NITROUS ACID

Toxicity

Oral LD50 of 157.9mg/kg observed in rats and 175mg/kg observed in mice . Estimated oral LD50 of 35mg/kg in humans . Sodium nitrite toxicity manifests as cardiovascular collapse following severe hypotension due to nitrite's vasodilatory action.

Description

Nitrous acid (molecular formula?HNO2) is a weak and monobasic acid known only in solution and in the form of nitrite salts. Nitrous acid rapidly decomposes into nitrogen oxide, nitric oxide and water when in solution:
2HNO2 ? NO2 + NO+H2O
It can also decompose into nitric acid and nitrous oxide and water.
4HNO2 ? 2HNO3 +N2O +H2O
Nitric acid (HNO3), also known as “aqua fortis” and “spirit of nitre”, is a highly corrosive and toxic strong acid that can cause severe burns. It is colorless when pure and a slight yellow when “glacial”. Older samples tend to acquire a yellow cast due to the accumulation of various oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as “fuming nitric acid”.

Chemical properties

A weak acid occurring only in the form of a light-blue solution.

Physical properties

Pale blue solution; stable only in solution; weak acid, Ka 4.5x10^-4.

The Uses of NITROUS ACID

Nitrous acid is a nitrogen oxoacid. It is a conjugate acid of a nitrite. It (as sodium nitrite) is used as part of an intravenous mixture with sodium thiosulfate to treat cyanide poisoning. There is also research to investigate its applicability towards treatments for heart attacks, brain aneurysms, pulmonary hypertension in infants, and Pseudomonas aeruginosa infections.

The Uses of NITROUS ACID

Formation of diazotizing compounds by reaction with primary aromatic amines, source of nitric oxide.

Indications

For sequential use with sodium thiosulfate for the treatment of acute cyanide poisoning that is judged to be life-threatening .

Background

Nitrous acid (as sodium nitrite) is used as part of an intravenous mixture with sodium thiosulfate to treat cyanide poisoning. It is on the World Health Organization's List of Essential Medicines, a list of the most important medications needed in a basic health system. There is also research to investigate its applicability towards treatments for heart attacks, brain aneurysms, pulmonary hypertension in infants, and Pseudomonas aeruginosa infections.

Definition

A weak acid known only in solution, obtained by acidifying a solution of a nitrite. It readily decomposes on warming or shaking to nitrogen monoxide and nitric acid. The use of nitrous acid is very important in the dyestuffs industry in the diazo reaction: nitrous acid is liberated by acidifying a solution of a nitrite (usually sodium nitrite) in the presence of the compound to be diazotized. Nitrous acid and the nitrites are normally reducing agents but in certain circumstances they can behave as oxidizing agents, e.g. with sulfur dioxide and hydrogen sulfide.

Definition

nitrous acid: A weak acid, HNO₂,known only in solution and in thegas phase.It is prepared by the actionof acids upon nitrites, preferablyusing a combination that removesthe salt as an insoluble precipitate(e.g.Ba(NO₂)₂ and H₂SO₄). The solutionsare unstable and decompose on heating to give nitric acid and nitrogenmonoxide.Nitrous acid can functionboth as an oxidizing agent(forms NO) with I– and Fe2+, or as areducing agent (forms NO₃^-) with,forexample, Cu²⁺; the latter is mostcommon.It is widely used (preparedin situ) for the preparation of diazoniumcompounds in organic chemistry.The full systematic name isdioxonitric(III) acid.

Preparation

Nitrous acid may be obtained in solution by adding a strong acid to nitrite; e.g., adding hydrochloric acid to sodium nitrite solution:
H⁺ + NO₂ ^ˉ → HNO₂.

Hazard

Rapidly forms nitric oxide and nitric acid in water; [Merck Index] A strong oxidizer; Causes burns; Highly toxic by ingestion and inhalation.

Pharmacokinetics

Sodium nitrite reverses cyanide toxicity and produces blood vessel dilation .

Safety Profile

Mutation data reported. Flammable by chemical reaction; a powerful oxidizer. Explodes on contact with phosphorus trichloride. Reacts violently with PH3 and Pcb. Reactions with l-amino- 5-nitrophenol, ammonium decahydroborate(2-), hydrazine (product is hydrogen azide) may give explosive products. Incompatible with anilines (e.g., 4- bromoahe , 2-chloroaniline, 3- chloroaniline, 2-nitroadine, 3-nitroaniline, 4-nitroaniline, aniline ), semicarbazone, silver nitrate. When heated to decomposition it emits hghly toxic fumes of NOx. See also NITRIC OXIDE.

Metabolism

Reduced by deoxyhemoglobin to form nitric oxide . Nitrite is also reduced to nitric oxide and further reduced to ammonia by gut bacteria . Nitrite can be oxidized to nitrate by oxyhemoglobin.