排序方式: 共有41条查询结果,搜索用时 15 毫秒
1.
Merlin Rosales Janeth Navarro Ligbel Sánchez Angel González Ysaías Alvarado Raúl Rubio Carlos De La Cruz Tamara Rajmankina 《Transition Metal Chemistry》1996,21(1):11-15
Summary The complex [RuH(CO)(NCMe)2(PPh3)2]BF4 (1) is an efficient and regioselective catalyst precursor for the hydrogenation of polyaromatic nitrogen compounds such as quinoline (Q), isoquinoline (iQ), indole (ln), 5,6- and 7,8-benzoquinoline (BQ) and acridine (A) under relatively mild reaction conditions (125 °C, 4 atm H2). The order of individual initial rates was: A > Q > 5,6-BQ > 7,8-BQ > ln > iQ, reflecting both steric and electronic effects. For the regioselective homogeneous hydrogenation of A to 9,10-dihydroacridine (DHA) catalysed by complex (1), a kinetic study was carried out; the experimentally determined rate law was r = k
1 [Ru] [H2]. These findings are consistent with a mechanism involving the hydrogenation of [RuH(CO)(A)(NCMe)(PPh3)2]BF4 to yield DHA and the unsaturated species [RuH(CO)(NCMe)(PPh3)2]BF4 in the rate-determining step. 相似文献
2.
Rosa M. Dominguez Gabriel Chuchani Jairo Quijano Luz Janeth Orozco Iliana Restrepo 《Reaction Kinetics and Catalysis Letters》1996,57(1):191-196
The pyrolysis kinetics of ethyl 3-hydroxy-3-methylbutanoate have been examined over the temperature range of 286–330°C and pressure range of 29–108 Torr. In a seasoned vessel and in the presence of the free radical inhibitor cyclohexene or toluene the reaction is homogeneous, unimolecular and obeys a first-order rate law. The elimination products are mainly acetone and ethyl acetate, and very small amounts of ethyl 3-butenoate, acetic acid, ethylene and H2O. The rate coefficient is expressed by the following equation: log k1(s–1)=(12.39±0.46)–(174.5±5.2) kJ mol–1 (2.303RT)–1. The mechanism appears to proceed via a six-membered cyclic transition state, where polarization of the (CH3)C(OH)+...-CH2COOCH2CH3 bond is rate determining. 相似文献
3.
Pichini S Pellegrini M Pacifici R Marchei E Murillo J Puig C Vall O García-Algar O 《Rapid communications in mass spectrometry : RCM》2003,17(17):1958-1964
A high-performance liquid chromatography (HPLC) method with mass spectrometric detection is described for determination of arecoline in newborn meconium, urine and cord serum, using pilocarpine as internal standard. The analytes were extracted from neonatal biological matrices with chloroform/isopropanol (95:5, v/v) at alkaline pH. Extracts were analyzed by HPLC coupled to an electrospray (ESI) interface and a quadrupole mass spectrometer. Chromatography was performed on a C(8) reversed-phase column using 10 mM ammonium acetate (pH 4.3)/acetonitrile (90:10, v/v) as mobile phase. The mass spectrometer was operated in selected ion monitoring mode. The method was validated over the concentration range 0.005-1.00 micro g/g meconium, 0.004-1.00 micro g/mL cord serum and 0.001-1.00 micro /mL urine. Mean recoveries ranged between 86.5 and 90.7% for arecoline in the different biological matrices, with precision always better than 10%. The quantification limits of arecoline were 0.005 micro g/g meconium, 0.004 micro g/mL cord serum, and 0.001 micro g/mL urine. The method was applied to the analysis of neonatal biological matrices to assess eventual fetal exposition to arecoline. Two newborns from Asian mothers who declared areca nut consumption presented arecoline in meconium with concentrations in the range 0.006-0.008 micro g/g; also the urine from one neonate tested positive for the drug. 相似文献
4.
The water solubility of 1,3,5,7-tetra azatricyclo[3.3.1.13,7]decane, hexamethylenetetramine (HMT) or urotropine was determined at temperatures between 275.15 K and 313.15 K. Van’t Hoff graphs of ln msat versus 1/T gave three different straight lines, suggesting the existence of three different forms of the substance in the temperature region studied.
Previous work reported both increasing and decreasing solubility with temperature. This work found the solubility does not have a simple behavior. 相似文献
5.
6.
Shellhamer DF Davenport KJ Forberg HK Herrick MP Jones RN Rodriguez SJ Sanabria S Trager NN Weiss RJ Heasley VL Boatz JA 《The Journal of organic chemistry》2008,73(12):4532-4538
Reactions of chlorine (Cl(2)) with 4-halo-1,1,2-trifluorobut-1-enes (1, 2, or 3) give open-ion intermediates A and E that are in equilibrium. The open-chloronium ions (E) rearrange to a five-membered-ring halonium ion during ionic chlorination of 3 when the number-4 halo-substituent is iodine. Three-membered-ring bromonium and iodonium ions from alkenes 1, 2, or 3 are rather symmetrical and similar in structure. Quantum chemical calculations show that five-membered-ring halonium ion intermediates are 11 to 27 kcal/mol more stable than the three-membered-ring halonium ions or the open-ions A and E. The five-membered-ring intermediates lead to rearranged products. Rearranged products increase as the number-4 halogen (Z) becomes more nucleophilic (Z: Cl < Br < I). Open chloronium ions from ionic chlorination of terminal fluorovinyl alkenes are compared to the open ions generated by protons to similar alkenes. 相似文献
7.
Joshua Roldan-Kalil Lidia Zueva Janaina Alves Vassiliy Tsytsarev Priscila Sanabria Mikhail Inyushin 《Photochemistry and photobiology》2023,99(4):1092-1096
One of the known important functions of hair is protection from extensive sunlight. This protection is accomplished in large part due to natural hair pigmentation which is known to reflect the number of melanin granules (melanosomes) in the hair shaft, and melanin variants. Melanin takes in excessive light energy and converts it to heat in a process called absorption; heat is then dissipated into the environment as infrared radiation, thereby protecting the underlying skin. We used transmission electron microscopy (TEM) to visualize the melanosome counts in samples of human hair, and used thermal microscopy to measure the temperature changes of the samples when exposed to green and blue light lasers. In our experiments green light conversion to heat was highly correlated to the number of melanosomes, whereas blue light conversion to heat was less correlated, which may be because the reddish melanosomes it contains are less effective in absorbing energy from the blue spectrum of light. Anyway, we have shown the metals accumulation in the melanin can be easily visualized with TEM. We confirmed that the amount of melanin granules in human hair defines the conversion to heat of light energy in the visible spectrum. 相似文献
8.
Sandra L. Gmez Carlos M. Sanabria Alirio Palma Ali Bahsas Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(9):o465-o469
In (2RS,4SR)‐7‐chloro‐2‐exo‐(2‐chloro‐6‐fluorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C16H12Cl2FNO, (I), molecules are linked into chains by a single C—H...π(arene) hydrogen bond. (2RS,4SR)‐2‐exo‐(2‐Chloro‐6‐fluorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C16H13ClFNO, (II), is isomorphous with compound (I) but not strictly isostructural with it, as the hydrogen‐bonded chains in (II) are linked into sheets by an aromatic π–π stacking interaction. The molecules of (2RS,4SR)‐7‐methyl‐2‐exo‐(4‐methylphenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C18H19NO, (III), are linked into sheets by a combination of C—H...N and C—H...π(arene) hydrogen bonds. (2S,4R)‐2‐exo‐(2‐Chlorophenyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C16H14ClNO, (IV), crystallizes as a single enantiomer and the molecules are linked into a three‐dimensional framework structure by a combination of one C—H...O hydrogen bond and three C—H...π(arene) hydrogen bonds. 相似文献
9.
10.
Guadalupe Alcerreca Rubén Sanabria René Miranda Gabriel Arroyo Joaquín Tamariz Francisco Delgado 《合成通讯》2013,43(7):1295-1301
Several benzaldehydes were condensed with barbituric acid under infrared irradiation, in absence of solvent, affording the corresponding 5-benzylidene barbituric acids. 相似文献