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Nucleophilic Aromatic Substitutions. Part XIV. . Investigation of the mechanism of hydroxy‐denitration of 4,2‐and 2,4‐chloronitrobenzenediazonium ions as a function of pH
Author(s) -
Pikulik Ivan I.,
Weber Rudolf U.,
Zollinger Heinrich
Publication year - 1981
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19810640607
Subject(s) - chemistry , nucleophile , diazo , hydrolysis , medicinal chemistry , aqueous solution , base (topology) , ion , rate determining step , kinetics , acidity function , catalysis , leaving group , stereochemistry , organic chemistry , mathematical analysis , physics , mathematics , quantum mechanics
Abstract 4,2‐Chloronitrobenzenediazonium ions in aqueous buffer solutions between pH 2.9 and 7.9 do not hydrolyze by dediazoniation as previous authors have assumed, but by denitration. The isomeric 2,4‐compound reacts by denitration ( ca . 70%) and dechlorination ( ca . 30%). The reactions are general base catalyzed. The products and kinetics are consistent with an S N Ar‐mechanism in which the general base‐catalyzed addition of a hydroxyl group at the reacting C‐atom is rate‐limiting. The rate maxima at or near the pH‐values corresponding to (p K 1 + p K 2 )/2 of the diazonium ⇄ cis ‐diazotate equilibria can be rationalized on the assumption that the diazonium ion is the only equilibrium form of the diazo compound which enters the substitution proper, and the superposition of the rate term B ∑k B [B] of all nucleophiles involved (H 2 O, OH − and buffer bases).