Difference Between Sulfonation and Sulfation

Main Difference – Sulfonation vs Sulfation

Sulfonation and sulfation are two chemical reactions that add or substitute sulfur-containing groups into molecules. These processes are major industrial chemical processes that are used to make a wide variety of products. Sulfonation is the process of preparing organic sulfonic acids. In this process, compounds like sulfur trioxide, sulfuric acid and chlorosulfuric acid react with organic compounds. Sulfation is also an important chemical process that involves the formation of a C-O-S bond. The main difference between Sulfonation and Sulfation is that Sulfonation involves the formation of a C-S bond whereas Sulfation involves the formation of a C-O-S bond.

Key Areas Covered

1. What is Sulfonation
     – Definition, Controlling the Reaction, Industrial Production
2. What is Sulfation
     – Definition, Reactions, End Product
3. What is the Difference Between Sulfonation and Sulfation
     – Comparison of Key Differences

Key Terms: Chlorosulfuric Acid, Sulfate, Sulfation, Sulfonate, Sulfonation, Sulfonic Acid, Sulfuric Acid, Sulfur Trioxide

What is Sulfonation

Sulfonation is the process of directly attaching the sulfonic acid group, –SO₃H, to carbon in an organic compound. The final product of the Sulfonation process is called the sulfonate. Sulfonation involves an organic compound reacting with a sulfur-containing acidic compound such as sulfur trioxide (SO₃), sulfuric acid (H₂SO₄) or chlorosulfuric acid.

Sulfonation reactions form a C-S bond between one of the carbon atoms of the organic compound and the sulfur atom of the sulfur-containing compound. The final compound is an acidic compound and is categorized as a sulfonic acid. After the production, sulfonic acids can be isolated and stored due to their stability.  

Figure 1: Benzene Sulfonation

Sulfonation reaction is very difficult to be used in industrial scale because it is a very rapid and extreme exothermic reaction. Most organic compounds form a black char when contacted with sulfur trioxide due to this rapid reaction and heat formation. The viscosity of organic compounds is also highly increased when it is converted into a sulfonic acid via sulfonation. When the viscosity is increased, it is difficult to remove heat from the reaction mixture. Therefore, a proper cooling operation is required. If not, unfavorable byproducts may form from side reactions. Due to these reasons, industrial-scale sulfonation reactions require special equipment.

On the other hand, the rapidity of the sulfonation reaction can be moderated by controlling the reactivity of sulfur trioxide. This can be done in two ways:

1. Diluting
2. Complexing

Complexing of sulfur trioxide can be done by following methods.

• Making sulfamic acid by reacting sulfur trioxide with ammonia
• Making chlorosulfuric acid by reacting sulfur trioxide with HCl
• Making Oleum by reacting sulfur trioxide with water

Therefore the sulfation process can be carried out using one or some of these compounds. But when choosing the type of compound for sulfonation process in industrial productions, several factors should be considered. Some examples are given below.

• Desired final product and its quality
• Required production capacity
• Reagent cost
• Equipment cost
• Cost of waste disposal.

What is Sulfation

Sulfation is the replacement of a hydrogen atom of an organic compound with a sulfate (-OSO₂OH) functional group. This process involves the formation of a C-O-S bond. But the final product (called sulfate) is not a stable product. It easily decomposes to form sulfuric acid and another compound. Therefore, after the progression of sulfation, the system should be neutralized.

Figure 2: The Compound inside the Red Colored Circle is a Product of the Sulfation in this System.

The above image shows a sulfation reaction. Since the system is not neutralized properly, the product of the sulfation process has been decomposed back to form sulfuric acid. Sulfates, due to their instability, are only available as neutral compounds.

In biochemistry, sulfation is the enzyme-catalyzed conjugation of a sulfo group to another molecule. The enzyme involved in this reaction is called sulfotransferase.

Difference Between Sulfonation and Sulfation

Definition

Sulfonation: Sulfonation is the process of attaching the sulfonic acid group, –SO₃H, directly to carbon in an organic compound.

Sulfation: Sulfation is the replacement of a hydrogen atom of an organic compound with a sulfate (-OSO₂OH) functional group.

Bond Formation

Sulfonation: Sulfonation forms a C-S bond.

Sulfation: Sulfation forms a C-O-S bond.

Stability

Sulfonation: The end product of Sulfonation is stable.

Sulfation: The end product of Sulfation is unstable.

Naming

Sulfonation: End product of Sulfonation is called a sulfonate or a sulfonic acid.

Sulfation: End product of Sulfonation is called a sulfate.

Availability

Sulfonation: Sulfonates are available as a pure compound that has been isolated from the reaction mixture.

Sulfation: Sulfates are available only as neutral compounds due to the instability.

Conclusion

Sulfonation and sulfation are two important chemical processes used in many industries to add a sulfur-containing group to an organic compound. The main difference between sulfonation and sulfation is that sulfonation involves the formation of a C-S bond whereas sulfation involves the formation of a C-O-S bond.

Reference:

1. “Sulfonation.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 25 Feb. 2015, Available here.
2. “Sulfonation.” Dictionary.com, Dictionary.com, Available here.
3. “The Sulfonation of Benzene.” Chemistry LibreTexts, Libretexts, 2 May 2017, Available here.
4. “Sulfation.” Wikipedia, Wikimedia Foundation, 1 Dec. 2017, Available here.

Image Courtesy:

1. “BenzeneSulfonation” By V8rik at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Electrophilic reaction of sulfuric acid with ethene” By Calvero. – Selfmade with ChemDraw (Public Domain) via Commons Wikimedia