Hydrolytic Cleavage of β-O-4 Ether Bonds of Lignin Model Compounds in an Ionic Liquid with Metal Chlorides

Abstract

The hydrolytic cleavage of β-O-4 ether bonds in lignin model compounds, guaiacylglycerol-β-guaiacyl ether (GG) and veratrylglycerol-β-guaiacyl ether (VG), was studied in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) with metal chlorides and water. FeCl3, CuCl2, and AlCl3 were found to be effective and functioned catalytically in cleaving the β-O-4 bond of GG, although a number of other metal chlorides are considerably less active. AlCl3 functioned more effectively in cleaving the β-O-4 bond of VG than did FeCl3 and CuCl2. After 120 min at 150 °C, GG conversion reached 100%, and about 70% of the β-O-4 bonds of GG were hydrolyzed, liberating guaiacol, in the presence of FeCl3 and CuCl2, while about 80% of the β-O-4 bonds of GG were hydrolyzed in the presence of AlCl3 with 100% GG conversion. About 75% of the β-O-4 bonds of VG were hydrolyzed in the presence of AlCl3 after 240 min at 150 °C. The catalytic activity is associated with the hydrochloric acid, working as the acid catalyst, formed in situ by the hydrolysis of the metal chlorides. A dehydration product and dimer products from GG were detected and proposed as the possible intermediate products in the GG reaction. One possible acid-catalyzed pathway accounting for the guaiacol production from GG is presented.

High Catalytic Efficiency of Lignin Depolymerization over Low Pd-Zeolite Y Loading at Mild Temperature

“…However, challenges remain for catalytic lignin depolymerization by zeolites because the current zeolite-based catalysis requires high temperature (250°C or above), which leads to faster catalyst deactivation by coking and dealumination (Jia et al, 2011). Furthermore, the high temperature for solid acidcatalyzed lignin hydrolysis process possibly results in extensive side products from condensation reactions (Jia et al, 2011;Li et al, 2015).…”

“…Furthermore, the high temperature for solid acidcatalyzed lignin hydrolysis process possibly results in extensive side products from condensation reactions (Jia et al, 2011;Li et al, 2015). Therefore, the development of low-cost zeolite-based catalysts for lignin conversion at mild temperature will enhance lignin conversion to valuable products.…”

Catalytic Conversion of Lignin: Studies on Oxidation of Lignin Model Phenolic Monomer over CoMCM-41 and CoMCM-48 Catalysts

“…It is suggested that catalytic oxidation of lignin or lignin derived fragments is interesting as it is expected to yield functionalized chemicals which can be employed in fine chemical synthesis [1]. In this subject, several reports have been appeared in literature largely focused on catalytic reactions of lignin model compounds which could provide useful information for the development of selective and high yield processes of lignin oxidation namely the conversion of lignin to aromatic monomers catalyzed by triflic acid [2], depolymerization of oxidized lignin to aromatics by formic acid [3], oxidation of phenolic and non-phenolic compounds in presence of metal chlorides in ionic liquid medium [4] are some of the significant achievements in the area of lignin valorization. Among the lignin model phenolic monomers, apocynol, 1-(4-hydroxy-3-methoxyphenoxy)-ethanol is commonly studied over many catalysts.…”

Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

“…The fragmentation of the C OAr linkage tends to generate water-soluble compounds containing phenolic hydroxyl groups [8]. Investigations have been carried out on C O activation of lignin model compounds in solutions [10][11][12][13][14]. Ekerdt and coworkers have studied ␤ O 4 cleavage in ionic liquids/metal solutions [10][11][12].…”