Synthesis Reaction Lab Report

Discussion

The fifth experiment of the semester entails a synthesis reaction geared towards analyzing the structure of a product. The starting material is isopentyl alcohol. When reacted with acetic acid with sulfuric acid as a solvent, isopentyl alcohol produces isopentyl acetate, which is the goal product, as shown in the reaction below:

Once isopentyl acetate is produced, it will become important to analyze its structure and purity.

This experiment involves performing various techniques, including heating under reflux, separation, drying, distillation, gas chromatography (GC), infrared spectroscopy (IR spectroscopy), and nuclear magnetic resonance (1H NMR). Heating under reflux is important to overcome any activation barrier of energy that may be present in order to complete the reaction.

Separation allows an organic layer to be separated from a solid following reflux, and it also permits an organic layer to separated from an aqueous layer following washings to ensure purification. Drying and distillation also help ensure purification by removing excess water and solid from the organic layer. GC, IR spectroscopy, and 1H NMR are three of many various ways available to analyze the components and structure of a compound. GC allows separation of compounds based on boiling point and attraction to materials inside of the GC. IR allows separation of compounds based on UV light. 1H NMR allows separation of compounds based on magnetic properties pertaining to hydrogen atom surroundings.
The experiment began with 13.22 grams of isopentyl alcohol, which was subsequently mixed with 17 mL of acetic acid and 1.0 mL of sulfuric acid. This mixture was refluxed under heat for approximately 50 minutes to ensure that the reaction could occur following the breaking of an activation barrier. Once reflux ended, the mixture was allowed to cool to room temperature and then poured into a separatory funnel. In the separatory funnel, the solution was washed with 50 mL of water and 60 mL (two 30 mL washes) of sodium bicarbonate. Unfortunately, following all of the washings, most of my organic solution ran out of the separatory funnel. I was left with only a few drops of my solution. Following the washings, the organic layer was dried with sodium or magnesium sulfate and separated from the solid via gravity filtration. Due to the low amount of organic solution remaining, I could not perform distillation or weigh the dried solid. I estimated that my remaining solution weighed approximately less than 1 gram, and I performed my calculations based on that estimation. Then, I proceeded to perform GC and IR spectroscopy on my remaining sample.
The results of the gas chromatography were consistent with the reaction performed. I had a small acetone peak, a large isopentyl acetate peak, and a smaller isopentyl alcohol peak; however, the acetone peak is negligible because it was simply used to wash the needle prior to GC. From my area calculations, I determined that the percent composition of isopentyl acetate for my solution was approximately 76%, whereas the percent composition of isopentyl alcohol was 24%. This chart also allowed me to determine the actual mass of my banana oil (less than 0.76 grams compared to less than 1 gram) and the actual percent yield of my banana oil (less than 76% yield). This shows that my banana oil was somewhat pure, but it was not completely pure. I think the GC would have gone better if I had more banana oil left.
In addition, the IR spectroscopy results showed that my banana oil contained a variety of different bonds. For example, it had an ester group, a C-O bond, and a carboxylic acid group; however, the IR also revealed impurities, such as an –OH group (hydroxide/alcohol). This –OH group is probably from the isopentyl alcohol. Here are the complete results of my IR spectroscopy run:
IR (cm-1): 3553.57, 3464.68, 2960.20, 2722.90, 2748.49, 2072.67, 1742.83, 1466.24, 1367.31, 1243.61, 1171.13, 1135.51, 1056.44, 961.67, 922.33, 900.69, 854.99, 818.43, 769.88, 635.40, 606.36
Please note that the IR was run with sodium chloride salt plates.
Although I did not perform a 1H NMR run myself, the results were provided for students. The 1H NMR separates compounds based on their magnetic attraction to surrounding hydrogens. The 1H NMR results are as follows:
1H NMR: (CDCl3, 200 MHz) δ 0.886 (2 H), 0.919 (2 H), 1.479 (0 H), 1.514 (1 H), 2.020 (0 H), 4.038 (3 H), 4.073 (3 H), 4.108 (3 H)
These results allowed me to confirm that the structure of isopentyl acetate is as follows:

Although I am sure of my GC results, I am unsure of my IR and the 1H NMR results. I believe I need more practice with reading the results and determining the structure of compounds.
Even though I took caution with my experiment, it was still prone to many errors. The most notable error was the spillage of my banana oil following use of the separatory funnel. Although it may not have affected the components of my organic layer, I could not perform distillation to decrease impurities in my solution. Distillation may have led to different results for the IR spectroscopy, and possibly even the GC. Also, I would have been able to weigh the solid isopentyl acetate following distillation, but this was not possible. If I had the chance, I would redo this experiment again and take extra caution with the separatory funnel. Other errors in my experiment could have been letting the solution reflux under heat for too little or too much time. If I did not reflux long enough, the reaction may not have been driven to completion. If I refluxed too long, the reaction product may have burned off. Additionally, I could have dried my product with too much or too little sodium or magnesium sulfate. If I did not dry the solution enough, excess water could have remained, which could have made my IR spectroscopy reading strange. If I dried to solution too much, the sodium or magnesium sulfate could have soaked up some of the solution, thereby decreasing the amount available for distillation, GC, and IR spectroscopy. I would need to repeat this experiment multiple times before providing any real data to ensure consistent results.
This experiment proved to involve challenging tasks, but I am beginning to grasp the concepts of GC, IR spectroscopy, and 1H NMR. Conducting a synthesis and proving its purity is difficult, and I would want to repeat this experiment again in order to obtain a more accurate result. I hope to become more comfortable with performing synthesis reactions, as well as utilizing gas chromatography, infrared spectroscopy, and nuclear magnetic resonance techniques, in future experiments.

Questions – IUPUI Custom Edition
2) Carbon dioxide escaped during the sodium bicarbonate washing.

CH3COOH + NaHCO3 ⇒ CH3COONa + CO2 + H2O

H2SO4 + 2NaHCO3 ⇒ Na2SO4 + CO2 + 2H2O

4) (a) If you failed to dry the reaction flask after washing it with water, then your newly added solution would contain water. While this could be removed through drying and distillation, there could still be some excess water. This would make your isopentyl acetate dilute. Furthermore, water would hinder the IR spectroscopy process by harming the salt plates used in the machine.

(b) If you forgot to add the sulfuric acid, then your reaction would not work. You would not produce isopentyl acetate because the sulfuric acid is required to drive the reaction forward towards isopentyl acetate.

(c) If you used twice the amount of acetic acid specified in the procedure, then there would be excess acetic acid in the solution. This may lead to a smaller yield of isopentyl acetate. It would also be very important to perform the washes with the separatory funnel diligently to get rid of the excess acetic acid, as well as distillation. You may observe an extra peak on your gas chromatograph or your IR

spectroscopy.
(d) If you left of the sodium bicarbonate washing step, then your organic layer would have a higher chance of containing impurities. You only want the isopentyl acetate, but your organic layer would most likely still contain any unreacted starting materials in excess. The sodium bicarbonate washes out any excess of these starting materials or other impurities. Thus, your organic solution would possibly be impure.
(e) If your thermometer bulb was 1 cm higher than it should have been, then you may have obtained an inaccurate temperature reading. Also, some of the solution could have escaped into the air as a gas.