Synthesis and spectroscopic investigation of azo derivatives of 4,6-dihydroxy-2-methylpyrimidine

Abstract

Three novel pyrimidine azo dyes having hetereoaromatic diazo component were prepared through a diazo coupling reaction between 4,6-dihydroxy-2-methypyrimidine and diazotised 2-amino-thiazole and 2-amino-(6-subtituted)benzothiazole(s). Their chemical structures were confirmed by using FT-IR, proton and carbon NMR spectroscopy, liquid chromatography/mass spectrometry, and elemental microanalysis techniques. FT-IR spectra of these dyes in solid state show that they exist in hydrazon tautomeric forms. ¹H NMR spectral data in dimethyl sulfoxide indicates that they are predominantly consistent with the hydrazon tautomeric form. The effects of solvent, acid–base, and temperature on the absorption spectra of the dyes were investigated. In the UV–Vis absorption spectra of the dyes in different solvents, there are no linear changing in maximum absorption wavelength values as depending on solvent polarity. The dyes show positive solvatochromism in chloroform and glacial acetic acid (AA) and also one shows more bathochromic shift. UV–Vis absorption spectra recorded at approximately 50 °C of the dyes have no significant change. To detail the properties of the absorption and reveal possible differences on the chemical structure, the data of the dyes were compared with those given for some dyes in the literature. UV–Vis absorption spectra of all dyes in methanol + HCl show that λ_max values of literature dyes have more hypsochromic shifts on contrary to those of methanol + NaOH and dyes reported here have less bathochromic shift. The results show that these dyes may be suitable for applications in the textile industry.

Graphic abstract