I. Pre-Lab Report
A. Introduction
The purpose of this experiment is to convert benzoic acid to methyl benzoate via an acid catalyzed reaction with methanol. The reaction will be prepared by Fischer esterification, which involves the reaction reaching equilibrium after refluxing for a few hours. The purity of the benzoate will then be determined using infrared spectroscopy.
B. Main Reaction
Benzoic Acid + Methanol —> Methyl Benzoate + Water
C. Mechanism
Refer to the attached sheet.
D. Side Reactions
There are no side reactions.
E. Table of Reactants and Product(s)
| Compound | Molecular Weight (g/mol) | Amount Used | Moles Used (mol) | Melting Point (ºC) | Boiling Point (ºC) | Hazards |
| Benzoic Acid | 122.21 | 10 g | 0.082 | 122.4 | 249.0 | Irritant |
| Methanol | 32.04 | 25 mL | 0.62 | -97.0 | 64.7 | Flammable, Toxic |
| Methyl Benzoate | 136.15 | -12.5 | 199.6 | None | ||
| Sulfuric Acid | 98.087 | 3 mL | 10.0 | 290.0 | Corrosive | |
| Dichloromethane | 84.93 | 50 mL | -96.7 | 39.0 | Carcinogen | |
| Sodium Bicarbonate | 84.007 | 40 mL | 50.0 | Irritant | ||
| Hydrochloric Acid | 36.46 | -26.0 | 110.0 | Corrosive |
II. Post-Lab Report
A. Experimental Procedure
The experimental procedure was followed pretty much as written. One change made was that an additional 15 mL of dichloromethane was added to the final dichloromethane solution because it was too concentrated. The one other change was that the IR spectrum of methyl benzoate was not taken.
B. Observed Yield of Product
Weight of benzoic acid: 10.008 g
Weight of distilled methyl benzoate: 6.274 g
Percent recovery: 62.69%
C. Calculations
(Weight of distilled methyl benzoate) / (Weight of benzoic acid) * 100 = Percent recovery
D. Conclusions
The percent recovery of methyl benzoate for the experiment was 62.69%. The theoretically yield for the experiment is 85%, so the percent recovery was low. Different factors could have contributed to this. First off, a small amount of the weighed benzoic acid did not make into the 100 mL round-bottomed flask. This means the actual starting amount was slightly lower than measured. While separating the layers, it gauge when to close the stopcock perfectly, so that led to a loss of eventual product. Also, while separating the layers, there was some emulsion during mixing, so again eventual product may have been lost because the layers did not completely separate. Lastly, if the concentration of methanol was higher, that would have also led to a higher percent yield.
If water was removed from the reaction mixture, it was cause equilibrium to shift towards methyl benzoate to make water and thus lead to an increased conversion of benzoic acid to methyl benzoate. When a compound on one side of the reaction is removed, equilibrium will shift towards the side it was removed from. If more of a compound is added to one side, then equilibrium will shift towards the other side.
