I hope You all like it. I hope It is very beneficial for you all. I really thought that you all get enough knowledge from this presentation. This presentation is about materials and their classifications. After you read this presentation you knowledge is not as before.

1. Presented by: Asad Raza
Roll No. :16102331-004

2. Contents:
 Definition
 General introduction
 General reaction
 Formation of electrophile
 Mechanism of sulphonation
 Stage 1
 Diagrammatic description
 Stage 2
 Diagrammatic description
 Reverse sulphonation

3. Definition:
 The introduction of sulphonic acid group in benzene
ring is called sulphonation.
 When benzene is heated with fuming sulphuric acid
or concentrated sulphuric acid it yields benzene
sulphonic acid.

4. General introduction:
 Unlike other electrophilic substitution reactions
sulphonation is a reversible reaction .
 Removal of water from the system favours the
formation of sulphonation product.
 Heating a sulphonic acid with aqueous sulphuric acid
can result be the reverse reaction desulphonation.
 The actual electrophile in this reaction is sulphur
trioxide.
 The sulphur in sulphur trioxide is electrophile because
oxygen pulls electron from it as oxygen is
electronegative.

5. General reaction:

6. The formation of electrophile:
 The sulphur trioxide electrophile arises in one of two
ways depending on which sort of acid you are using.
 Concentrated sulphuric acid contains traces of
SO3 due to slight dissociation of the acid.
 Fuming sulphuric acid, H2S2O7, can be thought of as a
solution of SO3 in sulphuric acid - and so is a much
richer source of the SO3.
 Sulphur trioxide is an electrophile because it is a
highly polar molecule with a fair amount of positive
charge on the sulphur atom. It is this which is attracted
to the ring electrons.

7. Mechanism of sulphonation:
 Stage 1:
 Two electrons from the delocalized system are used to
form a new bond with the slightly positive sulphur
atom. Because those two electrons aren't a part of the
delocalised system any longer, the delocalization is
partly broken, and in the process the ring gains a
positive charge.
 To make room for the new bond between the ring and
the sulphur, two of the electrons joining the sulphur to
one of the oxygen's are forced right out on to the
oxygen atom, giving it a negative charge.

8. Diagrammatic description:
 Stage 1:
 The hydrogen shown on the ring is the one which was
already attached to that top carbon atom. We need to show
it there because it has to be removed in the second stage.

9. Mechanism of sulphonation:
 Stage 2:
 This second step is different from all the other benzene
electrophilic substitution reactions you might have
already looked at on this site.
 This time there isn't a separate negative ion to remove
the hydrogen atom from the ring. Instead it is removed
by a lone pair on the negative oxygen atom.

10. Diagrammatic description:
 Stage 2:
 The lone pair forms a bond with the hydrogen atom,
releasing the electrons in the hydrogen-to-ring bond
so that they can re-establish the delocalization.