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Azo‐Coupling Reactions Used in Analytical Chemistry: The Role of Reactants, Intermediates, and Aqueous Medium
Author(s) -
Pankratov Alexei N.
Publication year - 2004
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.200490143
Subject(s) - chemistry , azo coupling , aqueous solution , regioselectivity , protonation , computational chemistry , coupling reaction , chemical reaction , aqueous medium , quantum chemistry , amine gas treating , selectivity , coupling (piping) , reaction coordinate , naphthalene , quantum chemical , reaction mechanism , chemical physics , organic chemistry , molecule , catalysis , ion , mechanical engineering , engineering
Abstract A quantum‐chemical study of the analytically important azo‐coupling reactions of naphthalen‐1‐amine ( 1 ) with naphthalene‐1‐diazonium ( 2 ) and 4‐sulphobenzenediazonium ( 8 ) cations has been carried out. The reactions have been found to be frontier‐controlled, and their regioselectivity is unequivocally determined by the thermodynamics of the intermediate σ ‐complexes, as well as by the aqueous medium. The latter defines high positional selectivity, providing the decision between two possible reaction routes predicted on the basis of quantum‐chemical computations for separate molecular systems. As a result, azo coupling occurs at the 4‐ rather than at the 2‐position of 1 . Furthermore, the aqueous medium makes the selection of analytical forms – protonated azo‐coupling products with a quinonehydrazone‐type structure.