Extractional Spectrophotometric Determination of New Substituted Tricyclic Pyridopyrimidines

A simple and sensitive method was developed for the extractional spectrophotometric determination of new substituted tricyclic pyridopyrimidine compounds (I) (7-chloro-2,3-trimcthylene-pyrido [1.2-a] pyrimidine-4-one), (II) (7-bromo-2,3-tetramethylene-pyrido [1,2-a] pyrimidine-4-one) and (III) (7- methyl-2,3-tetramethylene-pyrido [1,2-a] pyrimidine-4-one). The method was based on the formation of ion-pair complexes between compounds I, II and III with bromothymol blue (BTB). The absorbance of the produced ion-pair complexes were measured at 414, 418, and 418 nm for I-BTB, II-BTB and III- BTB respectively. Beer’s law was obeyed over the concentration ranges 0.04 -5.10, 0.12- 5.58 and 0.76-6.82 ug/ml for compounds I, II and III, respectively. Molar absorptivities for compounds I, II and III, were found to be 8.0 x 10ᶟ, 8.0 x 10ᶟ and 1.2 x 10⁴ L mol⁻¹ cm⁻¹, respectively. All factors affecting the sensitivity and reproducibility of the method were studied such as pH, shaking time, concentrations of BTB, amount of buffer, type of solvcnt, number of extraction times and stoichiometry. The method was applied for spectrophotometric determination for compounds I, II and III.