Spectral Study of 1,4-bis(3-(2-pyridyl)pyrazol-1-ylmethyl)benzene (PPB): UV-VIS Absorption Spectra Investigation in Single and Binary Solvents and Spectrophotometric Determination of the Dissociation Constant (pKb)
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Benghazi University, LIBYA
Misurata University, LIBYA
Khaled Muftah Elsherif   

Department of Chemistry, Benghazi University, Benghazi, Libya
Online publication date: 2016-12-06
Publication date: 2016-12-06
Eurasian J Anal Chem 2017;12(1):67–82
The effect of solvents of different polarity and hydrogen bonding ability on electronic absorption spectra of PPB was investigated. UV absorption spectra (200-400 nm) were recorded in five single solvents and one binary solvent (DCM-EtOH). PPB has two absorption maxima (250 and 280 nm) due to pyridyl pyrazole and benzene systems. The spectral shifts and absorption maxima in various solvents were correlated with the Kamlet and Taft parameters (α, β and π*) using linear solvation energy relationships. The multiparametric analysis indicates that hydrogen bond donor ability of the solvent (for band I) and non-specific dipolar interactions of the solvents (for band II) play an important role in absorption maxima of PPB in pure solvents. Index of preferential solvation was calculated as a function of solvent composition. Preferential solvation by ethanol (band I) and by dichloromethane (band II) was detected in DCM-EtOH solvent mixture. The pKb of PPB in two solvent mixtures; EtOH – H2O & THF – H2O, were determined using UV-Vis spectrophotometry. Two graphical methods were used to estimate the base dissociation constant (pKb) using absorbance measurements. The resulting average of pKb values in the two solvent mixtures using the two methods were 10.77 and 11.14 with a standard deviation of 0.03 & 0.33, respectively.
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