what happens when aniline is diazotized and the product is coupled with phenol
Answers
With water, rather than base, the reaction will tend to reverse and go to the left. You want basic conditions for this first step, because in order for the phenol to react, and form the nitrogen bridge, you want to deprotonate the hydroxyl (and create sodium phenoxide) that will be attracted to positively charge diazonium ion and then form the azo compound.
The diazonium ion is often prepared from aniline and nitrous acid in an acidic solution. Your goal is to keep this reaction to the right and promote oxidation (without making nitrobenzene, but this often requires a metal catalyst):
Then you cool the solution and add the cold benzenediazonium chloride.
Diazonium ion is an excellent leaving group, so if you did the entire reaction step in water, what would happen is that you would simply substitute the -N2+ with an -OH group via Sn1, rather than making your desired azo compound.
Chemists, please correct errors!!
Answer:
We know that, phenol is acidic in nature; for coupling with benzenediazonium salt basic medium should be required due to in presence of base phenol exists in equilibrium with the phenoxide ion ( the fully developed negative charge makes O- much more powerfully electron releasing than OH- , therefore the phenoxide ion is much more reactive than OH- towards electrophilic aromatic substitution).
Again, in presence of base, the diazonium ion exists in equilibrium with an unionised compound, Ar-N=N-to OH , and salts (Ar-N=N-O-) derived from it.; as a result,it doesn't couple with phenoxide ion .So, coupling occurs most readily in slightly alkaline solutions. The optimum pH for coupling with phenol is 9.
On the other hand,aniline is basic in nature.If medium is basic, then base only reacts with diazonium ion due to absence of other acid to form salt which doesn't couple with aniline .Thus, PhN2+Cl- couples with aniline in weakly or moderately acidic conditions. But here acidic conditions should be maintained because acid converts an amine into its ion ,which , because of the positive charge, is very much unreactive towards the weakly electrophilic diazonium ion. The optimum pH for coupling with aromatic amines is 5-7.
If the medium is neutral , phenol couples slowly with benzenediazonium ion because here phenoxide ion is not formed and negative charge of OH cannot fully developed in the benzene ring.
Amines readily couples with diazonium salt when pH of the medium is 7.
Explanation:
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