Effect of the N-based ligands in copper complexes for depolymerisation of lignin

Abstract

Several organic soluble N-based ligands and their copper complexes were firstly investigated as catalysts to depolymerise organosolv lignin in the organic solvent, dimethylformamide (DMF) and an ionic liquid (1-ethyl-3-methylimidazolium xylenesulfonate, [emim][ABS]). The results of screening depolymerisation reactions in DMF and [emim] [ABS] showed that all the copper-amine complexes catalysed lignin depolymerisation more efficiently in ionic liquids than in DMF. Among the seven types of ligands, copper complexes with two types of ligands ((E)-N-(pyridin-2-ylmethylene)aniline and (E)-4-methoxy-N-(pyridin-2-ylmethylene)aniline depolymerised the lignin more efficiently than the others. These two copper complexes with N-based ligand were further studied to determine the most efficient conditions for the depolymerisation of the lignin. The most effective depolymerisation by conditions involved treatment at 180°C for 12 h in [emim][ABS]. Cyclic voltammetric studies were carried out to investigate the reversible potential associated with the copper centers of their complexes with these N-based ligands. The results suggest that two types of ligands have more positive reversible potentials than those of other copper complexes.

Zinc (II), palladium (II) and cadmium (II) complexes containing 4‐methoxy‐N‐(pyridin‐2‐ylmethylene) aniline derivatives: Synthesis, characterization and methyl methacrylate polymerization

“…Ligands (L n = L‐a–L‐c) in the current study were synthesized as reported previously . Complexes, [(L) n MX 2 ] m (L = L‐a–L‐c; M = Zn, Pd; X = Cl; M = Cd; X = Br; n , m = 1 or 2; 67–98% yields), were obtained by direct ligation of metal starting materials with ligands in 1:1 ratio in CH 3 CN or EtOH at ambient temperature (Scheme ).…”

“…Modified methylaluminoxane (MMAO) was purchased from Tosoh Fine Chemicals as 5.90% weight aluminum of a toluene solution and used without further purification. Ligands L‐a , L‐b and L‐c have been prepared by literature methods. Complexes [(L‐a)PdCl 2 ] , [(L‐a)ZnCl 2 ] , ( [(L‐a)Cd(μ – Br)Br] 2 and [(L‐b)PdCl 2 ] have been synthesized as described previously.…”

“…Ligands (L n = L-a-L-c) in the current study were synthesized as reported previously. [25,[45][46][47] Complexes, [(L) n MX 2 ] m (L = L-a-L-c; M = Zn, Pd; X = Cl; M = Cd; X = Br; n, m = 1 or 2; 67-98% yields), were obtained by direct ligation of metal starting materials with ligands in 1:1 ratio in CH 3 CN or EtOH at ambient temperature (Scheme 1). The structures of these complexes were characterized by 1 H-NMR, 13 C-NMR, Fourier transform-infrared (FT-IR) and X-ray diffraction.…”

Oxidized Lignin Depolymerization using Formate Ionic Liquid as Catalyst and Solvent

“…Common lignins, such as organosolv lignin, alkali soluble lignin and kraft lignin were selected for screening the depolymerization reaction. A methanol separation method was presented in our previous work …”

CuSO4/H2O2-Catalyzed Lignin Depolymerization under the Irradiation of Microwaves

“…7,18 Compared to other methods, lignin reduction and oxidation methods utilize milder conditions to degrade lignin, which can thus be suitable for the industry. 19,20 Our group has previously reported several oxidative lignin depolymerization strategies 21,22 and also reviewed the recent developments in the chemical degradation of lignin involving catalytic oxidation. 23 Lignin catalytic oxidation methods normally show high selectivity in the products formed.…”