Role of Anhydride in the Ketonization of Carboxylic Acid: Kinetic Study on Dimerization of Hexanoic Acid

Ketonization of hexanoic acid (CH₃(CH₂)₄COOH) to produce 6-undecanone ((CH₃(CH₂)₄)₂CO) was performed and the reaction pathway was investigated through a kinetic study. Unlike studies suggesting β-keto acid as an undetectable intermediate of ketonization, hexanoic anhydride ((CH₃(CH₂)₄)­COOCO­(CH₂)₄CH₃) was observed to form as a result of the condensation of two hexanoic acid molecules by the loss of a water molecule. In order to investigate the role of hexanoic anhydride on the ketonization reaction, this kinetic study compared the performances of the reaction rate equations under different models for the reaction mechanism. Results indicate that ketonization occurs by the condensation of two hexanoic acid molecules producing hexanoic anhydride, followed by decarboxylation to produce 6-undecanone. By contrast, the formation of a β-keto acid is not observed in any experimental attempt

Role of Salts in Phase Transformation of Clathrate Hydrates under Brine Environments

Although ion exclusion is a naturally occurring and commonly observed phenomenon in clathrate hydrates, an understanding for the effect of salt ions on the stability of clathrate hydrates is still unclear. Here we report the first observation of phase transformation of structure I and structure II clathrate hydrates using solid-state ¹³C, ¹⁹F, and ²³Na magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy, combined with X-ray diffraction and Raman spectroscopy. The phase transformation of clathrate hydrates in salt environments is found to be closely associated with the quadruple point of clathrate hydrate/hydrated salts and the eutectic point of ice/hydrated salts. The formation of the quasi-brine layer (QBL) is triggered at temperatures a little lower than the eutectic point, where an increasing salinity and QBL does not affect the stability of clathrate hydrates. However, at temperatures above the eutectic point, all hydrated salts and the QBL melt completely to form brine solutions, destabilizing the clathrate hydrate structures. Temperature-dependent in situ NMR spectroscopy under pressure also allows us to directly detect the quadruple point of clathrate hydrates in salt environments, which has been determined only by visual observations

Enhanced Hydrogen-Storage Capacity and Structural Stability of an Organic Clathrate Structure with Fullerene (C₆₀) Guests and Lithium Doping

An effective combination of host and guest molecules in a framework type of architecture can enhance the structural stability and physical properties of clathrate compounds. We report here that an organic clathrate compound consisting of a fullerene (C₆₀) guest and a hydroquinone (HQ) host framework shows enhanced hydrogen-storage capacity and good structural stability under pressures and temperatures up to 10 GPa and 438 K, respectively. This combined structure is formed in the extended β-type HQ clathrate and admits 16 hydrogen molecules per cage, leading to a volumetric hydrogen uptake of 49.5 g L^–1 at 77 K and 8 MPa, a value enhanced by 130% compared to that associated with the β-type HQ clathrate. A close examination according to density functional theory calculations and grand canonical Monte Carlo simulations confirms the synergistic combination effect of the guest–host molecules tailored for enhanced hydrogen storage. Moreover, the model simulations demonstrate that the lithium-doped HQ clathrates with C₆₀ guests reveal exceptionally high hydrogen-storage capacities. These results provide a new playground for additional fundamental studies of the structure–property relationships and migration characteristics of small molecules in nanostructured materials