Ponceau 3R is a synthetic azo dye known for its bright red color. It is widely used in various industries, including food, cosmetics, and textiles, due to its color and excellent stability. It was used from 1908 to 1968.

Chemical Composition and Structure

Ponceau 3R is an azo dye, meaning it contains one or more azo groups (-N=N-) in its molecular structure. The chemical formula for Ponceau 3R is C20H12N2Na2O7S2. Its structure includes an azo group linked to aromatic rings and sulfonate groups, contributing to its solubility in water and its bright red hue.

Physical Properties

Ponceau 3R typically appears as a red powder. It is highly soluble in water, producing a bright red solution when dissolved. The dye exhibits excellent stability under various conditions, including resistance to light and heat, making it suitable for a wide range of applications.

Production Process

The production of Ponceau 3R involves the diazotization of aromatic amines followed by coupling with suitable aromatic compounds to form the azo dye. The process requires precise control of reaction conditions to ensure high purity and consistency in the final product. The sulfonation step enhances the dye's solubility and affinity for various substrates.

Chemical Industrial Synthesis Process

• Preparation of reagents. The main raw materials include 6-amino-1-naphthalene-3-sulfonic acid (6-amino-G acid), sulfuric acid (H₂SO₄), sodium nitrite (NaNO₂), a base such as sodium hydroxide (NaOH), and 1-naphthol-3,6-disulfonic acid (J acid).
• Diazotization. The 6-amino-1-naphthalene-3-sulfonic acid is treated with sulfuric acid and sodium nitrite to form a diazonium intermediate. This reaction produces a diazonium salt.
• Coupling. The diazonium salt is then coupled with 1-naphthol-3,6-disulfonic acid (J acid) in the presence of a base, such as sodium hydroxide, to form the azo compound intermediate.
• Formation of Ponceau 3R dye. The azo compound intermediate is further processed and stabilized to form the Ponceau 3R dye.
• Filtration. The resulting suspension is filtered to separate the solid precipitate from the aqueous solution.
• Washing. The precipitate is washed with deionized water to remove any soluble impurities.
• Drying. The washed precipitate is dried at controlled temperatures to remove residual moisture and obtain a dry powder.
• Grinding. The dried product is ground to obtain a fine and uniform powder.
• Classification. The dried powder is classified to ensure a uniform particle size. This step may involve sieving or the use of air classifiers.
• Stabilization. The Ponceau 3R powder is stabilized to ensure its stability during transportation and storage, preventing aggregation and degradation.
• Quality control. The Ponceau 3R undergoes rigorous quality testing to ensure it meets standards for purity, color intensity, and safety. These tests include chemical analysis, spectroscopy, and physical tests to determine particle size and rheological properties.

Safety

 The problem associated with azo dyes (monoazo or diazo) is photocatalytic degradation leading to eventual oxidation and subsequent formation of impurities such as aromatic amines some of which have carcinogenic activity (2).

Ponceau 3R, also known as Food Red 6, has been widely used in the past, mainly as a food coloring. However, its use has declined significantly due to concerns about its safety (2).

References__________________________________________________________________________

(1) 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.

Abstract. Azo dyes are widely used in the textile, printing, paper manufacturing, pharmaceutical, and food industries and also in research laboratories. When these compounds either inadvertently or by design enter the body through ingestion, they are metabolized to aromatic amines by intestinal microorganisms. Reductive enzymes in the liver can also catalyze the reductive cleavage of the azo linkage to produce aromatic amines. However, evidence indicates that the intestinal microbial azoreductase may be more important than the liver enzymes in azo reduction. In this article, we examine the significance of the capacity of intestinal bacteria to reduce azo dyes and the conditions of azo reduction. Many azo dyes, such as Acid Yellow, Amaranth, Azodisalicylate, Chicago Sky Blue, Congo Red, Direct Black 38, Direct Blue 6, Direct Blue 15, Direct Brown 95, Fast Yellow, Lithol Red, Methyl Orange, Methyl Red, Methyl Yellow, Naphthalene Fast Orange 2G, Neoprontosil, New Coccine, Orange II, Phenylazo-2-naphthol, Ponceau 3R, Ponceau SX, Red 2G, Red 10B, Salicylazosulphapyridine, Sunset Yellow, Tartrazine, and Trypan Blue, are included in this article. A wide variety of anaerobic bacteria isolated from caecal or fecal contents from experimental animals and humans have the ability to cleave the azo linkage(s) to produce aromatic amines. Azoreductase(s) catalyze these reactions and have been found to be oxygen sensitive and to require flavins for optimal activity. The azoreductase activity in a variety of intestinal preparations was affected by various dietary factors such as cellulose, proteins, fibers, antibiotics, or supplementation with live cultures of lactobacilli.

(2) Hansen, W. H., Davis, K. J., Fitzhugh, O. G., & Nelson, A. A. (1963). Chronic oral toxicity of Ponceau 3R. Toxicology and Applied Pharmacology, 5(1), 105-118.

Abstract. The results of two-year oral toxicity studies with Ponceau 3R using two strains of rats have been presented. Dosage levels were 5.0, 2.0, 1.0, and 0.5% for Osborne-Mendel rats and one dosage level of 2.0% for Bethesda Black rats. Preliminary results of the continuing dog and mouse studies are reported. Ponceau 3R at 5.0, 2.0, 1.0, and 0.5% of the diet produced high mortality, growth inhibition, and increased weight of the liver and kidneys. Malignant liver tumors occurred in both strains of rats at all dietary levels of Ponceau 3R, statistically significant (P < 0.01) in comparison with the controls at the 5.0% level of the Osborne-Mendel rats and the 2.0% level of the Bethesda Black animals. Incidence of benign liver tumors was also significant for all test levels. Marked weight loss and high mortality have been observed in dogs fed Ponceau 3R at dosage levels of 2.0% and 1.0%. After a feeding period of 32 weeks, changes in the liver were the most pronounced tissue changes. Increased mortality of C3HeBFe mice has been observed on 2.0% and 1.0% feeding levels. Hepatic adenomas and carcinomas have been observed on the 2.0% level.