There is a “green” route for synthesizing adipic acid from cyclohexane
by oxidation hydrogen peroxide in a halide free condition
[11,34]. This process is described as a “green” route because it did
not produce the greenhouse gases. This process is illustrated in
Fig. 1C. Recently, a N2O-free process for adipate synthesis has been
reported [31] (Fig. 1B). In a simple experiment, ozone gas was bubbled
through cyclohexane with concurrent UV irradiation at room
temperature. There was no metal catalyst or solvent involved in
this method. After 2–8 h, adipic acid was produced.