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Protonation of Pyridine Monocarboxylate‐N‐Oxides – Determination of Thermodynamic, Absorbance and Ion Interaction Parameters
Author(s) -
Dumpala Rama Mohana Rao,
Rawat Neetika,
Tomar Bhupendra S.
Publication year - 2017
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201601322
Subject(s) - protonation , chemistry , potentiometric titration , pyridine , enthalpy , endothermic process , deprotonation , ionic strength , ionic bonding , ion , inorganic chemistry , thermodynamics , organic chemistry , adsorption , aqueous solution , physics
The thermodynamic parameters ( pKa, ΔH, ΔG, ΔS ) for the protonation of three isomeric pyridine monocarboxylate‐N‐oxides (PCNO) namely picolinate‐N‐oxide (PANO) nicotinate‐N‐oxide (NANO) isonicotinate‐N‐oxide (IANO) were determined in the present study. The pKa determined by potentiometry follow the order: PANO > IANO > NANO at all ionic strengths. The calorimetric results revealed that the PANO protonation was endothermic and the other are exothermic, indicating the entropy driven protonation of PANO while the other two has minor contribution of enthalpy as well. The ion interaction parameters for PCNOs are obtained by determining the pKa for the same at various ionic strengths ( I =0.1 −3.0 M) and the data is extrapolated to find pKa0 ( pKa at I=0) by specific ion interaction theory (SIT). The pKa / pKa0 determined by absorption spectra are also in line with potentiometric results. The energetics and variations in charge densities on individual atoms on protonation were calculated theoretically. PCNOs protonation are compared with its base moieties: pyridine monocarboxylates to interpret the effect of the N‐oxide moiety on the protonation thermodynamics.