Question

Name the possible products of this reaction in the presence of ether and AlCl3: methylbenzene + 2-chlorobutane.
1. 1-ethyl-2-methylbenzene

2. 1-ethyl-3-methylbenzene

3. 1-ethyl-4-methylbenzene

		1
		2
		3
		1 and 2
		1 and 3
		2 and 3
		none of these choices

Answer 1

The given compounds are - Methylbenzene and 2-Chlorobutane. The given catalyst/solvent mixture is Aluminium chloride in ether.

The first step is to identify the given reaction. AlCl3 is primarily used in Friedel Craft's reactions . Since we are required to react methylbenzene with an haloalkyl group (chlorobutane) , it has to Friedel Craft's alkylation reaction.

Friedel craft's alkylation proceeds through a carbocation formation, which then enables an alkyl group to be substituted onto the benzene ring.

In this case, the AlCl3 acts as a catalyst . The 2-Chlorobutane reacts with the catalyst to form AlCl4- , and a secondary carbocation.

This carbocation can undergo rearrangement if possible, based on the stability of the carbocation. As we can see, the carbocation is a secondary carbocation, which is pretty stable. Observe that there is no way for this charge to transfer to a different position to form a tertiary carbocation. Hence, let's proceed with the secondary carbocation.

This carbocation now has to undergo electrophilic substitution on the methylbenzene. As we know, methyl benzene is an ortho para directing group.

The carbocation will hence attack the benzene ring at positions 2 and 4 , forming 2 products .

Refer to the image for the complete reaction.

Note: The answer contains 3 options with ethyl group . This could be a mistake from the source of the question creator. The correct options should have been 1-butyl 2-methyl benzene, 1-butyl 3-methyl benzene and 1-butyl 4-methyl benzene, in which case the answer would have been (1) and (3).

For the current options, the answer would be (none of the choices).