# Conditions for imine formation

Firstly, note that this is not a duplicate of Acid in Imine Formation. Clayden, Warren, & Greeves (2012) states explicitly on p. 231 that imine formation requires acid catalysis, and that the reaction takes place optimally under slightly acidic conditions, close to neutrality. This makes sense as we need to form the $$\ce {-OH2^+}$$ allowing water to leave. However, if we look at this list of literature, we would observe that most of the imine formation reactions do not necessarily require acidic conditions and some even take place under solely basic conditions. How do we explain this?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.

• Most of the imine formation reactions do not start from an aldehyde and an amine. Furthermore, I believe that ‘if we look at this list of literature’ almost immediately constitutes a too broad question because each case is slightly different but I’m willing to leave it open. – Jan Dec 6 '18 at 17:07
• @Jan The point I am trying to make from the reference to the list of literature is that acid catalysis is not a necessary condition for the reaction. I do not wish to discuss each particular case of the reaction mentioned in the list. – Tan Yong Boon Dec 6 '18 at 17:09
• But in most of those cases involving carbonyls and amines, I can boil it down to ‘X supplies the acidic proton’ or ‘harsh conditions cause higher proton mobility’. – Jan Dec 6 '18 at 17:10

Most reactions that you referenced use acidic catalysis, though sometimes it isn't immediately apparent because they use solid catalyst such as molecular sieves a.k.a. H-form zeolites. A few use Lewis acids, such as $$\ce{Ti(OEt)4}$$. They still count as acids.