chemrox
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byproduct from chlorination
Using benzoyl chloride to make propionyl chloride the cooled reaction flask filled with beautiful clear needles. These were slightly soluble in
hexanes, soluble in acetone and possessed of a pleasant, carbonyl odor. Reminiscent of cyclohexanone but sweeter... don't have my melting point
apparatus working yet. What is it? Benzoin?
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Sauron
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Only byproduct should be benzoic acid. Did you distill off the propionyl chloride? The point of the benzoyl chloride was to have it remain in the pot
while the more volitale acid chloride was taken off.
There should be some excess benzoyl chloride in there as well.
The only rxn of benzoic acid and benzoyl I can think of would be formation of the anhydride.
Anyway if the point of the exercise was propionyl chloride and you have (or can) take it off, do so and be happy. Your crystals could be benzoic acid,
benzoyl chloride, a mixture of the two, or even benzoic anhydride. Most likely a mixture of first two. You could rechlorinate any acid present to
benzoyl chloride and have a single byproduct but recycling hardly seems worthwhile.
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Sergei_Eisenstein
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Try to dissolve it in some boiling water. Benzoic acid should go in solution and precipitate on cooling (depending on the water volume, obviously). I
don't think the anhydride will dissolve as easily.
damnant quod non intelligunt
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chemrox
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I will try that, thanks. Do you think phenyl benzoate might be another possibility? I wish I had an NMR...
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Sauron
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Where would the phenol (to form phenyl benzoate) originate?
And if you dissolve those crystals in hot water you will certainly hydrolyze any excess benzoyl chloride to benzoic acid; same with any benzoic
anhydride; benzoic acid will remain unchanged, and all you will have is benzoic acid in there. Okay, so you can if you want then rechlorinate to
benzoyc chloride with TCT or your choice of reagent (but you can't use benzoyl chloride to make benzoyl chloride.)
If these are really nice well formed crystals why not take a mp and see what you have?
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chemrox
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you're right. it was a stupid idea .. just from the yield its benzoic acid. Now, what to do with it? Recrystallize it from hot water, as you say
getting rid of any Cl or anhydride.. then I'd like to get it truly dry.
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Sauron
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I'd select a crystallization solvent the classical way, one that it is very sol in at bp and only sparingly sol in when cold. The crystallization
process itself will exclude most impurities -- compare the solubilities of the chloride and anhydride in your chosen solvent.
Water is only a good idea if it meets the above requirements; if the stuff is freely soluble in cold water, it just won't recrystallize at all, and if
you cook it down you don't get any of the purifying effect (other than the hydrolysis, and that may be slow.)
Your main product, propionyl chloride, should be long gone as you were supposed to distill it off, it's a volatile liquid. So all you can have in the
pot is ubreacted excess benzoyl chloride (there was at least an extra equivant IIRC) and free acid from the reaction, and just maybe a wee bit of
anhydride from the interaction of those two but I suspect, little or none of that.
If you are going to save up your pot contents to chlorinate back to benzoyl chloride, damned little point in hydrolyzing what benzoyl chloride might
be in there. But whether or not there is merit to doing this depends on the scale on which you will be working and the cost of benzoyl chloride vs TCT
or whatever your chlorinating reagent is, not to mention bench time from you.
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