Video Transcript
Aspirin is one of the most widely
used medicines globally. The structure of aspirin is
shown. In moist conditions, aspirin can
undergo hydrolysis to form salicylic acid and another acid. Which of the following structures
is that of salicylic acid?
We’ve been given the structure of
aspirin, also called acetylsalicylic acid. A molecule of aspirin contains a
benzene ring which has a carboxylic acid substituent and an ester substituent. We are told that aspirin can
undergo hydrolysis. Hydrolysis is a chemical reaction
where water reacts with a compound breaking one or more bonds. Benzene rings and carboxylic acids
cannot undergo hydrolysis, but esters can.
Ester hydrolysis may be
acid-catalyzed or base-induced. The question does not specify if
the hydrolysis of aspirin is occurring in an acid or a base. But as aspirin is an acid, it could
act as both a reactant and a catalyst in the hydrolysis reaction. So, we should take a look at what
occurs during acid-catalyzed ester hydrolysis. During this reaction, the
carbon-oxygen single bond of the ester is broken and the hydroxy group of a water
molecule replaces the alkoxy group of the ester. This produces a carboxylic acid and
an alcohol.
Looking at the structure of
aspirin, we can identify the carbon-oxygen single bond of the ester. This is the bond that will be
broken during hydrolysis. The alkoxy portion of the ester
shown in blue can be replaced by the hydroxy group of a water molecule. Two molecules will be produced when
aspirin is hydrolyzed. One molecule will contain a
carboxylic acid group that was present in the original aspirin molecule and a newly
formed hydroxy group. The second molecule will contain a
newly formed carboxylic acid group. We know from the question that the
products of the hydrolysis of aspirin are salicylic acid and another unnamed
acid. We need to determine which of the
answer choices is salicylic acid.
We can see that each of the answer
choices contain a benzene ring. This indicates that the product of
the hydrolysis of aspirin that contains a benzene ring is salicylic acid. Comparing the structure to the
answer choices, we see that the structure that is the same is answer choice (C). Thus, the answer to the question
“Which of the following structures is that of salicylic acid?” is (C).
For the next part of the question,
we’ll keep only the relevant information on screen.
What is the name of the other acid
produced? (A) Butanoic acid, (B) methanoic
acid, (C) benzoic acid, (D) ethanoic acid, (E) propanoic acid.
The question is asking us to name
this molecule, which is a carboxylic acid. To name a carboxylic acid, we first
name the longest continuous chain of carbon atoms that contains the carboxyl
carbon. The carboxyl carbon is the carbon
of the carboxylic acid. The longest continuous chain of
carbon atoms that contains the carboxyl carbon is two carbon atoms long. This carbon chain is given the name
ethane, eth- meaning two carbon atoms and -ane for alkane.
Next, we drop the letter e from the
end of the name and add the suffix -oic acid, indicating that the molecule is a
carboxylic acid. This gives us the name ethanoic
acid. Thus, the answer to the question
“What is the name of the other acid produced?” is answer choice (D), ethanoic
acid.
