Inhomogeneous Distribution in Methanol/Acetone Mixture: Vibrational and NMR Spectroscopy Analysis

Abstract

The main aim of this paper is to quantify the inhomogeneous distribution of the components of acetone/methanol mixture and to give detailed insight into the interplay between the dipole-dipole and hydrogen bonding interactions inducing this inhomogeneity. To this end, we used the concept of infrared excess molar absorption of a given vibrational mode as an observable which contains all the information on the collective interactions in the mixture. Indeed, the changes in the infrared excess molar absorption may be associated with the inhomogeneous distribution (clustering, self-association, or high-density domains) of the components and consequently with the interaction between the two components of the mixture. The results show that acetone molecules are not homogeneously distributed in the mixture, particularly in the mole fraction range of acetone between 0.05 and 0.55. The spectral signature of this inhomogeneity is associated with the appearance of a shoulder in the C═O and C-C stretching vibrational profiles of acetone. This inhomogeneity is driven by the prevalence of the dipole-dipole interactions over those of hydrogen bonding between acetone and methanol molecules. The inhomogeneous distribution of methanol molecules is found to occur in the mole fraction range of acetone between 0.55 and 1. In this case, the hydrogen bond interactions between methanol molecules prevail over those between methanol and acetone. However, the extent of this inhomogeneity is small compared with that of acetone in the low mole fraction range. The spectral signature of this inhomogeneity is not visible in the O-H stretching vibrational mode; however, a second peak appears as a shoulder of the C-O stretching vibrational mode in this range of acetone mole fraction.

Molecular Solution Behaviour of an Intermediate Biofuel Feedstock: Acetone–Butanol–Ethanol (ABE)

“…This new band at 1707 cm −1 is red‐shifted from the position in pure acetone by about 10 cm −1 . For binary mixtures of acetone with methanol, this band has been attributed to acetone molecules involved in hydrogen bonding with alcohol molecules . Since this is in good agreement with the general theory on the effects of hydrogen bonding on the vibrational frequency of a given moiety involved in a hydrogen bond, the same assignment is used here.…”

“…Following the interpretation of Idrissi et al . that the blue‐shift of the hydroxyl stretching band is related with an increase in the number of acetone–alcohol hydrogen bonds upon mixing, the positive high‐frequency contribution of the excess molar absorption can be attributed to alcohol molecules interacting with acetone via hydrogen bonding.…”

“…Figure shows the molar absorption coefficient spectra of the pure solvents. Acetone exhibits a single free‐standing peak around 1716 cm −1 associated with the stretching vibration of the carbonyl group . The alcohols, on the other hand, show a distinct broad vibrational band between 3000 cm −1 and 3600 cm −1 associated with the stretching vibration of the hydroxyl group .…”

“…Acetone exhibits a single free‐standing peak around 1716 cm −1 associated with the stretching vibration of the carbonyl group . The alcohols, on the other hand, show a distinct broad vibrational band between 3000 cm −1 and 3600 cm −1 associated with the stretching vibration of the hydroxyl group . These bands are associated with those functional groups most likely involved in interspecies hydrogen bonding, that is, acetone–alcohol interactions.…”

“…Thus, the positive contribution to the excess molar absorption spectra can be attributed to acetone molecules hydrogen bonded to alcohol molecules, while the negative contribution is assigned to acetone molecules engaged in dipolar interactions with other acetone molecules . The integrated intensities of the positive and negative contributions to the excess molar absorption of the carbonyl stretching band can further be taken as a measure for the relative extent of acetone molecules engaged in either hydrogen bonding with alcohol or dipolar interactions with other acetone molecules …”