Lab 8: Fischer Esterification

is Fischer is acidic or basic conditions

acidic

what is the nucleophile and electrophile

nucleophile: alchol

electrophile: carboxylic acid

what are the two ways of increasing product in this reaction?

1. removing water/product as it forms

2. use an excess of one of the reactants

for this experiment, which method are we choosing to drive this reaction forward

using excess of the aldehyde/carboxylic acid

what is the carboxylic acid portion of this experiment

acetic acid

techniques

microwave reflux, liquid liquid extraction, decanting, IR, and HNMR

reagents

Glacial acetic acid (structure, MW, BP, density)
Sulfuric acid (structure, MW, BP, density)
Each unknown alcohol(s) provided by TA (structure, MW, BP, density)
5% Sodium bicarbonate (structure, MW, MP)
Sodium sulfate (structure, MW, MP)
Brine (structure, MW, BP, density)
Water (structure, MW, BP, density)
Each product ester(s) based on unknown alcohol (structure, MW, BP, density

explain procedure on broad terms

1. add glacial acetic acid and alcohol to your MW vessel then add concentrated sulfuric acid

2. let the 10 minutes reaction occur

3. take contents out and add water. remove the aqueous layer (ester is in organic)

4. wash ester with water and then 5% sodium bicarbonate until you get a basic solution (aqueous should be basic)

5. wash ester with brine

6. add sodium sulfate to dry

what kind of alcohols are we using

primary or secondary in the presence of acid catalyst

what is the purpose of the acid catalyst

enhance the electrophilic nature of the carboxylic acid’s carbonyl moiety

true or false: the catalyst changes the equilibrium of the reaction

false: it only increases the rate it achieves equilibrium but not the actual equilibrium itself

what are the three alcohol options here? what about the carboxylic acid?

alcohol: 1-propanol, 1-butanol, isopentanol

carboxylic acid: glacial acetic acid

Draw the skeletal structure of the product resulting from the Fischer esterification of sec-butanol and propionic acid.

balanced equation

reminder 2:1 ratio of carboxylic acid and alcohol

mechanism

remember we are in acidic conditions so the carbonyl will get protonated, nucleophilic attack by oxygen, the H on the nucleophile gets deprotonated, one of the OH groups gets protonated, water leaves as a LG, electrons from the other OH form the double bond, and the H on the new carbonyl gets deprotonated

limiting reagent

unknown alcohol

how can you tell your reaction went to completion

1. disappearance of OH group (broad peak around 3200-3400)

2. newly formed carbonyl group (C=O around 1720)

3. C-O bond around 1200 but in fingerprint region

Provide a brief description of how the microwave works in the context of this reaction. How does it supply heat/energy to the reaction solution? What does it mean for a reaction to be “microwave-promoted?”

the microwave accelerates the reaction and increases the yield because

1. rapid uniform radiation

2. interaction of polar molecules with the electromagnetic field

3. oscillating electromagnetic field allows for polar molecules to rote and be properly oriented for the reaction + higher collision rate

Explain how concentrated sulfuric acid catalyzes the Fischer esterification reaction. You must draw reactive intermediate structures to help explain your reasoning:

the protonation of the carbonyl is needed because it makes it more susceptible to a nucleophilic attack by the weak nucleophile (alcohol). also, the sulfuric acid is needed to protonate the OH to make water leave and to ultimately form the carbonyl

Once the initial extraction was performed (removal of the reaction mixture’s aqueous layer) how was your ester product further separated from any remaining unreacted carboxylic acid?

with 5% sodium bicarbonate because it reacts with glacial acetic acid to form a carboxylate salt, which is discarded with aqueous waste

balanced equation of how glacial acetic acid reacts with sodium bicarbonate

Provide the appropriate starting materials and reagents needed to form the following compounds via a Fischer esterification:

A. 2-methylbutyl 3-methylcyclohexane-1-carboxylate

B. 2-cyclohexylethyl 3,5-dimethylhexanoate

Provide the appropriate starting materials and/or product(s) needed to complete the following Fischer esterification reaction schemes: