Bestimmung von Epoxyendgruppen in modifizierten chromatographischen Sorbentien und Gelen

Zusammenfassung Zur Bestimmung der auf Silicagel oder Ethylenglykolmethacrylat-Gel Spheron chemisch gebundenen Epoxygruppen wurden die Methoden der Addition von Chlorwasserstoff aus einer Lösung von Pyridiniumchlorid in Pyridin, einer Lösung von Chlorwasserstoff in Dioxan oder Methylcellosolve, sowie die Addition von Thiosulfat und die direkte Titration mit Perchlorsäure in nichtwäßrigem Milieu in Anwesenheit von Tetraethylammoniumbromid untersucht und angewendet. Die besten Resultate mit einer guten Reproduzierbarkeit liefert die direkte Titration der in einer Tetraethylammoniumbromidlösung in Eisessig suspendierten Probe mit einer Perchlorsäurelösung in Eisessig. Die relative Standardabweichung in einem Bereich von 0,6–0,8 mmol Epoxygruppe/g ist nicht höher als 1%.

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Determination of epoxy end-groups in modified chromatographic sorbents and gels

Summary The addition of hydrogen chloride from solutions of pyridinium chloride in pyridine, or from solutions of hydrogen chloride in dioxan or in methylcellosolve, as well as the addition of thiosulphate and the direct non-aqueous titration with perchloric acid in the presence of tetraethylammonium bromide were studied and applied for the determination of bound epoxy groups in epoxidized silicagels and the ethyleneglycol methacrylate gels Spheron. Best results with high reproducibility were obtained by direct titration with perchloric acid of a sample suspended in a solution of tetraethylammonium bromide in acetic acid. The relative standard deviation in the range of 0.6–0.8 mmol epoxy group/g does not exceed 1%.

     

Tuning the Gate‐Opening Pressure in a Switching pcu Coordination Network,X‐pcu‐5‐Zn,by Pillar‐Ligand Substitution

Coordination networks that reversibly switch between closed and open phases are of topical interest since their stepped isotherms can offer higher working capacities for gas‐storage applications than the related rigid porous coordination networks. To be of practical utility, the pressures at which switching occurs, the gate‐opening and gate‐closing pressures, must lie between the storage and delivery pressures. Here we study the effect of linker substitution to fine‐tune gate‐opening and gate‐closing pressure. Specifically, three variants of a previously reported pcu ‐topology MOF, X‐pcu‐5‐Zn , have been prepared: X‐pcu‐6‐Zn , 6 =1,2‐bis(4‐pyridyl)ethane (bpe), X‐pcu‐7‐Zn , 7 =1,2‐bis(4‐pyridyl)acetylene (bpa), and X‐pcu‐8‐Zn , 8 =4,4′‐azopyridine (apy). Each exhibited switching isotherms but at different gate‐opening pressures. The N₂, CO₂, C₂H₂, and C₂H₄ adsorption isotherms consistently indicated that the most flexible dipyridyl organic linker, 6 , afforded lower gate‐opening and gate‐closing pressures. This simple design principle enables a rational control of the switching behavior in adsorbent materials.