Final answer:
In situations where no additional acid is added to an imine formation reaction, the carboxylic acid present in the mixture can act as a natural acid catalyst. Additionally, reagents like EDC-HCl in amide formation reactions also provide the necessary acidic environment for the reaction to proceed.
Step-by-step explanation:
In the context of imine formation, if an acid is not added explicitly to catalyze the reaction, the acid required for carbinolamine protonation may come from the reaction components themselves. One such source could be the carboxylic acid if present in the reaction mixture. During the reaction between carboxylic acids and amines, the carboxylic acid can donate a proton to the amine, leading to the formation of an ammonium salt, and this proton transfer essentially makes the carboxylic acid act as a catalyst in the reaction.
Looking at the process of amidine formation from carboxylic acids and amines, an acid by-product is not necessary as the carboxylic acid and amine can under the right conditions react to form an amide. Specifically, tertiary amines, which lack hydrogen on the nitrogen atom, can act as bases and accept a proton from the carboxylic acid, resulting in the formation of a carbinolamine which then dehydrates to form imines.
Additionally, in the procedure described for carboxylic acid-amine coupling reactions, the use of EDC-HCl (a common coupling agent) and HOBT (hydroxybenzotriazole) indicates an acid-mediated reaction is taking place without the need for an added strong acid, as the EDC-HCl provides a gentle protonation step that aids in activating the carboxylic acid for amide bond formation.