makfc
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Removing excess Benzoyl Chloride
Hi friends...!
I proceeded for one reaction in which I had to protect the hydroxy group of p-Hydroxybenzaldehyde thro' acylation with Benzoyl Chloride getting
Benzoyloxybenzaldehyde. For this I had to use excess (approx. 1.4 eq.) of Benzoyl chloride for complete acylation using acetone & K2CO3 (approx. 2
eq.).
Now, after the reaction completion, what should I do for removing this excess Benzoyl chloride ? 
Pls suggest me..... 
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Ozone
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Makfc,
What solvent are you using [OK, acetone]? Normally, workup goes something like this:
Distill it under reduced pressure or wash with K2CO3 ( this will both convert your benzoyl chloride to benzoic acid and render it soluble in water as
the salt). If you choose to wash it with K2CO3, wash then with water, then brine.
Usually, I would do this sort of thin in the presence of a nice organic base like pyridine (to soak the HCl from the rxn). In this case, a wash first
in dilute (cold) HCl is used to take residual pyridine to the hydrochloride (which is water soluble); the product can then be extracted from this into
a suitable organic solvent.
Hope this helps,
O3
[Edited on 24-12-2006 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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garage chemist
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Nope, a K2CO3 wash will not help. Benzoyl chloride is very unreactive with water and aqueous bases. I have seen drops of PhCOCl sit under water for 24
hours and only a very small amount of benzoic acid had appeared around them.
Benzoyl chloride can even be freed from HCl and benzoic acid by washing with aqueous bicarbonate solution, which nicely demonstrates its unique
properties for an acyl chloride.
However, it rapidly reacts with amines to form (substituted) benzamides. You could add e.g. aniline to your solution which will bind the benzoyl
chloride as benzanilide. This is a solid which should precipitate from your reaction medium and could be filtered off.
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makfc
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Thanks for the suggetions.....
Besides to this, I somewhere read that addition of Methanol can destroy the excess benzoyl chloride. Is it possible ? How ?
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Ozone
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It will react almost instantly to make methyl benzoate. The problem then is removing the methyl benzoate...(smells nice, though).
Oh, and benzoyl chloride will, if undisturbed, form a crust of benzoic acid at the interface. This effectively passivates the junction. If well
stirred or shaken (carefully), this goes much faster. Benzoyl chloride is more stable than most (sterics and conjugate electron delocalization), but
still decomposes in water.
The benzamide reaction is a good idea and it works quantitatively!
FYI, MSDS:
http://ptcl.chem.ox.ac.uk/MSDS/BE/benzoyl_chloride.html
Good luck,
O3
[Edited on 24-12-2006 by Ozone]
[Edited on 24-12-2006 by Ozone]
[Edited on 24-12-2006 by Ozone]
-Anyone who never made a mistake never tried anything new.
--Albert Einstein
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