Q16-16P - Organic Chemistry (Mcmurry)

Question

The herbicide oxyfluorfen can be prepared by reaction between a phenol and an aryl fluoride. Propose a mechanism.

Step-by-Step Solution

Answer

Step 1: Nucleophilic Aromatic Substitution Reaction

Aryl halides comprising electron-withdrawing substituents undergo nucleophilic substitution reaction. The first step in this reaction is the nucleophilic addition of hydroxide ion to the aromatic ring resulting in a stabilized carbanion intermediate. The elimination of halide ion further leads to a substitution product.

Step 2: Mechanism for the preparation of oxyfluorfen

The base KOH picks up the acidic proton of the phenol to generate a phenoxide ion. The nucleophilic attack of the phenoxide ion on the aryl fluoride generates a negatively charged Meisenheimer complex. The attack of this ion is facilitated by the electron-withdrawing nitro group present in the aryl fluoride. The fluoride ion gets eliminates to produce oxyfluorofen as the product.

Mechanism for the preparation of oxyfluorfen