Organic Chemistry: Why is the nitration and sulphonation of pyridine not possible?

Organic Chemistry: Why is the nitration and sulphonation of pyridine not possible?

Thereis different chemical process that takes place and so it is important that we should understand each one of them. The nitration and sulfonation of benzene is one of the most common processes and as such it is so important that we should be able to understand the process.

Nitration and sulfonation of benzene are the two examples thatexplain the process of electrophilic aromatic substitution. In the reaction process the nitronium ion (NO2+) and sulfur trioxide (SO3) are  considered the electrophiles and  in the subsequent time they will individually react with benzene to give nitrobenzene and benzenesulfonic acid as the resultant of each one of them.

Nitration of Benzene

In the reaction we will see that in contrast to nitration of alcohols, the nitration of benzene will produce relatively stable nitro compounds that will help them to go for more reaction levels as well. Say we can say that the high-explosive TNT (2, 4, 6-trinitrotoluene) is formed by triple nitration of toluene.  There are other important components that will be formed with the nitration process as well

Here the key reagent for nitration is nitric acid, HNO3. By nature, the nitric acid is a relatively slow-acting electrophile and that too in the presence of a poor nucleophile like benzene. The source of the nitronium ion can be found through the protonation of nitric acid by introduction of sulfuric acid, this will lead to the loss of a water molecule and formation of a nitronium ion.

Sulfuric Acid Activation of Nitric Acid

 Let us understand the first step in the reaction process. In the first step, the process of the nitration of benzene is carried out so as to active HNO3with sulfuric acid to produce a stronger electrophile. This will also lead to the formation of nitronium ion that will come out of the result of the chemical process. The reaction is elaborated below:

 In the above chemical reaction we can see that since nitronium ion is a good electrophile. This will also result that it is attacked by benzene to produce Nitrobenzene.


Sulfonation of Benzene

 The sulfonation of benzene is also another process that is to be carried out. Sulfonation is said to be a reversible reaction that will produce benzenesulfonic acid. This is done by adding sulfur trioxide and fuming sulfuric acid to the chemical reaction. The reaction can only be reversed by adding hot aqueous acid to benzenesulfonic acid that will lead to the formation of benzene.


In order produce benzenesulfonic acid from benzene, the process of fuming sulfuric acid and sulfur trioxide is to be added. Fuming sulfuric acid, also known as ileum, is a concentrated solution that is of dissolved sulfur trioxide in sulfuric acid. The sulfur that is presentin thesulfur trioxide is electrophilic. This is also because the oxygenpull electrons away from it because oxygen. This makes the is very electronegative and makes the reaction process very interactive. The benzene attacks the sulfur and as result the subsequent proton transfers occur in order to produce benzenesulfonic acid.

Reverse Sulfonation

Sulfonation of benzene is also consideredas a reversible reaction. Sulfur trioxide will   readily react with water in order toproduce sulfuric acid and heat. So in the reaction process, when we add heat to benzenesulfonic acid in thediluted aqueous sulfuric acid the reaction will be reversed.

Applications of Nitration and Sulfonation

Nitration is the process that is used to add nitrogen to a benzene ring. This can be used further in substitution reactions. The nitro group in this case acts as a ring deactivator. When we have nitrogen present in a ring itis very useful because this can be used in directing group also they can be used tomask amino group. The products of aromatic nitration’sare of great import naveas intermediates in industrial chemistry.

Just because sulfonation is a reversible reaction. This can be used for the substitution reactions that will be used for directing blocking group and this is also the reason that there can be ions that can be said to be in the substitution as well. The sulfonic group blocks the carbon that is being attacked by other substituents and after the reaction is completed the ions can be removed with the help of reverse sulfonation. Benzenesulfonic acids can alsouse in the synthesis of detergents, dyes, and sulfa drugs. Benzenesulfonic Chloride is one of the most important drugs that are used in many of the medicinal purposes and they are widely used for other commercial use as well.

Learning resource: aldehydes,ketones and carboxylic acids from class 12 chemistry – find all the questions & answers

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