Why is the sulfonic acid groups usually shown in it deprotonated form in the structure?

Organic Chemistry
8th Edition
ISBN:9781305580350
Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Publisher:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. Foote
Chapter24: Catalytic Carbon-carbon Bond Formation
Section: Chapter Questions
Problem 24.21P
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Why is the sulfonic acid groups usually shown in it deprotonated form in the structure?

Please provide original reasoning.

Experiment 7: Synthesis of Methyl Orange
Introduction
Methyl orange is an azo dye whose thesis can be accomplished by a diazo coupling reaction
between the diazonium salt of sulfanilic acid and N,N-dimethylaniline. Since the coupling reaction
is conducted in an acidic solution, the first product to form is the acid form of methyl orange,
called helianthin, which is bright red. The addition of a base leads to the conversion of helianthin
to its sodium salt, which is methyl orange.
H
H3C.
CH3
H3C-
N
CH3
OAc
НОАС
-SO3
H
H3C-
-N=N
SO,
CH3
proton transfer
H3C
H3C
Helianthin (red)
NaOH
H3C
N-
N =N
-SO;Na
H3C
Methyl orange
It is necessary to carry out the diazotization reaction in an acidic solution. However, sulfanilic acid
is insoluble in acidic solutions. To overcome this problem, the sulfanilic acid is first dissolved in
a basic solution: an aqueous solution of sodium carbonate- Sodium nitrite is then added to this
basic solution. Finally, the solution is chilled and then acidified with hydrochloric acid. The instant
the sulfanilic acid precipitates from the solution, it becomes diazotized, yielding a finely divided
white precipitate of the diazonium salt of sulfanilic acid. This diazonium salt is allowed to react
immediately with dimethylaniline in the solution in which it was precipitated.
Transcribed Image Text:Experiment 7: Synthesis of Methyl Orange Introduction Methyl orange is an azo dye whose thesis can be accomplished by a diazo coupling reaction between the diazonium salt of sulfanilic acid and N,N-dimethylaniline. Since the coupling reaction is conducted in an acidic solution, the first product to form is the acid form of methyl orange, called helianthin, which is bright red. The addition of a base leads to the conversion of helianthin to its sodium salt, which is methyl orange. H H3C. CH3 H3C- N CH3 OAc НОАС -SO3 H H3C- -N=N SO, CH3 proton transfer H3C H3C Helianthin (red) NaOH H3C N- N =N -SO;Na H3C Methyl orange It is necessary to carry out the diazotization reaction in an acidic solution. However, sulfanilic acid is insoluble in acidic solutions. To overcome this problem, the sulfanilic acid is first dissolved in a basic solution: an aqueous solution of sodium carbonate- Sodium nitrite is then added to this basic solution. Finally, the solution is chilled and then acidified with hydrochloric acid. The instant the sulfanilic acid precipitates from the solution, it becomes diazotized, yielding a finely divided white precipitate of the diazonium salt of sulfanilic acid. This diazonium salt is allowed to react immediately with dimethylaniline in the solution in which it was precipitated.
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