[endophytic]

Hello chemists !

I wondered if treatment of mono-methyl suberate with thionyl chloride form only the acyl chloride on the carboxylic acid ?



In other word will thionyl chloride react or no with the methyl ester ?
Else ... well how do I proceed ?

[salteen]

No, the thionyl chloride should not react with the methyl ester.  If you draw the mechanism of SOCl₂ with a carboxylic acid, and then try to complete the same mechanism using an ester, you may see why.

One of the common uses of SOCl₂ is to react it with a carboxylic acid in the presence of an alcoholic solvent - this is an efficient method of esterification by first generating the acyl chloride in situ which then immediately reacts with the alcohol.  The ester product will remain intact even if excess thionyl chloride is present.

[endophytic]

Hi salteen !!!

Thank you for the quick replie.
i looked at the mechanism. Could you tell me more in detail why it wouldnt be possible with the ester. I believe you a 100 percent i just want to understand clearly ... Which is not the case ..

So the first step would be nucleophilic attack of the carbonyl toward the S atom and one Cl atom leaving. This one is feasible even with an ester.
In the second step i guess here is the problem. Is it because Cl^- cant attack the methyl and form CH₃Cl (in the case of a methyl ester) ? Why isnt that possible.
Or Because the reaction is supposed to pass by a pericyclic state wich couldnt be possible with an ester.

I guess it is the first reason but i cant remember the exact explanation ... Can you help ??

Thanks a lot

[Dean]

If the ester was refluxed with excess of thionyl chloride, ester could be converted to the acyl chloride.
The explanation is here. Cl- is able to attack the acyl group. In the reaction of acid in excess of refluxing thionyl chloride, methanol was continuously evaporated from the reaction system. Therefore...
To get a acyl chloride, I recommend using oxalyl chloride instead of thionyl chloride. That's a very gentle condition.

[darkdevil]

I also recommend using oxalyl chloride with a catalytic amount of dimethylforamide (DMF). The reaction mixture quicly give out gases and you can directly use it as the acyl chloride source. Hope it helps

[Dean]

I also recommend using oxalyl chloride with a catalytic amount of dimethylforamide (DMF). The reaction mixture quicly give out gases and you can directly use it as the acyl chloride source. Hope it helps

Bingo

[endophytic]

Thanks all for your insights !

Dean sorry for my innoncence .. I guess I have some more dumb questions ...

I dont get clearly your explanation.
So with an excess of thionyl chloride the ester could react. Cl- would attack the methyl group. And therefore form CH₃Cl is that right ?
Why do you say Methanol was continuously evaporated from the reaction system ?
First why MeOH ? And second since you said it was with refluxing thionyl chloride how come it get out of the system ?

Thank you both (all) for your explanations. Oxalyl chloride with cat amount of DMF seems poretty cool.
Also I would like to now of possibilities to monoesterify a diacid of this type (linear) other than anhydride formation. But I'll maybe start another topic for it !

Thank you

[Dean]

Sorry. There is an obvious bug in my explanation, ignore that.

In the presence of catalytic base(Py. or DMF), the ester can be converted into acyl chloride. Or the ester will be safe.
The lone pair electron of N attacks thionyl to release Cl-; The Cl- attacks acyl , releases MeO-. MeO- was combined S=O to form (MeO)2SO

[Dean]

Hi salteen !!!

Thank you for the quick replie.
i looked at the mechanism. Could you tell me more in detail why it wouldnt be possible with the ester. I believe you a 100 percent i just want to understand clearly ... Which is not the case ..

So the first step would be nucleophilic attack of the carbonyl toward the S atom and one Cl atom leaving. This one is feasible even with an ester.
In the second step i guess here is the problem. Is it because Cl^- cant attack the methyl and form CH₃Cl (in the case of a methyl ester) ? Why isnt that possible.
Or Because the reaction is supposed to pass by a pericyclic state wich couldnt be possible with an ester.

I guess it is the first reason but i cant remember the exact explanation ... Can you help ??

Thanks a lot

1. Under this condition, nothing can launch a nucleophilic attack
2. Cl- can't attack Me because methyl is a relative electron-rich group, except methylium cation formed.

[darkdevil]

  I have another related issue with this.. Using both thionyl chloride or oxalyl chloride can both give out HCl as the side products. I wonder if simple distillation/evaporation (heat it above HCl b.p.) can remove HCl from the end products if my substrate for the Acid chloride is sensitive to HCl? 

[Dean]

I think it would be worse. In that case, why not  active ester?