CHAPTER 11. Advances in Catalysis for More Sustainable Synthesis of Phenolics

Abstract

In this chapter, we examine the synthesis of phenolic compounds via catalytic reactions and processes, with a special focus on sustainability issues. In recent years, considerable steps forward have been made with the aim of developing greener routes for the functionalisation of phenol and diphenols. Examples of these include: (a) the use of methanol instead of methylchloride or dimethylsulphate for the synthesis of ethers, such as anisole, guaiacol and veratrol, which are key intermediates for the synthesis of a plethora of fine chemicals and specialties; (b) the use of alkylcarbonates for the synthesis of alcohol-ethers (e.g. phenoxyethanol), cresols, and ethers; and (c) the use of aldehydes instead of halogenated alkanes for the hydroxyalkylation of phenolics to alcohols, such as piperonyl alcohol. Indeed, many of these reactions were inspired by the successful industrial application of methanol as an electrophile for the synthesis of o-cresol and 2,6-xylenol. The latter reaction may be considered the very first ‘green’ process for the functionalisation of phenol; surprisingly, despite its industrial use for several decades, only in recent years has the mechanism of this reaction been elucidated. Some emblematic examples of the more sustainable synthesis of phenolic compounds, briefly discussed here, are 2,6-xylenol, guaiacol, vanillin, methylendioxobenzene, phenoxyethanol, hydroxytyrosol and piperonal.