Transiting from Adipic Acid to Bioadipic Acid. 1, Petroleum-Based Processes

Adipic acid, which is a very important commodity chemical, is traditionally manufactured industrially by an aged and unsustainable multistep process that involves homogeneous catalysts, aggressive oxidants (concentrated nitric acid) and the production of large quantities of the greenhouse gas nitrous oxide. Much research and development into alternative and cleaner process routes to adipic acid have been carried out over the past 70 years. Improved reaction schemes have invoked variations in fossil raw materials (from benzene and phenol to cyclohexane, cyclohexanol, cyclohexanone, cyclohexene, butadiene, and adiponitrile, etc.), oxidants (O2, air, H2O2, t-BuOOH, ozone), catalysts (homogeneous, heterogeneous, phase transfer, biomimetic) and reaction conditions (low temperature, atmospheric pressure, and solvent-, metal-, halide-, and corrosion-free). No single proposed alternative pathwaysome of which are purely academicsimultaneously addresses the problems of petrochemical origin, toxic starting materials or reagents, generation of environmentally incompatible byproducts, use of forcing reaction conditions, and cost in an entirely satisfactory manner, despite very intense efforts. Recently, more benign bio-based reaction pathways have been proposed starting from renewables, such as glucose or vegetable oils (which will be discussed in Part 2 of this series).