Question

Depending on the reaction conditions, two different imines of formula ${\mathbf{C}}_{\mathbf{8}}{\mathbf{H}}_{\mathbf{9}}\mathbf{N}$ might be formed by the reaction of benzaldehyde with methylamine. Explain, and give the structures of two imines.

Short answer

Two imines formed are (Z)-N-methyl-1-phenylmethanimine and (E)-N-methyl-1-phenylmethanimine. The structure of the imines are shown below.

Step-by-step solution

Introduction Part

The mechanism for imine formation can be divided into two parts. First part is the acid-catalyzed addition of the amine to the carbonyl group in which protonation of the carbonyl takes place followed by addition of the amine and deprotonation. Second part is the acid-catalyzed dehydration in which protonation of the $-\mathrm{OH}$group followed by the loss of water and deprotonation.

Structure of the two imines

Acid-catalyzed addition of methylamine takes place to the carbonyl group of benzaldehyde. This results in protonation of the carbonyl followed by the addition of amine and deprotonation. Again, acidcatalyzed dehydration takes place where protonation of the $-\mathrm{OH}$group occurs followed by the loss of water and deprotonation which gives the desired imine.