Disclosed is a process for the oxidation of at least one chroman (C1) in a solvent mixture comprising at least two solvents or in a C-bearing solvent, with a gaseous compound comprising, essentially consisting of, or consisting of oxygen in the presence of a copper catalyst, said copper catalyst exhibiting the oxidation state (+1) or (+2). A further part of the disclosure is a composition comprising at least one chroman (C1) and/or at least one quinone (C30), a solvent mixture comprising at least two solvents or a C-bearing solvent, a copper catalyst, said copper catalyst exhibiting the oxidation state (+1) or (+2) and a gaseous compound comprising, essentially consisting or consisting of oxygen. A quinone preparation and a process of making same is also part of the invention.
