Week 10: Synthesis of Isopentyl Acetate (Banana Oil)

1) Source(s) This lab was developed by a team of students from a website: “Preparation of Banana Oil” http://cas.bellarmine.edu/chem116a/lab/banana_oil.htm. Many websites and lab manuals have versions of this very same experiment. I performed this experiment in 1979 from Pavia D. L.; Lampman G. M.; Kriz G. S. “Introduction to Organic Laboratory Techniques: a contemporary approach” 1st edition 1976 W. B. Saunders Company.

2) Changes to published procedure
We used 9 mL of isopentyl alcohol (3-methyl-1-butanol), 12 ml acetic acid, and 3 mL H2SO4.
Reflux was done for 40 min.
The routine liquid-liquid washings were done.
The ester was distilled to its final purified form.
We performed an IR spectrum of the products.

3) Positive
+ A classic experiment that covers an important reaction.
+ The product is easy to put between salt plates for the IR.
+ It smells nice. Well, about as nice as any organic chemistry experiment is going to smell.

4) Neutral
± It seems like a lot of acid is needed. Isn’t excess acetic acid enough acid?
± During reflux the mixture turns a dark color. Is this because of impurities in the alcohol?

5) Negative
– This would be much more interesting if the students could mix-and-match several alcohols and carboxylic acids. Wade P.A.; Rutkowsky S.A.; King D.B. A simple combinatorial experiment based on Fischer esterification – An experiment suitable for the first-semester organic chemistry lab. J Chemical Education 2006, 83(6), 927-928.

6) Inquiry & Extension ideas.
● The combinatorial approach is very cool. Any carboxylic acid matched with a primary alcohol should give a decent yield. At a certain point it would be impractical to distill the resulting esters, possibly.
● Acid-catalyzed reactions have the option of changing the acid.
● Acid-catalyzed reactions always have the possibility of interesting side reactions occurring: eliminations, polymerization, etc…

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