Difference between revisions of "Sulfanilic acid"

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Latest revision as of 16:35, 30 June 2020

Sulfanilic acid
Sulfanilic acid.JPG
Sulfanilic acid skeletal structure.png
IUPAC name
4-aminobenzene-1-sulfonic acid
Preferred IUPAC name
4-Aminobenzene-1-sulfonic acid
Molar mass 173.12 g/mol
Appearance Off white or purple crystalline solid
Odor Odorless
Density 1.485 g/cm3 (25 °C)
Melting point 288 °C (550 °F; 561 K)
Boiling point 300 °C (572 °F; 573 K) (decomposes)
12.51 g/L
Solubility Soluble in fuming HCl
Insoluble in benzene, diethyl ether and ethanol
Vapor pressure 1·10-9 mmHg (25 °C)
Acidity (pKa) 3.25
Safety data sheet Sigma-Aldrich
Lethal dose or concentration (LD, LC):
12.300 mg/kg (rat, oral)
6.000 mg/kg (rat, IV)
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sulfanilic acid is an arylsulfonic acid that is mainly used as a precursor for making azo dyes, such as methyl orange, and sulfa drugs, such as sulfanilamide. It is also used in the quantitative analysis of nitrate and nitrite ions. It can be synthesized easily by sulfonation of aniline with concentrated sulfuric acid.



Sulfanilic acid is zwitterionic. It is highly soluble in basic solutions, and moderately soluble in strongly acidic solutions. Its isoelectric point is 1.25, which would be the optimum pH for precipitating and recrystallizing it.[1] It crystallizes from water as a dihydrate, but can be dehydrated by heating.


Sulfanilic acid is a white solid when pure, but commercial and home made samples are usually off-white or even purple, due to contamination with trace amounts of strongly colored polyaniline compounds.


Sulfanilic acid may be available from some online chemical suppliers, but is not usually sold to the general public. It is more practical to make if one has access to aniline.


The main route for preparation of sulfanilic acid is by sulfonation of aniline using concentrated sulfuric acid.[2]


Synthesis of azo dyes:

Synthesis of sulfanilamide



Sulfanilic acid is not particularly dangerous but should be handled with gloves.


Sulfanilic acid acid is best kept in a clean bottle, away from bases.


Neutralize it first using sodium carbonate or bicarbonate, before destroying it with an oxidizing agent.


  1. https://www.ncbi.nlm.nih.gov/pubmed/19872329
  2. http://www.prepchem.com/synthesis-of-sulfanilic-acid/

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