Study of molecular association in acetic acid-water binary solution by Raman spectroscopy

Raman spectra of acetic acid-water binary solutions with different concentrations have been measured in order to study molecular association of acetic acid. We find that the symmetric and asymmetric O-H stretching vibration ofwater (3242 and 3443 cm(-1)) have marked changes of Raman shift when the volume fraction of acetic acid (V-AA) is 0.3 and 0.8, respectively, which demonstrates that the hydrogen bonding of the water is affected, causing association molecule (acetic acid-water structure) to undergo two phase transitions. Furthermore, the peak of the H-C-H bending vibration is blue-shifted at V-AA = 0.8, which shows that the acetic acid-acetic acid structure undergoes a phase transition and the acetic acid side-on dimer is formed. These results also indicate that the C-H vibration mode in C-H center dot center dot center dot O is H-C-H bending vibration. Finally, the phase transition process of association molecules (hydrated monomer, linear dimer, acetic acid side-on dimer and water-separated dimer) has been obtained in acetic acid-water binary solutions through theoretical analysis. (C) 2018 Published by Elsevier B.V.