A modified RP-HPLC method for the determination of the pKa values of synthesized β-hydroxy-β-arylalkanoic acids

Abstract

The pKa values of twelve ?-hydroxy-?-arylalkanoic acids and ibuprofen were determined using a modified RP-HPLC method. The stationary phase was octadecyl modified (C-18) silica gel, and the mobile phases were mixtures of methanol and one of ten different buffers (60:40 volume ratio). The mean retention time of each compound was plotted against the pH of each of the ten used mobile phases. The inflection point of the obtained sigmoidal curve represents the s w pKa of a compound. Using s w pKa in previously established equations for the specific methanol/buffer mixture, the w w pKa values (in pure water) were calculated. The obtained w w pKa values for the synthesized compounds were in a range from 3.40 to 3.74, and the w w pKa for ibuprofen was 4.27. The Predicted pKa values for this type of compounds in the MarvinSketch 5.11.5. Program were in poor correlation with the experimental results, while in ACD/ /I-Labs pKa values were calculated as a wide range. [Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172041]

pH‐responsive cotton fibre dyed by natural madder dye

“…To simplify the calculation, alizarin was selected as the research model to explain the halochromic behaviour displayed by the alizarin‐based component of madder, because the properties of cotton dyed by madder mainly come from alizarin. The ratio of concentrations of alizarin and alizarin ions was calculated using pKa, which can be predicted with Advanced Chemistry Development (ACD/Labs) pKa DB (version 10.0) software 26,27 . The pKa 1 and pKa 2 of alizarin are 6.90 and 11.94, respectively.…”

“…The ratio of concentrations of alizarin and alizarin ions was calculated using pKa, which can be predicted with Advanced Chemistry Development (ACD/ Labs) pKa DB (version 10.0) software. 26,27 The pKa 1 and pKa 2 of alizarin are 6.90 and 11.94, respectively. The ratios of the concentrations of alizarin and alizarin ions at different pH were calculated according to Equation 2 and are plotted in Figure 3.…”