Mm. Habeeb et Mm. Elkholy, HYDROGEN-BONDED COMPLEXES OF 4-AMINOANTIPYRINE WITH 2-CHLORO-3,5-DINITROBENZOIC ACID AND MONOCHLOROACETIC ACID, Bulletin des Societes chimiques belges, 106(3), 1997, pp. 125-135
1:1 Hydrogen-bonded complexes of 4-aminoantipyrine (4-amino-2,3-dimeth
yl-1-phenyl-3-pyrazoline-5-one; 4AAP) with 2-chloro-3,5-dinitrobenzoic
acid (CNBA) and monochloroacetic acid (MCAA), were prepared in the so
lid state. Fourier transform infrared spectra confirmed the formation
of proton transfer complexes between 4AAP and the two acids under inve
stigation. Analysis of the spectra in the v(NH2) and v(C=O) regions st
rongly suggest that the interaction occurs at the -NH2 site for the 4A
AP-MCAA system while it occurs at the -C=O site for the 4AAP-CNBA syst
em. The equilibrium constants, K-eq, Of proton transfer between 4AAP a
nd the two acids were determined in methylene chloride. 1,2-dichloroet
hane and acetonitrile by using UV spectroscopy. The results are in goo
d agreement with the FT-IR results. It was found that K-eq in acetonit
rile is affected by short range solvation. The thermodynamic parameter
s for the proton transfer complex formation were estimated in 1,2-dich
loroethane. The proton transfer process is entropy and enthalpy contro
lled. The thermodynamic parameters are consistent with the FT-IR and U
V results.