Video Transcript
Which of the following is not a typical use of esters? (A) Medical drugs, (B) flavorings, (C) plastic bottles, (D) fuel for power stations, or (E) industrial solvents.
An ester is an organic compound with the general chemical formula of RCOOR prime. Within an ester, there is one carbon that has a double bond to oxygen and one single bond to oxygen. And this is known as the ester linkage. There’s also an R group attached directly to the ester linkage carbon. Chemists use the capital letter R to represent a general substituent. In this case, R can equal a hydrogen, an alkyl group, or an aryl group. And there is also an R prime group that is bonded to the oxygen of the ester linkage. This R prime group can be an alkyl or an aryl group, but you’ll notice that it cannot be a hydrogen.
Now, because the R and R prime group can have a large variety of substituents with different reactivities and inherent chemical properties, esters are used in a large number of applications. In order to answer the question at hand, let’s go through each of the answer choices and discuss whether or not esters can be used in each of the applications.
Methyl salicylate is an aromatic ester that naturally occurs in the roots of birch trees. It’s a naturally occurring derivative of the active ingredient in aspirin. And just like aspirin, it can be used to relieve muscular aches and pains as well as other rheumatic conditions. Methyl salicylate is just one example of the numerous esters that are used as medical drugs. And since the question is asking which of the following is not a typical use of esters, we know that the answer cannot be (A).
Esters are also commonly found in fruits and vegetables and tend to be very fragrant. So they are a major contributor to what you smell and therefore taste in fresh foods. For example, ethyl pentanoate is a fragrant ester, and it’s a major component in what makes apples smell and taste like apples. Because scientists are able to discern which chemical components give foods their distinct flavors, they use that information to synthesize molecules like ethyl pentanoate in a lab, making flavorings. And so we know that answer choice (B) cannot be the correct answer.
Polyester is one of the most commonly made industrial plastics in the world. It’s made by reacting terephthalic acid with ethylene glycol. And when a large number of these two molecules are reacted with acid and heat, the polymer, known as polyester, is created. And as the name suggests, polyester is an ester plastic that’s used to make clothing fibers and plastic items, such as water bottles. And so we can eliminate answer choice (C).
Most power stations in the world burn fossil fuels, such as coal, oil, and natural gas, to generate electricity. Each of these fuel sources is made up of hydrocarbon components, which burn easily. An example of one such hydrocarbon is methane, or CH4. Methane is the primary component in natural gas. But as you can see, in this hydrocarbon, as well as in the longer hydrocarbon chains that make up coal and oil, there are no ester linkages. And because we know that hydrocarbons are used as fuel for most power stations, we can correctly choose answer choice (D), because it is not a typical use of esters.
To confirm answer choice (D) as the correct answer, let’s take a look at (E) and consider the case of ethyl acetate. Ethyl acetate is a very commonly used industrial solvent. It’s used as a solvent because of its polarity due to the fact that it has multiple carbon-oxygen bonds. But it dissolves many organic compounds due to the alkyl R and R prime groups. Ethyl acetate also has a relatively low boiling point of 77 degrees Celsius. These characteristics make ethyl acetate a great choice as an industrial solvent. And so we can eliminate answer choice (E).