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 $\ce{AlCl3}$, 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 $\ce{OH}$ 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 $\ce{AlCl3}$. On the contrary, it is quite probable that such complexes do form due to the interaction of the methoxy oxygen with $\ce{AlCl3}$.


Therefore, and to compensate the formation of complexes with the resulting ketone, $\ce{AlCl3}$ is added in more than two-fold excess in the above synthesis.


No comments:

Post a Comment

periodic trends - Comparing radii in lithium, beryllium, magnesium, aluminium and sodium ions

Apparently the of last four, $\ce{Mg^2+}$ is closest in radius to $\ce{Li+}$. Is this true, and if so, why would a whole larger shell ($\ce{...