Abstract
Attenuated total reflectance - Fourier transform infrared (ATR-FTIR) spectra of ethylene glycol–water (abbreviated as EG–H2O) mixtures were measured at 298 K with the ethylene glycol molar ratio ranging from 0.01 to 1400. The two bands at 1033 and 1082 cm-1 were assigned to be the C-C stretching vibration modes related to the trans- and gauche- conformation of EG. The absorbance of the two bands was found to be sensitive to the molar ratios. We made theoretical calculation for ten conformations of the EG molecules to understand the conformational transformation of EG molecules changing with EG–H2O molar ratios. The absorbance ratio (A1033/A1082) was used to determine the trans- and gauche- conformation ratio with the calculated (AνO-C-C-O-T/AνO-C-C-O-G) as standard. When the molar ratio of water and EG (xH2O/xEG) is smaller than 0.4, strong associations formed by the intermolecular hydrogen bonds were dominant in the solutions and the proportion of gauche- conformation was about 0.5. Within the region of 0.4< xH2O/xEG < 20, the intermolecular hydrogen bonds structure between EG molecules were broken by the water molecules and the structure of most EG molecules changed from trans- to gauche- conformation. The blue shift of the peaks indicated the increasing hydrogen bonding between water and EG. When xH2O/xEG is larger than 20, the monomers of molecules started to appear in the EG–H2O solution. The gauche- conformation was the dominated conformation in the dilute EG–H2O solution with proportion of 0.87. In the CH2 rocking vibration (δC-H) region, the computational results showed that the majority bands in this region were influenced by the gauche- conformation which can be divided into group G1 or G2. The transformation between the gauche- conformations of EG molecules can be studied by combining the experimental results and the computational results, The proportion of G1 for the EG-rich solution was about 0.71 while it decreased to 0.55 for the H2O–rich solution.
Highlights
Ethylene glycol (EG) is extensively used as antifreeze and coolant in automobiles, deicing fluid for windshields and aircraft, wetting agent for fibers and leather, desiccant, plasticizer in plastic industry, precursor for manufacture of polyester fibers and polyester resins.[1,2,3,4,5] Fundamental aspects of reformation of EG to hydrogen and chemicals[6,7,8] as well as the electro-oxidation of EG in fuel cells[9,10,11,12] has been attracting increasing concentration
They concluded that such kind of shifts indicated the EG behaves as a hydrogen-bond receptor when solvated by additional water molecules
The results showed the interaction between epoxy networks with free or bound water was obviously stronger than which of EG molecules
Summary
Chemist via saponification of ethylene glycol diacetate with potassium hydroxide.[13,14] Currently, the global production and consumption of ethylene glycol are about 20 million metric tons in 2010 with an estimated increase of 5 – 10 % per year.[1]. Blue shift of the CH2 symmetric stretch peak was observed in the SFG spectra with an increase of water content They concluded that such kind of shifts indicated the EG behaves as a hydrogen-bond receptor when solvated by additional water molecules. Complemented with the result from quantum calculations at HF/6-31+G* level, two-dimensional infrared correlation and excess spectroscopy analysis, they concluded that with the increasing water to 1-propanol molar ratio (WPR), the penetrated water molecules disrupt the 1-propanol chains and the conformation of 1-propanol was found to transform from gauche-aggregate chains to trans-aggregate chains. The ATR–FTIR spectra and computational simulation results were used to analyze the conformational changes of EG–H2O mixtures with the EG-water molar ratio ranging from 0.01 to 1400 at 298 K. The skeletal stretching vibration (νO-C-C-O) and the CH2 rocking vibration (δC-H ) for EG–H2O mixed solutions with different concentrations were analyzed in detail to understand the proportional changes between the trans-conformation and the gauche-conformation
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