Synthesis of banana oil
this is my discussion and below it is the professors comments.Can you correct it for me?
Discussion:
           The purpose of the experiment performed was to synthesize isopentylacetate, or more commonly known as banana oil, from isopentylalcohol and glacial acetic acid. Both liquids were combined andremained clear until the addition of concentrated sulfuric acid.The addition of an acid caused a reaction to occur that resulted ina polymer, which gave the mixture color. The liquid turned darkbrown when the polymer formed. The polymer was removed viadistillation.
           After creating the ester, the biggest challenge was separating itfrom all the other chemicals in the flask, which include water,acetic acid, sulfuric acid, and isopentyl alcohol. The isopentylacetate is not soluble in water; so two layers are created in theseparatory funnel. While the product will not dissolve in water,both acetic acid and sulfuric acid are. Since the acids are alsoslightly in the organic layer, sodium bicarbonate is used toconvert the acids into a salt, which is soluble in water, as seenin Figure 2. The sodium bicarbonate reaction also produces carbonicacid, which is unstable and will break down into water andCO2 as seen in Figure 3. The little amount of unreactedisopentyl alcohol is separated by removing the first ten drops ofproduct during the distillation. This is possible because it has alower boiling point then the ester that is produced.
           This whole reaction was first done and called the Fischeresterification. The general reaction scheme can be seen above. Inthe experiment, isopentyl alcohol and acetic acid react in thepresence of sulfuric acid to form isopentyl acetate. This reactionmechanism can be seen below in Figure 5.
Figure 5 – Fischer esterification mechanism
In the reaction above, Acetic acid takes a proton fromconcentrated sulfuric acid. Then it reacts with isopropentylalcohol. Delocalization of electrons and protons in later stepsleads to elimination of water molecule to form final product.
           During the distillation, the temperature was recorded for theboiling point of isopentyl acetate. It was found to be at 129degrees Celsius. This is low compared to the literature value of142 degrees Celsius. This difference is believed to be due to thedifferent typed of thermometers used to record the boiling point.The literature value most likely used a mercury thermometer, whilethe experiment performed used an alcohol thermometer. Alcoholthermometers are not as accurate as mercury thermometers, but haveto be used due a law banning mercury thermometers in the state ofNew Jersey. Because of this, not much can be said about the purityof the substance obtained.
           While an NMR was not taking during the experiment, nor was an IRspectrum, attached is both an NMR example and an IR example ofisopentyl acetate. On the NMR sheet, all hydrogen peaks are labeledon a drawing of the molecule, and all the information is written inthe chart. On the IR sheet, peaks above 1500 cm-1 arelabeled for what they are believed to be. While the pictures werefound from a reputable source, they were not from the experimentperformed so one cannot be perfectly sure that the desiredsubstance was obtained.
           The last topic for the reaction was the product loss. Most organicreactions are not perfect and have relatively low yields. The 42percent yield was most likely due to side reactions occurring inthe flask. Since there were several chemicals in the flasktogether, side reactions are bound to occur, creating a loweryield. For example, a polymer was formed which changed the color ofthe flask. This was not intended to happen so this reaction loweredthe yield of the experiment.
professors comments.
You need to explain what substances should have been in theflask at the end of refluxing. Show a flow
diagram of the purification process. You did an extraction, adrying and a distillation.
Alcohol thermometers are quite accurate in the range they aredesigned to function. This type of
alcohol thermometer was not designed to work around 142 degreesC.
Treat the NMR and IR spectra as if they were obtained by you foryour product. You should have tables
in your Results Section for IR, NMR and GC. You should discussthese results in more detail in the
discussion. What do we learn from each measurement.
Give more details of the many causes for obtaining less than100% Yield.
Discuss whether this experiment is a good example of GreenChemistry. Does the Atom efficiency make
it a good candidate. Does the Reaction efficiency make it a goodexample of Green chemistry. What
about other things.
