Conversion of 1,3‐Dimethyl‐5‐(Arylazo)‐6‐Amino‐Uracils to 1,3‐Dimethyl‐5‐(Arylazo)‐Barbituric Acids: Spectroscopic Characterization, Photophysical Property and Determination of pK_a of the Products

Abstract

The study of inter‐conversion between molecules, especially biologically and pharmaceutically important molecules, is extremely important. This study reports the inter‐conversion between two azo‐derivtives: azo‐6‐aminouracils to azo‐barbituric acids. We successfully converted the 1,3‐dimethyl‐5‐(arylazo)‐6‐aminouracils (Uazo‐1 to Uazo‐4) to 1,3‐dimethyl‐5‐(arylazo)‐barbituric acids (BAazo‐1 to BAazo‐4) (where aryl⇒C6H5‐(1); p‐MeC6H4‐(2), p‐ClC6H4‐(3), and p‐NO2C6H4‐(4)) following an acid‐hydrolysis path. The products were characterized using spectroscopic tools like UV‐vis, IR, and NMR spectroscopy. UV‐vis spectra of the as‐prepared dyes reveal that in contrast to the azo‐6‐aminouracils they are hardly responsive towards solvatochromism. IR spectra exhibit three characteristic >CO frequencies for as‐prepared azobarbituric acids instead of two for mother azo‐6‐aminouracils. 1H NMR spectra which reflect the existence of solution species evidence the absence of >CNH group (characteristic imido‐H at the 6‐position of hydrazone species of azo‐6‐aminouracils) and consequence presence of >CO group at the same position in as‐prepared azobarbituric acids. They exhibit structural emissions in the range of 400–440 nm upon excitation at 360 nm. The determined acid dissociation constant (pKa) values of BAazos increase according to the following sequence: BAazo‐2>1>3>4.

Atropisomers and a copper(ii) complex derived from 1,3-dimethyl-5-(8′-quinolinylazo)-6-aminouracil: structures, magnetism and biological properties

“…Moreover, bond lengths of the two distinguishable carbonyl groups (CO) on the uracil moiety for 2 are 1.217(2) (C11–O1) and 1.215(2) Å (C12–O2). 18,19 The slightly longer bond length of the former bond may be due to its involvement in ring current through the O1–C11–C10–N3 framework, which supports the IR data. A weak intermolecular C–H⋯O interaction (C7–H7⋯O1 1 , 2.37 Å) may stabilize the crystals (Table 3 and Fig.…”

“…In solution, the ligand H 2 L exists in hydrazone form. 18 It is confirmed by the presence of singlet peaks at 13.52 ppm and 10.39 ppm, which correspond to hydrazone (N–NH–) and imine (NH–) protons, respectively. 18 These two proton signals are entirely absent in the α-atropisomer, indicating that the triazole ring formed during the synthesis of the 8-azaxanthine derivate.…”

“…18 It is confirmed by the presence of singlet peaks at 13.52 ppm and 10.39 ppm, which correspond to hydrazone (N–NH–) and imine (NH–) protons, respectively. 18 These two proton signals are entirely absent in the α-atropisomer, indicating that the triazole ring formed during the synthesis of the 8-azaxanthine derivate. 17 In addition, a multiplet for aromatic protons present in the quinoline moiety appears in the range of 7.105–9.065 ppm for H 2 L and 7.531–8.982 ppm for the α-atropisomer.…”

“…1,3-Dimethyl-5-(8′-quinolinyl-azo)-6-aminouracil was synthesized following diazotization methods that were previously described. 18,19 An aqueous solution of 8-aminoquinoline (0.763 g, 7.0 mmol) was diazotised using an aqueous solution of NaNO 2 (0.483 g, 7.5 mmol) in 15 mL of 6 N HCl while maintaining 0–5 °C temperature. The diazotized solution was then added dropwise to the 1,3-dimethyl-6-aminouracil (1.08 g, 7.0 mmol) dissolved in acetic acid–water mixture (2 : 3 v/v), resulting in a bright orange coloured solution.…”

“…16 We demonstrated a modified method of Islam and Nagamatsu 15 d using 1,3-dimethyl-5-(arylazo)-6-aminouracil as a starting material and Cu( ii )-salt as a catalyst in DMF solvent to synthesize exclusively 8-(aryl-substituted)-azaxanthine. 17 In continuation of developing chemistry and applications encircled to 1,3-dimethyl-5-(arylazo)-6-aminouracils, 18 their metal complexes 19 and an earlier report on 8-(aryl)-azaxanthine, 17 we attempted to develop 1,3-dimethyl-8-(hetaryl)-azaxanthine tuning the reaction conditions with an emphasis on solvent variation and Cu( ii )-salt. The results have been remained indeed encouraging.…”