Solvent Yellow 2 is a synthetic azo dye primarily used in industrial applications such as coloring oils, waxes, plastics, and sometimes fuels. This dye produces a bright yellow hue and has historically been used in various manufacturing processes. However, its use in consumer products has been heavily restricted or banned due to its classification as a possible human carcinogen. Regulatory bodies, including the International Agency for Research on Cancer (IARC), have classified Solvent Yellow 2 as a Group 2B carcinogen, meaning it is “possibly carcinogenic to humans.” The European Union places it in Category 2 for its carcinogenic risk, while the U.S. National Toxicology Program (NTP) has listed it as “reasonably anticipated to be a human carcinogen.”

Chemical Composition and Structure

Solvent Yellow 2 is an azo dye with the chemical formula C₁₄H₁₅N₃, composed of two aromatic rings connected by an azo bond (-N=N-). This structure, typical of azo dyes, contributes to its bright yellow color. Its chemical structure makes it lipophilic, meaning it is soluble in organic solvents such as oils, but insoluble in water. The compound's aromatic rings and azo bond provide stability, but the presence of an aromatic amine group raises concerns about its potential to degrade into harmful by-products, such as aromatic amines, which are known carcinogens.

Physical Properties

Solvent Yellow 2 is typically found as a yellow crystalline powder or solid, with high solubility in organic solvents like hydrocarbons, oils, and waxes. It is insoluble in water but exhibits good thermal and light stability, making it suitable for use in environments where exposure to heat or light is frequent. This stability contributes to its long-lasting color performance in industrial applications.

Production Process

Solvent Yellow 2 is synthesized through an azo coupling reaction, where aromatic amines are reacted with nitrous acid, creating diazonium salts that are then coupled with another aromatic compound. This process forms the azo bond responsible for the compound’s bright yellow color. The production process is closely regulated, especially given the concerns about the compound's potential health risks. Handling and production require strict safety protocols to minimize exposure.

Applications

• Industrial Use: Solvent Yellow 2 is widely used in the industrial sector for:

  • Plastics and Waxes: Used as a colorant in plastics and waxes where its bright yellow color is required.
  • Oils and Fuels: Employed as a marker in oils and fuels for identification purposes due to its strong solubility in hydrocarbons.
  • Industrial Coatings: Occasionally used in coatings and inks, particularly in applications where water resistance is required.

• Historical Use in Consumer Products: Solvent Yellow 2 was historically used in consumer products such as inks, dyes, and even some cosmetics. However, due to its carcinogenic potential, its use in these products has been phased out.

• Dyes and Textiles: In the past, it was also used in the textile industry for dyeing fabrics, but its use in this sector has declined significantly due to health and safety concerns.

Health and Safety Concerns

Carcinogenicity

Solvent Yellow 2 has been classified by the IARC as a Group 2B carcinogen, meaning it is possibly carcinogenic to humans. This classification is based on evidence suggesting that the compound may degrade into aromatic amines, which are recognized carcinogens, particularly for bladder cancer. In the European Union, it is classified as a Category 2 carcinogen, indicating that it is suspected of causing cancer. The U.S. National Toxicology Program (NTP) lists Solvent Yellow 2 as “reasonably anticipated to be a human carcinogen.” These classifications are based on studies showing potential carcinogenic effects in animal models and concerns about long-term human exposure.

Toxicity

In addition to its carcinogenic potential, Solvent Yellow 2 can cause acute toxicity if ingested, inhaled, or absorbed through the skin. Prolonged exposure may lead to serious health issues, including skin irritation, respiratory problems, and an increased risk of developing cancer. It is particularly dangerous when handled in industrial settings without proper protective equipment, where workers may be exposed to fumes or dust from the dye.

Environmental and Safety Considerations

Solvent Yellow 2 is not biodegradable and can persist in the environment, particularly in water and soil, leading to potential contamination of ecosystems. Due to its toxic nature, improper disposal of products containing this dye can lead to long-term environmental harm. Regulatory guidelines require industries to manage waste products containing Solvent Yellow 2 responsibly, including its safe disposal and handling to prevent environmental contamination. Strict environmental controls are in place in many regions to limit the release of this substance into the environment.

Regulatory Status

Given its carcinogenic classification, Solvent Yellow 2 is heavily regulated. In the European Union, its use is restricted or banned in consumer products under REACH regulations, particularly in cosmetics and textiles. In the United States, the FDA and EPA have limited its use, and it is monitored closely in industrial applications. NTP has listed it as a suspected carcinogen, meaning industries must follow strict guidelines for its use, including labeling, safety precautions, and waste management.

Applications Under Strict Control

• Industrial use: Despite its carcinogenic potential, Solvent Yellow 2 continues to be used in highly controlled industrial applications where its bright color and stability are required.
• Markers for fuels: In some regions, it is still used as a fuel marker for taxation and product identification purposes.
• Laboratory uses: It may also be used under strict regulation in research settings, primarily for specific analytical purposes.

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  C₁₄H₁₅N₃

Molecular Weight   225.29 g/mol

CAS     60-11-7

UNII    A49L8E13FD

EC Number  200-455-7

Synonyms:

4-(Dimethylamino)azobenzene

Methyl yellow

Dimethyl Yellow

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.....