Week 11: “Synthesis of Aromatic Esters”

Source(s): This lab was developed from a recent JCE article: 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. This, of course, is a version of the ever-popular “banana-oil” lab found in a multitude of laboratory manuals such as: Pavia D. L.; Lampman G. M.; Kriz G. S. “Introduction to Organic Laboratory Techniques: a contemporary approach” 1st edition 1976 W. B. Saunders Company.

Changes to published procedure
In this lab we were aiming to synthesize three “novel” aromatic esters: propyl 4-methoxycinnamate, propyl 4-methylbenzoate, propyl 2-methylbenzoate.
These are novel in the sense, that there is currently no chemical information for these compounds in “chemspider” nor “emolecules” databases.
We added a large excess of 1-propanol to push the equilibrium towards the products.

Positive
+ Simple procedure, the emphasis was more on characterizing novel compounds.
+ The products smell okay – olfactory confirmation of a successful synthesis.

Neutral
± At first, I recommended too little alcohol and some unfortunate side reactions happened between the carboxylic acid and sulfuric acid.
± To my surprise, the products were liquids at room temperature. I was expecting some waxy solids.

Negative
– An additional purification step is needed. Vacuum distillation? Column chromatography?
– Our instruments and skills are pretty limited to do much characterization: I will have to outsource the MS and NMR data.

Inquiry & Extension ideas.
● A combinatorial scheme projects the synthesis of hundreds of novel esters from carboxylic acids and alcohols ordered from Aldrich.
● Milder conditions would make the use of secondary alcohols possible.

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