Q33E - Organic Chemistry (Mcmurry)

Question

Triphenylmethane can be prepared by reaction of benzene and chloroform in the presence of ${\mathbf{AlCl}}_{\mathbf{3}}$ . Propose a mechanism for the reaction.

Step-by-Step Solution

Answer

Mechanism followed as shown below.

Step 1: Reaction of chloroform with aluminium chloride

When a reaction of chloroform occurs with aluminium chloride, it leads to the formation of dichloro carbocation which acts as an electrophile in reaction with the benzene.

Formation of Electrophile

Step 2: Reaction of benzene with an electrophile

When the dichloro carbocation reacts with benzene, one of the double bond of the aromatic ring breaks and addition of ring occurs followed by the reaction with aluminium chloride which protonates the hydrogen. As a result, the ring regains its aromaticity and the formation of dichloro methyl occurs as shown below.

Formation of (dicholromethyl) benzene

Step 3: Formation of triphenylmethane

Similarly, the reaction of the dicholromethyl benzene with 2 moles of benzene in the presence of aluminium trichloride is shown below

Formation of Triphenylmethane