2-methyl-5-hydroxy-1,4-naphthoquinone prodn. - from 1-hydroxy-5-methoxy:naphthalene, useful as antimicrobial against bacteria and fungi

摘要

Prodn. of 2-methyl-5-hydroxy-1,4-naphthoquinone (I) comprises first carboxylating 1-hydroxy-5-methoxynaphthalene by the Kolbe synthesis, then reacting the acid formed with a haloformate ester, in mole ratio at least 1:2 in presence of base, then reducing with a borohydride. The prod. is then oxidised with potassium nitrosodisulphonate (A), photo-oxidised with oxygen and the resulting methoxy cpd. demethylated with an ether-cleaving reagent. Alternatively, (IV) is demethylated first to 1,5-dihydroxy-2-methylnaphthalene, then this oxidised in 2 stages as above. (I), known as plumbagin, in an antimicrobial effective against bacteria and fungi. Good yields of (I) are achieved in fewer stages than in known processes and without the use of the dangerous acetyl peroxide.