Not Unhydrolyzed at pH 8

Abstract

Anders als kürzlich behauptet ist das zwitterionische Bis(diolato)silicat 1 bei pH 7–8 nicht erstaunlich hydrolysestabil. Dies ergab eine genauere Analyse der 29Si‐ und 13C‐NMR‐spektroskopischen Daten von 1 unter einer Vielzahl unterschiedlicher Bedingungen (Lösungsmittel, pH, Konzentration), nach der in Lösung vor allem Hydrolyseprodukte vorliegen.

From Simple Diols to Carbohydrate Derivatives of Phenylarsonic Acid

“…To check for the significance and spectroscopic characteristics of syn/anti isomers, the starting point of this investigation thus was the condensation of phenylarsonic acid with meso-2,3-butanediol (meso-Butd), the C s -symmetric dimethyl derivative of ethane-1,2-diol. Assignment of 13 C NMR signals to the different isomers was done by analogy to the corresponding phenyl silicates. 9 13 C NMR spectra of redissolved crystals of the reaction product PhAs(meso-ButdH -2 ) 2 (1) showed the expected characteristics of syn/anti isomerism.…”

“…Data were processed using the Delta software (by JEOL). 1 H and 13 C NMR-signal shifts were referenced to TMS as primary internal or the solvent signal as secondary internal standard, CFCl 3 served as external reference for the shifts of 19 F signals. All measurements were performed at room temperature.…”

“…In the course of 2 months the oil completely crystallized yielding colorless platelets with a slightly sweet odor (1.56 g, 4.75 mmol, 95.0% yield). (27), 1578 (19), 1461 (10), 1445 (19), 1350 (7), 1323 (9), 1291 (12), 1172 (14), 1160 (17), 1142 (7), 1113 (9), 1089 (10), 1017 (18), 1000 (71), 795 (12), 689 (11), 666 (100), 638 (7), 615 (13), 599 (14), 521 (9), 432 (10), 342 (51), 283 (14), 245 (22). UV/vis (acetonitrile): λ max /nm ) 258, 263, 269, UV/vis (cyclohexane): λ max /nm ) 258, 264, 271.…”

“…The hydrolysis of the Si−O−C link in neutral aqueous solution, which becomes more dominant at lower pH values and higher dilution, has remained problematic, however. ,, Gaining structural and spectroscopic information about assumed silica-containing carbohydrate compounds in aqueous solutions at physiological pH values is thus hampered. A possible solution for this problem might be to shift the focus of research away from silicon toward another central atom that exhibits some degree of similarity.…”

Optically Active Zwitterionic λ5Si,λ5Si′‐Disilicates: Syntheses, Crystal Structures, and Behavior in Aqueous Solution

“…This is in sharp contrast to the behavior of the zwitterionic λ 5 Si‐silicate 25 , which upon dissolution in water forms an equilibrium mixture with the corresponding silsesquioxanes (Scheme ) 2g. k…”