Side chain oxidation Lab 2

Side chain It’s the aliphatic portion of the alkylbenzene.

Benzylic Radicals and Cations Free Radicals: An atom or group of atoms that has at least one unpaired electron,so: Unstable Highly reactive

Benzylic Radicals and Cations Benzyl radical: is a specific name for the radical produces from the Hydrogen abstraction from the methyl group of methylbenzene (tolune).

Benzylic Radicals and Cations Benzylic radical: is the general name applies to all radicals that have unpaired electron on the side- chain carbon atom that attached directely to the benzene ring.

Benzylic Radicals and Cations Benzylic hydrogen atoms: is the hydrogen atom of the carbon atom that directly attached to the benzene ring.

Benzylic Radicals and Cations Benzylic cation: is the departure of a leaving group (LG) from a benzylic position.

Benzylic Radicals and Cations They have approximately the same stabilities, this stability can be explained by resonance theory.

Halogenation of the side chain Side- chain halogenationRing halogenation It take place when the reaction is carried out in the absence of lewis acid Require condition that favor the formation of the radicals. The halogens dissociate to produce halogen atoms The halogen atoms initiate chain reaction by abstracting hydrogens of the methyl group. The electrophiles are positive ion or they are Lewis acid complexes with positive charge Need catalyst e.g. Lewis acid These positive electrophiles attack the ∏ electron of the benzene ring. Stabilized by Arenium ions the aromatic substitution takes place.

Bromination Chlorination

Benzylic halogenation Chain Initiation Step 1 Chain propagation Step 2

Benzylic halogenation Step 3 Chain Termination Step 4

Oxidation of the side chain The oxidation can be carried out by the action of hot alkaline potassium permanganate.

Oxidation of the side chain Oxidation of the side- chain take place initially at the benzylic carbon; alkylbenzenes with alkyl group longer than methyl are ultimately degraded to benzoic acids:

Oxidation of the side chain Reaction:

Procedure: Dissolve 1 gm NaOH in 75 ml of distal water in round flask (500ml). Add 7 gm of potassium permanganatr KMnO4, and 4 ml of toluene. And heat it on hot plate for 3 hr.

Procedure: In case if the KMnO4 color don’t change, add few drops of ethanol until the violet color disappear. Filtre by Buchner, take the filtrate and heat it until the volume reduced to ml.

Procedure: Cool the filtrate on a iced cold water, then add HCL drop wise until the ppt stop. Fitre by Buchner.

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