# In imine formation, why are the reaction conducted at pH=5-6?

Jan 31, 2017

Because such a $p H$ is optimal for bond-making, and for the elimination of water.

#### Explanation:

The general equation for the formation of an imine is:

${R}_{1} C \left(= O\right) {R}_{2} + {H}_{2} N {R}_{3} \rightarrow {R}_{1} C \left(- O - H\right) \left(N H {R}_{3}\right) {R}_{2}$

With arrow pushing, the lone pair on the nitrogen is conceived to make a $C - N$ bond, and one of the originally nitrogen bound hydrogens transfer to the oxygen centre. If this oxygen centre becomes protonated to give:

R_1C(-""^+OH_2)(NHR_3)R_2

We now have a potential leaving group, that can be lost to give a $C = N$ bond:

${R}_{1} C \left\{= N \left({R}_{3}\right)\right\} {R}_{2} + {H}_{2} O$

The given $p H$ optimizes bond formation, the formation of the $N - C$ bond, and is acidic enough to allow the elimination of water.

Most of this will be discussed in greater detail, and with much greater sofistication in your organic text. I urge you to consult it.