On the Perturbation of the Intramolecular H-Bond in Diols by Supercritical CO₂:  A Theoretical and Spectroscopic Study

Abstract

The role played by supercritical carbon dioxide used as a dispersant medium in the synthesis of polyurethane particles has been investigated. High-temperature-high-pressure in situ infrared spectroscopic measurements combined with ab initio calculations were performed to investigate the hydroxyl stretching vibrations of ethylene glycol (EG) and 1,4-butanediol (BD), two monomers commonly used in the field of step growth polymerization. Specific interactions between the diols and CO2 have been put in evidence. While the structural characteristics of EG and BD are very similar--both diols have a gauche conformation due to an internal H-bond between the two hydroxyl functions--they behave differently in the presence of dense CO2. In the case of EG, this internal H-bond is broken, allowing the diol and CO2 to form a complex through the conjunction of a Lewis acid-Lewis base (LA-LB) interaction and a new H-bond. When BD complexes to CO2, this internal H-bond remains and is even reinforced indirectly by the LA-LB interaction occurring between the two moieties. In both cases, such a complex formation induces a polarization of the hydroxyl groups and consequently an increase of their nucleophilicity.

Gold-Catalyzed Aerobic Oxidation of Benzyl Alcohol: Effect of Gold Particle Size on Activity and Selectivity in Different Solvents

“…Generally, CO 2 is considered a Lewis acid. It has been shown that CO 2 can interact with surfaces of oxides such as TiO 2 and CeO 2 as a Lewis acid through the carbon atom and bind to a surface oxygen atom, but bond formation is also possible between the oxygen atoms and Lewis acid surface sites possibly because CO 2 exhibits also weak Lewis base properties [46][47][48][49][50][51]. Note that scCO 2 as the solvent is present in large excess and hence, also a weak basicity could contribute significantly to the reaction.…”

“…Here we elucidate the effect of the gold particle size of titania and ceria-supported gold catalysts used in the aerobic oxidation of benzyl alcohol at atmospheric pressure in conventional solvents as well as at high pressure in supercritical CO 2 which can act as a (weak) Lewis base [46][47][48][49][50][51]. The almost gas-like diffusion coefficients of solutes in dense carbon dioxide and the avoidance of phase boundaries under single-phase conditions in combination with its ability to solvate nonpolar gases as well as many organic compounds render it a promising reaction medium [52][53][54][55].…”

Tailoring Metal–Organic Frameworks for CO2 Capture: The Amino Effect

“…[19,33,34,[37][38][39][40] During recent years, quantum mechanical studies on the interaction between CO 2 and amines were mainly targeted to the study of supercritical CO 2 as an alternative to toxic organic solvents in industrial applications [41,42] and, in particular, as a dispersion medium in the synthesis of polymeric materials, such as polyurethane. [42,43] Studies have been also performed on the interaction between CO 2 and polymers. [13,41] Only recently, some works concerning the interaction between CO 2 and MOFs have appeared.…”

1H NMR study of the hetero‐association of non‐symmetrical diols with pyridine; GIAO/DFT calculations on diols

“…Relative energies of conformers (PBE1PBE/6-311þG(d,p)) and chemical shifts of OH protons (PBE1PBE/cc-pVTZ//PBE1PBE/ 6-311þG(d,p)) of propan-1,2-diol, 1-Me, in benzene at 298 K Conf. IR, [7,8,24,30,32,42,[84][85][86] Raman, [3] microwave [4,31] , and NMR [6,14,27,87] spectroscopies, and other less common experimental techniques, [29,40,42,88] but none gives direct evidence for hydrogen bonding, only for the proximity of hydrogen and oxygen on different OH groups. Theoretical calculations of various degrees of sophistication (molecular dynamics and Monte Carlo calculations, [2,[9][10][11]81,89] molecular mechanics [19,90] and semi-empirical [19,20] and ab initio [1,5,8,9,12,13,[15][16][17][18]21,25,28,30,33,[35][36]…”