rubelin

Rubelin is a term that appears in older chemical and dye literature as an organic substance associated with the madder plant Rubia tinctorum. In contemporary chemistry, rubelin is not regarded as a single, well-defined compound; instead, the name has been used inconsistently to refer to different substances, which has led to ambiguity about its true identity.

Historical sources describe rubelin as a red pigment or dye constituent within extracts of madder. Some accounts linked rubelin to broader classes such as anthraquinones or flavonoid-like constituents, but these identifications varied between authors and time periods. Because there is no standardized definition, modern databases and reference works do not converge on a definite structure, molecular formula, or spectral data for rubelin.

The inconsistent usage of the term means rubelin cannot reliably be assigned to a specific chemical class. Reported descriptions range from pigment-related substances to natural products with limited characterization, and there is no universally accepted chemical profile.

Occurrence and extraction notes suggest that rubelin was mentioned in the context of madder root preparations and historical dye mixtures. It is not listed as a major or routinely characterized dye component in current analytical references, and its presence is typically described as historical or incidental rather than foundational to modern dye chemistry.

Uses and current status: rubelin is largely of historical interest and is not used as a defined compound in contemporary dyes or pharmaceuticals. References to rubelin tend to emphasize ambiguity or deprecation, reflecting the term’s lack of a stable, widely recognized definition.

See also: alizarin, purpurin, Rubia tinctorum.