Question

The structural formula of the ester isopropyl ben- 2. zoate is CHs CH-O- CH3 (1) Write the structu ral formulas of the acid and alcohol that react to form this ester. (2) Label the structural formulas in your answer to (1) with the names of the acid and the alcohol. 3. A student wants to prepare ethyl acetate. He cor- rectly starts with ethyl alcohol, but he mistakenly com bines it with formic acid, HCO2H, rather than acetic acid. Write the structural formula and name of the es- ter formed.

Answer 1

2. (1) Esterification

Carboxylic acid reacts with alcohol to give ester and water in the presence of acidic medium is called as Esterification reaction. In the absence of acid catalyst, no reaction occurs. Though in this reaction water molecules is removed, it is considered as condensation reaction.

Carboxylic acid group react with hydroxyl group of alcohol to remove water molecules to give ester compounds.

OH^- ion from acid and H⁺ ion from alcohol combine to water molecules. Acidic medium as catalyst.

Isopropyl benzoate is formed by the reaction of isopropyl alcohol with benzoic acid in the presence of acid catalyst. The reaction scheme is given below.

HO OH Esterification + Hydrolysis isopropyl alcohol O benzoic acid isopropyl benzoate

Isopropyl benzoate cleavages

isopropyl benzoate
(or)
isopropyl benzoate

Mechanism of formation of isopropyl benzoate:

Step 1: Protonation of carbonyl oxygen in presence of acid catalyst.

НО 0 —Н benzoic acid

It makes the carbonyl group as electrophilic center.

Step 2: Carbonyl group acts as electrophile and leads to nucleophilic attack by the alcohol.

0- H OH isopropyl alcohol

Step 3: Protonation of hydroxyl group and rearrangement of bonds gives water and ester.

opbaa -H2O -H isopropyl benzoate

(2) Carboxylic acid is Benzoic acid. Structural formula is given below

benzoic acid

Alcohol used is isopropyl alcohol. Structural formula is given below

isopropyl alcohol

3. Reaction of acetic acid and ethyl alcohol gives ethyl acetate. The reaction is given below

HO— НО ethyl alcohol ethyl acetate acetic acid

Though the students unfortunately combine ethyl alcohol with formic acid instead of acetic acid, it gives ethyl formate compound. The reaction of formic acid and ethyl alcohol gives ethyl formate.

HO ethyl alcohol མ་མེ་བས། Ho o formic acid ethyl formate

Mechanism of formation of ethyl formate:

Step 1: Protonation of carbonyl oxygen in presence of acid catalyst.

It makes the carbonyl group as electrophilic center.

Step 2: Carbonyl group acts as electrophile and leads to nucleophilic attack by the alcohol.

HO O- formic acid ОН ethanol
$\rightleftharpoons$
H0 ethanol

Step 3: Protonation of hydroxyl group and rearrangement of bonds gives water and ester.

HO ethyl formate