4631370379

402 J. KOWALSKI, J. PŁOSZYNSKA, A. SOBKOW1AK

ABSTRACT

The preparation of 2-methyl-1,4-naphthoq uinone (menadione) is a chal-lenging problem in catalysis research. This reaction is the key step in the synthesis of vitamin K and its derivatives.

The preparation of naphthoąuinones usually reąuires the direct oxidation of arenes by stoichiometric quantities of chromie acid/sulfuric acid [3-6]. The reaction can be also achieyed by the use of Ce(IV) compounds and other transition metal compounds as oxidants [7-11] and with hydrogen peroxide [13, 14]. The other approach is to use Diels-Alder reaction between 1,3-buta-diene and p-benzoquinone with the subsequent oxidation of the adduct formed [20, 21]. The indirect electrolysis with ruthenium compounds and dichromate as mediators were also applied in the process [25, 26]. In the previous work [34] we reported that the electrochemical oxidation of 2-methylnaphthalene in glacial acetic acid gives monoacetates, mainly 2-methylnaphthalene-l-acetate, but 2-methylnaphthalene-l,4-diacetate and 2-methyl-l,4-naphthoquinone were also formed. This prompted us to investigate the electrochemical behavior of 2-methylnaphthalene-l,4-diacetate [38]. It is shown that the electrochemical oxidation of the compounds in glacial acetic acid yields 2-methyl-1,4-naph-thoquinone as a sole product. The process is irreversible and diffusion control-led. The materiał and current yields of the process are 94 and 99%, respec-tively.