Digest paper Recent developments in chemical degradation of lignin: catalytic oxidation and ionic liquids Jinhuo Dai, Antonio F. Patti, Kei Saito ⇑ School of Chemistry, Monash University, Clayton, VIC 3800, Australia article info Article history: Received 30 June 2016 Revised 22 September 2016 Accepted 26 September 2016 Available online 28 September 2016 Keywords: Lignin Lignin oxidation Depolymerisation Ionic liquids Green chemistry abstract Lignin, considered as the second most abundant resource of aromatic chemicals in nature, has attracted a great deal of attention in academia and industry. Recently, numerous investigations have been carried out to consider the production of aromatic chemicals with high value, sourced from lignin. Among all these methods, oxidative treatments of the lignin show a promising way to generate highly function- alised monomeric or oligomeric chemicals, which can be further applied in chemical industries. Moreover, ionic liquids, known as salts with melting point below 100 °C, have also been introduced into oxidative lignin depolymerisation as these are known to disrupt the lignocellulose structure as well as partially dissolving the lignin. Herein, we reviewed various significant pathways of catalytic lignin oxida- tion and also discussed strengths and weaknesses between different lignin oxidation routes reported in the recent literature. Several innovative strategies for oxidative lignin depolymerisation in ionic liquid are also discussed, along with some recommendations and pathways in the field of catalytic lignin oxidation and depolymerisation involving ionic liquids. Ó 2016 Elsevier Ltd. All rights reserved. Contents Introduction.......................................................................................................... 4945 Lignin oxidation ...................................................................................................... 4946 Organometallic catalysed oxidation ................................................................................... 4946 b-O-4 linkages targeted oxidation .................................................................................... 4947 Ionic liquids in lignin chemistry ......................................................................................... 4949 Oxidation of lignin in ionic liquids ................................................................................... 4949 b-O-4 linkages targeted oxidation in ionic liquids ....................................................................... 4949 Conclusion ........................................................................................................... 4950 Acknowledgments ................................................................................................... 4950 References and notes ................................................................................................. 4950 Introduction With the increasing demand for clean energy and renewable materials, biomass utilisation has attracted significant research attention. As an energy source, biomass can not only be used for producing heat via combustion but can also be converted to vari- ous fine chemicals and biofuel. 1,2 The biomass-to-biofuel conver- sion process has been studied for several decades. However, converting biomass into valuable chemicals with an acceptable cost is still a big challenge, and the conversion of the better under- stood carbohydrate components has achieved considerable success (see Table 1). http://dx.doi.org/10.1016/j.tetlet.2016.09.084 0040-4039/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel.: +61 3 9905 4600; fax: +61 3 9905 8501. E-mail address: kei.saito@monash.edu (K. Saito). Tetrahedron Letters 57 (2016) 4945–4951 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet