Vibrational spectral studies of solutions at elevated temperatures and pressures. IX. Acetic acid

Raman spectra of glacial acetic acid from 350 to 3700 cm^–1 have been measured at temperatures up to 275°C and at a pressure of 9 MPa. Raman spectra of aqueous solutions of acetic acid from 3.9 to 16 molar have been measured up to 200°C at a pressure of 7 MPa. The spectral region 800 to 1850 cm^–1 for both glacial acetic acid and its aqueous solutions have been studied in detail since this region is significantly affected by variations in temperature and concentration. An interpretation of the bands in this spectral region was made with the aid of factor analysis, difference spectroscopy, band resolution techniques and the existing extensive literature. The results suggest that the major equilibrium in glacial acetic acid is between cyclic and linear dimers; however, in aqueous solutions in the concentration range studied, mono- and di-hydrated dimers and cyclic dimers are the predominant species.