Esterification lab
Introduction: The purpose of this experiment is to derive Isopentyl acetate (banana oil) from the reaction of an alcohol and a carboxylic acid in a process called Fischer esterification (Fischer-Speier esterification). The name, banana oil, is due to banana odour released by formation of Isopentyl acetate. The alcohol and the carboxylic acid used in this experiment are Isopentyl alcohol and Glacial Acetic Acid. Both the overall reaction of Fischer esterification and the specific Fischer esterification reaction that was carried out in this lab is shown in figure 1. It worth mentioning that the by-product of such reaction is water. In organic chemistry, the reaction in which water molecule is released is known as condensation reaction (Hornback, 2006). Figure1 is drawn using Chem Sketch software.
a)
b)
Figure 1: Typical Fischer esterification reaction (a) in comparison to the specific esterification reaction used in this lab (b)
The reaction can also be categorized in terms of its mechanism as nucleophilic substitution reaction. The alcohol which contains a hydroxyl group (OH-) has a partial negative charge compared to the alkyl group bound to it which is Isopropyl in this lab. The reason is that oxygen has higher electronegativity compared to carbon. So, there is more attraction to the lone pair electrons around oxygen which makes the hydroxyl group partially negative. Analyzing the structure of the glacial acetic acid, we notice that the hydroxyl group and the oxygen on the carbonyl group will draw electrons towards themselves to a higher extent compared to the carbon which is bound to the both functional groups. Accordingly, the carbon will have a partial positive charge compared to the two functional groups mentioned. In nucleophilic substitution reaction, the electrons of the partially negative hydroxyl group of the alcohol (nucleophile) attacks the partially positive carbon on the acid (electrophile). Eventually, the nucleophile donates its electrons to
a)
b)
Figure 1: Typical Fischer esterification reaction (a) in comparison to the specific esterification reaction used in this lab (b)
The reaction can also be categorized in terms of its mechanism as nucleophilic substitution reaction. The alcohol which contains a hydroxyl group (OH-) has a partial negative charge compared to the alkyl group bound to it which is Isopropyl in this lab. The reason is that oxygen has higher electronegativity compared to carbon. So, there is more attraction to the lone pair electrons around oxygen which makes the hydroxyl group partially negative. Analyzing the structure of the glacial acetic acid, we notice that the hydroxyl group and the oxygen on the carbonyl group will draw electrons towards themselves to a higher extent compared to the carbon which is bound to the both functional groups. Accordingly, the carbon will have a partial positive charge compared to the two functional groups mentioned. In nucleophilic substitution reaction, the electrons of the partially negative hydroxyl group of the alcohol (nucleophile) attacks the partially positive carbon on the acid (electrophile). Eventually, the nucleophile donates its electrons to