Question

Hello all please take a look at the following lab about preparation of para red. basically a diazonium salt (p-nitroaniline) was coupled with a phenol (2-napthol) to produce para red dye.

>> QUESTION: Explain why coupling of p-nitrobezne diazonium chloride occurs mainly at the position that is para to the -n(ch3)2 group of N,N-dimethylaniline but ortho to the -oh group of 2-napthol

May be helpful to to write out a few resonance forms of the intermediate to explain this. The lack of para coupling in napthalene is easy to explain but we have two distinct ortho positions, and that selectively is maybe harder to explain.

Heres the overall reaction if confused:

Diazotization NH + 2HCI + NaNO, ) + 2H2O + NaCl NO p-nitroaniline NO p-nitrobenzenediazonium chloride Coupling NO =N& + NaCl ОН NO 2-naphthol (sodium salt) NO DIO Para Red

Answer 1

va-position OV Logo cha cu Әи «р. Ryo Carbanional Bensafic position RC Moesteingle) I pro Carb he Callification) Allylica Caron is less stable than bensylic Carbanion. Hence, the coupling occurs at the x-position.