Infrared Study of Mixtures of n-Butyl Acetate and 1-Butanol

Abstract

This thesis presents a study on various mixtures of BA, BuOH, and H2O, including known azeotropic compositions of 1BA:3.2BuOH, 1BA:2.4H2O, and 5BA:1BuOH:15H2O, investigated using FTIR spectroscopy. This thesis consists of four chapters. Chapter 1 provides an introduction, explaining the background and purpose of this study and previous research. Chapter 2 describes experimental details, including sample preparation, data acquisition, and data analysis methods. Chapter 3 presents the experimental results, data analysis, and discussion. Conclusion and future work are presented in Chapter 4. The contents of this study are summarized as follows. This study investigates the H-bond interactions, in mixtures of n-butyl acetate (BA), 1- butanol (BuOH), and water, which are products of the esterification process. The purification of BA is challenging due to the azeotropic mixture, which cannot be effectively separated by simple distillation. To address this issue, FTIR spectroscopy was used to investigate various mixtures of BA, BuOH, and H2O, including known azeotropic compositions of 1BA:3.2BuOH, 1BA:2.4H2O, and 5BA:1BuOH:15H2O. For mixtures of BA and BuOH, as BA concentration in BuOH increases, the relative population of H-bonded C=O groups decreases. At the azeotropic composition of 24% BA, no local maximum or minimum of H-bonded C=O population was observed. Instead, the population ratio of H-bonded C=O groups to free C=O groups was ~50%:50%, suggesting that the entropic effect is the essential reason for the azeotrope formation at this composition. The infrared spectrum in the C=O stretch region of the ternary mixture of 5BA:1BuOH:15H2O in the organic phase shows three peaks at 1743.3 cm-1 (73%, free C=O), 1731.7 cm-1 (3.6%, H-bonded with BuOH), and 1724.4 cm-1 (23%, H-bonded with H2O). Such a distribution supports the idea that though BuOH contributes to hydrogen bonding, water plays a significant role in H-bonding with BA’s carbonyl group. The comparison between the spectra of pure BA and an azeotropic mixture of 1BA:2.4H2O in the organic phase also shows that BA and water interact through H-bond dynamics. In this regard, a redshift of the carbonyl absorption band is observed because of the interaction of the carbonyl (C=O) group of BA with the hydroxyl (O–H) group of water. Thus, this interaction changes the electronic environment around the carbonyl group, weakening the C=O bonds and shifting the absorption to lower frequencies.