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91.
Antonio Lozano José Usero Eva Vanderlinden Juan Raez Juan Contreras Benito Navarrete Hicham El Bakouri 《Microchemical Journal》2010,96(2):406-411
The assessment of air quality is necessary in order to control and reduce pollution to levels which minimise harmful effects on human health and the environment. This paper describes a method to design air quality monitoring networks for nitrogen dioxide and ozone and its application in Jaen (southern Spain). A fibre-glass filter impregnated with triethanolamine was used in diffusive sampling badges for NO2 determination. For O3 analysis, sodium nitrite was selected and nitrate, a product of the reaction of ozone and nitrite, was used to assess the ozone concentrations. Sampling campaigns with passive diffusion samplers at 62 sites were then carried out to obtain information on the pollution emissions in Jaen. The sampling campaigns in 2001–2002 revealed an average concentration of 10.4 μg/m3 NO2 with maximum values up to 22.5 μg/m3 in Jaen City centre. The average ozone concentrations were recorded downwind from the emission source, reaching 96.2 μg/m3; the average ozone value in Jaen was 72.0 μg/m3. After spatial interpolation of the obtained values with Geographical Information Systems, a selection of the best locations for the monitoring stations was made, in line with the macro- and microscale siting requirements of the European Directive 2008/50/EC on ambient air quality and cleaner air for Europe. A second sampling campaign with diffusive samplers was carried out in 2005–2006 to control if the locations of the air quality assessment stations were still representative for their zone. 相似文献
92.
Benito Alcaide Prof. Dr. Pedro Almendros Dr. Carmen Pardo Prof. Carolina Rodríguez‐Ranera Dr. Alberto Rodríguez‐Vicente Dr. 《化学:亚洲杂志》2009,4(10):1604-1611
Diastereocontrolled Lewis acid‐catalyzed preparation of enantiopure carbacepham derivatives have been developed starting from 2‐azetidinone‐tethered enals. The BF3?Et2O‐promoted reaction of alkenylaldehydes 1 and 16 is effective as carbocyclization protocol to afford 4‐substituted 5‐hydroxycarbacephams or 3‐substituted 4,5‐dihydroxycarbacephams, respectively, by a type I carbonyl‐ene reaction, while the BF3?Et2O or SnCl4‐mediated type II carbonyl‐ene cyclization of alkenylaldehydes 2 furnishes 3‐methylene 5‐hydroxycarbacephams along with the corresponding 3‐halo 5‐hydroxycarbacepham. The stereochemical outcome of these carbonyl‐ene cyclizations leading to carbacepham derivatives can be explained in terms of six‐membered, cyclic chair‐like transition‐state models. The formation of halocarbacepham derivatives is proposed to proceed by a stepwise mechanism. 相似文献
93.
In this paper we describe some advances in the knowledge of the behavior of aliquot sequences starting with a number less than . For some starting values, it is shown for the first time that the sequence terminates. The current record for the maximum of a terminating sequence is located in the one starting at 4170; it converges to 1 after 869 iterations getting a maximum of 84 decimal digits at iteration 289.
94.
Alcaide B Almendros P Aragoncillo C Rodríguez-Acebes R 《The Journal of organic chemistry》2004,69(3):826-831
The reaction of various activated vinyl systems, including 2-cyclopenten-1-one, with enantiopure azetidine-2,3-diones 1 was promoted by DABCO to afford the corresponding optically pure Baylis-Hillman adducts 2 without detectable epimerization. However, the reaction of alpha-keto lactams 1 with but-3-yn-2-one was not as successful, giving the corresponding beta-halo Baylis-Hillman adduct in low yield. Metal-mediated bromoallylation reaction between 2,3-dibromopropene and azetidine-2,3-diones 1 was investigated in aqueous media. Surprisingly, indium was unable to promote the bromoallylation reaction of alpha-keto lactams 1, but the Sn-Hf(4)Cl-promoted bromoallylation of ketones 1 proceeded efficiently to achieve bromohomoallyl alcohols 5 as single diastereomers. On this basis, simple and fast protocols for the asymmetric synthesis of the potentially bioactive 3-substituted 3-hydroxy-beta-lactam moiety were developed. 相似文献
95.
Alcaide B Almendros P Alonso JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(23):5793-5799
A novel application of the Grubbs carbene complex has been discovered. The first examples of the catalytic deprotection of allylic amines with reagents other than palladium catalysts have been achieved through Grubbs carbene mediated reaction. Significantly, the catalytic system directs the reaction toward the selective deprotection of allylic amines (secondary as well as tertiary) in the presence of allylic ethers. A variety of substrates, including enantiomerically pure multifunctional piperidines, are also usable. The new method is more convenient, chemoselective, and operationally simple than the palladium-catalyzed method. The current mechanistic hypothesis invokes a nitrogen-assisted ruthenium-catalyzed isomerization, followed by hydrolysis of the enamine intermediate. We believe that the reactive species involved in the reaction may be an Rubond;H species rather than the Grubbs carbene itself. Thus, the isomerization may occur according to the hydride mechanism. The synthetic utility of this ruthenium-catalyzed allyl cleavage is illustrated by the preparation of indolizidine-type alkaloids. 相似文献
96.
Metal-mediated 1,3-butadien-2-ylation reactions between 1,4-dibromo-2-butyne or 1,4-bis(methanesulfonyl)-2-butyne and optically pure azetidine-2,3-diones were investigated in aqueous media, offering a convenient asymmetric entry to the potentially bioactive 3-substituted 3-hydroxy-beta-lactam moiety. The diastereoselectivity of the addition reaction was controlled by the bulky chiral auxiliary at C4. However, while the regioselectivity of the process was full, the chemical yield of the addition was a function of the nature of both the metal reagent and the system solvent as well. In addition, 2-azetidinone-tethered 1,3-butadienes can easily be transformed into other functionalities via Diels-Alder reaction. 相似文献
97.
[reaction: see text] Thermolysis of beta-lactam-tethered enallenyl alcohols gave tricyclic ring structures via a formal [2 + 2] cycloaddition of the alkene with the distal bond of the allene, while the tin-promoted radical cyclization in 2-azetidinone-tethered allenynes proceeded to provide bicyclic beta-lactams containing a medium-sized ring. The access to cyclization precursors was achieved by regio- and stereoselective metal-mediated carbonyl allenylation of 4-oxoazetidine-2-carbaldehydes in an aqueous environment. 相似文献
98.
Benito Flores-Chávez Bernat Abeit Martínez-Ortega José Guadalupe Alvarado-Rodríguez Noemí Andrade-López 《Journal of chemical crystallography》2005,35(6):451-456
The preparation and characterization by X-ray crystallography and NMR spectroscopy of the 2,2′-dipyridyl-N-methylimine (dpNmei) and the complex [cloro-bis(N,N′-2,2′-dipyridyl-N-methylimine)]lithium [Li(dpNmei)2(Cl)] is reported. The dpNmei was prepared from the reaction of the 2,2′-dipyridyl ketone (dpk) and methylamine and crystallizes in the monoclinic P21/n space group with a = 6.3887(6), b = 10.1709(10), c = 16.7594(17) (Å), β = 100.918(2)∘ and V = 1069.29(18) Å3. The lithium complex was obtained from the reaction of dpNmei and LiCl in a molar ratio 2:1. [Li(dpNmei)2Cl] crystallizes in the orthorhombic Pbcn space group with a = 10.0092(12), b = 9.8201(12), c = 23.669(3) (Å) and V = 2326.4(5) Å3. The crystallographic data show that the lithium ion is five-coordinated with four coordination bonds N→Li due the chelation of dpNmei and one Li–Cl bond. 相似文献
99.
Classical finite difference schemes are in wide use today for approximately solving partial differential equations of mathematical physics. An evolution of the method of finite differences has been the development of generalized finite difference (GFD) method, that can be applied to irregular grids of points. 相似文献
100.
Reactions of 2,3-indolinediones (isatins) with stabilized organometallic reagents were investigated in aqueous media. Isatins and a variety of stabilized organic halides undergo coupling under Barbier-type conditions in the presence of different metals (indium, tin, zinc) and additives (ammonium chloride, hydrobromic acid, bismuth(III) chloride, hafnium(IV) chloride). The regiochemistry of the processes (carbonylallylation, bromoallylation, 1,3-butadien-2-ylation, propargylation, or allenylation reactions) were generally excellent. On this basis, simple and fast protocols for the synthesis of the potentially bioactive 3-substituted 3-hydroxyoxindole moiety were developed. 相似文献