hello everyone please explain what kind of method i will synthesis
acidchloride ? i already tried in rt and different type of temperature
,different kinds of solvent also ,then how to check the tlc ? because
some suddenly changes is there in tlc .
Thionyl chloride in an aprotic solvent should work. Quench a sample of the reaction mix in an alcohol to form the ester. Do TLC of the quenched sample. The ester and acid should be easy to separate by TLC.
Many acid chlorides are unstable and cannot be isolated for long, it may be easier to just form the actual product you want.
Oxalyl chloride in DCM with catalytic amount of DMF is another common method.
Acyl chlorides are pretty unstable (they can decompose on TLC plate which is what you are observing probably).
you might want to consider acyl fluoride which is more stable yet still reactive. There are more modern methods for generation of acyl fluoride.
I used the oxalyl chloride method for many years - it never failed me.
Thionyl chloride, however, is more cost-effective for large scale reactions. Word of warning: avoid toluene as the solvent, because it can be chlorinated by thionyl chloride. The resulting benzyl chloride is an unpleasant contaminant at large scale.
When I was an active chemist, I used thionyl chloride for this reaction. The advantage is that the two by-products of this reaction, namely, hydrochloric acid and sulphur dioxide, are in gaseous form and hence no extra effort is required to remove them from the reaction mixture.
The disadvantage is removal of residual amount of thionyl chloride from the reaction pot. For this couple of times addition of a suitable solvent and removal by distillation is required to be done. This step for removal of excess thionyl chloride is required to be carried out in case your target molecule is an amide.
If I remember correctly, a major disadvantage of using oxalyl chloride is formation of carbon monoxide as a by-product, giving rise to safety issue.
In general, acyl chlorides are unstable and not isolated as a product. These class of compounds are made as an intermediate for the synthesis of the target molecule directly, avoiding the step of isolation of the acyl chloride.
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