State Friedal Craft reaction.
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Friedel-Crafts acylation
Friedel-Crafts acylation of benzene
What is acylation?
An acyl group is an alkyl group attached to a carbon-oxygen double bond. If "R" represents any alkyl group, then an acyl group has the formula RCO-. Acylation means substituting an acyl group into something - in this case, into a benzene ring.
The most commonly used acyl group is CH3CO-. This is called the ethanoyl group, and in this case the reaction is sometimes called "ethanoylation". In the example which follows we are substituting a CH3CO- group into the ring, but you could equally well use any other acyl group.
The facts
The most reactive substance containing an acyl group is an acyl chloride (also known as an acid chloride). These have the general formula RCOCl.
Benzene is treated with a mixture of ethanoyl chloride, CH3COCl, and aluminium chloride as the catalyst. The mixture is heated to about 60°C for about 30 minutes.
A ketone called phenylethanone (old name: acetophenone) is formed.
Friedel-Crafts acylation of methylbenzene (toluene)
The reaction is just the same with methylbenzene except that you have to worry about where the acyl group attaches to the ring relative to the methyl group.
Normally, the methyl group in methylbenzene directs new groups into the 2- and 4- positions (assuming the methyl group is in the 1- position). In acylation, though, virtually all the substitution happens in the 4- position.
Friedel-Crafts alkylation
Friedel-Crafts alkylation of benzene
What is alkylation?
Alkylation means substituting an alkyl group into something - in this case into a benzene ring. A hydrogen on the ring is replaced by a group like methyl or ethyl and so on.
The facts
Benzene reacts at room temperature with a chloroalkane (for example, chloromethane or chloroethane) in the presence of aluminium chloride as a catalyst. On this page, we will look at substituting a methyl group, but any other alkyl group could be used in the same way.
Substituting a methyl group gives methylbenzene.
By Alkylation
➻ When chlorobenzene reacts with methyl chloride in the presence of Anhr Alcl3 as a catalyst, a mixture of Ortho Chloro toulene and
Para Chloro toulene is formed.
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