Method for preparing active monomer rubimaillin from radix rubiae

The method comprises the following steps: (1) taking a dried rubia cordifolia medicinal material, crushing into coarse powder, putting into a steam distillation extractor, adding water, decocting and extracting, collecting distillate, refrigerating, and collecting crystal substances, so as to obtain a yellow flaky rubia cordifolia crude product; and (2) recrystallization: completely dissolving the rubimaillin crude product with a solvent, filtering after complete dissolution, adding distilled water into the filtrate, refrigerating, repeatedly crystallizing, and drying to obtain the rubimaillin. The preparation method disclosed by the invention does not depend on special equipment such as supercritical extraction, does not need various column chromatography technologies for impurity removal and product enrichment, is convenient to operate, and is easy for industrial large-scale production; the use of an organic mixed reagent or a high-toxicity reagent is avoided, and the cost control and the environmental prot