As the most abundant renewable aromatic resource on Earth, lignin is a preferred starting material for producing bulk chemicals via a sustainable route. In this study, we provide a novel and efficient "clip-off" approach for producing methyl p-coumarate, an important and versatile fine chemical by selective cleavage of the ester linkage in herbaceous lignin in the presence of commercial metal chlorides. When bagasse lignin was depolymerized at 155 °C for 4 h, a 12.7% yield of aromatic chemicals was obtained in the presence of CuCl2, 71.7% of which was identified as methyl p-coumarate (the yield was 9.1%). Further investigation of the structural evolution of lignin revealed that the ester linkages in lignin were efficiently broken via intensive transesterification with methanol accompanied by the simultaneous weakening of the inter-/intramolecular hydrogen bonds. Moreover, this observation of selective cleavage of ester linkages could be further confirmed by the conversion of model compounds with characteristic bonds under identical reaction conditions. Therefore, this work provides a new insight into the production of value-added chemicals from renewable resources.
Keywords: herbaceous lignin; metal chlorides; methyl p-coumarate; transesterification.