Acylation: Process & Agents

Instructor: Korry Barnes

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

In this lesson we will be learning about the concept in organic chemistry called acylation. We will get a brief introduction as to what acylation is and then spend most of our time discussing acylation reactions and the reagents used for the transformations.

A Remedy as Old as Time (Almost)

When you have a headache, what's your go-to pill from the medicine cabinet? Although we have a lot of choices available to us to help treat short-term mild to moderate pain, a lot of people choose aspirin as their remedy. What most people don't know is that ancient civilizations have been using plants rich in aspirin-like compounds dating back to as early as 400 B.C. Now that's a remedy that has stood the test of time!

Aspirin itself is actually an acylated version of a compound known as salicylic acid. The true name of aspirin therefore is acetylsalicylic acid. Simple enough right? I'm afraid not. What does ''acylated'' mean? How does it work? That's exactly what we are going to discuss today: the process known as acylation. We'll start with a definition, move on to talking about some common acylating reagents, and then discuss a few common acylation reactions in organic chemistry.

What is Acylation?

Obviously the first thing we need to get out of the way is what acylation actually is. Acylation is an organic reaction that involves adding an acyl group to an organic substrate. Alright, but what's an acyl group? An acyl group is a carbon double bonded to an oxygen and also a -CH3. There are several different acylating agents available for an organic chemist to use, but notice that in the reaction below the acylating agent is labeled and how the end product has the acyl group bonded to the substrate. That's the general form of any acylation: organic substrate + acylating agent = acylated organic substrate.

General acylation reaction

Common Acylating Reagents

As we mentioned before, there are several acylating agents (reagents that supply the acyl group) available for one to use, but let's talk about a couple here. One common reagent is called an acyl chloride. An acyl chloride is when a carboxylic acid is converted to an acid chloride (which is the same thing as acyl chloride) by the action of thionyl chloride SOCl2. Due to the electronegative nature of both the chlorine and oxygen, an acyl chloride is extremely reactive and a great acylating agent.

Formation of an acyl chloride

Another very common reagent that's used to supply an acyl group is acetic anhydride. The carbonyl group (carbon-oxygen double bonded carbon) is very reactive and ready to donate an acyl group due to the nature of the anhydride functionality.

Acetic anhydride as an acylating agent

Common Acylation Reactions

Acylation of Ammonia and Amines

Both ammonia and primary amines (organic amines) react with acyl chlorides or acetic anhydride to give functional groups called amides. Amides are useful building blocks in the fields of materials and pharmaceuticals so this reaction is of great importance.

Acylation of ammonia and primary amines

Acylation of Water and Alcohols

Water and organic alcohols react with acyl chlorides and acetic anhydrides very similarly to ammonia and amines; the only difference is that the products are carboxylic acids if they react with water or esters if they react with alcohols. Esters find substantial application in the cosmetics and perfume industries.

Acylation of organic alcohols and water

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