Synthesis, identification and application of aldehyde reactive dyes

• –CHO was introduced into reactive dyes as reactive group for the first time.
• Nine aldehyde reactive dyes were synthesized and identified.
• These dyes could dye leather at mild conditions without adding of neutral salts.
• The dyed leather possessed a satisfactory washing-fastness.
• These dyes do not hydrolysis during the process of storage and application.

Nine aldehyde reactive dyes, designated D1- D9, were synthesized. Among them, D1 and D2 were synthesized by “grafting” alizarin red and alizarin yellow GG, respectively, to the α-C of n-butyl-aldehyde; D3 and D4 were synthesized by “grafting” alizarin red and alizarin yellow GG, respectively, to the methyl-C of 4-methyl-cinnamaldehyde; D5- D9 were synthesized by “grafting” alizarin red, alizarin yellow GG or self-prepared colorants to the α-C of glutaraldehyde. UV–Vis, FTIR, ESI-MS, elemental analysis and 1H NMR were applied to identify the target products. Aluminum-tanned wet-white sheep leather was chosen as substrate for the application experiments, and their four dyeing property indexes, i.e., substantivity (S), exhaustion (E), fixation (F) and reactivity (R) were measured. The results indicated that, without adding of neutral salts and under mild conditions (T = 35–45 °C, pH = 4.0–6.5), all these dyes could dye wet-white leather within 1.5 h, and the dyed leather possessed a satisfactory washing-fastness.