Addition-elimination mechanism of nucleophilic aromatic

The Addition-Elimination Mechanism of Nucleophilic Aromatic Substitution... 

THE ADDITION-ELIMINATION MECHANISM OF NUCLEOPHILIC AROMATIC SUBSTITUTION... 

The reaction of benzenesulfomc acid with sodium hydroxide (first entry m Table 24 3) proceeds by the addition-elimination mechanism of nucleophilic aromatic substi... 

The reaction of benzenesulfonic acid with sodium hydroxide (first entry in Table 24.3) proceeds by the addition-elimination mechanism of nucleophilic aromatic substitution (Section 23.6). Hydroxide replaces sulfite ion (S03 ) at the carbon atom that bear s the leaving group. Thus, p-toluenesulfonic acid is converted exclusively to p-cresol by an analogous reaction ... 

Scheme 47. The addition-elimination mechanism of nucleophilic aromatic fluorination in the pyridine series.

The reaction between an alkoxide ion and an aryl halide can be used to prepare alkyl aryl ethers only when the aryl halide is one that reacts rapidly by the addition-elimination mechanism of nucleophilic aromatic substitution (Section 12.21). 

Scheme 1 Addition-elimination mechanisms of nucleophilic aromatic substitution...

Nucleophilic Aromatic Substitution 490 The Addition-Elimination Mechanism of Nucleophilic Aromatic Substitution 492 Related Nucleophilic Aromatic Substitutions 494 12.22 Summary 496 Problems 500... 

The outcome of the regioconservative reactions is vaguely attributed to a "direct displacement" process or to a "chelation-driven nucleophilic aromatic ipso substitution". Presumably both times the authors refer to the well-known two-step addition/elimination mechanism of nucleophilic aromatic substitution. However, to make this option practically feasible, the haloarene has to be activated by powerful electron-acceptors, in particular, nitro groups (as in 2- or 4-halonitroarenes) or by ring-incorporated nitrogen (as in 2- or 4-halopyridines). Without that, the crucial Meisenheimer complex is energetically out of reach. 

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