GreenD
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SOCL2 -> Acid Chloride... Overnight?
I had a reaction of SOCl2 in with a benzoic acid which is reported to be quantitative under reflux for 4 hours.
My timer is broken, so my heating mantle never shut off.
The oddest thing:
I had a yellowish solution with a white ppt at the bottom (what I thought was my acid chloride crashing out of excess SOCl2 which had now somewhat
boiled away).
So, I poured in some more SOCl2 in order to dilute it and make it easily transferrable - but to my surprise the flask boiled vigorously upon the
addition, meaning water was probably present (in large quantities).
How the hell could this have happened? It was roughly 16 hours of reflux.
No thionyl chloride left, yet approximately 75% of the volume initially added was present, obviously water, though.
I had a base scrubber attached at the top, but I see of no reason or possibility of it actually climbing into the condenser, espcially since the flask
is giving off gas, not using it, it should have a constantly evolving pressure...
What the f*ck
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GreenD
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Totally lost now.
Tried to distill off the liquid, and the current temperature reading is 110°C...
What the hell is going on?
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Ephesian
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Ok, first of all...
You just rambled off a bunch of observations on a reaction I have no idea what you put into the reaction. Did you keep a laboratory notebook handy? or
is this all stored up there in that little noggin of yours?
Did you use a solvent in this benzoic acid/SOCl2 acid chloride formation? What was your addition rate? what was the internal temperature prior to your
addition? During reaction? etc... How many moles of benzoic acid to thionyl? are you getting the point? It certainly sounds like your yellowish
solution with white ppt was your acid chloride, because nearly every acid chloride that I've made resembles these features that you describe...but in
all the times I've made acid chlorides did I ever think by adding more of this extremely reactive compound would help me transfer the resulting
product...what happened to solvents? does your laboratory have these?
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GreenD
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Lo Siento.
The reaction was simple;
5g of o-methoxybenzoic acid was dissolved in 50mL of Thionyl Chloride.
The reaction was refluxed over night with a base scrubber attached at the top.
The reaction was refluxed for ~16 hours (4 intended).
Upon addition of some thionyl chloride to the remaining yellowish liquid (which I had presumed to just be the concentrated Benzoyl Chloride), vigorous
boiling was observed.
In my confusion, I thought perhaps water had gotten into the flask - nearly 50mL of it.
So I distilled off the liquid, but only 75% of it came off at 107°C at 1 ATM.
The remaining liquid would not come off.
I attempted a vacuum distillation, but the remaining solution was rather violently exploding, so I left it.
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Ephesian
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I think I see your issue GreenD 50mL of SOCl2 is over 80 grams of Thionyl chloride. I would only use at most 10% excess, and I would also try using a
solvent, I mean...you are in fact using thionyl chloride, there is no use being "green" at this point.
Here is what I would do
(0.033 moles, 5.0g) of 2-methoxybenzoic acid added to a round bottom with some ethyl acetate and a catalytic amount of a dipolar aprotic solvent
heated to ~50-70C. In an addition funnel add 10% excess (0.036 moles, 4.30g) SOCl2 and add dropwise while keeping the addition rate slow enough to
keep the reaction at that temperature (I would say over the course of 1.5-2 hours, however with that little thionyl it would be hard to keep the rate
slow enough before emptying your addition funnel). Your product should be a clear colorless solution with some cloudiness to it depending on the
initial purity of your starting material. I've had yellow acid chlorides, brown acid chlorides as well.
Depending on what you are doing in the following reaction I would not bother refluxing this solution if you are using 1:1 ratio, however in your case
you were just boiling off all that excess thionyl, and I would have hated to be in the room you were doing it in.
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GreenD
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So.. Do you have any idea what I synthesized there?
I am out of LC/MS solvent at the moment but am really eager to understand what the hell was made.
I understand there is a lot of SOCl2, but I don't see what other reaction would have taken place... even given 16 hours at reflux.
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GreenD
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Attempted again;
5g 0-methoxybenzoic acid was added to 25mL SOCl2 and the reaction stirred and brought to reflux.
The end was capped and a syringe connected to basic water was employed.
The evolution of gas was quick, but subsided before reflux could even occur, and reflux did not induce any more gas evolution.
The mixture was yellow, but upon concentration via distillation (atmospheric) the solution turned red and no more liquid came off at 76 celsius.
Knowing that thionyl chloride mp is -106 C I decided to cool the flask and obtain the solid benzoyl chloride (which is reported to be clear, light
yellow, or even brown).
Now I have a flask with a pastel red solid, covered by thin crystals.
Guys. I really don't know what else could be made here. I would assume I could only have 1 of three things;
SOCl2
Benzoic acid
Benzoyl chloride
I have just read this as well;
Thionyl Chloride is a colorless to pale yellow or red liquid with a pungent odor.
So this may in fact be the impurity... does anyone understand what exactly is making the red color? Since SOCl2 from the bottle is colorless.
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