It is advisable to titrate the crude anthranilic acid with standard alkali and phenolphthalein before starting the experiment. In checking these directions, an 80 per cent anthranilic acid was used; it gave a correspondingly lower yield of methyl red (650-700 g.). The yield of methyl red is about 65 to 70 per cent based on the dimethylaniline actually used up, but only 58-63 per cent based on the anthranilic acid actually present in the technical anthranilic acid employed.
3. Other Methods of Preparation
Methyl red was first prepared[1] by diazotization of anthranilic acid in alcoholic solution, the product being allowed to react with dimethylaniline in the same solvent. It has been stated[2] that this process does not work satisfactorily and yields a different product, of brownish-red color.
The preparation of methyl red in aqueous solution has been described by two workers, one of whom[3] gives but few details and claims a nearly quantitative yield; the other[4] gives fuller details and states the yield to be 43.1 per cent of the theory. The recrystallization of methyl red from toluene is stated[5] to yield a product melting at 183'0.
[1] Ber. 41, 3905 (1908).
[2] Chem. Zentr. 1910, (1), 960; 1910, (11), 1561.
[3] J. Chem. Soc. 97, 2485 (1910).
[4] C. A. 14, 3406 (1920)
[5] J. Chem. Soc. 99, 1334 (1911).