Solvent selection is a pressing challenge in developing efficient and selective liquid phase catalytic processes, as predictive understanding of the solvent effect remains lacking. In this work, an attenuated total reflection infrared spectroscopy technique is developed to quantitatively measure adsorption isotherms on porous materials in solvent and decouple the thermodynamic contributions of van der Waals interactions within zeolite pore walls from those of pore-phase proton transfer. While both the pore diameter and the solvent identity dramatically impact the confinement (adsorption) step, the solvent identity plays a dominant role in proton-transfer. Combined computational and experimental investigations show increasingly favorable pore-phase proton transfer to pyridine in the order: water < acetonitrile < 1,4dioxane. Equilibrium methods unaffected by mass transfer limitations are outlined for quantitatively estimating fundamental thermodynamic values using statistical thermodynamics.
Amines are widely used in the manufacture of pharmaceuticals, agricultural chemicals, polymers, and surfactants. However, amines are mostly produced via petrochemical means, which motivates amine production from renewable resources, such as biomass. However, biomass compounds present added challenges involving poor carbon balances. We show that furfural reacts homogeneously with ammonia to produce reactive primary imines, which form large side products and leads to significant carbon losses. The carbon balance is improved by mixing furfural with furfurylamine prior to reaction to form a secondary imine for use as the reaction substrate. While controlling the primary to secondary amine selectivity is a common challenge in reductive amination, supported metal catalysts, including Ni/SiO2, Co/SiO2, and Ru/SiO2 optimize the primary amine yield to 90 to 94 % by using the secondary imine as the reaction substrate. A qualitative correlation between the primary to secondary amine selectivity with the nitrogen binding energy of metals is identified.
Noncovalent interactions allow associating polymers to self-assemble into structures that assist in applications such as contaminant removal and drug delivery. Using single-particle tracking (SPT) diffusion studies, we show that poly(ethylene glycol monomethacrylate) (pPEGMA) is a hydrophobically associating polymer, where polymer chains may diffuse individually or in clusters. Aided by the single-molecule resolution of SPT, we observe that the mean-squared displacements of pPEGMA chains in solution show a clear two-population division, which corresponds to unimers and clusters in our hypothesis. This bifurcation is also seen in the distributions of polymer mean-squared displacements and the van Hove distributions. Clustering behavior can be tuned by altering the concentration and molecular weight of the polymer, as well as the polarity of the solvent. Combined with dynamic light scattering (DLS) and diffusion ordered spectroscopy (DOSY), polymer diffusive regimes up to the semidilute entangled regime are experimentally observed.
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