ISOCYANIC ACID

Chemical Properties

Isocyanic acid (HNCO) is a volatile, moderately acidic compound, and the simplest member of the isocyanate family.
Isocyanic acid is a colourless, volatile, poisonous inorganic compound with the formula HNCO; the simplest stable chemical compound that contains carbon, hydrogen, nitrogen, and oxygen, the four most commonly-found elements in organic chemistry and biology. It is a hydracid and a one-carbon compound. It is a conjugate acid of a cyanate. It is a tautomer of a cyanic acid.

Physical properties

Isocyanic acid (ICA, Cas no. 75-13- 8) is a strong organic acid with a kPa of 3.5. ICA is a very reactive compound that can readily transform into other substances. It can lose a proton in an aqueous environment under certain conditions, particularly if a strong base is present, forming an isocyanate. ICA is a tautomer of the less stable, cyanic acid (CAS no. 420-05-3). These forms interchange by a tautomerisation reaction, involving the migration of a hydrogen atom or proton accompanied by a switch of a double bond. ICA is an unstable liquid above 0o C with a tendency to polymerise. The primary polymerisation product, which is also generated in the gas form, is cyanuric acid (CAS no. 108-80-5), a cyclic trimer. ICA is soluble in water, but disintegrates both via ionisation and by formation of ammonia and carbon dioxide.

Uses

The primary use of methyl isocyanate (MIC, CAS no. 624-83-9) is as a chemical intermediate in the production of carbamate pesticides. MIC is also used to produce polyurethane foam and plastics (ATSDR, 2002). Isocyanic acid (ICA, Cas no. 75-13- 8) does not have commercial uses because of its instability. The potential for occupational exposure to ICA largely arises when it is generated as a thermal degradation product of other industrial processes. Ethyl isocyanate is a liquid used commercially to make pharmaceuticals and pesticides (NJDHSS, 2000). Phenyl isocyanate (PIC, CAS no. 103-71-9) is a trace constituent in commercial diphenyl methane diisocyanate products.

Preparation

Isocyanic acid was prepared in pure form by reaction of KOCN or NaOCN with stearic or oxalic acid in good yield.

Definition

ChEBI: A colourless, volatile, poisonous inorganic compound with the formula HNCO; the simplest stable chemical compound that contains carbon, hydrogen, nitrogen, and oxygen, the four most commonly-found elements in organic chemistry and biology.

Hazard

Severe explosion risk. Strong irritant to eyes, skin and mucous membranes.