Milde alkalische Hydrolyse von Aconitin

Mild Alkaline Hydrolysis of Aconitine Hydrolysis of aconitine ( 1 ) with 0.04N K₂CO₃ in 90% MeOH at room temperature yields, besides the alkamine aconine 3 considerable amounts of 8-O-methylaconine ( 6 ) and smaller quantities of desbenzoyl-pyroaconitine ( 4 ) and 16-epi-desbenzoyl-pyroaconitine ( 5 ). Better yields of 4 and 5 are obtained when heating a solution of aconitine in 0.04N K₂CO₃ in 90% EtOH.     

Synthese und 1H-NMR-Studie der vier unverzweigten peracetylierten β-D-Glucopyranosyl-β-gentiobiosen

Synthesis and ¹H-NMR Study of the Four Unbranched Peracetyl-β-D -glucopyranosyl-β-gentiobioses With regard to the structure elucidation of an unknown trisaccharide isolated from the stigmas of garden crocusses (Crocus neapolitanus var.), the four unbranched (1→6)-, (1→4)-, (1→3)-, and (1→3)-, and (1→2)-connected β-D -glucopyranosyl-β-gentiobiose peracetates were synthesized. A complete analysis of the ¹H-NMR spectra of the four trisaccharide peracetates was carried out.     

Stable Quinome Methides: Regioselective Para-Oxidation of a 2,4-Bisalkylthiomethenol and Addition Reaction Reaction to Quinonemethides

Abstract

The 2.4-bisfunctionalized phenol 1, a commercial antioxidant, is dehydrogenated regioselectively with potassium ferricyanide. affording the corresponding p-quinone methide 2. 1,6-Addition of nucleophiles e.g. thiols to 2 gives rise to the corresponding addition products e.g. the dithioacetals 4 of the corresponding substituted benzaldehyde. On the other hand, treatment of 2 with αα′-azoisobutyronitrile at 90°C leads to compounds 5a-b and 6, addition products of the cyanopropyl radical to the quinone methide 2. The structures of all products are confirmed mainly by ¹H-NMR-and ¹³C-NMR-spectroscopy and the mode of their formation is discussed.     

The Radical Anion,Dianion and Electron Transport Properties of Tetraiodotetraazapentacene

Tetraiodotetraazapentacene I₄TAP , the last missing derivative in the series of halogenated silylated tetraazapentacenes, was synthesized via condensation chemistry from a TIPS-ethynylated diaminobenzothiadiazol in three steps. Single and double reduction furnished its air-stable monoanion and relatively air-stable dianion, both of which were characterized by crystallography. All three species are structurally and spectroscopically compared to non-halogenated TAP and Br₄TAP . I₄TAP is an n-channel material in thin-film transistors with average electron mobilities exceeding 1 cm² (Vs)⁻¹.     

Reaction of N′-(Arylmethylidene)-2-oxo-2H-chromene-3-carbohydrazides with Methyl 1-Bromocycloalkanecarboxylates and Zinc

Russian Journal of General Chemistry - Depending on the ring size in the Reformatsky reagent and the nature of substituents in arylmethylidene fragment, the reactions of Reformatsky reagents...     

The controlled flocculation of submicron emulsion particles. I. A three-step synthetic route to supermicron polymer particles

The basic features of a three-step experimental process to produce supermicron polymer particles are described. First, a submicron emulsifier-free latex is prepared by a well-known technique. Second, the latex is aggregated by destabilizing with cetyl pyridinium chloride under constant stirring conditions, to yield roughly spherical clusters of 6-12 μ diameter. Third, the aggregates are stabilized with poly(vinyl alcohol) and internally coalesced by heating at or above the glass transition temperature. The final product particles have relatively smooth surfaces. Results are qualitatively interpreted in terms of a dynamic equilibrium where the aggregate size is determined by a balance between attractive interparticle potentials and stirring shear forces. Bimodal aggregate size distributions suggest the aggregate break-up mechanism may involve the erosion of individual latex particles and small fragments from the surface of aggregates. © 1996 John Wiley & Sons, Inc.     

Effects of data analysis on accuracy and precision of GPC results

The effects of data imprecision and baseline uncertainties have been investigated by computer simulation of GPC data from a polymer sample with a truncated log-normal molecular weight distribution. If the data are very accurate, as few as five data points can be sampled without serious error in computed molecular weight averages. The number of data points required is much larger, however, if these are taken at equal increments of molecular weight rather than elution volume. The effects of noise can be counteracted by increasing the sampling frequency. Baseline uncertainties present a more serious problem, especially for broad-distribution samples. If the detected signal is too noisy to permit accurate location of the baseline, errors can be minimized by using a second, more sensitive detector to determine the peak start and end. It is very difficult to estimate M?_z and higher molecular weight averages accurately if the noise level is greater than 0.5%.