- Synthesis of trimethylsilyl carboxylates by HMDS under solvent-free conditions
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A broad set of structurally different carboxylic acids were transformed into their trimethylsilyl esters with HMDS in a practically completely solvent-free process, while a catalytic amount of iodine was required in some cases. The process has several advantages over the known methods: untreated reactants, air atmosphere, mild and neutral conditions, no evolution of hydrogen halide, no need of an additional base, low amount of waste, completely without chromatography, low consumption of energy, and operational simplicity.
- Jereb, Marjan,Lakner, Janja
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p. 5713 - 5723
(2016/08/23)
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- Partition coefficients of ketones, phenols, aliphatic and aromatic acids, and esters in n-hexane/nitromethane
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Liquid-liquid partition is used in sample preparation and in countercurrent and liquid-liquid chromatographic separations. Partition coefficients are widely used in toxicology, environmental, and analytical chemistry. The K hn determination procedure for the n-hexane/ nitromethane system was optimized and partition coefficients for 99 ketones, esters and trimethylsilyl derivatives of phenols, aliphatic and aromatic acids were determined. For 130 compounds, Khn values were predicted using mathematical relationships between Khn and other physicochemical and structural parameters. Versita Sp. z o.o.
- Kotowska, Urszula,Isidorov, Valery A.
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scheme or table
p. 813 - 824
(2012/03/27)
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- Gas-phase photocatalytic degradation and detoxification of o-toluidine: Degradation mechanism and Salmonella mutagenicity assessment of mixed gaseous intermediates
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The photocatalytic degradation of toluidine over titanium oxide (TiO 2) thin films under UV irradiation was investigated. The degradation efficiency of 98.7% was obtained for a toluidine concentration of about 4500 μg L-1 and illumination of 240 min. The degradation intermediates produced during photocatalytic oxidation were identified using Fourier transform-infrared spectrometry (FTIR) and gas chromatography-mass spectrometry (GC-MS). Only a small amount of intermediates, including phenol and toluene, were found in the gas phase. Many other trace amount intermediates, such as 2-hydroxybenzaldehyde, 2-nitrobenzaldehyde, 2-hydroxybenzenemethanol, 2-hydroxybenzoic acid, phenol etc., were detected on the TiO2 surface. An Ames assay of the Salmonella typhimurium strains TA98 and TA100 was employed to evaluate the mutagenicity of toluidine and its gaseous photocatalytic degradation intermediates. With or without rat liver microsomal fraction (S9 mix) activation, neither toluidine nor its gaseous intermediates presented mutagenic activity against strains TA98 (±S9) and TA100 (-S9) at all tested doses. Toluidine, however, can induce a weak positive response to the TA100 strain with an S9 mix at doses as high as 4000 μg plate -1. An increase of revertants per plate was obtained after 30 min photocatalysis in the TA100 strain with S9 mix. As reaction time further increased, photocatalytic technology exhibited the ability to completely and efficiently detoxify toluidine. Both our chemical analysis and toxic evaluation indicate that all mutagenic intermediates in the gas can be completely eliminated within 240 min, which further suggests that photocatalytic technology is an effective approach for degrading aromatic amines.
- An, Taicheng,Sun, Lei,Li, Guiying,Wan, Shungang
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experimental part
p. 128 - 135
(2011/02/23)
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- Characterization of phenolic compounds in rooibos tea
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Polyphenols present in rooibos, a popular herbal tea from Aspalathus linearis, were isolated in two steps. First, phenolic ingredients were separated by multilayer countercurrent chromatography (MLCCC). Preparative high-performance liquid chromatography (HPLC) was then applied to obtain pure flavonoids. The purity and identity of isolated compounds was confirmed by different NMR experiments, HPLC-diode array detector (DAD), or gas chromatography-mass spectrometry (GC-MS) analysis. This strategy proved to be valid to isolate material in up to gram quantities and to verify known and previously not published polyphenol structures. In addition the chemistry of dihydrochalcones and related intermediates was studied. The dihydrochalcone aspalathin was oxidized to the corresponding flavanone-C-glycosides ((R)/(S)-eriodictyol-6-C-β-D-glucopyranoside and (R)/(S)-eriodictyol-8-C- β-D-glucopyranoside). Flavanone-6-C-β-D-glucopyranosides were further degraded to flavones isoorientin and orientin.
- Krafczyk, Nicole,Glomb, Marcus A.
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p. 3368 - 3376
(2008/09/20)
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- ESR and ENDOR Investigations of Spin Exchange in Mixed Galvinoxyl/Nitroxide Biradicals. Syntheses
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The synthesis of a variety of mixed biradicals consisting of galvinoxyl and nitroxide moieties is given.For the first time successful fluid solution ENDOR experiments on mixed biradicals could be performed.The magnetic properties of these systems are significantly dependent (a) on the relative magnitudes of the exchange integral J as compared to the hyperfine interactions, (b) on the sign of J, and (c) on the difference of the g values of the constituent monoradical fragments.It is demonstrated that the ENDOR technique allows direct determination of the hyperfine coupling constants even in cases where is comparable in magnitude to the hyperfine coupling constants.Moreover, the sign of the exchange integral can be deduced from these measurements.It is shown that the ENDOR spectroscopy in combination with spin labeling to obtain "weakly coupled biradicals" may serve as a technique to measure signs of hyperfine coupling constants.
- Kirste, B.,Krueger, A.,Kurreck, H.
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p. 3850 - 3858
(2007/10/02)
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- Syntheses and Reactions of (Trimethylsiloxy)benzoyl Chlorides
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The (trimethylsiloxy)benzoyl chlorides 1-7 are easily to obtain under mild conditions from silylated hydroxybenzoic acids by means of thionyl chloride.Whereas these acid chlorides are stable at room temperature, they undergo condensation polymerisation at temperatures above 100 deg C.Reactions with various nucleophils, such as thioalcohols, phenols, amines, N,O-bis(silylated)amino acids and N-silylated lactams were investigated.With hexamethyldisilazane and thionyl chloride the (trimethylsiloxy)benzonitriles 21, 22 are accessible, and by means of trimethylsilylazide the (trimethylsiloxy)phenyl isocyanates 23-25 were obtained.Conversion with phenyl carbazate and subsequent silylation lead to the 2-(trimethylsiloxy)phenyl-1,3,4-oxadiazol-5-ones 27a-c.
- Schwarz, Gerd,Alberts, Heinrich,Kricheldorf, Hans R.
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p. 1257 - 1270
(2007/10/02)
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