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21.
Mohamed Rifaat Hamza Elmoghayar Mohamed Hilmy Elnagdi Mohamed Kamal Ahmed Ibrahim Mohamed Mohamed Mohamed Sallam 《Helvetica chimica acta》1977,60(7):2171-2176
The Carbo(3-phenylpyrazol-5-yl-hydrazonoyl) halides 1a , b react with active methylene compounds to yield the 1-(3-phenylpyrazol-5-yl)-pyrazole derivatives 2a – k (Scheme 1). The acyclic intermediates 3a , b could be isolated from reaction of 1a , b with acetylacetone, thus establishing the substitution mechanism for these reactions. Compounds 1a , b reacted with carbon disulfide, phenyl isothiocyanate, methyl cyanide, and with p-chlorobenzaldehyde to yield the corresponding heterocyclic derivatives 5 – 8 , respectively (Scheme 2). The behaviour of compounds 2 with hydrazine hydrate is reported. 相似文献
22.
Ahmed Kamal K. Laxma Reddy V. Devaiah N. Shankaraiah Y. Narasimha Reddy 《Tetrahedron letters》2004,45(41):7667-7669
A methodology based on reductive cleavage followed by cyclization, for the solid-phase synthesis of pyrrolo[2,1-c][1,4]benzodiazepines employing DIBAL-H, is described. 相似文献
23.
24.
Using the experimentally measured values ofx=A 2(0)/A 1(0) andy=V(0)/A 1(0) and the measured ratiosR st=Γ(D s + →φl + ν l)/Γ(D ins + →φπ +) andR h=Γ(D s + →φρ +)/Γ(D s + →φπ +), we present evidence for significant nonfactorization contribution in the decay amplitude forD s + →φπ +. We analyze the role of nonfactorization inD s + →φρ + and conclude that present data onR h are consistent with factorization inD s + →φρ +. A measurement of polarization inD s + →φρ + would greatly assist our analysis. 相似文献
25.
26.
The redox behaviour of adsorbed species of 2,4,6-tri(2-pyridyl)-1,3-5-triazine (TPTZ) at the surface of a mercury electrode was examined using cycling voltammetry. Based on the adsorption and accumulation of TPTZ at the charged mercury surface cathodic adsorptive stripping voltammetry (CSV) is applied for the trace determination of TPTZ using a differential pulse (DP) technique. Experimental and operational parameters for the quantitative analysis of TPTZ are optimized and the detection limit was found to be 3×10–9 mol/l. The effect of some interferences, e.g. organic compounds, cations and anions, are investigated. 相似文献
27.
Polyethylene glycol (PEG) is found to be an inexpensive, nontoxic, environmentally friendly reaction medium for the conjugate addition of thiols to conjugated alkenes to afford the corresponding adducts in excellent yields under mild and neutral conditions. Products of undesirable side reactions resulting from polymerization are not observed. The use of PEG avoids the use of either acid or base catalysts for this conversion and moreover PEG can be recovered and reused. 相似文献
28.
Kumar K Michalik D Garcia Castro I Tillack A Zapf A Arlt M Heinrich T Böttcher H Beller M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(3):746-757
A practical route for the synthesis of new biologically active 5-HT(2 A) receptor antagonists has been developed. In only three catalytic steps, this class of central nervous system (CNS) active compounds can be synthesized efficiently with high diversity. As the initial step, an anti-Markovnikov addition of amines to styrenes provides an easy route to N-(arylalkyl)piperazines, which constitute the core structure of the active molecules. Here, base-catalyzed hydroamination reactions of styrenes with benzylated piperazine proceeded in high yield even at room temperature. After catalytic debenzylation, the free amines were successfully carbonylated with different aromatic and heteroaromatic halides and carbon monoxide to yield the desired compounds in good to excellent yields. The two key reactions, base-catalyzed hydroamination of styrenes and palladium-catalyzed aminocarbonylation of haloarenes/heterocycles, showed tolerance towards various functional groups, thereby demonstrating the potential to synthesize a wide variety of new derivatives of this promising class of pharmaceuticals. 相似文献
29.
Dula Amarasiriwardena Kamal Sharma R. M. Barnes 《Analytical and bioanalytical chemistry》1998,362(5):493-497
The presence of lead as a contaminant in calcium supplements has aroused considerable public health interest in recent years. In this investigation lead and lead isotope ratios were determined by ICP-MS in ten brands of calcium supplements after high pressure/temperature digestion. Calcium supplements (200 to 250 mg) were digested in 2 mL of nitric acid at 230?°C and at a pressure of 1770 psi (1.2 × 104 kPa). Lead concentrations were determined by matrix-matched lead standards prepared in a high-purity calcium carbonate matrix. Good recoveries of lead and calcium were obtained for certified animal bone reference material. High levels of Pb (8 to 28 μg Pb per g of calcium) were found in calcium supplements that contain dolomite or bone meal. Chelated and refined calcium supplements had lower Pb levels (0.8 to 0.9 μg Pb/g Ca). Application of lead isotope ratios to distinguish the origin of calcium sources was also explored. 相似文献
30.
Robert C. Richter Kamal Swami Steven Chace Liaquat Husain 《Fresenius' Journal of Analytical Chemistry》1998,361(2):168-173
The capability of inductively coupled plasma mass spectrometry in determining trace levels of As, Se, and Sb in cloud water
was evaluated. Preliminary studies focused on identifying and eliminating potential interferences in the cloud water matrix,
the choice of appropriate internal standards, and system optimization. The detection limits for As, Se, and Sb were 20, 100,
20 pg/mL using pneumatic nebulization, and 5, 25, 5 pg/mL, respectively, using ultrasonic nebulization with a precision of
better than 5% RSD. The accuracy was demonstrated by the analysis of a NIST commercial reference material, SRM 1643d. In all
cases, the results from ICP-MS analysis agreed within 4% of the certified values. Comparative analysis of cloud water samples
obtained from a site downwind from large pollution sources (Whiteface Mountain, New York) and Changlagali Pakistan, a rural
mountain peak, was carried out by hydride generation atomic absorption (HGAA) spectrometry. There was excellent agreement
between the ICP-MS and HGAA results.
Received: 31 July 1997 / Revised: 28 October 1997 / Accepted: 31 October 1997 相似文献