Elbs persulfate oxidation hydroquinones

The oxidation of phenol with potassium persulfate (K2S2O8) in an alkaline medium to p-hydroquinone is known as the Elbs persulfate oxidation. Elbs used ammonium persulfate for the oxidation of 2-nitrophenol (7.42) to 2-nitro-p-hydroquinone (7.43), but the potassium salt is commonly used for the hydroxylation of phenols. 

Looker et al used a modification of the Elbs persulfate oxidation procedure in which tetraethyl-ammonium hydroxide was used as the base in their synthesis of S,8-quinoflavone. The phenol (65) was oxidized to the hydroquinone, primetin (66), which upon further oxidation with LTA afforded 5,8-flavo-quinone (67) in 34% overall yield (Scheme 24). 

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