Solvent Red 24, also known as Sudan IV, is a synthetic azo dye primarily used for coloring oils, waxes, plastics, and solvents. It is classified as a Category 2 carcinogen by the European Union, meaning it is suspected of being carcinogenic to humans. A major concern associated with Solvent Red 24 is its ability to release hazardous aromatic amines, such as o-Toluidine, through the cleavage of the azo bond. These aromatic amines are classified as EU22 hazardous substances and are recognized carcinogens. Solvent Red 24 is included in the Screening Assessment for Aromatic Azo and Benzidine-based Substance Grouping Certain Azo Solvent Dyes, as noted in Section 7.2.2 of the report by Environment Canada.

Chemical Composition and Structure

Solvent Red 24 is an azo dye consisting of an azo bond (-N=N-) connecting two aromatic rings. Its chemical structure includes groups that can degrade into aromatic amines, particularly o-Toluidine, a known carcinogen. The presence of the azo bond gives the dye its characteristic bright red color but also poses significant health risks due to its potential degradation into hazardous by-products.

Physical Properties

Solvent Red 24 appears as a bright red crystalline powder. It is soluble in organic solvents such as oils and waxes but insoluble in water. It has good light and heat stability, making it suitable for use in industrial environments, particularly in sectors that require coloring oils and solvents.

Production Process

Solvent Red 24 is produced through an azo coupling process, where aromatic amines are treated with nitrous acid to form a diazonium salt, which is then coupled with another aromatic compound. The production process must be carefully monitored to prevent the release of hazardous aromatic amines, such as o-Toluidine, which pose significant health risks.

Applications

• Coloring Oils and Waxes: Solvent Red 24 is widely used to color lubricating oils, waxes, and fuels due to its high solubility in organic solvents.

• Plastic Industry: The dye is also used in coloring plastics and other synthetic materials, where a stable bright red color is required.

• Inks and Coatings: In some industrial applications, it is used for coloring inks and coatings that require resistance to environmental conditions.

Health and Safety Concerns

Carcinogenicity

Solvent Red 24 is classified as a Category 2 carcinogen by the European Union, meaning it is suspected of causing cancer in humans. The primary concern is its potential to degrade into hazardous aromatic amines, such as o-Toluidine, through azo bond cleavage. o-Toluidine is a well-known carcinogen, particularly associated with bladder cancer. This makes Solvent Red 24 a highly controlled substance in industrial settings and banned in many consumer products.

Toxicity

In addition to its carcinogenicity, Solvent Red 24 can cause acute toxicity if ingested, inhaled, or absorbed through the skin. Prolonged exposure may result in skin and respiratory irritation and increase the risk of cancer. For this reason, safety measures in industrial processes involving this dye must be stringent, with protocols aimed at minimizing worker exposure.

Environmental and Safety Considerations

Solvent Red 24 is not biodegradable and can accumulate in the environment, particularly in aquatic ecosystems. Its ability to degrade into toxic aromatic amines poses a significant environmental health risk. Regulations enforce strict waste management and disposal protocols to prevent environmental contamination. Companies using this dye must comply with stringent regulations to protect the environment and public health.

Regulatory Status

Due to its classification as a possible carcinogen, the use of Solvent Red 24 is heavily regulated in the European Union and many other countries. Its use is banned in cosmetics, food products, and textiles intended for consumer use. However, it continues to be used in certain industrial applications, where strict safety measures are enforced to reduce the risk of exposure.

Applications Under Strict Control

• Manufacturing: Despite the carcinogenic risk, Solvent Red 24 is still used in some industrial applications for coloring oils and waxes.

• Research and Analytical Use: In some research contexts, the dye is used under controlled conditions, where strict safety protocols are applied.

Safety

 The problem with azo dyes (monoazo or diazo) is photocatalytic degradation leading to oxidation and the subsequent formation of impurities such as aromatic amines, some of which have carcinogenic activity. (Chung KT, Stevens SE Jr, Cerniglia CE. The reduction of azo dyes by the intestinal microflora. Crit Rev Microbiol. 1992;18(3):175-90. doi: 10.3109/10408419209114557. )

Molecular Formula  C₂₄H₂₀N₄O

Molecular Weight  380.4 g/mol

CAS     85-83-6

UNII    I35E9QU96C

EC Number  201-635-8

CHEBI:88014

CHEMBL1707454

DTXSID8041743

Synonyms:

Scarlet red

Sudan IV

Solvent red 24

References__________________________________________________________________________

Screening Assessment Aromatic Azo and Benzidine-based Substance GroupingCertain Azo Solvent Dyes. Environment and Climate Change Canada Health Canada May 2016

Synopsis. Pursuant to sections 68 or 74 of the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of the Environment and of Health have conducted a screening assessment on 22 Azo Solvent Dyes. These substances constitute a subgroup of the Aromatic Azo and Benzidine-based Substance Grouping being assessed as part of the Groupings Initiative of Canada’s Chemicals Management Plan (CMP) based on structural similarity and applications. Substances in this grouping were identified as priorities for assessment as they met the categorization criteria under subsection 73(1) of CEPA 1999 and/or were considered as a priority based on other human health concerns. The Chemical Abstracts Service Registry Number (CAS RN)1, Domestic Substances List (DSL) name, and Colour Index (C.I) name or common name of the 22 substances are presented in the following table.....