Selective Aerobic Oxidation of Alcohols by Non-metallic Oxidation Systems --- Towards Green Chemistry

Introduction Selective oxidation of organic compounds is one of the major challenges facing the chemical industry. The selective transformation of alcohols to aldehydes and ketones, in particular, is among the most important synthetic operations in organic chemistry. Numerous methods have been reported and widely used for this purpose utilizing various organic and inorganic oxidants, for example DMSO and Cr(VI)-based regents. However, those conventional oxidants are generally employed in greater than one equivalent quantities, with large amounts of toxic waste being produced. From the viewpoints of atom economy, cost efficiency and green chemistry, atmospheric oxygen is obviously superior to other reagents, and thus represents the quintessential oxidant. In the past decades, most efforts have been directed to the development of heterogeneous and homogeneous transition metal-based catalysts, summarized in many recent review papers. In contrast, much less attention has been paid to the development of non-metallic oxidation systems, largely ignoring their inherent advantages. Our interests are in the exploration of the potential of carbon-based materials to be applied as metal-free catalysts for selective aerobic oxidation of alcohols. We have revealed a novel nitric acid-assisted carboncatalyzed oxidation system, called NACOS. Also we have successfully expanded the original system by incorporating nitroxide radical cocatalysts to deliver a more efficient and more environmentally friendly protocol.