Well, I already know that this reagent is a little bit tricky because of the quench part but my problem is that in a chlorination of alcohol using POCl3 I do TLC and it looks like all the start material is gone. However, when I work up my reaction, pouring my mixture in water and extracting my compound, I notice that the start material shows up again in TLC.
I would like to know if I have to keep my reaction for a longer time even if my start material does not show up in TLC anymore. What is the common way to quench the reaction?
SOCl2 and POCl3 can chlorinate alcohols, but when is which reagent preferable? SOCl2 is used with primary and secondary alcohols. POCl3 reacts with water and alcohols to give hydrogen chloride, alcohols have much higher boiling points than hydrocarbons and alkyl halides.secondary alcohols undergo chlorination, When treated with phosphorus oxychloride (POCl3) alcohols are converted to alkenes via an elimination reaction. POCL3 hydrolyses in moist air releasing phosphoric acid and choking fumes of hydrogen chloride. POCl3 is used as a safe liquid phosphorus source in diffusion processes. The phosphorus acts as a dopant used to create N-type layers on a silicon wafer.POCl3 is in the Vilsmeier-Haack reaction, where it reacts with amides to produce a "Vilsmeier reagent," a chloro-iminium salt, which subsequently reacts with electron-rich aromatic compounds to produce aromatic aldehydes upon aqueous work-up
A couple of thoughts ...
First, since I don't know the structure of you alcohol, it is difficult to say if the TLC is a reliable method to monitor the progress of the reaction. Perhaps the reaction is indeed incomplete.
Second, your produced chloride might be hydrolyzed during aqueous work-up, especially if you use inorganic base to get rid of the excess HCl/H3PO4 (the tricky part you mentioned). To minimize the possibility of hydrolysis, you may try several things, for example: a) dilute the reaction mixture with the organic solvent like CH2Cl2 before the aqueous work-up; b) cool it down to make sure the mixture is not getting hot when adding water; c) consider using a base like diethylaniline or pyridine when doing your reaction. It is also usually a good idea to evaporate excess of POCl3 (partially or completely) before work-up.
These are very general recommendations; depending on the structure of your substrate, you may need to take other measures. Good luck.
Hi Vladimir,
I did different things and in the end I could get good results. So, I left my reaction for a longer time and when it was done, I evaporated the excess of POCL3 down. The solid remained was diluted in organic solvent. Finally I quenched the solution with NaHCO3, which is not a strong base, and I could get only the Cl compound.
Thanks for helping
Dear Matheus Andrade Meirelles,
Using a mixture of POCl3 and PCl5 (3:1) at reflux temp. (8-10 h) and poured onto ice-water saturated with NaHCO3 is very useful for chlorination of the OH.
I have the same problem but this time I do Chlorination for cyclic amide in nicotinotrile ring system. I keep refluxing for long times and I do the work up using ice/water. What is your recommendations?
Naglaa Aboud,
I left my reaction for a longer time and when it was done (by TLC), I evaporated the excess of POCl3 down in a rotovap. The solid remained was diluted in organic solvent. Finally I quenched the solution with NaHCO3, weak base, and I could get only the Cl compound. Remember to rotovap the POCl3 first, then quench with weak base. You may get only the chlorinated compound.
Best.
You have to quench the reaction in reverse manner, than you will be successful
Hi,
can I get reference article for conversion of primary alcohol to chloride using POCl3?
Thanks in advance.
Could I use SOCl2 if I try to chlorinate a 4 - hydroxy quinazoline? What are the risks that I take instead of using POCl3?
Thank you all for your answers, are really useful.
Martin, I am sure you can use thionyl chloride for your reaction if you decide to do it this way for some reasons.
At the same time, POCl3 is certainly more common for chlorinating nitrogen heterocycles, while SOCl2 usually used for chlorination primary, and to some degree, secondary alcohols.
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