Acid Red 27

Applications:
Acid Red 27 is mainly used in the production and processing of various foods, producing products with bright color, resistance to light and high temperatures, and no fading even after long-term storage.

Content Analysis:
Determined according to Method 2 in OT-15. Weigh approximately 3g of the sample (accurate to 0.0002g) and dissolve it in freshly boiled and cooled to room temperature water. Transfer the solution to a 500ml volumetric flask, dilute to the mark, and mix well. Pipette 50ml of the sample solution into a 250ml Erlenmeyer flask, add 15g of trisodium citrate and 150ml of water. While passing a gas stream of carbon dioxide below the liquid surface, heat to boiling and titrate with 0.1mol/L titanium trichloride standard solution until colorless. Simultaneously, perform a blank test using 50ml of water instead of the sample solution, following the same method.

Chemical Properties:
Reddish-brown to dark reddish-brown powder or granules. Odorless. Highly resistant to light and heat (105℃), but poorly resistant to oxidation and reducing agents. Not suitable for fermented foods or foods containing reducing substances. Stable to citric acid and tartaric acid. Turns dark red in the presence of alkali. Easily fades in the presence of copper and iron. Slightly soluble in water (17.2 g/100 ml, 21℃) and glycerol. Aqueous solution is purple. Slightly soluble in ethanol (0.5 g/100 mL 50% ethanol).

Uses:
Redox indicator, such as for titrating trivalent arsenic, antimony, and hydrazine; coloring of food, pharmaceuticals, and cosmetics; cell staining in tissue culture; color photomicrography; staining of wool and silk fabrics.

Uses:
Biological staining agent.

Production method;
Preparation of Acid Red 27: Dissolve sodium 1-naphthylamine-4-sulfonate in 8-9 times its weight (by mass) of water at 75-85°C, filter, and cool to 0-5°C; add 1.2-1.5 times its weight (by mass) of hydrochloric acid to the original sodium salt, stir well, and let stand to precipitate fine 1-naphthylamine-4-sulfonate crystals, then cool to below 5°C; slowly add a 1:2 (by mass) sodium nitrite solution at 3-5°C to diazotize, obtaining a slightly yellow paste-like diazo solution. After the reaction is complete, the solution is strongly acidic (shows blue) to Congo red test paper. Sodium 2-naphthol-3,6-disulfonic acid (R-sodium) is dissolved in 9-10 times its weight (by mass) of water at 60-65°C. A portion of sodium carbonate (1/5 of the total amount) is added, dissolved, and filtered. The filtrate is then added to a reaction vessel, followed by the addition of the remaining sodium carbonate. The mixture is stirred until dissolved and cooled to 5-8°C. At 10-15°C and a pH of 8, diazonium solution is slowly added to initiate a coupling reaction for several hours. After the reaction is complete (with a slight excess of 2-naphthol-3,6-disulfonic acid), the solution is heated to 50-60°C, purified sodium chloride is added, and the mixture is stirred. The solution is then allowed to cool naturally to room temperature, where crystals are precipitated. The crystals are dissolved in 15 times their weight (by mass) of clean water at 70°C. An appropriate amount of sodium carbonate is added to make the solution slightly alkaline. After filtration, refined salt is added, the mixture is stirred, and the pH is adjusted to 6.5-7.0 with hydrochloric acid. The solution is allowed to crystallize, separated, and dried to obtain the final product. The amaranth red aluminum lake is prepared by using aluminum salts such as aluminum chloride and aluminum sulfate and alkalis such as sodium carbonate to produce aluminum hydroxide, which is then added to an aqueous solution of amaranth red to precipitate the product.