MathSci Problems
Intro to Imine Formation
Consider the reaction below
a) What is the name of the functional group formed in the product?
b) Provide a mechanism for this reaction
c) Although HCl is used as acid in this reaction, why isn’t it used as a direct proton source in the mechanism?
d) What is the problem with writing the “proton transfer” event as an intramolecular process here? (People often write the mechanism like this, but it is problematic!)
Solution
a) Imine
b) Note that slight variations in the mechanism are okay, as long as they are reasonable. For instance, one could first protonate the leaving group before kicking it off, instead of drawing the process as concerted (step 4 of mechanism). Also, it is common to see the mechanism where the carbonyl is protonated first before the amine attacks; however, the amine is sufficiently nucleophilic to attack the unprotonated carbonyl.
c) HCl is a strong acid, so it protonates the amine in solution. Thus, HCl exists in solution as the protonated amine.
d) The transition state is a 4 membered ring, so it’s too high in energy. Therefore, it is more reasonable to draw the process as a 2 step, intermolecular event (as seen in the mechanism in part b).
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