How is methyl orange made?
Methyl orange is synthesized by reaction of sulfanilic acid, sodium nitrite, and dimethylaniline. First, sulfanilic acid is dissolved in dilute aqueous acid. Sodium nitrite is added to produce a diazonium salt This reaction is called diazotization and it is extremely useful in organic synthesis. The nitrous acid provides NO+ which replaces a hydrogen on the -NH3+ group to produce -NH2NO+ and water; a second water is eliminated to produce the -N2+ group. The diazonium salt is then coupled with dimethylaniline. The coupling takes place in the opposite (“para”) position from the -N(CH3)2 group: The sodium acetate makes the solution weakly basic; the acetate ion accepts the hydrogen displaced from the dimethylaniline ring. References and notes • The Merck Index, 8th ed., Merck & Co., Rahway NJ, 1968. The index gives the following reference for details on the synthesis of methyl orange: L. Gattermann, Die Praxis des organischen Chemikers, 40th ed., de Gruyter & Co., Berlin, 1961, pp 260-261