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141.
Richard A. Bartsch David A. Babb Bronislaw P. Czech Dhimant H. Desai Eddy Chapoteau Carl R. Gebauer Wolodymyr Zazulak Anad Kumar 《Journal of inclusion phenomena and macrocyclic chemistry》1990,9(2):113-123
Four novel chromogenic benzocryptands and one side-armed chromogenic cryptand have been synthesized and their complexing abilities for alkali metal cations are described. 相似文献
142.
S.Vasudeva NaiduPradeep Kumar 《Tetrahedron letters》2003,44(5):1035-1037
An enantioselective synthesis of d-ribo-C18-phytosphingosine as its tetraacetate derivative 10, starting from d-mannitol and employing the Sharpless asymmetric dihydroxylation reaction on allylic alcohol 6 as the key step, is described. 相似文献
143.
A procedure has been developed for the direct fourth-derivative spectrophotometric determination of iron(III) dimethyldithiocarbamate by converting it into an iron(II) 2,2'-bipyridyl complex, which is then dissolved in Triton X-100. Beer's law is obeyed over the concentration range 0.5-20 microg mL(-1 )in the final solution. Various parameters such as the effect of pH and interference of large number of ions on the determination of ferbam have been studied in detail. The method is sensitive, highly selective and can be used for the determination of ferbam in a commercial sample and in mixtures with various dithiocarbamates (ziram, zineb, maneb, etc.) and from wheat grains. 相似文献
144.
The first example of the use of (195)Pt PGSE diffusion data (D values) to recognize the solvent dependence of aggregation of the hexachloroplatinate dianion in Na(2)PtCl(6) (1) and in H(2)PtCl(6) (2) is reported. In water, the ions are separated; however, in methanol the D values suggest ion pairing and/or aggregation. Additional (1)H and (31)P diffusion data for organometallic Pt complexes trans-PtX(Aryl)(L)(2) (where L = PEt(3) or PPh(3)) and Pt(C(7)H(4)O(2))(L(1))(L(2)) (where L(1) and L(2) = a variety of ligand types) reveal that phenyl phosphines afford relatively large hydrodynamic radii r(h). The presence of a substituent on the aryl ligand of PtX(Aryl)(L)(2) does not markedly affect the D values, whereas a substituent of similar size added to a PPh(3) group in Pt(C(7)H(4)O(2))(L(1))(L(2)) markedly changes both D and r(h) values. There is only a small concentration dependence of the D values in PtX(Aryl)(L)(2) on changing from 2 to 10 mM. 相似文献
145.
146.
Double [2,3] sigmatropic rearrangements of bis(propargyl sulfenates) to bis(allenic sulfoxides) and of bis(propargyl sulfinates) to bis(allenic sulfones) are shown to be a convenient and effective method for the preparation of conjugated diallene systems bearing two electron withdrawing trihalomethyl sulfoxide or sulfone substituents either on C-1 and C-6, or on C-3 and C-4. Such substituents are further shown to facilitate cyclization to bis(methylene)cyclobutenes, and to stabilize the latter. The electron withdrawing group substitution on the exocyclic methylene extremities proved more effective than similar substitution on the endocyclic double bond. 相似文献
147.
Ashok K. Singh Alka Srivastava Ashutosh Kumar Bharat Singh 《Transition Metal Chemistry》1993,18(4):427-430
Summary The kinetics of iridium(III)-catalysed oxidation of 1,2-ethanediol and 1,4-butanediol by N-bromoacetamide (NBA) in HClO4 in the presence of [Hg(OAc)2] as a scavenger for Br– have been investigated. The reactions are zero-order with respect to both diols, and first-order in NBA at low NBA concentrations, tending to zero order at high concentrations. The order in IrIII decreases from unity to zero at high iridium(III) concentrations. A positive effect on the oxidation rate is observed for [H+] and [HgII] whereas a negative effect is observed for acetamide and [Cl–]. Ionic strength does not influence the oxidation rate. (H2OBr)+ is postulated as the oxidizing species. A mechanism consistent with the observed kinetic data is proposed. 相似文献
148.
149.
Summary The coagulation concentration for a titania sol decreases if the concentration of a mixture of electrolytes and papain decreases. If the concentration of papain is increased then lesser amount of electrolytes is needed to coagulate the sol. If glycine is added as an additional substance then the value decreases more rapidly. There is no significant change in the pH and the electrical conductance of the sol by the addition of papain or electrolytes. There is a little change, when glycine is added as an additional substance. These observations are explained due to the formation of negative papain ions in a low pH region. The possibility of the adsorption or the release of the counter ions is ruled out.The authors wish to thank Dr.R. C. Mehrotra, Professor and the Head of the Chemistry Department for providing all the facilities for this work. We are also thankful to the Ministry of Education, Government of India, for the award of a research scholarship to one of us (V.K.S.). 相似文献
150.
An efficient method for the synthesis of enantiomerically pure (R)-phenylephrine hydrochloride 1 is described using a Sharpless asymmetric dihydroxylation as the key step. 相似文献