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Preparartion of Benzoic acid from Benzamide


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#1 phagocytes

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Posted 26 October 2007 - 10:31 AM

The benzoic acid is prepared by alkaline hydrolysis of benzamide

I would like to ask why the shape of benzoic acid obtained is Needle-like and why there is yellow ppt. after boiling benzamide with NaOH for about 15 minutes?

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#2 YT2095

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Posted 26 October 2007 - 10:48 AM

I can see it making sodium benzoate sure.
to make benzoic acid, don`t you need another Acid? and not a Base.

even if you did it "dry" the best you`de get maybe sodamide, but that`s pretty unstable esp around an Acid.


I also would like to see the reaction mechanism for what you describe :)
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#3 John Cuthber

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Posted 26 October 2007 - 08:10 PM

Hydrolysis of benzamide with sodium hydroxide solution will give sodium benzoate and ammonia. This will have a different crystal structure from the acid.
There is a procedure for hydrolysis of amides by dissolving them in sulphuric acid then poring the solution into water. I've never tried it but it should make the acid directly.
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#4 phagocytes

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Posted 27 October 2007 - 10:00 AM

There is a procedure for hydrolysis of amides by dissolving them in sulphuric acid then poring the solution into water. I've never tried it but it should make the acid directly.


http://aycu10.websho...37034140_rs.jpg


Yes, after boiling with NaOH ,suction filtration is then carried out ,then excess HCl is added to the yellow ppt. .Finally the mixture is dissolved in HOT water(recrystallization).Then the solid obtained is Needle-like .

I would like to ask if the yellow ppt. is sodium benzoate and why the benzoic acid is Needle-like .By the way ,will there any side product be formed ?

I think the reason of carring out alkaline hydrolysis is to shift the equilbrium to the right in order to obtain more crystals since NH3 can be esaily removed, but i am not sure if i am right.
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