley 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1993,26(1):331-333
The kinetics of chemical reactions of cobalt clusters Con with deuterium are described. Absolute rate constants have been measured in the size range n=7–68 at 293 K. The rate constants are found to be a strong function of cluster size, varying by a factor of 400. This size dependence is most prominent for n=7 to 25: Co15 is the most reactive cluster, and Co7–9 and Co19–20 are particularly unreactive. Abrupt changes in the rate constants from one cluster size to the next are observed. For the clusters above n=25, the rate constants show several less prominent maxima and minima superimposed on a slow, nearly monotonic increase with cluster size. 相似文献
146.
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
147.
148.
Fluorinated phenethyl bromides 1,2 , and 3 , prove to be totally inert under Ritter reaction conditions in the presence of either SnCl4 or AgNO3, due to the strong deactivation by the gem‐difluoro unit. Subjecting 2‐bromo‐1‐fluoro‐1‐phenylethane to SnCl4 in MeCN at elevated temperatures led to formation of 2‐methyl‐4‐phenyl‐4,5‐dihydrooxazole. 相似文献
149.
A variable-low-temperature scanning tunneling microscope (STM) was used to observe oxygen (O2), ethylene (C2H4), and acetylene (C2H2) molecules on a Ag(110) surface and the various complexes that were formed between these two hydrocarbons and oxygen at 13 K. Ethylene molecule(s) were moved to the vicinity of O2 either by STM tunneling electrons at 13 K or thermally at 45 K to form (C2H4)x-O2 (x = 1-4) complexes stabilized by C-H...O hydrogen bonding. Acetylene-oxygen complexes involving one or two acetylene molecules were observed. 相似文献
150.
Ji-Wang Chern Ching-Po Ho Ying-Hwa Wu Jiann-Gwo Rong Kang-Chien Liu Ming-Chu Cheng Yu Wang 《Journal of heterocyclic chemistry》1990,27(7):1909-1915
Reactions of 2-aminobenzenesulfonamide ( 1 ) with allyl, methyl, 2-chloroethyl aor 3-chloropropyl isocyanates gave 2-(methylureido)-, 2-(allylureido)-, 2-(2′-chloroethylureido)- and 2-(3′-chloropropylureido)-benzene sulfonamides 3a,b and 7a,b in excellent yields. Treatment of 3a,b at refluxing temperature of DMF afforded 2H-1,2,4-benzothiadiazin-3(4H)-one 1,1-dioxide ( 4 ) in good yield. However, when compounds 7a,b were refluxed in 2-propanol, 3-(2′-aminoethoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 11a ) and 3-(3′-aminopropoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 11b ) were obtained in a form of the hydrochloride salts 10a,b in 87% and 78% yields respectively. Heating 11b in ethanol gave a dimeric form of 2H-1,2,4-benzothiadiazin-3(4H)-one 1,1-dioxide and 3-(3′-aminopropoxy)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 12 ) in 55% yield. Treating of 7a,b or 11a,b with triethylamine at the refluxing temperature of 2-propanol afforded 3-(2′-hydroxyethylamino)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 2a ) and 3-(3′-hydroxypropylamine)-2H-1,2,4-benzothiadiazine 1,1-dioxide ( 2b ) via a Smiles rearrangement. 相似文献