Thursday, June 28, 2018

organic chemistry - Friedel-Crafts reaction of anisole?



We know that phenol and aniline, despite being strongly activating, are unable to to undergo Friedel-Crafts reactions because they form complexes with AlClX3, thanks to the lone pair on nitrogen and oxygen atoms.


However, according to my notes (and Google) anisole does undergo Friedel-Crafts reactions. How can it be possible, why is there no complex formation this time?


Also, I wanted to know how can we say that a certain group like OH will surely form a complex? Is containing a lone pair a sufficient condition?



Answer



Friedel-Crafts acylation of anisole with acetyl chloride and aluminium chloride as catalyst is a standard laboratory procedure to synthesize acetanisole.


            source: Wikipedia, user Jü


The fact that this reaction is possible does not imply that there is no complex formation with AlClX3. On the contrary, it is quite probable that such complexes do form due to the interaction of the methoxy oxygen with AlClX3.


Therefore, and to compensate the formation of complexes with the resulting ketone, AlClX3 is added in more than two-fold excess in the above synthesis.


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