Supercritical carbon dioxide fluid-assisted green production and dyeing of N,4-dialkyl-substituted 1,8-naphthalimide derivatives

In this study, three N,4-dialkyl-substituted 1,8-naphthalimide fluorescent dyes (NPBA, NPHA, and NPOA) were synthesized in supercritical carbon dioxide (scCO₂) by reacting 4-bromo-1,8-naphthalic anhydride with three amines (n-butylamine, n-hexylamine, and n-octylamine). The optimal reaction conditions and highest yields of these dyes were obtained. The yield of NPHA was 92% ± 0.57% using an organic solvent-free synthetic method. The results also indicate that the reaction time was gradually shortened by elongating the alkyl chain in the amines, and the required reaction pressure was 12 MPa or lower. Additionally, the dyeing of polyester fabrics with these three dyes was investigated using scCO₂. The optimal dyeing time and temperature for NPBA were 70 min and 150 ℃, but they decreased at 10 gradients with the addition of two carbon atoms to the alkyl chain in the amines. The optimal dyeing pressure increased from 20 MPa to 24 MPa.