HYDROGEN-BONDED COMPLEXES OF 4-AMINOANTIPYRINE WITH 2-CHLORO-3,5-DINITROBENZOIC ACID AND MONOCHLOROACETIC ACID

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.