EXPERIMENT 5- A FISCHER ESTERIFICATION SYNTHESIS OF PEAR OIL
One of the major uses of Esterification (C(=O)-C-R) is forming compounds with different odors which can be used to make different synthetic and natural flavorings. Using the chemical and physical properties of organic compounds, an ester was catalyzed from the reaction of a carboxylic acid with an alcohol, producing an odor similar to that of pear oil. The mechanism of this Fischer- Esterification process is outlined as follows:
Carboxylic Acid Alcohol
Ester water Particularly, 1-hexanol was reacted with an excess of acetic acid, using an acid catalyst to yield its ester: hexyl acetate. The reaction was performed under reflux which sped up the reaction by continuous vapor-condensation cycles of the solution mixture as the solution boiled. The vapors were blocked from escaping the solution by a stream of cold water running up the reflux column. Also, to increase the reaction rate, an acid catalyst: sulfuric acid, was added to the reactant mixture (³). The main reaction is as follows:
However, the actual reaction does not only produce the expected ester and water but also unreacted reactants along with byproducts; the actual mixture contains:
Hexyl Alcohol (aq) + Acetic Acid (aq) Hexyl Acetate (l) + H2O (aq) + H2SO4 (aq) + Acetic Acid (aq) +hexanol(aq) +Byproducts To produce a better yield, le chatelier’s principle was applied which states that increasing the amount of a compound will force the reaction in the opposite direction; having an excess of the acetic acid, allowed the reversible reaction to proceed towards the products more efficiently (²). As mentioned previously, the unwanted compounds in the product mixture were separated by taking advantage of their different physical properties outlined in table 2. Using solubility differences, the product mixture was washed with water to separate the acids ( acetic acid, sulfuric acid,) in an aqueous layer, from the water insoluble Hexyl acetate(organic layer). Hexyl Acetate (aq)+ H2SO4(aq) +Acetic Acid(aq)Hexyl Acetate (Organic Layer)) + aqueous layer The organic layer, containing trace amounts of acid, was reacted with bicarbonate, producing a gentler acid/base reaction; the reaction produces CO2 gas which was indicative of the acid base reaction, separating the organic layer from the less dense aqueous layer containing the salts with water: Hexyl Acetate (aq) + H2SO4 (aq) +Acetic acid (aq) Hexyl Acetate (aq) + Na2SO4+ NaOAC +water Organic Layer Aqueous Layer The organic layer was then further purified by drying it with anhydrous magnesium sulfate which is an effective drying agent since it can absorb 7 water molecules for each MgSO4 molecule. H2O (aq) + MgSO4(s) [MgSO4.7H2O](s) The drying agent absorbed any water molecules remaining in the ester and sunk to the bottom, allowing it to be separated using gravity filtration (¹).
Finally, simple distilattion was conducted, using the different boiling points of each compound in the product mixture, the ester was separated from highboiling point impurities and any remaining alcohol(118°C) and water (100°C) which were low boiling point impurities. The mixture was heated to a boiling point range of 158-171°C which was between that of hexanol and hexyl acetate; any distilate produced before that was the forerun while any remaining liquid above 171°C was by product...
Please join StudyMode to read the full document