I have to make tribromoacetyl chloride from the acid. A collegue used SOCl2 in toluene with traces of DMF and recovered the acid. She then used oxalyl
chloride and DMF with apprently good results. But considering the price of oxalyl chloride, it would be great if I could get the thionyl chloride to
work.
Now recently I used SOCl2 to make 2-bromopropionyl chloride from the acid with 65% yield, refluxing the acid in 25% excess SOCl2.
I am thinking of using this method on CBr3COOH. My question is, how can i control that the acyl chloride has indeed ben formed? TLC won't work I
suppose as the acyl chloride would surely hydrolyse on teh silica plates, no? And I would need a pretty polar solvant to get the acid moving in any
case, but can't use MeOH or any other alcohol for obviosu reasons...
Any ideas?Sandmeyer - 20-7-2009 at 18:33
run the reaction in SOCl2 neet, I don't understand why people use other solvents in this kind of reaction. SOCl2 is an excellent solvent and being
volatile is easy to vac off leaving you with acid chloride needing no further purification, use it directly. no need to reflux, let it stirr at rt
overnight. imo, this is among the simplest and cleanest reactions.
[Edited on 21-7-2009 by Sandmeyer]Klute - 20-7-2009 at 20:12
Well with 2-bromopropanoic acid there was no reaction until the SOCl2 was at reflux. I left it a couple of hours before gas evolution stopped. So I
guess I could do the same for the tribromo, to complete the reaction in an afternoon.
To determine presence of the acyl chloride I suppose I could do a hydroamic test: Link
It won't tell me if there is some acid left though. I guess I could run a IR or even NMR for that. At least I will get the proportions with NMR.not_important - 20-7-2009 at 20:25
Treat a little of the product in ether solution with diethylamine in ether. Et2NH2Cl should mostly ppt out, the amide won't have any O-H or N-H
absorption or signals while the acid salt RCO2H2NEt2 will. You could perhaps titrate the amount of salt, or dump into water and do a conductivity
measurement to estimate the amount.
Klute - 20-7-2009 at 20:55
Yes, forming an amide seems like a good idea. I can then check by TLC if there is some acid left... I guess I will rather use aniline as I have only
aq. Me2NH..
[Edited on 21-7-2009 by Klute]bfesser - 21-7-2009 at 10:45
Is this for your job or your personal use? Sigma-Aldrich sells this reagent.Klute - 21-7-2009 at 10:50
For my job... I will be acylating a lithium amide salt afterwards. The acyl chloride is more expensive, and I have the acid at hand, considering that
lately orders from sigma are taking two weeks to arrive (!!) I'm better off trying forming it myself..chemrox - 21-7-2009 at 16:18
I'm sorry to hear Sigma dragging it's feet. My I recommend one of my better suppliers to you? Nice thread by the way.. lots of chemistry discussion.
No idiocy unless ...oh dear.Klute - 21-7-2009 at 20:49
Well, it common practice to get reagents from sigma and acros here at work, but indeed local suppliers might be mich quickier.. Problem is they are
no match concerning variety of reagents.. I haven't found a distributor for Panreac up north... So please, do send me your list of suppliers!Klute - 21-7-2009 at 20:58
Nice thread by the way.. lots of chemistry discussion. No idiocy unless ...oh dear.
This is what I like!
No flamming or pointless ego demonstrations, just the chemistry.. Real chemistry..
And I realized H NMR with be useless, as there isn't any H in the acyl chloride. I could detect traces of the acid, but I guess I will have to form
the amide first. I will use aniline as I distilled some recently and don't want to mess with dry dimethylamine. The NH proton will give a large
singulet near 8-9. Traces of acid will be seen by the COOH I suppose.
