Nitrosylsulfuric acid

Nitrosylsulfuric acid, HNO₅S, is a straw-colored, oily liquid furnished as a 40% solution in 87% sulfuric acid,and stable at room temperature. It is used as a diazotizing agent for dyes,chemical intermediate, drugs and pharmaceuticals.

Nitrosylsulfuric acid is produced as an intermediate in the manufacture of sulfuric acid using the lead chamber process by the reaction of sulfur dioxide, nitrogen dioxide, oxygen, and water.
Nitrosylsulfuric acid also is made from absorption of nitrogen oxides (NO_x) in oleum (fuming sulfuric acid):
N₂O₃ + 2H₂SO₄ → 2ONSO₄ + H₂O
or by the reaction of nitrosyl chloride with concentrated sulfuric acid:
ClNO + H₂SO₄ → ONSO₄ + HCl
Another method of preparation involves the reaction of nitrosyl bromide with silver bisulfate:
AgHSO₄ + BrNO → ONHSO₄ + AgBr
In making disperse azo dyes, nitrosylsulfuric acid is produced by the addition of sodium nitrite, NaNO₂, to concentrated sulfuric acid (1g NaNO₂ per 13 g H₂SO₄).

Nitrosylsulfuric acid is used for diazotisation, nitrosation, oxidation and oximation reactions. Product Data Sheet

For bleaching cereal milling products.

Nitrosylsulfuric acid (40wt. % in sulfuric acid) is a reagent used for the preparation of new heterocyclic disperse azo dyes.

Shipped in solution with sulfuric acid (solutions are usually 40% Nitrosylsulfuric acid and 54% sulfuric acid (Hawley)). Solution is a straw-colored oily liquid with a sharp odor. When pure, a crystalline solid decomposing at 73°C. Very irritating to skin and eyes. Used to make dyes and other chemicals.

Nitrosylsulfuric acid is an oxidizing agent. Neutralizes chemical bases in exothermic reactions. An attempt to diazotize dinitroaniline using Nitrosylsulfuric acid resulted in an explosion with loss of life. The event was blamed on the high concentration of the reactants dinitroaniline hydrochloride and Nitrosylsulfuric acid [MCA Case History 1763. 1971].

Strong irritant to skin and mucous membranes.

TOXIC; inhalation, ingestion or contact (skin, eyes) with vapors, dusts or substance may cause severe injury, burns or death. Reaction with water or moist air will release toxic, corrosive or flammable gases. Reaction with water may generate much heat that will increase the concentration of fumes in the air. Fire will produce irritating, corrosive and/or toxic gases. Runoff from fire control or dilution water may be corrosive and/or toxic and cause pollution.

Non-combustible, substance itself does not burn but may decompose upon heating to produce corrosive and/or toxic fumes. Vapors may accumulate in confined areas (basement, tanks, hopper/tank cars etc.). Substance will react with water (some violently), releasing corrosive and/or toxic gases and runoff. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated or if contaminated with water.

A poison. A corrosive irritant to skin, eyes, and mucous membranes. Explosive reaction above 50°C with 2-chloro-4,6-dinitroaniline and 4- chloro-2,6-d1nitroalne. Potentially explosive reaction with dmitroaniline. When heated to decomposition it emits toxic fumes of SOx and NOx. See also SULFATES and NITRATES.