Cyclotetrabenzil Oxime Derivatives

Cyclotetrabenzil octaketone has been elaborated into its octaoxime and octaoxime acetate derivatives. Their crystal structures reveal the arrangement of these macrocycles into nanotubes, albeit with quite different characteristics. Gas sorption data reveals type I isotherms for CO₂, N₂, C₂, and C₃ hydrocarbons, typical of narrow micropores. Water sorption isotherms register low (<10%) uptakes even under high relative humidity, suggesting hydrophobic nature of the channels.

Abstract

Cyclotetrabenzil, a shape-persistent macrocyclic octaketone, is found to undergo eightfold condensation with hydroxylamine hydrochloride to yield its octaoxime. Subsequent acetylation of this macrocyclic oxime afforded the corresponding octaoxime acetate. Single-crystal X-ray diffraction reveals that both new derivatives assemble into nanotubular structures. However, their packing differs: the oxime forms hydrogen-bonded tubes that bundle via included dimethyl sulfoxide (DMSO) molecules, whereas the acetate—lacking hydrogen-bond donors—forms more loosely packed tubes with molecules tilted ∼54.5° relative to the tube axis. Gas sorption studies (CO₂, C₂, and C₃ hydrocarbons) show that cyclotetrabenzil is nonporous, whereas the oxime and acetate exhibit modest microporosity with BET surface areas of ∼200 m² g⁻¹. Both derivatives display preferential uptake of propyne over propene and propane, and the acetate also adsorbs more acetylene than ethylene or ethane. Nonetheless, these capacities and selectivities are suboptimal for dynamic separation of C₂ and C₃ hydrocarbons. This study illustrates how oxime functionalization can modulate macrocyclic assembly and gas uptake behavior, providing insights for the design of future porous organic macrocycles.

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