Pigments & Colorants
REACH
Rhein
CAS Number
478-43-3
EC Number
207-521-4
What is Rhein?
Rhein (CAS 478-43-3), also known as Cassic acid and Rhubarb Yellow, is an anthraquinone compound derived from rhubarb root and related botanical sources.
Where is Rhein used?
- Pharmaceuticals: reference standard and active ingredient in preparations from traditional botanical extracts
- Personal care: natural yellow pigment and antioxidant active for skin tone evenness and photoprotection
- Textile and leather: natural dye imparting yellow to orange hues
- Paper processing: surface-modifying agent influencing substrate wettability and coating adhesion
- It is applied to protein-based and cellulosic fibers, often with mordants to improve wash fastness.
Commercial specifications
- Purity typically 95% to 98%+ by HPLC
- Botanical extract standardized forms commercially available
Other Names (Synonyms)
Monorhein|Cassic acid|Rhubarb Yellow|Rheic acid|4,5-Dihydroxyanthraquinone-2-carboxylic acid|Chrysazin-3-carboxylic acid|1,8-Dihydroxyanthraquinone-3-carboxylic acid|4,5-dihydroxy-9,10-dioxoanthracene-2-carboxylic acid
What are the physical properties of Rhein?
Melting Point 334.8 °C
Boiling Point 346.72°C (rough estimate)
Density 1.3269 (rough estimate)
Appearance Yellowish Brown Solid
Color Yellow to Dark Orange
Form neat
Water Solubility <0.1 g/100 mL at 17 ºC
Refractive Index 1.4413 (estimate)
Log P 4.290 (est)
How is Rhein classified and handled safely? Learn More
Warning
GHS07· Irritant
Hazard Statements
H315 Causes skin irritation
H319 Causes serious eye irritation
H335 May cause respiratory irritation
Precautionary Statements
P261 Avoid breathing dust/fume/gas/mist/vapours/spray.
P264 Wash … thoroughly after handling.
P271 Use only outdoors or in a well-ventilated area.
P280 Wear protective gloves/protective clothing/eye protection/face protection.
Which trade and regulatory codes apply to Rhein?
HS Code 29189900
Storage Class 11 - Combustible Solids
WGK (Germany) 2