Sulfamic acid

Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colorless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen. Sulfamic acid, also known as amidosulfonic acid, amidosulfuric acid, aminosulfonic acid, and sulfamidic acid, is a molecular compound with the formula H3NSO3. This colorless, water-soluble compound finds many applications. Sulfamic acid melts at 205 °C before decomposing at higher temperatures to water, sulfur trioxide, sulfur dioxide and nitrogen. Sulfamic acid (H3NSO3) may be considered an intermediate compound between sulfuric acid (H2SO4), and sulfamide (H4N2SO2), effectively replacing a hydroxyl (–OH) group with an amine (–NH2) group at each step. This pattern can extend no further in either direction without breaking down the sulfonyl (–SO2–) moiety. Sulfamates are derivatives of sulfamic acid. 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: In this way, approximately 96,000 tonnes were produced in 1995. The compound is well described by the formula H3NSO3, not the tautomer H2NSO2(OH). The relevant bond distances are 1.44 Å for the S=O and 1.77 Å for the S–N. The greater length of the S–N is consistent with a single bond. Furthermore, a neutron diffraction study located the hydrogen atoms, all three of which are 1.03 Å distant from the nitrogen. In the solid state, the molecule of sulfamic acid is well described by a zwitterionic form. Aqueous solutions of sulfamic acid are unstable and slowly hydrolyze to ammonium bisulfate, but the crystalline solid is indefinitely stable under ordinary storage conditions. Its behavior resembles that of urea, (H2N)2CO. Both feature amino groups linked to electron-withdrawing centers that can participate in delocalized bonding. Both liberate ammonia upon heating in water. Sulfamic acid is a moderately strong acid, Ka = 0.101 (pKa = 0.995). Because the solid is not hygroscopic, it is used as a standard in acidimetry (quantitative assays of acid content). Double deprotonation can be effected in ammonia solution to give the anion HNSO2−3. With nitrous acid, sulfamic acid reacts to give nitrogen: