SULFAMIC ACID

SULFAMIC ACID

Chemical Formula:                 HSO3NH2

CAS Number:                          5329-14-6

Molecular Weight:                   97.10

Equivalent Weight:                  97.10

Density at 25 ^oC:                                 2.126 g/cm³

Specific heat:                                      1.1467 J/g

Melting point:                                     205 ^oC

Decomposition Temperature:             209◦C

Vapor pressure:

20 ^oC                                                  0.8 Pa

100 ^oC                                               0.25 Pa

Sulfamic acid has a unique and important combination of properties. Sulfamic acid is a white or colorless, odorless, crystalline (sand like), nonhygroscopic, dry, strong inorganic acid. At room temperature it is non-volatile. Therefore it is conveniently handled and packaged in solid form in bags and is easily transported commercially. It is highly stable and can be stored for years without change in properties. Sulfamic Acid is monoamide of sulphuric acid.

Alternatively it is also known as amidosulfonic acid, amidosulfuric acid (IUPAC recommended), aminosulfonic acid, sulphamic acid.

Pure Sulfamic Acid melts at 205 ^oC and starts decomposing at 209 ^oC. On decomposition Sulfur trioxide, sulfur dioxide, water, ammonia, and nitrogen are evolved.

Aqueous Sulfamic Acid solutions are practically stable at room temperature but hydrolyze exothermically to ammonium hydrogen sulfate at high temeratures :

NH2SO3H+H2O → NH4HSO4

Rate of  hydrolysis increases with the increase of concentration and temperature and at lower pH.

Sulfamic Acid reacts with metals, alkali and alkaline earth metals and their oxides, hydroxides and carbonates and forms metal sulfamates. These metal sulfamates are, with but few exceptions, soluble in water. The sulfamates of lead, magnesium, and sodium are more soluble in water than the corresponding sulfates, nitrates, chlorides, and acetates. Therefore it is used in cleaning and descaling operations. Its corrosiveness towards metals can be controlled by adding corrosion inhibitors. Metal sulfamate solutions are stable at high temperatures and can be evaporated to dryness on a steam bath without hydrolysis of the amide group. Acidic metal oxides react with sulfamic acid less readily or not at all.

Nitrites react rapidly with sulfamic acid, liberating nitrogen and forming sulfuric acid. This reaction is utilized for the analytical determination of nitrites or of sulfamic acid even in the presence of nitrates.

Sulfamic Acid reacts with primary alcohols, glycols and glycerine upon heating and form corresponding esters.

Sulfamic acid is highly ionized in aqueous solution, and its pH range approaches that of nitric, sulfuric, and hydrochloric acids.

At low temperatures chlorine, bromine, and chlorates oxidize sulfamic acid to sulfuric acid. Potassium permanganate, chromic acid, and ferric chloride do not oxidize sulfamic acid.

Sulfamic acid reacts with concentrated nitric acid to form nitrous oxide:

NH₂SO₂OH + HNO₃ →  H₂SO₄+ H₂O+N₂O

This reaction is used as a convenient method for preparing pure nitrous oxide.

Sulfamic Acid is fairly soluble in water and nitrogenous solvents such as liquid ammonia formamide, slightly soluble in methanol, and insoluble in ethanol, acetone, and ether. Sulfamic acid is insoluble in organic oxygen-containing and most nonpolar organic solvents, hydrocarbons, chlorinated hydrocarbons, carbon disulfide, toluene and sulfur dioxide. The solubility of sulfamic acid in water is decreased markedly by sulfuric acid and sodium sulfate. Sulfamic acid is practically insoluble in 70-100% sulfuric acid. Its solubility in Fuming Sulfuric Acid     (21% SO₃) is 2.38 gram in 100 grams of acid.

Solubility of Sulfamic Acid in water:

Temperature oC	Solubility per 100 gram water	Temperature oC	Solubility per 100 gram water
0	14.68 grams	50	32.82 grams
10	18.56 grams	60	37.10 grams
20	21.32 grams	70	41.91 grams
30	26.09 grams	80	47.08 grams
40	29.49 grams

Solubility of Sulfamic Acid in Organic solvents at 25 ^oC per 100 grams of solvent:

Methanol                        4.3 gram

Ethanol                          1.7 gram

Acetone                          0.4 gram

Ether                              0.009 gram

Formamide                    20.0 gram

pH of Sulfamic Acid solutions in water at 25 ^oC are :

5%                        0.63

2.5%                     0.86

1%                        1.18

0.5%                     1.41

Upon brief contact with the skin sulfamic acid shows no noticeable effect but, as a normal safety precaution, it is recommended that prolonged exposures be avoided. Similarly, in two hundred human test cases, fabric treated with ammonium sulfamate produced no skin irritation.

In 1936 a practical process, which became the basis for commercial preparation was developed. In this production process, urea is first dissolved in excess cold sulfuric acid. Oleum of suitable sulfur trioxide strength is then added, and the reaction is allowed to proceed under controlled conditions. During the reaction carbon dioxide is evolved, and the sulfamic acid formed precipitates from the solution. The product is isolated by filtration and purified by recrystallization from water. This process involving urea with sulphur trioxide and sulphuric acid continues to be the main method for production of sulphamic acid today.