Calculation of pKa values some 2-sübstituted pyrimidine derivatives

In this study, acidic ionization constants of fourteen number some pyrimidine derivatives (2-benzyl-1H-pyrimidine (1), 2-(2-fluorobenzyl)-1H-pyrimidine (2), 2-(3-fluorobenzyl)-1H-pyrimidine (3), 2-(4-fluorobenzyl)-1H-pyrimidine (4), 2-(2-bromobenzyl)-1H-pyrimidine (5), 2-(3-bromobenzyl)-1H-pyrimidine (6), 2-(4-bromobenzyl)-1H-pyrimidine (7), 2-(3-methylbenzyl)-1H-pyrimidine (8), 2-(2-chlorobenzyl)-1H-pyrimidine (9), 2-(3-chlorobenzyl)-1H-pyrimidine (10), 2-(4-chlorobenzyl)-1H-pyrimidine (11), 2-(2,6-dichlorobenzyl)-1H-pyrimidine (12), 2-(2,6-dichlorobenzyl)-1H-pyrimidine (13), 2-((3,4,5-trimethoksybenzyl)-1H-pyrimidine (14)) were determined in several solvent (izo-propyl alcohol, N,N-dimethylformamide, tert-buty alcohol, acetonitrile) media by potentiometric titration method according to half-neutralization method. Using the potentiometric titration data, acidic ionization constants were calculated. The pKa values obtained experimentally were compared to theoretic pKa values obtained from SPARC programme (online theoretic pKa calculation programme). pKa values of compounds as experimentally were in the range of 14.65 (compound 13) - 16.57 (compound 2) for 2-propanol, 15.03 (compound 13) - 16.70 (compound 5) for N,N-dimethylformamide, 15.00 (compound 13) - 17.44 (compounds 2. and 9.) for tert-butylalcohol, 15.55 (compound 11) - 17.61 (compound 3) for acetonitrile. Furthermore, the structural effect and solvent effect on the acidity of pyrimidine derivatives were discussed Keywords : Pyrimidine, Half-neutralization method, pKa