Synthesis Of Metel Complexes Of Mimic Enzyme Containing Macrocyclic Triamine Lignd And Its Application In Low Temperature Bleaching Of Cotton Fabric As Catalyst For H₂O₂

Bleaching of cellulose fabric with hydrogen peroxide is conducted usually at high temperature and highly alkaline conditions, which leads to a more energy consumption and fiber damage. Therefore, it is significant to reduce the temperature in bleaching process by using catalysts which have high efficiency in catalytic activity. Metal complexes of macrocyclic polyamines, which are a kind of mimic enzyme, are potent catalysts and extensively employed in laundry cleaning, pulp bleaching and organic synthesis. However, bleaching of raw cotton using the complex as catalyst for hydrogen peroxide is seldom reported.In the first part of this study,1,4,7-trimethyl-1,4,7-triazacyclononane (L) was selected as target ligand. Firstly,1,4,7-trimethyl-1,4,7-triazacyclononane was synthesized via a six-steps method. Secondly, a simplified and promising route for synthesis of 1,4, 7-trimethyl-1,4,7-triazacyclononane was developed. The synthesis of 1,4,7-trimethyl-1,4, 7-triazacyclononane only consists four steps and gave a yield of 34%. Finally, three binuclear manganese complexes were prepared by a reaction of ligand with metal manganese salts or iron salts. The chemical structures of the complexes were characterized by FTIR, UV-Vis, element analysis and TGA and confirmed that the prepared compounds were the desired complexes and had the structure:[MnⅣ2 (μ-O)3L2][PF6]2.1H2O (MnTACN),[L2Mn2Ⅲ(μ-O) (μ-CH3CO2)] [PF6]2.1H2O (MnAcL),[L2Fe2Ⅲ(μ-O) (μ-CH3CO2) 2] [PF6]2.1H2O (FeAcL)The application of the three complexes in low temperature bleaching of cotton knitted fabric using exhaustion method was investigated in the second part of this study. Firstly, the complex MnTACN which shows the highest catalytic activity in the low temperature as catalyst for H2O2 was screened out through preliminary experiment. Secondly, low temperature bleaching of scoured cotton knitted fabric with MnTACN and effect of key bleaching variables such as temperature, concentrations of MnTACN, hydrogen peroxide and stabilizer on the bleaching performance were investigated in detail. The optimal bleaching process was obtained through orthogonal test and listed as follows:30% H2O2 10 g/L, MnTACN 10μmol/L, pH=10.5, stabilizer 1.5 g/L, liquor to goods ratio of 20:1, and the process was carried out at 70℃for 60 min. The fabric bleached with the optimal process achieves the whiteness index to 73.7% and the bursting strength retention is 92%. The whiteness index and wettability of the fabric bleached with MnTACN at low temperature are comparable with those of fabric bleached with the conventional high temperature technique. The bursting strength retention is much better for the fabric bleached at low temperature. Thirdly, combined scouring using alkaline pectinase or scouring agent and catalytic bleaching of cotton gray fabrics was studied. The results indicated that MnTACN was compatible with scouring agent HS-188 and KDN and the treated fabrics could reach a whiteness index of 65% with high wettability and bursting strength retention. The properties of the fabric treat with alkaline pectinase were inferior to those treated with scouring agent. Nevertheless, the process still possesses practical applicability for those fabrics with no need for high degree of whiteness. Finally, we found that acetonitrile could enhance the bleaching effect of MnTACN in the catalytic bleaching system at low temperature.In the last part of this study, morin(3,5,7,2',4'-pentahydroxyflavone) was selected as model pigment owing to its presence in native cotton fiber and the kinetics of catalytic bleaching of morin with MnTACN as catalyst for H2O2 was investigated under homogeneous system. The results showed that the catalytic bleaching reaction of MnTACN as catalyst for H2O2 belong to first order reaction, and the activation energy of H2O2/MnTACN system and H2O2/MnTACN/acetonitrile system was 18.81 kJ.mol-1 and 19.40 kJ.mol-1, respectively. The decoloration rate of morin was improved significantly by introducing a small amount of acetonitrile into the system of H2O2/MnTACN. In addition, the decoloration mechanism of the catalytic system of H2O2/MnTACN/acetonitrile was speculated base on the experimental results and literatures. However, what role acetonitrile played in the discolored process is still unknown and deserves further studies.