Heterolytic Activation of Substrate

SCHEME 14.10 Pathways in Pd(II)-catalyzed nuclear oxidation (Elaborated from Ref. [50]). 

Pd-catalyzed orf/to-acetoxylations involve coordination of an arene functional group followed by cyclopalladation, two-electron oxidation to Pd(lV) intermediate, reductive C—O elimination, and, finally, ligand exchange to release the product [12,13]. 

Until recently, noncatalytic stoichiometric oxidations of arenes with toxic inorganic reagents, such as CrOj and K Cr O., MnO and KMnO, OsO, Pb(OAc), TllNOj), nitric acid, ceric ammonium nitrate, and some others, were the main route for the production of oxygenated aromatic compounds [1, 2, 6, 51]. A classic example is the manufacture ( 1500t/year) of vitamin via stoichiometric oxidation of 2-methylnaphthalene (MN) with carcinogenic CrO in sulfuric acid (Eq. 14.14) [52]. 

In this method, about 18 kg of toxic inorganic waste is produced per 1kg of the target product (the so-caUed E-factor is ca. 18) [52]. Chromic acid is also used in theproduction of 9,10-anthraquinone (AQ) from anthracene (AN) [53]. 

Organic peroxy acids are well-known reagents for aromatic hydroxylation of arenes [42, 43]. m-Chloroperbenzoic acid was applied to prepare quinones in low to moderate yields [54]. Peroxy acids can be generated in situ from and carboxylic acids or via aldehyde autoxidation [42]. Arnold et al. reported the synthesis of menadione in ca. 30% yield by using 30% in acetic acid [55]. Following this strategy, Orita et al. oxidized a range of arenes by an excess of in formic 

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