The aldehyde shown reacts with a primary amine to give an imine. Select the correct statement(s) about the pH dependence of the rate.

Imine formation needs both an unprotonated amine to attack the carbonyl and acid to catalyse loss of water from the carbinolamine. At low pH the amine is protonated and non-nucleophilic, so addition is slow. At high pH there is too little acid to protonate the carbinolamine OH, so dehydration is slow. The maximum rate lies near pH 4 to 5. The claim that protonation of the carbonyl at high pH slows the reaction is wrong, because the carbonyl is hardly protonated at high pH.