384 PRACTICAL ORGANIC CHEMISTRY (C) AMINO-AROMATIC SULPHONIC ACIDS. SuI-phanilic acid. Physical Properties. Colourless crystalline solid, soluble in boiling water, very sparingly soluble in cold water: crystallises + 2H 2 O. The strongly acidic -SO 3 H group suppresses the normal basic properties of the -NH 2 group: the acid therefore dissolves readily in alkalis, but not in dilute mineral acids. REACTIONS. 1. Soluble in Na 2 CO 3 solution with the evolution of CO 2 . 2. Gives aniline when heated with soda-lime. 3. Forms diazonium derivative which can be coupled with 2-naphthol or with dimethylaniline to form azo-dyes. 1. Solubility in sodium carbonate solution. See Section 5 (p. 330), and also Test 2 for carboxylic acids (p. 347). 2. Heating with soda-lime. See Test 2 for anthranilic acid (p. 383) and also Section 3, p. 327. 3. Formation of methyl-orange (cf. p. 214). Dissolve about 0*3 g. of sul-phanilic acid in 2 ml. of 10% aqueous Na 2 CO 3 solution. Cool in ice-water and add 2 to 3 drops of 20% NaNO
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