Zur Kenntnis der anomalen Reaktionen bei der Aminostickstoffbestimmung. VII. Die Anomalie der Sulfonsäureamide

Zusammenfassung In der vorliegenden Arbeit wurde versucht, einen Einblick in die Reaktion der Sulfonsäureamide mit salpetriger Säure zu gewinnen, zumal diese Verbindungen — zum Unterschied von Carbonsäureamiden — bei der Aminostickstoffbestimmung relativ leicht Gas entwickeln. Es wurde gefunden, daß die Sulfonsäureamidgruppe dabei kaum desamidiert wird. Im Mittel entstehen etwa 1,5 Mole N₂O und 0,25 Mol N₂. Die Reaktion der Sulfonsäureamidgruppe ist bei 50° C abgeschlossen. Mit großer Wahrscheinlichkeit dürfte die Reaktion der Sulfonamide mit salpetriger Saure über folgende Zwischenstufen verlaufen: Zunächst entsteht unter Entwicklung eines Mols (N₂O+N₂) die entsprechende Sulfinsäure. Diese reagiert mit salpetriger Säure weiter, wobei sich als Zwischenprodukt Diarylsulfonylhydroxylamin bildet. Dieses wird unter Entwicklung von 0,5 Mol N₂O zur Sulfonsäure abgebaut. Setzt man zur Desaminierungslösung Jod bzw. Jodid zu, so wird die intermediär entstandene Sulfinsäure zur Sulfonsäure oxydiert und die Reaktion bleibt bei etwa 1 Mol (N₂O+N₂) stehen.

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Summary In the preceding investigation, it was attempted to obtain an insight into the reaction of the sulfonic acid amides with nitrous acid, especially because these compounds, in contrast to carboxylic acid amides, readily evolve gas in the determination of the amino nitrogen. It was found that the sulfonic acid amide group is scarcely deaminated at all under these circumstances. As an average, around 1.5 mols of N₂O and 0.25 mol of N₂ are produced. The reaction of the sulfonic acid amide group is concluded at 50° C. In all probability, the reaction of the sulfonamides with nitrous acid proceeds via the following intermediate stages: Firstly, the corresponding sulfinic acid is formed, with production of one mol of (N₂O+N₂). This product reacts further with nitrous acid and yields diarylsulfonylhydroxyl-amine as intermediate product. The latter breaks down to sulfonic acid with evolution of 0.5 mol N₂O. If iodine or iodide is added to the deaminating solution, the intermediate sulfinic acid is oxidized to sulfonic acid and the reaction stops at around one mol (N₂O+N₂).

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Résumé Dans le présent travail les auteurs cherchent à éclaircir la réaction des sulfonamides sur l'acide nitreux d'autant plus que ces combinaisons au contraire des amides des acides carboxyliques donnent facilement lieu à un dégagement gazeux lors de la détermination de l'azote aminé. Il a été établi que le groupement sulfonamide est à peine désamidé lors de cette réaction. Il se forme en moyenne environ 1,5 molécule de N₂O et 0,25 molécule de N₂. La réaction du groupement sulfonamide est achevée à 50° C. Selon toute vraisemblance la réaction des sulfonamides sur l'acide nitreux doit se produire suivant deux phases intermédiaires: tout d'abord il se forme l'acide sulfinique correspondant avec dégagement d'une molécule du mélange N₂O+N₂. Cet acide réagit ultérieurement sur l'acide nitreux en donnant naissance à un produit intermédiaire qui est une diarylsulfonylhydroxylamine. Cette dernière se dégrade en acide sulfonique avec dégagement de 0,5 molécule de N₂O. Si à la solution de désamination on ajoute de l'iode ou encore un iodure l'acide sulfinique qui s'est formé intermédiairement est oxydé en acide sulfonique et la réaction donne lieu qu'au dégagement d'environ une molécule du mélange N₂O+N₂.

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6. Mitteilung: Anomalie der Indole 1.     

1H-and 13C-NMR Investigation of Pentafulvenes

¹H- and ¹³C-NMR spectra of a series of 6-(p-X-phenyl)pentafulvenes 1 – 9 as well as of 6-R-substituted and 6,6-R¹,R²-disubstituted pentafulvenes 10 – 23 have been analysed. It turns out that the π-system of pentafulvenes is an attractive probe for the investigation of electronic substituent effects. Changes of vicinal H,H-coupling constants with increasing electron-donating capacity of the substituents X and R are interpreted in terms of an increasing π delocalisation in the 5-membered ring, and linear correlations of Hammett Substituent constants σ or MNDO-calculated C–C bond lengths and ³J values are observed. On the other hand, a systematic high-field shift of ₁₃C chemical shifts of the ring C-atoms is induced by electron-releasing substituents R and X, which decreases in the series C(5) > C(2)/C(3) > C(1)/C(4), and which mainly reflects changes in π-charge density.     

Synthesis and biological evaluation of 3-beta,20(R)-dihydroxy-protost-24-ene

The possible lanosterol precursor, 3β, 20(R)-dihydroxy-protost-24-ene ( 1 a ) has been prepared, in thirteen steps, from 3α-hydroxy-4α, 8, 14-trimethyl-18-nor-5α, 8α, 9β, 13ξ, 14β-androstan-17-one (mixture of 2 and 3 ). In vitro experiments with rat liver homogenates failed to convert 1 a to lanosterol.     

Surface tension of concentrated cellulose solutions in 1-ethyl-3-methylimidazolium acetate

Four sources of cellulose with different molecular weights were dissolved in the ionic liquid 1-ethyl-3-methylimidazolium acetate at 100 °C over a 10 h period. The solution densities were determined and these results were subsequently utilised to access the influence of dissolved cellulose on surface tension properties of cellulose/ionic liquid solutions. Surface tension measurements revealed increasing molecular weight and concentration reduced surface tension while temperature increases showed the opposite effect. These results are consistent with that of repulsive polymer-wall interactions near the interface in good solvent conditions. The semi-flexible nature of this carbohydrate in solution can help explain deviations of these results when compared to ideal flexible chains.     

Error estimates for finite element approximations of nonlinear monotone elliptic problems with application to numerical homogenization

We consider a finite element method (FEM) with arbitrary polynomial degree for nonlinear monotone elliptic problems. Using a linear elliptic projection, we first give a new short proof of the optimal convergence rate of the FEM in the L² norm. We then derive optimal a priori error estimates in the H¹ and L² norm for a FEM with variational crimes due to numerical integration. As an application, we derive a priori error estimates for a numerical homogenization method applied to nonlinear monotone elliptic problems. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 955–969, 2016     

Antiparallel arrangement of the helices of vesicle-bound alpha-synuclein

alpha-Synuclein (alphaS) is the main component of Lewy bodies from Parkinson's disease. That alphaS binds to membranes is known, but the conformation it adopts is still unclear. Pulsed EPR on doubly spin-labeled variants of alphaS sheds light on the most likely structure. For alphaS bound to vesicles large enough to accommodate also the extended conformation, an antiparallel helix conformation is found. This suggests that the bent structure shown is the preferred conformation of alphaS on membranes.     

Electrical conductance of conjugated oligomers at the single molecule level

We determine and compare, at the single molecule level and under identical environmental conditions, the electrical conductance of four conjugated phenylene oligomers comprising terminal sulfur anchor groups with simple structural and conjugation variations. The comparison shows that the conductance of oligo(phenylene vinylene) (OPV) is slightly higher than that of oligo(phenylene ethynylene) (OPE). We find that solubilizing side groups do neither prevent the molecules from being anchored within a break junction nor noticeably influence the conductance value.