Synthesis of pure esters from long-chain alcohols using Fischer esterification
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Fischer esterification is straightforward when making esters from small alcohols, up to 5-carbon alcohols, because water washes can remove any remaining alcohol in workup.
Once you get to 6 carbons and higher, water washes are unable to remove the alcohol from the crude ester, and this affects the smell.
Larger esters, such as octyl acetate and nonyl acetate, have interesting smells. octyl acetate is citrus, orange, earthy, while nonyl acetate is mushroom, but the presence of residual 1-octanol and 1-nonanol can contaminate the smell.
I tried making octyl acetate and nonyl acetate, but even after washing with large amounts of water, the crude ester consistently boiled at a too low temperature, likely due to an azeotrope of ester and residual alcohol. I also smelled some of the alcohol scent in the distilled ester. It's apparent that you must have the reaction consume all the alcohol before working up.
One way is to have the reaction go to completion, so that all the alcohol is used up. Use an excess of carboxylic acid, since it can be easily neutralized to its carboxylate salt and extracted with water. Instead of using acid chlorides or anhydrides, which are harder to get, you can use the Dean-Stark method for fischer esterification, which dissolves all reactants and catalysts in toluene, and uses a Dean-stark trap to capture formed water. Removing water from the reaction will drive it nearly to completion, and an excess of carboxylic acid should ensure all alcohol is reacted. A nice thing about this method is that you can track reaction progress by looking at the volume of water in the trap, and once water stops forming, the reaction is done.
Also do vacuum distillation so that heat doesn't hydrolyze the ester.
Source: vogel's practical organic chemistry
Once you get to 6 carbons and higher, water washes are unable to remove the alcohol from the crude ester, and this affects the smell.
Larger esters, such as octyl acetate and nonyl acetate, have interesting smells. octyl acetate is citrus, orange, earthy, while nonyl acetate is mushroom, but the presence of residual 1-octanol and 1-nonanol can contaminate the smell.
I tried making octyl acetate and nonyl acetate, but even after washing with large amounts of water, the crude ester consistently boiled at a too low temperature, likely due to an azeotrope of ester and residual alcohol. I also smelled some of the alcohol scent in the distilled ester. It's apparent that you must have the reaction consume all the alcohol before working up.
One way is to have the reaction go to completion, so that all the alcohol is used up. Use an excess of carboxylic acid, since it can be easily neutralized to its carboxylate salt and extracted with water. Instead of using acid chlorides or anhydrides, which are harder to get, you can use the Dean-Stark method for fischer esterification, which dissolves all reactants and catalysts in toluene, and uses a Dean-stark trap to capture formed water. Removing water from the reaction will drive it nearly to completion, and an excess of carboxylic acid should ensure all alcohol is reacted. A nice thing about this method is that you can track reaction progress by looking at the volume of water in the trap, and once water stops forming, the reaction is done.
Also do vacuum distillation so that heat doesn't hydrolyze the ester.
Source: vogel's practical organic chemistry
