I am running a synthetic step to get Schiff's base today.
Methyl-4-aminosalicylate and benzaldehyde (in 1:1 molar ratio) in presence of 2-3 drops of acetic acid and absolute ethanol as solvent were taken and subjected to reflux for about 4 hrs.
To my surprise, from the reaction mixture, I am getting benzaldehyde odor and there is no precipitate formed from the reaction mixture.
Why the reaction not occured...? Is there any other method to get Schiff's bases of Methyl-4-aminosalicylate...kindly let me know.
Thank you.
Presumably, the so formed imine is hydrolyzed back to SMs. I would use any dehydrating agent like 3 or 4 A molecular sieves. Or use toluene as the solvent and remove water by azeotropic removal by using Dean-Stark trap.
Did you monitor the reaction progress on TLC plates? If you did not, I advise you to co-spot on silica TLC plates, the reaction mixture with the starting materials (aldehyde and amine) to ascertain whether a reaction took place or not. Note that not all Schiff's bases formed from amines and benzaldehydes do precipitate when the reaction is complete.
Presumably, the so formed imine is hydrolyzed back to SMs. I would use any dehydrating agent like 3 or 4 A molecular sieves. Or use toluene as the solvent and remove water by azeotropic removal by using Dean-Stark trap.
React Methyl-4-aminosalicylate and benzaldehyde (in 1:1 molar ratio) in presence of 2-3 drops of acetic acid and 96 % ethanol, add acetic acid few drops , still it well, then heat for 3 hrs, remove excess of solvent , pour in ice water mix. with stirring pale yellow product will separate as Schiff,s base .
@ Dr. Madhukar Baburao Deshmukh: Thank you very much sir for the information. Yesterday, I had followed a method similar to the method you had mentioned by taking equimolar concentrations of Methyl ester of PAS and Benzaldehyde in absolute ethanol with 2-3 drops of glacial acetic acid.
Went for refluxing for 3 hours, in between I check for any precipitate formation by placing few drops of reaction mixture in cold water. After placing in water, white turbidity came and slowly, benzaldehyde odor is pungent. After completion of 3 hrs of reflux, I allowed the reaction mixture to cool to room temperature, but no precipitate formed. Then I had added crushed ice to the reaction vessel, after 10 min, I had witnessed the slow formation of precipitate which is pale yellow in color.
Recrystallization and TLC are pending.
Thank you Sir, for giving me confidence on the procedure. I would be happy to have your support for my research. I had attached the image of product with this text.
Methyl-4-aminosalicylat is a weak base. 3-4 drops of acetic acid ONLY is not enouph. The reaction rate will be too slow. Use acetic acid (acid catalisis) or pyridine (base catalisis) in large quantutues. May be as a mixture with ethanol (10-30%) may be as a SOLVENTS for this reaction. And distill water off.
In addition of Madhukar Baburao Deshmukh's method, you can try to make it without solvent nor acid in the rotavap at 70°C under vacuum to dry the formed water.
You can increase the yield and decrease the reaction time by using ultasound bath (sonication) and monitoring the reaction by TLC.
some Schiff base reactions need more time to accrue, try to add 2-3 drops of glacial acetic acid and monitoring the reaction by TLC.
Most of the answers above are equally worthy. You could also use solvents with high BP such as toluene coupled with Dean-Stark arrangement.
Reaction monitor with TLC, once form the newspot(imine) , continue the reaction upto complete the reaction.thenisolate the products using different methods like reaction mass poured into ice-coled water or concentrate and cool it.
choose the non protic solvent like toluene or xylene and remove the water from dean stark apparatus.so that the reaction moves forward.
if you stick with protic solvent use cyclo hexane as a co solvent and collect water with dean stark apparatus
Try to use Ultrasound bath instead of reflux,I think you will get the desired product in very short time, monitoring the reaction by TLC every 15 min.
Use absolute ethanol as solvent and 2-3 drops of glacial acetic acid as well as refluxed the solution for 8h .
Best regards
Don't expect solid in the reflux temperature always, check whether any new spot appeared in TLC. Add RM to crushed ice, u may get the solid.
or
Try the reaction in neat glacial acetic acid at reflux, or Toluene with acetic acid with dean stark at reflux Temp.
you can carry out the reaction without solvent (no effect of media) and under microwave activation (the water will be evaporated). the reaction will also be faster 5 to 10 minutes.
The above mentioned method seems ok. Just remove excess water during reflux, I hope you will get desired precipitation.
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