Thiazole Yellow
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This article is compiled based on the United States Pharmacopeia (USP) – 2025 Edition
Issued and maintained by the United States Pharmacopeial Convention (USP)
(CI Direct Yellow 9; Clayton Yellow; Titan Yellow), C28H19N5Na2O6S4 695.74 CAS RN: 1829-00-1.-Yellowish-brown powder.
Soluble in water and in alcohol to yield in each instance a yellow solution; soluble in dilute alkali to yield a brownish-red solution. Protect from light.
Solubility: A 200-mg portion mixed with 50 mL of water shows not more than a faint haze.
Residue on Ignition: Accurately weigh about 1.5 g, previously dried at 105° for 2 hours, and ignite until thoroughly charred. Cool, add 2 mL of nitric acid and 2 mL of sulfuric acid, ignite gently to expel excess acids, then at 600° to 800° to constant weight: the residue of sodium sulfate (Na2SO4) is between 19.8% and 21.5% of the weight of the test specimen (theory is 20.4%).
Sensitiveness to Magnesium: Add 0.2 mL of a solution (1 in 10,000) and 2 mL of 1 N sodium hydroxide to a mixture of 9.5 mL of water and 0.5 mL of a solution prepared by dissolving 1.014 g of clear crystals of Magnesium sulfate in water, diluting with water to 100 mL, then diluting 10 mL of the resulting solution with water to 1 L: a distinct pink color is produced within 10 minutes.
