Sulfamic acid

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Sulfamic acid
Sulfamic acid sample on a watch glass.jpg
OTC sulfamic acid sample
Names
IUPAC name
Sulfamic acid
Systematic IUPAC name
Sulfamic acid
Other names
Amidosulfonic acid
Amidosulfuric acid
Aminosulfonic acid
Imidosulfonic acid
Sulfamidic acid
Properties
H3NSO3
Molar mass 97.10 g/mol
Appearance Colorless solid
Odor Odorless
Density 2.15 g/cm3
Melting point 205 °C (401 °F; 478 K) (decomposes)
Boiling point Decomposes
14.68 g/100 ml (0 °C)
18.56 g/100 ml (10 °C)
21.32 g/100 ml (20 °C)
26.09 g/100 ml (30 °C)
29.49 g/100 ml (40 °C)
32.82 g/100 ml (50 °C)
37.10 g/100 ml (60 °C)
41.91 g/100 ml (70 °C)
47.08 g/100 ml (80 °C)
Slow hydrolysis
Solubility Moderately soluble in ammonia, DMF, formamide
Sparingly solubility in methanol, sulfuric acid
Insoluble in acetone, acetonitrile, carbon disulfide, carbon tetrachloride, chloroform, DCM, diethyl ether, ethanol, hydrocarbons
Solubility in acetone 0.4 g/100 g[1]
Solubility in diethyl ether 0.009 g/100 g
Solubility in formamide 20 g/100 g
Solubility in methanol 4.3 g/100 g
Solubility in sulfuric acid 2.38 g/100 g
Vapor pressure ~0.06 mmHg (20 °C)
Acidity (pKa) 1.0
Thermochemistry
Hazards
Safety data sheet Sigma-Aldrich
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
3,160 mg/kg (rat, oral)
1,312 mg/kg (mouse, oral)
1,050 mg/kg (guinea pig, oral)
Related compounds
Related compounds
Sulfuric acid
Sulfamide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Sulfamic acid, also known as amidosulfonic acid, aminosulfonic acid or sulfamidic acid, is a chemical compound with the formula H3NSO3 or H2NSO3H, a solid strong acid at room.

Properties

Chemical

Sulfamic acid is a moderately strong acid, Ka = 0.101 (pKa = 0.995).

Aqueous solutions of sulfamic acid are unstable and slowly hydrolyze to ammonium bisulfate, but the crystalline solid is indefinitely stable under ordinary storage conditions.

Sulfamic acid reacts with nitrous acid to give nitrogen, while reaction with nitric acid, it affords nitrous oxide:

HNO2 + H3NSO3 → H2SO4 + N2 + H2O
HNO3 + H3NSO3 → H2SO4 + N2O + H2O

Upon heating sulfamic acid will react with alcohols to form the corresponding organosulfates.

Refluxing sulfamic acid with methanol will yield methylamine.

Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen.

H3NSO3 → H2O + SO3 + SO2 + N2

Physical

Sulfamic acid is a colorless odorless solid acid, soluble in water, but insoluble in organic solvents. Sulfamic acid is not hygroscopic, though finely powdered form may appear "sticky", similar to wet snow in appearance.

Availability

Sulfamic acid is readily available as solid acidic descaling agent, sold in many hardware stores. Sometimes it's sold as coffee machine cleaning powder, though always read the label, as many have producers have replaced it with citric acid.

Preparation

Sulfamic acid is produced industrially by treating urea with a mixture of sulfur trioxide and sulfuric acid (or oleum). The conversion is conducted in two stages:

(NH2)2CO + SO3 → OC(NH2)(NHSO3H)
OC(NH2)(NHSO3H) + H2SO4 → CO2 + 2 H3NSO3

Hydrolysis of sulfamide will yield sulfamic acid.

Preparation of sulfamic acid is not something any amateur chemist can do at home, due to the extreme conditions the preparation requires. As such, it's much more economical to simply purchase the compound, and usually is readily available.

Projects

Handling

Safety

Sulfamic acid is irritant and should be handled with care.

Storage

Sulfamic acid is best stored in closed plastic bottles, away from ammonia and moisture.

Disposal

Can be neutralized with an aq. base, then poured down the drain.

References

  1. Cupery, M. E.; Industrial and Engineering Chemistry; vol. 30; (1938); p. 627 - 631
  2. Patron, M.; Ind. chim.; vol. 42; (1955); p. 237 - 243

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