(a) When anthranilic acid is treated with NaNO₂ in aqueous HCl solution, and the resulting solution is treated with N,N-dimethylaniline, a dye called methyl red is formed. Give the structure of methyl red.

(b) When an acidic solution of methyl red is titrated with base, the dye behaves as a diprotic acid with pK_a values of 2.3 and 5.0. The color of the methyl red solution changes very little as the pH is raised past 2.3, but, as the pH is raised past 5.0, the color of the solution changes dramatically from red to yellow. Explain.

Transcribed Image Text:

CO₂H NH₂ anthranilic acid