# 22.10: Oxidation Reactions

The reagents usually employed for the oxidation of alkenes (e.g., $$\ce{CrO_3}$$, $$\ce{KMnO_4}$$, $$\ce{H_2O_2}$$, $$\ce{OsO_4}$$) normally do not attack benzene. At high temperatures, benzene can be oxidized to cis-butenedioic (maleic) anhydride by air with a vanadium pentoxide catalyst. Naphthalene can be similarly oxidized to 1,2-benzenedioic (phthalic) anhydride:

Both anhydrides are prepared in this manner on a large scale for use in the production of ester polymers (Section 29-5A). Phthalic anhydride also is prepared by the oxidation of 1,2-dimethylbenzene:

Phthalic anhydride is used to make anthraquinone and to make esters of phthalic acid, which are used widely to plasticize polymers.

Ozonization of aromatic hydrocarbons is possible. Benzene itself gives ethanedial (glyoxal):

The double-bond character of the 9,10 bond in phenanthrene is particularly evident in ozonization. This bond is attacked preferentially, which leads to the formation of a dialdehyde when the ozonide is reduced with iodide ion: