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Pigments & Colorants

Rhein

CAS: 478-43-3

Overview

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. It functions as a natural colorant, antioxidant, and UV-stabilizing agent across pharmaceutical, cosmetic, and industrial applications.

In personal care formulations, it is incorporated as a natural yellow pigment and antioxidant active, particularly in products targeting skin tone evenness and photoprotection. The textile and leather industries use it as a natural dye capable of imparting yellow to orange hues.

This compound is applied to protein-based and cellulosic fibers, often in combination with mordants to improve wash fastness. Pharmaceutical manufacturers source it as a reference standard and active ingredient in preparations derived from traditional botanical extracts.

It contributes to the documented bioactivity of rhubarb-based formulations in various medicinal contexts. In paper processing, it is evaluated as a surface-modifying agent that influences substrate wettability and coating adhesion for specialized industrial uses.

The material is supplied as a yellow to orange crystalline powder for ease of handling. It is available in research-grade and pharmaceutical-grade specifications, with purity levels typically ranging from 95% to 98%+ by HPLC analysis.

Botanical extract standardized forms are also commercially available for buyers sourcing at scale for cosmetic or nutraceutical applications. Our supply chain ensures consistent quality and compliance with international chemical distribution protocols.

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Physical Properties

Melting Point334.8 °C
Boiling Point346.72°C (rough estimate)
Density1.3269 (rough estimate)
AppearanceYellowish Brown Solid
ColorYellow to Dark Orange
Formneat
Water Solubility<0.1 g/100 mL at 17 ºC
Refractive Index1.4413 (estimate)
Log P4.290 (est)

Safety & Handling

Warning GHS07 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. P319 Get medical advice/attention if you feel unwell. P321 Specific treatment (see … on this label). P405 Store locked up. P501 Dispose of contents/container in accordance with local regulations. P264+P265 Wash … thoroughly after handling. P302+P352 IF ON SKIN: Wash with plenty of water. P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing. P332+P317 Get emergency medical help. P337+P317 If eye irritation persists: Get medical advice/attention. Get emergency medical help. P362+P364 Take off contaminated clothing and wash it before reuse. P403+P233 Store in a well-ventilated place. Keep container tightly closed. P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.

Trade & Regulatory

HS Code29189900
Storage Class11 - Combustible Solids
WGK (Germany)2

Other Names

Monorhein | Cassic acid | Rhubarb Yellow | Rheic acid | 45-Dihydroxyanthraquinone-2-carboxylic acid | Chrysazin-3-carboxylic acid | 18-Dihydroxyanthraquinone-3-carboxylic acid | 45-dihydroxy-910-dioxoanthracene-2-carboxylic acid

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Chemical Properties

CAS Number
478-43-3
EC Number
207-521-4
Mol. Weight
284.22
HS Code
29189900

Industries

Documentation