Oxidation of phenols Elbs reaction

In alkaline solution phenols are readily oxidised by peroxodisulphate. The normal result of the reaction is the substitution of sulphate in the position para to the hydroxy group, viz. 

Some ortho substitution usually occurs as well. For preparative purposes the sulphate is hydrolysed by acid to give a para-diphenol. Behrman and Walker studied the kinetics of oxidation of 2-hydroxy-pyridine and o-nitrophenol. For both these compounds the kinetics are second order, viz. 

The rate coefficient 2 is proportional to the concentration of phenolate ion thus for 2-hydroxy-pyridine (pA A = 11-6) oxidation below pH 8 is slower than the spontaneous decomposition of peroxodisulphate. For the reaction of 2-hydroxy-P5rridine in 2 M sodium hydroxide, the variation of 2 with temperature is expressed by 

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