Natural anthraquinonoid colorants as platform chemicals in the synthesis of sustainable disperse dyes for polyesters

Natural anthraquinonoid dyes (alizarin and purpurin) were used as platform chemicals to synthesise sustainable alternatives to existing synthetic dyes by alkylation of hydroxy groups in the 1- and 2-positions. In comparison with the parent compounds, the derivatised dyes were insensitive to pH change, insoluble in alkali and the λmax for the mono-alkylated derivatives was unchanged and that of the bis-alkylated derivatives was reduced by 53–54 nm. Melting points decreased with derivatisation as the ability of the dyes to form inter-molecular interactions decreased. Dye exhaustion and colour strength values for dyeings on PET were relatively high for the parent and mono-alkylated derivatives and lower for the larger bis-alkylated derivatives. Mono-alkylation with methyl-4-butanoate groups improved the dyeing properties of the dyes on PLA. All dyeings displayed excellent wash fastness and the light fastness was improved in the case of the mono-alkylated derivatives owing to the removal of the photo-sensitive 2-hydroxy group.