Purification of ethoxyquin and its two oxidation products

2,6-Dihydro-2,2,4-trimethyl-6-quinolone (QI) and 1,8'-bis(1, 2-dihydro-6-ethoxy-2,2,4-trimethylquinoline) (DM) are two oxidation products of 1,2-dihydro-6-ethoxy-2,2,4-trimethylquinoline (ethoxyquin, EQ). This paper describes several methods for the purification of technical grade EQ and for the production of pure QI and DM as standards with the purity required (>99%) for calibration of quantitative determination methods. EQ of high purity was obtained through vacuum distillation followed by a quick column chromatographic purification on silica gel. Preparative scale purity DM could be obtained through recrystallization from methanol, but QI could be purified only by a high-pressure liquid chromatographic method.