STUDIES IN ELBS PERSULPHATE OXIDATION. PART I. OXIDATION OF SOME COUMARIN DERIVATIVES

4-Methylcoumarin, 7-methoxy-4-methylcoumarin, 5-methoxy-4 : 7^-dimethylcoumarin, 5 : 7^-dime^­thoxy-4-methylcoumarin and 7 : 8-dimethoxy-4-methylcoumarin have been oxidised with potassium persulphate in alkaline solution and the corresponding 6-hydroxycoumarin derivatives are obtained in good yields. The methyl ethers have been demethylated and the hitherto unknown 5 : 6-dihydr­oxy-4 : 7-dimethyl-, 5 : 6 : 7-trihydroxy-4-methyl -, and 6 : 7 : 8-trihydroxy-4-methylcoumarins have been obtained. The completely methylated coumarins are dissolved by opening out the α-pyrone ring by warming on a steam-bath and then oxidised with potassium persulphate. In actual practice therefore it is the o-hydroxycinnamic acid derivative which is oxidised in each case, the coumarin ring being formed again when the reaction mixture is acidified.