Sulfanilic acid structure, properties, synthesis, uses

The sulphanilic acid is a crystalline compound whose molecule is formed by a benzene ring to which a basic group (-NH_two) and an acid group (-SO₃H). Its chemical formula is NH_twoC₆H₄SW₃H.

It is also known as 4-aminobenzenesulfonic acid. It is prepared by sulfonation of aniline in the para position. Its crystals are white or greyish-white. Its behavior is more similar to that of a salt than that of an organic compound with NH groups_two bear₃H. Therefore, it is insoluble in most organic solvents.

One of its main uses is in the synthesis of colorants, as it easily forms a diazo compound that is a raw material for this application..

Both sulfanilic acid and its derivatives have been used as antibacterial agents. It is used in the synthesis of mucolytic compounds, since they have the ability to decrease the viscosity of mucus or highly viscous biological fluids..

It is also used in the paper industry and in formulas for engravings or lithographs. It is part of the resins that are used in concrete or mortar mixtures to allow them to maintain their fluidity for a long time, without influencing the final setting time.

It is a xenobiotic metabolite, this means that it is not produced naturally by living beings. It is irritating to the skin, eyes and mucous membranes. In addition, it can pollute the environment.

Article index

• 1 Structure
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Density
  • 3.5 Solubility
  • 3.6 Chemical properties
  • 3.7 Other properties
• 4 Synthesis
• 5 Uses
  • 5.1 In the dye industry
  • 5.2 In analytical chemistry
  • 5.3 In medicine as an antibacterial agent
  • 5.4 In medicine as a mucolytic agent
  • 5.5 In bioassay laboratories
  • 5.6 In the paper industry
  • 5.7 In prints, engravings or lithographs
  • 5.8 In building materials
• 6 References

Structure

Sulfanilic acid has white crystals formed by orthorhombic or monoclinic sheets. Its monohydrate crystallizes in water in the form of orthorhombic sheets. If the crystallization proceeds very slowly, the dihydrate crystallizes. The monohydrate becomes anhydrous when it is close to 100 ºC.

Nomenclature

- Sulfanilic acid.

- P-Aminobenzenesulfonic acid.

- 4-Aminobenzenesulfonic acid.

Properties

Physical state

White or off-white crystalline solid.

Molecular weight

173.19 g / mol.

Melting point

It decomposes at around 288ºC without melting. It is also reported at> 320 ºC.

Density

1.49 g / cm³

Solubility

Almost insoluble in water: 10.68 g / L at 20 ºC.

Insoluble in ethanol, benzene and ether. Slightly soluble in hot methanol.

Soluble in aqueous solutions of bases. Insoluble in aqueous solutions of mineral acids. Soluble in concentrated hydrochloric acid.

Chemical properties

Its properties differ from those of other amino or sulfonated compounds, being similar to those of a salt. This is because its structure actually contains the -NH groups₃⁺ And so₃^-, which gives it zwitterionic characteristics.

It contains an acid group and a basic group at opposite poles of the same molecule. But the hydrogen ion is bonded to nitrogen instead of oxygen because the -NH group_two is a stronger base than the -SO group₃^-.

Because it is a dipole ion, it has a high melting point and insolubility in organic solvents..

Sulfanilic acid is soluble in alkaline solution because the hydroxide ion OH^-, being strongly basic, it starts a hydrogen ion (H⁺) of the weak basic group -NH_two, forming the ion p-aminobenzenesulfonate, which is soluble in water.

In acid solution the structure of sulfanilic acid does not change, therefore it remains insoluble.

Other properties

When heated to decomposition, it emits toxic fumes of nitrogen oxides and sulfur..

Exposure to sulfanilic acid can lead to symptoms such as irritation of the skin, eyes, and mucous membranes. It is a corrosive compound.

Synthesis

It is prepared by reacting aniline with sulfuric acid (H_twoSW₄) at high temperatures. Initially, the acid anilinium sulfate salt is formed, which when heated to 180-200 ºC is reorganized to form the substituted ring in the para position, since it is the most stable product.

To prepare it with a high degree of purity, the sulfonation of a mixture of aniline and sulfolane with H_twoSW₄ at 180-190 ºC.

Applications

In the dye industry

Sulfanilic acid is used in the synthesis or preparation of various colorants, such as methyl orange and tartrazine. For this, it is diazotized, generating diazotized sulfanilic acid..

It is important to note that tartrazine has been used as a coloring in food. But once ingested, it generates certain metabolites in the human body, including sulphanilic acid, which are possibly responsible for the formation of reactive oxygen species. These can affect kidney (kidneys) or liver (liver) tissues..

In analytical chemistry

It is used as a reagent in the determination of various chemical compounds, including nitrites..

In medicine as an antibacterial agent

Sulfanilamide, derived from sulfanilic acid, has application in the pharmaceutical industry as it has antibacterial activity.

In the human body, bacteria confuse it with p-aminobenzoic acid, which is an essential metabolite. This substitution means that the bacteria do not reproduce and die.

Another derivative of sulphanilic acid, obtained by condensation with other compounds, also has antibacterial properties, which are based on its ability to displace folic acid (a member of the vitamin B complex)..

This compound can be taken orally, injected intravenously, or applied externally in an ointment..

In medicine as a mucolytic agent

A derivative of sulphanilic acid that has mucolytic activity has been used. This is that it presents liquefactive activity of the mucus, to dissolve the mucus itself or very viscous biological fluids.

The compound can be used to produce liquefaction of mucus produced by a tissue due to pathological conditions. For example congestion of the respiratory system or that from the vaginal tract, among others.

When it comes to liquefaction of mucus in the respiratory tract, the product is administered by inhalation, drops in the nose, mist, aerosols or nebulizers. It is a treatment applicable to humans or mammals. It is a more powerful compound than those based on cysteine.

It is also used in the laboratory when it is desired to reduce the viscosity of biological fluids to facilitate analytical determinations..

In bioanalysis laboratories

Diazotized sulfanilic acid (a derivative prepared by reacting sulfanilic acid with sodium nitrite) is used in the determination of bilirubin.

Bilirubin is a yellow pigment found in bile. Excess bilirubin in the blood is a consequence of liver diseases, hematological (or blood) disorders, or disorders of the biliary tract.

To measure the amount of bilirubin in the blood, the diazo derived from sulfanilic acid is reacted with bilirubin to form the azobilirubin complex, the intensity of which is measured with a colorimeter or spectrophotometer. In this way, the bilirubin content in blood serum is determined..

In the paper industry

Sulfanilic acid makes it possible to synthesize a paper polish, that is, a compound that gives it an optical shine or white appearance, as it neutralizes the yellow color of natural or untreated paper..

It has the advantage over other compounds in that it can be used in relatively high concentrations to treat paper pulp under low pH conditions, without increasing the yellowness of the paper..

The result is evident when the paper is observed with UV light (ultraviolet), under which it fluoresces much more than when other compounds are used, and with visible light it is observed that the degree of yellowness is very low.

It is very soluble in water, which allows it to be used in more concentrated solutions. Can be used on any type of paper, including paper produced from ground wood pulp, sulphite pulp, or any other process.

In prints, engravings or lithographs

Sulfanilic acid works as an acidifier in concentrated solutions for lithography, without presenting the problems of other acids such as phosphoric, being less toxic and less polluting than the latter..

In building materials

Sulfanilic acid modified aqueous melamine-formaldehyde resin solutions have been tested in concrete (concrete), mortar or cement paste. The purpose has been to reduce the water content and prevent a decrease in the fluidity of the mix over time, without reducing the setting time..

Concrete or mortar prepared with these solutions is very effective in summer, when the decrease in fluidity over time is a problem..

With these solutions, if the mortar or concrete is prepared and for whatever reason must be left to rest, the cement composition can easily be poured into molds or similar, as it has not lost fluidity over time..

References

1. Windholz, M. et al. (editors) (1983). The Merck Index. An Encyclopedia of Chemicals, Drugs and Biologicals. Tenth Edition. Merck & CO., Inc.
2. Kirk-Othmer (1994). Encyclopedia of Chemical Technology. Volume 2. Fourth Edition. John Wiley & Sons.
3. National Library of Medicine. (2019). Sulfanilic acid. Recovered from: pubchem.ncbi.nlm.nih.gov
4. Urist, H. and Martin, G.J. (1950). Sulfanilic acid derivatives. US Patent No. 2,504,471. Assignors to The National Drug Company. April 18, 1950.
5. Villaume, Frederick G. (1964). Brightener composition for paper derived from methanilic and sulfanilic acids. US Patent No. 3,132,106. May 5, 1964.
6. Martin, Tellis A. and Comer, William T. (1979). Benzoic acid derivative and benzenesulfonic acid mucolytic process. US Patent No. 4,132,802. January 2, 1979.
7. Druker, L.J. and Kincaid, R.B. (1979). Lithographic fountain concentrate. US Patent No. 4,150,996. April 24, 1979.
8. Shull, Bruce C. (1983). Bilirubin assay. US Patent No. 4,404,286. September 13, 1983.
9. Uchida, J. et al. (2001). Process for preparing an aqueous solution of sulfanilic acid modified melamine-formaldehyde resin and a cement composition. US Patent No. 6,214,965 B1. April 10, 2001.
10. Corradini, M.G. (2019). Volume 1. In Encyclopedia of Food Chemistry. Recovered from sciencedirect.com.