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排序方式: 共有48条查询结果,搜索用时 187 毫秒
41.
Determination of trace metals in Nile River and ground water by differential pulse stripping voltammetry 总被引:1,自引:0,他引:1
Zanaty R. Komy 《Mikrochimica acta》1993,111(4-6):239-249
The determination of trace metals in river water and ground water by DPSV is seriously disturbed by the presence of organic complexes. The influence of these substances can be eliminated by acidification of the samples with acids. Cd, Pb and Cu were determined at pH 1.1 (HNO3 medium) and Zn, Cd, Pb and Cu at pH 2 (HCl medium), in both the Nile river and ground water. Zn was determined at pH 3.5 in HCl and pH 4.5 in HNO3, after neutralizing the samples with NH3/NH4Cl buffer. Manganese could then be determined, after further addition of ammoniacal buffer solution up to pH 7.5 and 8.5. Ni and Co were determined in the adsorptive mode after formation of dimethylglyoximates at pH 9.2. The effect of pH on the stripping peaks of manganese was studied. Good agreement was observed between DPSV and AAS results for Zn, Cd, Pb, Cu and Mn, but the concentrations of Ni and Co were below the detection limits for AAS. Good agreement was obtained between DPSV results in HCl and HNO3 for Ni and Co. The results indicate that decomposition of organic complexes by acidification with HNO3 is better than in the case with HCl for Zn, Pb, Cu, Ni and Co, but HCl is better than HNO3 for Cd and Mn. 相似文献
42.
M. A. Rady 《Heat and Mass Transfer》2009,45(5):545-561
Enhanced efficiency of the adsorption process in the dehumidifier is a key element for improved performance of desiccant cooling
systems. Due to the exothermic nature of the adsorption process, the dehumidification and cooling capacity are limited by
significant temperature changes in the adsorption column. In the present study, the effects of integration of sensible and
latent heat storage particles in the desiccant bed for in situ management of released adsorption heat are investigated. For
this purpose, column experiments are performed using an initially dry granular bed made of silica-gel particles or a homogeneous
mixture of silica gel and inert sensible or latent heat storage particles. The packed bed is subject to a sudden uniform air
flow at selected values of temperature and humidity. Also, a packed bed numerical model is developed that includes the coupled
non-equilibrium heat and moisture transfer in the solid and gas phases. Investigations of the heat and mass transfer characteristics
are reported using the composite structure and the results are compared with the base case of simple silica gel bed. Improved
desiccant cooling system performance can be obtained by appropriate adjustment of desiccant cycle operation and proper choice
of the volume ratio of thermal energy storage particles. 相似文献
43.
N-(Furan-2-ylmethylidene)-4,6-dimethyl-1H-pyrazolo[3,4-b]pyridine-3-amine was prepared and alkyla- ted with the corresponding
halo compounds to afford N-alkylated products. 2-[3-(Furan-2-ylmethy- lideneamino)-4,6-dimethyl-1H-pyrazolo[3,4-b]pyridin-1-yl]acetohydrazide
was converted into the key intermediate thiosemicarbazide, which undergoes cyclization reactions under acidic and basic conditi-
ons to give 1,2,4-triazole, 1,3,4-oxadiazole, and 1,3,4-thiadiazole derivatives. Condensation of the hyd- razide with monosaccharide
aldoses gave the corresponding sugar hydrazones, which on treatment with acetic anhydride readily undergo cyclization reaction
to afford oxadiazoline derivatives. 相似文献
44.
Eman A. El Rady 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2213-2224
2-Amino-3-cyano-4-(2-thienyl)[1,5]benzothiazepine 5 has been synthesized and reacted with some active methylene and nucleophile reagents to yield new pyrido[6,5-b][1,5]benzothiazepine and pyrimido[6,5-b][1,5]benzothiazepine derivatives. 相似文献
45.
46.
1,2‐Dihydro‐2‐imino‐6‐(2‐imino‐2H‐chromen‐3‐yl)‐1,4‐diphenyl‐pyridine‐3‐carbonitrile 4 has been synthesized and reacted with ethyl cyanoacetate to yield the new 5‐amino‐1,7‐dihydro‐2‐(2‐imino‐2H‐chromen‐3‐yl)‐7‐oxo‐1,4‐diphenyl‐1,8‐naphthyridine‐6‐carbonitrile 6 , which consider a good and available starting intermediate for synthesis of series of functionalized chromenes. So, the compound 6 was utilized as a key for the synthesis of some new pyrimido[5,4‐c][1,8]naphthyridinones, pyrido[2,3‐c][1,6]naphthyridinones, triazolo[3′,4′:1,6]triazino][5,4‐c][1,8]naphthyridinones, triazolo[2′,3′:1,6]pyrimido[4,5‐c][1,8]naphthyridinones, triazepino[6,5‐c][1,8]naphthyridinone, and triazino[5,4‐c][1,8]naphthyridinones. The structures of these compounds were established by elemental analysis, IR, MS, and NMR spectral analysis. J. Heterocyclic Chem., (2012). 相似文献
47.
Magda A. Barsy Eman A. El Rady Mostafa A. Ismael 《Journal of heterocyclic chemistry》2012,49(2):388-393
A simple one‐pot and efficient method is described for the synthesis of pyrimido[5,4‐c]pyridazines 5 and of thiino[2,3‐d] pyrimidines 15 by a domino process involving an aza‐Wittig reaction/heterocyclization. The iminophosphorane 2 reacted with phenylisocyanate, followed by heterocyclization on addition of amines to give the corresponding guanidine intermediates 4 . The guanidine intermediates were cyclized in the presence of catalytic amount of sodium ethoxide to pyrimido[5,4‐c]pyridazines 5 . Similarly, iminophosphorane 12 reacted with phenylisocyanate and amines to give thiino[2,3‐d]pyrimidines 15 in moderate yields. Furthermore, pyridazino[4,3‐d]oxazines 10 and thiino[2,3‐d]oxazines 19 were synthesized by the intremolecular aza‐Wittig reaction of phosphazenes 2 and 12 , respectively, with acid chlorides followed by heterocylization via imidoyl chloride intermediates. J. Heterocyclic Chem., (2012). 相似文献
48.