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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: anishd on March 08, 2011, 11:44:05 PM

Title: Why is aniline basic while phenol is acidic?
Post by: anishd on March 08, 2011, 11:44:05 PM

When separating phenol from aniline, we use a strong base to separate the phebol and a strong acid to separate the aniline. Any thoughts as to why?

Title: Re: Why is aniline basic while phenol is acidic?
Post by: Mandeep Deka on March 12, 2011, 08:34:38 AM

Phenol being a strong acid reacts with the strong base to form a salt which can be expected to get precipitated. Something the same for aniline as well!!

Title: Re: Why is aniline basic while phenol is acidic?
Post by: g-bones on March 14, 2011, 12:49:11 PM

Phenols have a convenient pH of about 11 which means they can be deprotonated by a typical "workup" solution like NaOH (pKa of water is 15.7).  Aniline on the other hand has a pKa of about 30 (in DMSO) which is not appropriate for deprotonation by a typical base like hydroxide.  In addition, nitrogen is much more basic in nature than oxygen (the result of a difference in electronegativity) so protonation of aniline to form the positively charged species is much easier with a typical HCl solution. 

Hope this helps.

Title: Re: Why is aniline basic while phenol is acidic?
Post by: mcdonabe on March 17, 2011, 02:57:27 PM

To expound upon g-bones' point of electronegativity, oxygen is more stable with a negative charge due to electronegativity, so it then follows that the pka of phenol is lower than aniline, since pka is representative of the stability of the anion resulting in from deprotonation. As a side note, phenol is not a strong acid..