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Application of 4-Hydroxy-, 4-Oxo-, and 4-Hydroxyimino Derivatives of Stable 2,2,6,6-Tetramethylpiperidine N-Oxyl Radical for the Measurements of Lewis Acidity of Solvents

Głowacka J., Szczepek W. J., Wrona P. K.

Polish Journal of Chemistry

2000

Vol. 74, nr 9

1341-1341

UV-VIS spectra of 2,2,6,6-tetramethylpiperidine N-oxyl (TMPNO) stable radical measured in 18 solvents were compared with the spectra of its derivatives functionalized in the 4 position (4-hydroxy- (h-TMPNO), 4-oxo- (o-TMPNO) and 4-hydroxyimino- (i-TMPNO)). The results obtained proved, that the max values corresponding to the n * transition in the N–O chromophore are for all TMPNO derivatives intercorrelated, and they also correlate very well with other acidity parameters (Z, ET and AN). Thus, all these compounds could be used as standard bases for determination of the experimental acidity of solvents. Detailed analysis of the spectral characteristics of all compounds leads to the conclusion, that the molar absorptivities ( ) ofTMPNOand h-TMPNO corresponding to the n* transition are of the order of 10 dm3 mol–1 cm–1, whereas those of the o-TMPNO and i-TMPNO are two times lower. In the case of the* transition we observed an opposite behaviour – the molar absorptivities ( ) of TMPNO and h-TMPNO are close to 2103 dm3 mol–1 cm–1, whereas those of the oxo and hydroxyimino derivatives are equal to ~4.4103 dm3 mol–1 cm–1. The integral intensities of both bands behave accordingly. These differences were attributed to the formation of the head-to-tail dimers, in which the N–O chromophore interacts with the exocyclic double bond in the 4-position of the piperidine.

Determination of chloramines in aqueous solutions. The NCl3 sensor

Piela B., Wrona P. K.

Chemia Analityczna

1998

Vol. 43, No. 6

1041-1052

Reactions of sodium chlorate (I) and NH' carried out in aqueous solutions produce mono-, di- and trichloramine. The stability of the products of this reaction is strongly pH and time dependent. Electrochemical properties of chloramines have been investigated and compared with their spectrophotometric behaviour. Mono- end dichloramine are reduced at Pt electrodes in single, irreversible peaks. The electrode processes of NCl(3) occur in the region of Cl(-) oxidation, and the whole system behaves reversibly. The formation of NCl(3) has been observed by using biamperometry. This method has been used for determination of NCl3 concentration in synthetic samples.

Produktami reakcji chloranu (I) sodu z jonami amonowymi w roztworach wodnych są mono-, di- i trichloroamina. Względne stężenia tych związków silnie zależą od pH i czasu reakcji. Zbadano procesy elektrodowe chloroamin i stwierdzono, że na elektrodzie platynowej mono- i źdichloroamina ulegają jednoetapowej i nieodwracalnej redukcji. Trichloroamina (NCl3) redukuje się w obszarze potencjałów gdzie obserwuje się utlenianie jonów Cl i w efekcie cały proces elektrodowy ma charakter odwracalny. Tworzenie NCl3 obserwowano za pomocą amperometrü z dwiema elektrodami spolaryzowanymi. Metodę tę zastosowano do oznaczania stężenia NCl3 w próbkach syntetycznych.