Then the isocyanate can be trapped by alcohol to form a carbamate.
related rxn: Hofmann Rearrangement, Schmidt Reaction.
Condition I used (to amine):
toluene, dppa, tea, 80C 2h,
then water added, 80C, overnight.
turned out the above transformation is not high yielding.
seems trapping the isocyanate by water is not a good idea.
generally, t-BuOH or BnOH was used to make a carbamate. then remove the carbamate by acid or hydrogenation.
2nd condition I used to make amine:
1. toluene, oxalyl chloride 60C. then concentrated invacuo.
2. acid chloride made in step 1 was dissolved in acetone, then added into NaN3 in water at zero degree. then rt. excess water was used to precipitate the product.
3. heated in toluene to 80C for 2 hr.
4. BnOH added. heated for another 2 hr.
isolate product by column.
5. MeOH, acoh, water + pd/c + H2. rt.
2 hr, then celite filtration.
K2CO3 solution was used to neutralize acoh and make free amine( pH>9). then extract the amine to DCM. the crude product is very clean. no column needed.
turned out the above transformation is not high yielding.
seems trapping the isocyanate by water is not a good idea.
generally, t-BuOH or BnOH was used to make a carbamate. then remove the carbamate by acid or hydrogenation.
2nd condition I used to make amine:
1. toluene, oxalyl chloride 60C. then concentrated invacuo.
2. acid chloride made in step 1 was dissolved in acetone, then added into NaN3 in water at zero degree. then rt. excess water was used to precipitate the product.
3. heated in toluene to 80C for 2 hr.
4. BnOH added. heated for another 2 hr.
isolate product by column.
5. MeOH, acoh, water + pd/c + H2. rt.
2 hr, then celite filtration.
K2CO3 solution was used to neutralize acoh and make free amine( pH>9). then extract the amine to DCM. the crude product is very clean. no column needed.
1 comment:
Trapping with water seems not to be a good reaction. The low yield may be caused by formation of urea, so the isocyanate must be trapped with some alcohol.
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