214 PRACTICAL ORGANIC CHEMISTRY Methyl-orange (Sodium salt). NaO 3 SC 6 H 4 N : NC 6 H 4 N(CH 3 ) 2 . When hydrochloric acid is cautiously added to an aqueous solution con-taining both sodium nitrite and the sodium salt of sulphanilic acid, NaO 3 SC 6 H 4 NH 2 , the amino group of the latter undergoes normal diazotisation, giving the diazonium chloride (A). The latter, however, ionises in solution, giving sodium and chloride ions and the internal salt (B), which possesses two opposite charges and is therefore neutral: this internal salt is stable under +- - + (A) NaO 3 SC 6 H 4 N 2 Cl -> Na + Cl + O 8 SC 6 H 4 N 2 (B) these conditions, and being only moderately soluble in water, will be largely precipitated unless the solution is very dilute. If now dimethylaniline hydro-chloride is added to the solution, coupling will occur between the internal salt and the tertiary amine, with the formation of methyl-orange: On the addition of sodium hydroxide, the sparingly soluble sodium salt of
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.