[AlphaScent]

See below

[orgopete]

The amines are predominately protonated. The HCl never goes away, so it can always protonate any amines. However, some free amine can form and catalyze reactions. I assume this because the reactions are not carried out under strongly acidic conditions that would drive free amine concentrations down.

[PhDoc]

With the Mannich (pronounced "Mahn-eesh") reaction comes the introduction of a β-amino group that is mostly protonated (pKa nonconjugated alkylamines 36-40; pKa HCl -7) under the reaction conditions. The reaction sequence starts because the aldehyde (or carbonyl compound) enolizes in acidic media. Once the reaction is completed, the aldehyde will still exist to some degree in the enol (vs. "keto") form. Heating such a mixture provides access to the higher energy β-elimination pathway, leading to the formation of your enal.

Good mechanism question for an exam!