**NOTE: MORE THAN ONE POSSIBLE ANSWER FOR FIRST 3 QUESTIONS** Suppose you carrie
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Question
**NOTE: MORE THAN ONE POSSIBLE ANSWER FOR FIRST 3 QUESTIONS**
Suppose you carried out the following synthesis of 3-methylbutyl ethanoate (isoamyl acetate):
As the chemical equation shows, 3-methyl-1-butanol (also called isoamyl alcohol or isopentyl alcohol) was mixed with an excess of acetic acid (ethanoic acid by its systematic name) and a trace of sulfuric acid (which serves as a catalyst). This reaction is an equilibrium reaction, so it is expected that not all of the starting materials will be consumed. The equilibrium should lie quite far to the right due to the excess of acetic acid used, but not completely.
After an appropriate length of time, isolation of the desired product from the reaction mixture was begun by adding a volume of 5% aqueous sodium bicarbonate (NaHCO3 has an effective pKa of 7) roughly equal to the volume of the reaction mixture. Bubbling occurred and a mixture consisting of two layers resulted—a basic aqueous layer and an organic layer. The layers were separated and the aqueous layer was removed. The addition of aqueous sodium bicarbonate to the layer of organic materials and separation of the layers were repeated twice. Each time the predominantly aqueous layers were removed, they were combined in the same collection flask. The organic layer that remained after the three bicarbonate extractions was dried and then subjected to distillation in order to obtain a pure sample of 3-methylbutyl ethanoate (isoamyl acetate).
Use a table of pKa values to estimate pKa values for any of the potentially acidic hydrogens in each of the following species, which are likely to be present at the end of the reaction but before adding aqueous NaHCO3.
Explain, on the basis of polarities and solubility, why separate layers formed when aqueous sodium bicarbonate was added to the reaction mixture. (Hint: Most sodium salts of organic acids are soluble in water, as are neutral oxygen-containing organic compounds of four carbons or less.)
Choose the chemical species likely to be present after the reaction with NaHCO3 in the organic layer.
Choose the chemical species likely to be present after the reaction with NaHCO3 in the aqueous layer.
Why was the aqueous sodium bicarbonate extraction step repeated three times?
Because 3-methyl-1-butanol is miscible in both the organic layer and the aqueous phase.
**NOTE: MORE THAN ONE POSSIBLE ANSWER FOR FIRST 3 QUESTIONS**
Suppose you carried out the following synthesis of 3-methylbutyl ethanoate (isoamyl acetate):
As the chemical equation shows, 3-methyl-1-butanol (also called isoamyl alcohol or isopentyl alcohol) was mixed with an excess of acetic acid (ethanoic acid by its systematic name) and a trace of sulfuric acid (which serves as a catalyst). This reaction is an equilibrium reaction, so it is expected that not all of the starting materials will be consumed. The equilibrium should lie quite far to the right due to the excess of acetic acid used, but not completely.
After an appropriate length of time, isolation of the desired product from the reaction mixture was begun by adding a volume of 5% aqueous sodium bicarbonate (NaHCO3 has an effective pKa of 7) roughly equal to the volume of the reaction mixture. Bubbling occurred and a mixture consisting of two layers resulted—a basic aqueous layer and an organic layer. The layers were separated and the aqueous layer was removed. The addition of aqueous sodium bicarbonate to the layer of organic materials and separation of the layers were repeated twice. Each time the predominantly aqueous layers were removed, they were combined in the same collection flask. The organic layer that remained after the three bicarbonate extractions was dried and then subjected to distillation in order to obtain a pure sample of 3-methylbutyl ethanoate (isoamyl acetate).
Use a table of pKa values to estimate pKa values for any of the potentially acidic hydrogens in each of the following species, which are likely to be present at the end of the reaction but before adding aqueous NaHCO3.
Explanation / Answer
Part:A
When water is present, energy supplied by formation of hydrogen bonds and ion-dipole forces is great enough to overcome the intermolecular forces between the polar solutes.
Part:B
The species which are slightly polar/ completely non polar will be in organic layer. Therefore -
3-methyl-1-butanol,
3-methylbutyl ethanoate
The above species will be present in the organic layer.
Part:C
Because a buffer solution is established when sodium bicarbonate is added, requiring multiple additions of base in order to neutralize the final solution.
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