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11.
Angelo Mugnoli Domenico Spinelli Giovanni Consiglio Renato Noto 《Journal of heterocyclic chemistry》1988,25(1):177-183
The geometry obtained by a crystal structure determination of the title compounds, as compared with that of the analogous benzene derivatives, along with results of ab initio calculations, is used to interpret the different SNAr reactivities in some thiophene and benzene compounds. The smaller rotation of the nitro groups with respect to the aromatic rings observed in thiophene derivatives should be considered a relevant factor in the higher reactivity in the thiophene series. 相似文献
12.
Renato Spigler Marco Vianello 《Proceedings of the American Mathematical Society》1996,124(6):1763-1771
Rigorous asymptotic approximations of the WKB (or Liouville-Green) type are obtained for a basis of solutions to in the framework of -algebras. Both cases and are included, thus generalizing the classical theory for scalar equations developed by F.W.J. Olver to matrix as well as to infinite-dimensional equations.
13.
A method to synthesize 2-phenylselenenyl-1,3-anti-diols and 2-phenyl- selenenyl-1,3-anti-azidoalcohols via hydroxy- or azido-selenenylation of trans-allylic alcohols is reported. Moreover, the first example of hydroxyl-selenenylation of an allylic azide is presented. Yields ranging from moderate to good and diastereomeric ratios up to 95:5 are achieved. 相似文献
14.
Reto Stahl Renato Galli Rolf Güller Hans-Jürg Borschberg 《Helvetica chimica acta》1994,77(8):2125-2132
The oxidative transformation of synthetic (+)-aristoteline ((+)- 6 ) into other metabolites which had been isolated from Aristotelia species was investigated. Thus, treatment of (+)- 6 with I2 as the single oxidant furnished the naturally occurring indole alkaloids (+)-makonine ((+)- 9 ),(+)-aristotelinone ((+)- 11 ), or (+)-11, 12-didehydroaristoteline ((+)- 7 ) in good yields, the selectivity of the oxidation process depending on the chosen reaction conditions. 相似文献
15.
Renato Noto Giuseppe Werber Francesco Buccheri Caterina Arnone 《Journal of heterocyclic chemistry》1987,24(5):1457-1459
The dissociation constants (K1) of both acids 4a-c and esters 5a-c and the rate constants of the decarboxylation reaction of acids 4a-c have been measured at various high concentrations of hydrochloric acid (0.5-8.0 M range). The results obtained have enabled us to suggest the probable structure of the zwitterion which undergoes decarboxylation. 相似文献
16.
This paper describes the use of a thin-layered dual-band electrochemical cell operating at flow conditions to determine dipyrone (sodium salt of 1-phenil-2,3-dimethyl-4-methylaminomethanesulfonate-5-pyrazolone) by reaction with electrogenerated iodine. The electrolytic cell consisted of two closely spaced gold electrodes, the upper stream electrode serving as the generator electrode and the downstream electrode working as the collector electrode. A linear dynamic range from 2 to 15 μmol l−1 dipyrone was obtained by using a sample volume of 100 μl, with a detection limit of 1.1 μmol l−1. Standard deviation (S.D.) of 3.4% for 20 repetitive injections of a 40 μmol l−1 dipyrone solution and sampling frequency of 90 h−1 were achieved. The results obtained with the thin-layered dual-band electrochemical cell for dipyrone determination in three different pharmaceutical samples compared well with those found by iodimetry with coulometrically generated iodine. 相似文献
17.
We have studied the reduction of SeIV in acidic medium (1 M HCl and 1 M HClO4) by classical and alternating current polarography and single sweep linear voltammetry with dropping mercury electrode and hanging mercury drop (HMDE). Two steps are observed distinctly: (1) The reduction of SeIV→Seo leads to a deposit of adsorbed elementary selenium. A mathematical expression is shown for the variation of current which is related to the surface covered at the HMDE. (2) The second step is the reduction of Seo→Se2? which takes place at more negative potentials. The accumulation of Seo may be used for the determination of traces in trace analysis by cathodic stripping. It appears that the behavior of selenium in these two mineral acids is similar. But sometimes it behaves in a different manner, especially in a.c. polarography (in this connection the influence of frequency and demodulation angle are important). 相似文献
18.
Dalpozzo R De Nino A Maiuolo L Procopio A Tagarelli A Sindona G Bartoli G 《The Journal of organic chemistry》2002,67(25):9093-9095
A new and chemoselective method for the cleavage of alkyl and cyclic acetals and ketals at room temperature in wet nitromethane by using catalytic cerium(III) trifluoromethane sulfonate is presented. The high yields, the observed selectivity, the very gentle reaction conditions, and the almost neutral pH make this procedure particularly attractive for multistep synthesis. 相似文献
19.
This paper describes the development of a new system for amperometric determination of phenolic compounds, and its application for monitoring these compounds in paper mill effluent. The method was based on a flow system, a dialysis sampler, and a laccase-based biosensor. The performance of this system was investigated with respect to pH, ionic strength, working potential, and flow-rate dependence. The biosensor showed an excellent long-term stability allowing measurements for over than 3 months. The sensitivity of laccase-based biosensor was tested for phenol, p-chlorophenol, guaiacol and chloroguaiacol; the detector presented selective measurements of micromolar concentration of these compounds. The integration of a dialysis membrane sampling in the system protected the biosensor surface from fouling and gave independence of sample conditions that commonly influence the biosensor performance. These favorable characteristics allowed its application for direct measurements in complex media with no sample pretreatment. This ability was confirmed employing this system in a continuous analysis of phenolic compounds during the remediation of paper mill effluent by ozonization process. 相似文献
20.
Renato Barbieri M. Teresa Musmeci 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):103-107
Abstract The title compounds, representative of classes of diorganotin (IV) derivatives active against murine leukemia P-388. interact with rat hemoglobin (selected as a model protein) by: i) co-crystallization. with formation of microcrystalline pellets, and: ii) diffusion into hemoglobin crystals from the supernatant solution (as determined for the 2-mercaptoethanesulfonato derivative). The nature of the Me2SnIV species in hemoglobin has been investigated by 119Sn Mössbauer spectroscopy, and a C2SnS2 tetrahedral geometry has been assigned by the point-charge model rationalization of the nuclear quadrupole splitting parameter. Binding into crystalline hemoglobin has been ascribed to Coulomb interactions and to hydrogen bonding between the sulfonate and the aminoacid tails of the organotin (IV) derivatives and functional groups of the globin. 相似文献