Lignin is an alternative renewable feedstock for the production of low molecular weight aromatics. The cleavage of phenyl side-chain C-alpha-C-beta bond is a valid depolymerization pathway to obtain aromatic monomers. The selective cleavage of the C-alpha-C-beta bonds in two lignin model dimers and lignin with ferric sulfate as the catalyst was investigated to narrow the distribution of aromatic monomers. The C-alpha-C-beta bonds in phenolic and non-phenolic dimers were selectively cleaved under microwave irradiation. The acidity promoted the etherification of C-alpha-hydroxyl groups with methanol solvent. Both the etherification and the decomposition of alkenyl products occurred in fast reaction steps, but the formation of alkenyl products was a decomposition-determining step. Density functional theory (DFT) calculations indicated that the phenolic dimer was more thermodynamically favorable to form alkenyl product than non-phenolic dimer, which resulted in the C-alpha-C-beta bond cleavage reactivity of phenolic dieter being higher than that of non -phenolic dimer. Microwave heating contributed to 96.3% of C-alpha-C-beta bond cleavage of organosolv lignin (OL), and a narrow distribution of aromatic monomers which mainly contained vanillin, syringaldehyde, methyl vanillate, and methyl syringate. This work highlights the prospect of microwave-assisted selective cleavage of the C-alpha-C-beta bond to achieve the selective production of aromatic monomers from lignin. (C) 2017 Elsevier B.V. All rights reserved.