My compound is having both primary and secondary amine. I want to couple only the primary amine with substituted phenyl isocyanates. Can any suggest me which product will be formed in this case?
Primary & secondary amines react with isocyanates to give substituted ureas.
R-N=C=O + R'R"NH → R-NH-(C=O)-NR'R"
Where R' and R" can be H, alkyl or aryl groups.
While primary & secondary alkyl amines are more basic than ammonia, they may be regarded as very weak acids. That is why they protonate the (N) in R-N=C=O in this reaction. The difference in reactivity is not a big one.
The reactive part of isocyanates is the positive charge on C of carbonyl. Hence, the secondary amines are expected to be more reactive with isocyanates as they have an excess of negative charge on N. However you should consider wether the benzyl group imposes any stereochemical effect (due to its bulkiness).
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