Sulfamic acid: structure, properties, synthesis, uses - science - 2023



The sulfamic acid is an inorganic compound formed by a sulfur atom (S) covalently bonded and by single bond to a hydroxyl group (–OH) and an amino group (–NH2), and by double bonding to two oxygen atoms (O). It is a white crystalline solid. Its chemical formula is NH2SW3H. Also known as aminosulfonic acid, amidosulfonic acid, amidosulfuric acid, and sulfamidic acid.

Sulfamic acid is a strong acid. It can react with metals, metal oxides and carbonates. Its salts are generally soluble in water, making it a good scale remover in process equipment. It is frequently used in sugar mills to clean carbonate incrustations in evaporator equipment.

Sulfamic acid is a nitrite reducer (NO2) and this chemical property is used in various applications, such as in the dye industry and in nitrite analysis.

It is used in leather tanning and pulp bleaching for papermaking. In fact, it is a food contaminant, since it is often found in the papers and cardboard used to pack groceries.

It is also used in the electrodeposition of metals, as a laboratory standard and one of its derivatives is a very effective herbicide.


Sulfamic acid crystallizes in the form of orthorhombic dipyramidal crystals. It forms compact prisms and sheets when crystallizing from cold solution, as well as diamond sheets when crystallizing from hot aqueous solution.


- Sulfamic acid

- Aminosulfonic acid

- Amidosulfonic acid

- Amidosulfuric acid

- Sulfamidic acid


Physical state

White crystalline solid.

Molecular weight

97.1 g / mol.

Melting point

205 ° C, decomposes at 209 ° C.


2.15 g / cm3


Soluble in water:

- 12.8% at 0 ºC

- 17.57% at 20 ºC

- 22.77% at 40 ºC

Slightly soluble in methanol, slightly soluble in acetone, insoluble in ether.

Freely soluble in nitrogenous bases and in organic solvents containing nitrogen.

Insoluble in carbon disulfide (CS2) and carbon tetrachloride (CCl4).


0.41 (in 1 N solution, that is, 1 equivalent / L).

Dissociation constant

0.101 at 25 ° C.

Chemical properties

It is a strong acid. Almost as much as hydrochloric (HCl), nitric (HNO3) and sulfuric (H2SW4).

Aqueous solutions of sulfamic acid are highly ionized. Its pH is lower than the solutions of formic, phosphoric and oxalic acids.

In water, sulfamic acid loses only the proton that is bound to oxygen. Hydrogens attached to nitrogen hold tightly together.

In aqueous solution it hydrolyzes slowly to give acid ammonium sulfate (NH4HSO4). It is stable in dry conditions.

Sulfamic acid attacks metals, metal oxides, and carbonates to generate sulfamates. For example, with the metal potassium (K) it forms potassium sulfamate (KOSO2NH2) and hydrogen (H2).

All salts of sulfamic acid are soluble in water. The salts of calcium, lead and barium are very soluble in water, unlike the corresponding salts of sulfuric acid.

Nitrous acid (HNO2) reacts quantitatively with the amino group of sulfamic acid, liberating nitrogen (N2). The sulphamate ion is believed to function in this reaction as an amide, not an amine.

Sulfamic acid is oxidized by chlorine, bromine, or potassium chlorate to convert it to sulfuric acid. This reaction does not occur with other oxidants such as chromic acid or potassium permanganate.

It is not compatible (reacts) with strong alkalis, chlorine, hypochlorous acid, hypochlorites, cyanides and sulfides.

Other properties

It is not hygroscopic (this means that it does not absorb moisture from the air).

When heated to decomposition it emits highly toxic fumes of sulfur oxides and hydrogen chloride (HCl).

One of its derivatives, ammonium sulfamate, is a fire retardant.

It is moderately toxic.


Sulfamic acid is obtained by reacting urea CO (NH2)2 with fuming sulfuric acid, that is, sulfuric acid (H2SW4) concentrate containing sulfur trioxide (SO3).

It can also be synthesized by reacting chlorosulfonic acid (HClO3Cl) and ammonia (NH3).


In the dye industry

Sulfamic acid is used to remove excess nitrites quickly and effectively in diazotization reactions in the synthesis of dyes. It is much more practical than urea for this purpose.

In leather processing

During leather tanning, the use of sulfamic acid instead of sulfuric acid provides a finer and silky texture.

Furthermore, since calcium sulfamate is soluble in water, unlike calcium sulfate, sulfamic acid can be used in the deliming process without leaving the stains that sometimes occur on leather when sulfuric acid is used.

In cleaning process equipment

Sulfamic acid is used as a descaling cleaner in kettles, reactors, pipes, cooling systems, and heat exchangers.

In this equipment scale is formed by the circulation of water or process compounds in power plants, chemical plants, steel mills, paper mills, compression stations and other industries.

Scale or solid deposits can be organic (algae, silt, fungi) or inorganic (iron oxides, iron sulfides, calcium or magnesium carbonates, sulfates, phosphates or silicates).

Sulfamic acid is very effective when used to remove calcium carbonate scale. It can be used on copper, brass, stainless steel, cast iron and galvanized steel equipment.

It is used in the form of a 5-10% solution by weight. It is used especially in sugar mills to clean the evaporators made of cast iron with copper heat exchangers.

It should be used at temperatures no higher than 50-60 ºC. Temperatures of 70 ºC lead to the formation of insoluble sulfates such as CaSO4.

When used in combination with sodium chloride, a synergistic effect occurs and the solution allows the ferric oxide to slowly dissolve. In this case it should not be used with stainless steel because hydrochloric acid is released, which can cause corrosion in this material.

In metal refining

Electrodeposition of metals such as copper, silver, cobalt, nickel, zinc, cadmium, iron, and lead can be successfully performed in sulfamic acid solutions. This can be handled much more easily than hydrofluorosilicic acid (H2SiF6).

As a standard reagent in the laboratory

Given certain characteristics of sulfamic acid such as: its strength as an acid, its ease to be purified by recrystallization in water, its stability and its non-hygroscopicity, it has been used as a primary standard at the laboratory level. This means that it is used for quantitative alkali determinations.

In nitrite analysis

Due to its easy reaction with nitrites, sulfamic acid is used to determine these in solution.

In the analysis of dissolved oxygen in water

Since sulfamic acid reacts with nitrites in the water, nitrogen is released, it is possible to determine dissolved oxygen in water, since the interference caused by nitrites is eliminated.

In the preparation of nitrous oxide

Sulfamic acid reacts with nitric acid to generate nitrous oxide (N2OR). This reaction is safer than that of ammonium nitrate to obtain this gas.

In agriculture

A derivative of sulfamic acid, ammonium sulfamate, is an effective non-toxic herbicide for animals.

It is applied by dew on the leaves of the species to be removed at the end of summer or early autumn, preferably in humid weather. As the compound moves from the leaves to the roots, the plant dies.

Another advantage of this compound is that it does not permanently sterilize the soil. Indeed, some of the nitrogen from ammonium sulfamate will be available in the soil for plant growth in the next season.

In fireproof fabrics

Its compatibility with cellulose and its fire retardant characteristics make ammonium sulphamate an agent for obtaining fire resistant fabrics and paper.

10% of the weight of the fabric is used, whose appearance and feel to the touch remain unaltered. The fabric when in use should be dry cleaned, never washed with water so as not to dissolve the sulfamate.

It is especially useful in theater curtains or similar places.

In various applications

It is used as a catalyst in some chemical reactions, such as in the preparation of urea-formaldehyde resins. It is also useful as a bactericide and chlorine stabilizer in swimming pools and as a wood pulp bleach in pulp and paper mills.


  1. U.S. National Library of Medicine. (2019). Sulfamic acid. Recovered from
  2. Williams, D.L.H. (2004) Nitrosation at nitrogen centers. In Nitrosation Reactions and the Chemistry of Nitric Oxide. Chapter 2. Recovered from
  3. Clapp, Leallyn B. (1943). Sulfamic acid and its uses. Chem. Educ. 1943, 20, 4, 189. Recovered from
  4. McDonald, James. (2003). Sulfamic acid. Recovered from
  5. Sastri, V.S. (2010).Management and Control of Corrosion. In Shreir’s Corrosion. Recovered from
  6. Pratima Bajpai. (2018). Miscellaneous Topics. In Biermann’s Handbook of Pulp and Paper. Third Edition. Recovered from