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What is Methyl Red? - Synthesis & Structure

Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

The primary focal point of this lesson will be on a specific organic compound known as methyl red. Our main topics of discussion will include the structure of methyl red, how it's synthesized, and it's most important use.

Molecules and Food Coloring

Have you ever taken a glass of water and slowly added a drop or two of a food coloring to the glass? Once the first drop hits the water, it immediately begins to disperse until the water is eventually no longer clear and takes on whatever color you used for the coloring. What's fascinating is that the dispersion of the coloring happens all on its own with virtually no outside assistance from us.


Various food colorings in glasses of water
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Just like red food coloring will turn water into a bright red solution, did you know that there is an organic compound that is also a bright red substance and can turn solutions from colorless to red, and even yellow and orange too? The compound we're referring to is methyl red, and is going to be the focal point of our discussion today. We will be learning about methyl red in terms of its structure, how it's made synthetically, and an important use it finds application towards. Let's get to coloring!

Structure of Methyl Red

Let's get started by taking a look at the structure of methyl red to get things going in the right direction. Methyl red is an organic compound, which means that it is primarily constructed of carbon and hydrogen atoms, but contains nitrogen and oxygen atoms as well. It contains several important structural features, which in organic chemistry are referred to as functional groups. First notice the two rings of the molecule that have double bonds inside of them. These are called aromatic or benzene rings. The two aromatic rings are connected to one another by two nitrogen atoms, which is known as an azo group.


Structure of methyl red showing all of the relevant functional groups within the molecule
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Methyl red also contains a carboxylic acid functional group (-COOH), which helps to explain its ability to serve as an acid or hydrogen ion source. Directly on the other side of the molecule from the carboxylic acid group, we find a nitrogen atom connected to two methyl (-CH3) groups, which is called an amine functional group. In organic chemistry, amines can act as bases, which means they can serve as hydrogen ion acceptors.

Synthesis of Methyl Red

Let's now transition into talking about how methyl red is synthesized in the lab by organic chemists. Even though it looks like a rather complicated and complex molecule, chemists have devised a way to synthesize methyl red in only two simple steps that utilize cheap and commercially available starting materials.

In the first step of the synthesis, anthranilic acid is reacted with hydrochloric acid (HCl) and sodium nitrite (NaNO2) to produce an intermediate compound called a diazonium salt. Once the diazonium salt is formed, the second step involves reaction with a compound known as dimethylaniline which actually gives methyl red as the final product!


The preparation of methyl red involves two simple synthetic steps from commercially available starting materials
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Syntheses such as the one involving methyl red can be extremely useful to organic chemists, mainly because they allow them construct rather large and complex molecules economically and with only a few steps.

What is Methyl Red Used For?

Now that we know about the general structure of methyl red and how it's made, what exactly is it good for in terms of use? Remember when we learned that it has both an amine functional group as well as a carboxylic acid? It turns out that the presence of both an acidic and basic functional group allows it to act as a pH indicator in solutions. The pH of a solution is a way chemists talk about the relative acidity (or basicity) of a given solution.

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