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1. Microwave Heating Outperforms Conventional Heating for a Thermal Reaction that Produces a Thermally Labile Product: Observations Consistent with Selective Microwave Heating

   https://doi.org/10.1002/asia.201900625  

   Duangkamol, Chuthamat; Batsomboon, Paratchata; Stiegman, Albert E.; Dudley, Gregory B. (June 2019, Chemistry – An Asian Journal)

   Abstract Microwave (MW) heating is more effective than conventional (CONV) heating for promoting a high‐temperature oxidative cycloisomerization reaction that was previously reported as a key step in a total synthesis of the natural product illudinine. The thermal reaction pathway as envisioned is an inverse electron‐demand dehydro‐Diels–Alder reaction with in situ oxidation to generate a substituted isoquinoline, which itself is unstable to the reaction conditions. Observed reaction yields were higher at a measured bulk temperature of 200 °C than at 180 °C or 220 °C; at 24 hours than at earlier or later time points; and when the reaction solution was heated using MW energy as opposed to CONV heating with a metal heat block. Selective MW heating of polar solute aggregates is postulated to explain these observations. 

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2. Speciation and Photoluminescent Properties of a 2,6‐Bis(pyrrol‐2‐yl)pyridine in Three Protonation States

   https://doi.org/10.1002/cptc.202300094  

   Leary, Dylan C.; Martinez, Jordan C.; Gowda, Anitha S.; Akhmedov, Novruz G.; Petersen, Jeffrey L.; Milsmann, Carsten (June 2023, ChemPhotoChem)

   Abstract 2,6‐Bis(pyrrol‐2‐yl)pyridines are important building blocks for supramolecular assemblies and photoluminescent main group and transition metal compounds. Sterically encumbered 2,6‐bis(5‐(2,4,6‐trimethylphenyl)‐3‐phenyl‐1H‐pyrrol‐2‐yl)pyridine, H₂^MesPDP^Ph, can adopt monomeric and dimeric structures in the solid state and in solution, controlled by competing inter‐ and intramolecular hydrogen bonds. Deprotonation in the presence of lithium cations provides Li₂^MesPDP^Ph, which can be isolated in monomeric and dimeric forms depending on solvent polarity. Protonation of H₂^MesPDP^Phdisrupts intramolecular hydrogen bonding and provides the monomeric pyridinium salt [H₃^MesPDP^Ph]Cl. Independent of solvent polarity, all three derivatives exhibit intense fluorescence in solution. The absorption and emission spectra are highly sensitive to the level of protonation, which can be rationalized by the effects of (de)protonation on the HOMO and LUMO of the tricyclic π‐system. 

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3. Mechanism and Kinetics of Na ₂ S _x (x ≤ 2) Precipitation in Sodium-Sulfur and Sodium/(Oxygen)-Sulfur Batteries

   https://doi.org/10.1149/1945-7111/ad14cb  

   Zhang, Qipeng; Yang, Tairan; Li, Zheng (January 2024, Journal of The Electrochemical Society)

   Room-temperature sodium-sulfur (RT Na-S) batteries have attracted ever-increasing attention because of their enhanced energy density and low price. Although the performance of RT Na-S batteries is obtained in many other research, the basic mechanism and kinetics have not involved yet, especially in discharge product growth, which affects electrochemical performance. Meanwhile, designed additional redox activities (in the presence of oxygen) could simultaneously suppress sodium polysulfide shuttling and enhance energy density according to our group reported. However, the kinetic study of the intermediate has not been explored. In this work, we discussed the deposition of low-order sodium polysulfide (Na₂S_x, x ≤ 2) in different potentials and types of glyme-solvents in Na-S and Na/(O₂)-S system. The results show that the morphology of deposition Na₂S_x(x ≤ 2) is affected by interfacial energy barrier controlled by overpotentials and the radius of sodium ions, which produced the precipitation of particle shape rather than film. Potentiostatic experiments show the kinetics are elevated in the presence of oxygen. In addition, the exchange current density of different sodium polysulfides was studied. The high-order sodium polysulfide has a lower exchange current density than that of low-order sodium polysulfide in Na-S system, requiring greater driving force, while transformation of the intermediate from high-order oxy-sulfur to low-order oxy-sulfur species require less impulse in Na/(O₂)-S systems. This paper provides new understandings of the deposition mechanism and kinetics of Na₂S_x(x ≤ 2) Na-S and Na/(O₂)-S system in and to choose the appropriate solvent and potential. 

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4. Solvent mixtures for improved electron transfer kinetics of titanium-doped polyoxovanadate-alkoxide clusters

   https://doi.org/10.1039/D3TA01179H  

   Dagar, Mamta; Corr, Molly; Cook, Timothy R.; McKone, James R.; Matson, Ellen M. (June 2023, Journal of Materials Chemistry A)

   Emergent, flowable electrochemical energy storage technologies suitable for grid-scale applications are often limited by sluggish electron transfer kinetics that impede overall energy conversion efficiencies. To improve our understanding of these kinetic limitations in heterometallic charge carriers, we study the role of solvent in influencing the rates of heterogeneous electron transfer, demonstrating its impact on the kinetics of di-titanium substituted polyoxovanadate-alkoxide cluster, [Ti 2 V 4 O 5 (OMe) 14 ]. Our studies also illustrate that the one electron reduction and oxidation processes exhibit characteristically different rates, suggesting that different mechanisms of electron transfer are operative. We report that a 1 : 4 v/v mixture of propylene carbonate and acetonitrile can lead to a three-fold increase in the rate of electron transfer for one electron oxidation, and a two-fold increase in the one electron reduction process as compared to pure acetonitrile. We attribute this behavior to solvent–solvent interactions that lead to a deviation from ideal solution behavior. Coulombic efficiencies ≥90% are maintained in MeCN–PC mixtures over 20 charge/discharge cycles, greater than the efficiencies that are obtained for individual solvents. The results provide insight into the role of solvent in improving the rate of charge transfer and paves a way to systematically tune solvent composition to yield faster electron transfer kinetics. 

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5. Ultralight and Flexible Monolithic Polymer Aerogel with Extraordinary Thermal Insulation by A Facile Ambient Process

   https://doi.org/10.1002/admi.201900314  

   Li, Man; Qin, Zihao; Cui, Ying; Yang, Chiyu; Deng, Changyu; Wang, Yunbo; Kang, Joon Sang; Xia, Hongyan; Hu, Yongjie (May 2019, Advanced Materials Interfaces)

   Abstract High performance thermal insulation materials are desired for a wide range of applications in space, buildings, energy, and environments. Here, a facile ambient processing approach is reported to synthesize a highly insulating and flexible monolithic poly(vinyl chloride) aerogel. The thermal conductivity is measured respectively as 28 mW (m K)⁻¹at atmosphere approaching the air conductivity and 7.7 mW (m K)⁻¹under mild evacuation condition. Thermal modeling is performed to understand the thermal conductivity contributions from different heat transport pathways in air and solid. The analysis based on the Knudsen effect and scattering mean free paths shows that the thermal insulation performance can be further improved through the optimization of porous structures to confine the movement of air molecules. Additionally, the prepared aerogels show superhydrophobicity due to the highly porous structures, which enables new opportunities for surface engineering. Together, the study demonstrates an energy‐saving and scalable ambient‐processing pathway to achieve ultralight, flexible, and superhydrophobic poly(vinyl chloride) aerogel for thermal insulation applications. 

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