Above `(C - N)` coupling reaction take place at:

Options

A. low pH
B. Intermediate pH
C. high pH
D. any pH

Answer

B

Explanation

Effect of pH on the coupling reaction:
Coupling is best carried out in solutions that are neither too strongly acidic nor alkaline. The reason for this can b seen if we examine a typical case, the coupling of benzenediazonium chloride with dimethylaniline. At high pH, the diazonium ion is present in very low concentration, since most of it has been converted to `ArN = N - OH` and `ArN = N - O^(-)`. Neither `ArN = NOH` (the diazohydroxide) nor `ArN = N - O^(-)` (the diazotate ion) is electrophilic, and thus does not couple with the amine. At low pH, the dimethylaniline will be largely protonated to `ArN^(+) Me_(2)H`, and thus the activating effect of the `- NMe_(2)` group is destroyed, since the nitrogen atom no longer possesses an unshared pair of electrons :