# Design, ecofriendly synthesis and spectroscopy of new pyrazolopyrimidine derivatives as potential candidates for dyeing and ultraviolet protection of wool fabrics

## TL;DR

Researchers developed new water-soluble pyrazolopyrimidine dyes that can be used to dye wool fabrics and provide UV protection.

## Contribution

The study introduces a new class of pyrazolopyrimidine dyes suitable for wool dyeing and functional finishing with improved UV protection.

## Key findings

- Microwave heating significantly reduced synthesis time from hours to minutes.
- Dyed wool fabrics showed high color strength (K/S of 40.86) under optimal conditions.
- Dyeing did not create new crosslinks in wool keratin macromolecules.

## Abstract

Pyrazolopyrimidine dyes are usually used as disperse dyes for coloring polyester (PET) fabrics due to lack of solubilizing groups. Herein, new water-soluble pyrazolopyrimidine dyes were synthesized and used as acid dyes for wool dyeing, which makes them suitable candidates for dyeing wool/PET blends. Designing and synthesizing a new pyrazolopyrimidine moiety via a one-pot multi-component reaction were reported using 4-((3,5-diamino-1H-pyrazol-4-yl)diazenyl)benzenesulfonic acid 1; its behavior and reactivity toward some 2-(aryl-diazenyl)malononitrile (ADM) derivatives was investigated. Both conventional and microwave heating were used in this investigation. The structures of the synthesized compoundswere confirmed using spectroscopic data. The synthesized compounds were used as potential candidates for dyeing and functional finishing of wool fabrics. The dyeing process was carried out by the exhaustion method at different dyeing conditions, including dye shade, pH, temperature, and duration. The color strength (K/S) of the dyed wool fabrics along with the dye absorption was measured, from which the dye exhaustion percentage, the dye fixation percentage, and the total dye fixation on the dyed fabrics were calculated. The colorimetric coordinates (L*, a*, b*) as well as the chromaticity (c) and hue (h°) of the dyed fabrics were monitored. The chemical structures of the dyed fabrics were examined by determining their urea-bisulfite solubility (U-BS) and base combining capacity (BCC). The effect of the dyeing on some inherent properties of wool was assessed. Results of this investigation proved that the synthesized dyes (SDs) are suitable candidates for dyeing wool fabrics.Results of this investigation revealed that the time consumed for synthesis of the said compounds were reduced from 4–10 h using the conventional heating to 1–4 min up on using microwave heating technique.The nature of the substituent of the ADM derivatives had significant influence on the K/S and the colorimetric data of the dyed fabric.The highest K/S (40.86) of the dyed fabrics was obtained when dyeing of wool was carried out using 3% of the synthesized dye-2 at pH 4 and 90 °C for 1 h. The ultraviolet protection factor of the dyed wool fabrics was immensely improved, with a very limited decrease in the tensile properties. The results of U-BS and BCC indicated dyeing wool with the SDs did not result in the formation of new crosslinks between the polypeptide chains of wool keratin macromolecules. Due to their sulfonic groups, the SDs bind to wool as acid dyes by forming salt links with the protonated amino groups in wool when in acidic media.

The online version contains supplementary material available at 10.1038/s41598-026-38297-x.