Journal
MATERIALS
Volume 15, Issue 16, Pages -Publisher
MDPI
DOI: 10.3390/ma15165507
Keywords
pyrazole azo dyes; IR spectroscopy; UV-VIS spectroscopy; density functional theory; color investigation
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Funding
- Project 1.1 of the Coriolan Dragulescu Institute of Chemistry of the Romanian Academy
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This paper describes the synthesis and characterization of eight new pyrazole azo dyes using ethyl 5-amino-3-methyl-1H-pyrazole-4-carboxylate as the diazotization component and various active methylene derivatives as coupling components. The results suggest that these newly synthesized dyes have good color properties and can be used for light color paints in the varnishes industry.
This paper presents the synthesis of eight new pyrazole azo dyes using ethyl 5-amino-3-methyl-1H-pyrazole-4-carboxylate as the diazotization component and various active methylene derivatives as coupling components. These new azo dyes were characterized by spectroscopic (FT-IR, UV-VIS), and spectrometric (H-1 NMR, C-13 NMR, MS) analyses. The dye structures were modeled by the MMFF94s force field and quantum chemical density functional theory (DFT) calculations using the B3LYP functional and the 6-311G(d,p) basis set, in the gas phase. Weak electrostatic hydrogen bonds for the azo and hydrazo dye tautomers were found in the ground state. The CIS, TD (using the B3LYP and M06-2X functionals), and ZINDO methods were used to estimate the dye UV-VIS spectra in ethanol, which were compared with the experimental ones. The anti-configuration arrangement of the pi-bonds and the presence of the prevalent hydrazo dye tautomer were supported by the computed H-1 NMR and C-13 NMR spectra. A good accordance between the experimental and predicted absorption maxima and chemical shifts was observed. Color investigations using the CIEL*a*b* space were conducted for all dyes in powder and for their mixtures in water-based acrylic resins. The results confirm the newly synthesized dyes' color properties and that they might be used for light color paints in the varnishes industry.
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