Video Transcript
The following equation describes an
esterification reaction. Propanoic acid plus ethanol are in
equilibrium with X plus water. What is the name of the
unidentified ester product? (A) Ethyl ethanoate, (B) propyl
ethanoate, (C) ethyl propanoate, (D) propyl propanoate, or (E) methyl
propanoate.
Esterification is a type of
chemical reaction where an ester is formed. In the chemical equation provided,
X represents the ester. To answer the question, we need to
determine the name of this ester product. But first, we’ll need to determine
its structure. To do this, let’s take a look at
the reactants propanoic acid and ethanol.
The structure of propanoic acid
contains a carboxyl group. And the name ends in “-oic
acid.” These are both indicators that
propanoic acid is a carboxylic acid. The structure of ethanol contains a
hydroxy group, and the name ends in O-L. These are both indicators that
ethanol is an alcohol. Now that we know that this
esterification reaction involves a carboxylic acid and an alcohol, let’s take a look
at how this type of reaction works.
This type of esterification is
often performed in the presence of an acid catalyst like sulfuric acid and is known
more specifically as Fischer esterification. During this reaction, the hydroxy
group of the carboxylic acid is replaced by the alkoxy portion of the alcohol. This produces an ester and
water. With this in mind, let’s take a
look at the original equation.
We know that during this reaction,
the hydroxy group of the carboxylic acid, propanoic acid, will be replaced by the
alkoxy portion of the alcohol, ethanol. The hydroxy group will become a
part of the water molecule, and the rest of the propanoic acid molecule will become
a part of the ester. So the unidentified ester product X
has this structure.
Now we need to name this ester. The name of an ester is derived
from the parent carboxylic acid and alcohol. To determine the name of an ester,
we need to change the endings of the parent names. We’ll change the ending of the
carboxylic acid name to -ate and the ending of the alcohol name to Y-L. So propanoic acid becomes
propanoate, and ethanol becomes ethyl.
To complete the name of the ester,
we write the portion of the name which was derived from the alcohol first followed
by the name that was derived from the carboxylic acid. So the name of the ester is ethyl
propanoate. Therefore, the esterification
reaction between propanoic acid and ethanol produces the ester ethyl propanoate,
answer choice (C).
