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Tautomerism studies of 3‐( ω ‐sulphoalkylamino)benzoic acids. Substituent effects
Author(s) -
Jesús Marcelo Nunes de,
Hioka Noboru,
Costa Willian Ferreira da,
Maionchi Florângela
Publication year - 2002
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.518
Subject(s) - chemistry , substituent , tautomer , benzoic acid , methylene , medicinal chemistry , acid dissociation constant , potentiometric titration , titration , ionic bonding , derivative (finance) , ionic strength , computational chemistry , organic chemistry , aqueous solution , ion , financial economics , economics
Abstract Two SAABA [3‐ and 4‐( ω ‐sulphoalkylamino)benzoic acid] derivatives, 3‐(3‐sulphopropylamino)benzoic acid and 3‐(4‐sulphobutylamino)benzoic acid, were studied by a potentiometric method to determine two macroscopic constants ( K a 2and K a 3) for each derivative. The combination of these values with 13 C NMR spectroscopic titration data was used to determine their tautomeric ( K T ) microscopic constants at 25.0 °C and ionic strength 1.00 mol dm −3 (KCl). From these results, it was possible to estimate the other microscopic constants and consequently the Hammett substituent constants ( σ m ) for two m ‐aminoalkylsulphonates and the electronic effects of two alkylsulphonate substituents separately. For the m ‐aminoalkylsulphonate substituents the σ m values are −0.12 for m ‐aminopropylsulphonate and −0.27 for m ‐aminobutylsulphonate, and therefore the electron‐donating effect prevails when three methylene units are present. On the other hand, in alkylsulphonate substituents, this effect prevails only for four methylene units. Copyright © 2002 John Wiley & Sons, Ltd.