Cyclotetrabenzoin: Esterification, Hosts for Thin Guests, Purification, and By-Product Analysis



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Porous molecular crystals are a unique developing class of porous materials composed of discrete molecules. Macrocycles, which inherently have a central cavity, are a class of molecules that could be utilized in the continued development of porous molecular crystals. Cyclobenzoins are a class of macrocycles that were first reported in 2015 by the Miljanić group. Of the two reported macrocycles, cyclotribenzoin and cyclotetrabenzoin, this dissertation will mostly focus on our efforts to deepen the understanding and development of cyclotetrabenzoin. While published reaction conditions only produce one macrocycle with a 20% yield, analysis of other reaction components was attempted to determine what other products were being synthesized. A major limiting factor to studying cyclobenzoins is their insolubility in most common organic solvents. Previous modifications to cyclotetrabenzoin resulted in a major shape change in the pore, not enabling exploration of the intrinsic pore. Simple esterification with anhydrides was found to greatly increase cyclobenzoins solubility while not changing the shape of the intrinsic pore. Crystallization resulted in crystals with solvent molecules that could be removed resulting in a permanently porous crystal. A crystal structure was found to have CS2 molecules in the intrinsic pore, which was the first indication of a small molecule interacting with the pore. Continued exploration to crystalize thin guest molecules resulted in several host-guest complexes with terminal alkynes and nitriles as guests. Lastly, CO2 was shown in the crystal structure by X-ray crystallography and breakthrough curve analysis resulted in the ability to separate a N2/CO2 gas mixture.



benzoin condensation, macrocycle, carbon dioxide, porous molecular crystal, alkyne sensing


Portions of this document appear in: McHale, Corie M., Christina R. Stegemoller, Mohamed I. Hashim, Xiqu Wang, and Ognjen Š Miljanić. "Porosity and Guest Inclusion in Cyclobenzoin Esters." Crystal Growth & Design 19, no. 2 (2019): 562-567.