Synthesis of 2-methyl-1,4-naphthoquinone (vitamin K3) using nanostructured gold catalysts in acetic acid and in supercritical carbon dioxide

Abstract

The synthesis of 2-methyl-1,4-naphthquinone (vitamin K3) by the oxidation of 2-methylnaphthalene and 2-methyl-1-naphthol using nanostructured gold catalysts supported on super-cross-linked polystyrene ((5% Au)/SCP) has been investigated. The temperature effect on the oxidation process is reported. An attempt has been made to replace acetic acid, a common solvent, with supercritical carbon dioxide, an environmentally friendly substance. With supercritical CO2, the selectivity of the process toward 2-methyl-1-naphthol oxidation into the target product remains at a high level (close to 100%) and the substrate conversion is 10–15% higher. In the oxidation of 2-methylnaphthalene, use of supercritical CO2 leads to a dramatic decrease in substrate conversion and target-product selectivity. This is due to the fact that peracetic acid, which is the main oxidizer in this process, does not form under these conditions. The nanostructured gold catalysts are usable in the selective oxidation of 2-methyl-1-naphthol and 2-methylnaphthalene into 2-methyl-1,4-naphthquinone (99 and 58 %, respectively).