A rapid and reliable method is given for the determination of vanadium based on oxidation of the V(IV) with a known excess of bromate to V(V). The unreacted oxidant as well as V(V) are subsequently reduced with sulfurous acid to V(IV). The resulting Br?1 was potentiometrically titrated with Hg(I) using silver amalgam as the indicator electrode. The method finds application to the analysis of some binary and ternary mixtures. 相似文献
From a single‐crystal study, Nd2Te3 is found to be isostructural with Gd2Te3, crystallizing in the U2S3 structure type. Each of the two non‐equivalent Nd atoms is surrounded by seven Te atoms, with the polyhedra best described as a seven‐octahedron and a monocapped trigonal prism. All atoms lie on mirror planes. 相似文献
The biomimetic catalytic enantioselective addition of aldehydes to amines is reported. This was accomplished by combining biomimetic coupled catalytic aerobic oxidation of amines involving ruthenium-induced dehydrogenation and organocatalytic asymmetric Mannich reactions. The novel one-pot reactions furnished β-amino aldehyde and α-amino acid derivatives in high yields with excellent chemoselectivity and up to >99% ee. 相似文献
The reaction of an aromatic lithium reagent, LiR, with a perfluoroacid anhydride (RfCO)2O, in ether solution at low temperatures, produces esters of composition in addition to the expected ketone . Mixed esters of composition may be prepared by starting with a ketone and reacting with a lithium reagent LiR followed by perfluoroacid anhyride (RfCO2O. Hydrolysis of the esters provide a convenient route to trertiary alcohols of composition Rf(R) 2COH. 相似文献
Thermolysis of perfluoroazidobenzene, perfluoro-4- azidotoluene, perfluoro-4-azidopyridine, 4-azido-3- chlorotrifluoropyridine, and 4-azido-3, 5-dichlorodifluoropyridine (ArFN3) in the presence of a large excess (. 10 molar) of 1,3,5-trimethyl- or 1,3,5-trimethoxy-benzene (ArH) gave the diarylamines expected from nitrene ‘insertions’ at nuclear CH bonds (ArFN3 + ArH→ArFNHAr + N2); product yields in the cases of the perfluorinated azides are the highest ever recorded for this type of reaction. By contrast, no recognisable products were obtained when either perfluoro-(2-azido-4-isopropylpyridine) or 2-azido- 4-chlorotrifluoropyridine were decomposed thermally in 1,3,5-trimethylbenzene. 相似文献
Effects of cetyltrimethylammonium bromide (CTABr) micelles on second-order rate constants (k(n)(obs)) for nucleophilic reactions of amines (piperidine and n-butylamine) with ionized phenyl salicylate (PS(-)) reveal a nonlinear decrease with the increase in [D(n)] (where [D(n)] = [CTABr](T) - cmc) at a constant [NaBr] and 35 degrees C. The observed data, at a constant [NaBr], fit reasonably well to a pseudophase model of micelles, and such a data fit gives kinetic parameters such as CTABr micellar binding canstant (K(S)) of PS(-). The effect of [NaBr] upon K(S) is explained with the empirical relationship K(S) = K(S)(0)/(1 + psi[NaBr]), where psi is an empirical parameter. 相似文献
Thermolysis of 4-azidotetrafluoropyridine in the presence of an excess of mesidine at 170 °C yields tetrafluoro-4-(2,4,6-trimethylphenylazo)- pyridine, which undergoes intramolecular dehydrofluorination to provide 1,3,4-trifluoro-7,9-dimethyl-11-pyrido[4,3-]benzo[1,2]diazepine. 相似文献
Poly(methyl methacrylate) (PMMA) was found to be suitable for the immobilization of lipase fromCandida rugosa. The best result based on hydrolytic activity was obtained by adsorption of the purified unbuffered enzyme solution onto PMMA beads without any modification of the beads. Prolonged exposure of the protein to the beads increased its adsorption but the expressed activity decreased after 1 h of exposure. The magnitude of the immobilized activity also varied with the size of the beads. Immobilization of the lipase shifted its optimal reaction temperature from 37 to 45°C. The immobilized enzyme is also more stable than the free enzyme in solution. The operational half-life of the immobilized lipase packed in a column and assayed in a closed system is 40 d. 相似文献
The effects of Brij 35 micelles, CTABr micelles, and mixed Brij 35–CTABr micelles on the acid–base behavior of phenyl salicylate (PST) have been studied in aqueous solution containing 2% v/v acetonitrile. The apparent pKb (pKappb) of PST is decreased by 1.5 pK units with the increase in [Brij 35] from 0 to 0.02 M which is attributed to micellar medium effect. The values of pKappb remain almost independent of [CTABr] within its range 0.01–0.03 M. The increase in [CTABr] from 0 to 0.03 M in aqueous solution containing 0.02 M Brij 35 has not resulted in a change in pKappb. This shows that the characeristic structural features of nonionic Brij 35 micelles remain essentially unchanged on addition of CTABr under the present experimental conditions. 相似文献