NITROSYLSULFURIC ACID 661
4FNO + SiO2 → SiF4 + 2N2O3
Hazard
Nitrosyl fluoride is a dangerous irritant to the eyes, skin, and mucous membranes. Explosive reactions can occur with alkenes.
NITROSYLSULFURIC ACID
[7782-78-7]
Formula: HSO4NO; MW 127.08 Structure:
ture:
O HO—S—O—N=O
O
Synonyms: nitrosyl sulfate; chamber crystals; nitroxylsulfuric acid; nitrososulfuric acid; nitrosyl hydrogen sulfate
Uses
Nitrosylsulfuric acid is used in making caprolactam from benzoic acid and in preparing many disperse azo dyes. Other applications are bleaching, maturing, dough-conditioning cereal products, and in preparing crystalline diazonium sulfates.
Physical Properties
Colorless crystalline solid; rhombohedral structure; decomposes at 73.5°C; decomposes in water; soluble in sulfuric acid.
Preparation
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 (NOx) in oleum (fuming sulfuric acid):
N2O3 + 2H2SO4 → 2ONSO4H + H2O
or by the reaction of nitrosyl chloride with concentrated sulfuric acid:
ClNO + H2SO4 → ONSO4H + HCl
Another method of preparation involves the reaction of nitrosyl bromide with silver bisulfate:
662 NITROUS ACID
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)
Reactions
The compound decomposes in moist air forming nitric and sulfuric acids.
2ONHSO4 + O2 + 2H2O → 2HNO3 + 2H2SO4
However, above 50°C decomposition in moist air forms nitric oxide, nitrogen dioxide, and sulfuric acid:
2ONHSO4 + H2O → NO + NO2 + 2H2SO4
Nitrosylsulfuric acid hydrolyzes in water forming sulfuric acid and oxides of nitrogen as shown above.
Nitrosylsulfuric acid reacts with cyclohexane carboxylic acid to form caprolactam. The starting material in such large-scale production of caprolactam is benzoic acid. The reactions are:
H2 |
C6H11COOH |
ONHSO4 |
C6H5COOH −−−→ |
−−−−−−→ |
|
Pd |
|
|
(benzoic acid) |
(cyclohexane carboxylic acid) |
|
cyclo—(C6H10NH)=O + CO2 + H2SO4
(caprolactam)
Analysis
Elemental composition: S 25.23%, H 0.79%, N 11.02, O 62.95%. Nitrosylsulfuric acid may be analysed by IR, NMR and mass spectrometry, as well as by elemental microanalysis. Wet analysis involves hydrolyzing the compound in the presence of excess NaOH and measuring excess base by potentiometric titration.
NITROUS ACID
[7782-77-6]
Formula: HNO2; MW 47.014; exists only in solution and has not been isolated.
Uses
Nitrous acid is a diazotizing agent. The acid diazotizes primary aromatic
NITROUS ACID 663
amines to diazo derivatives in manufacturing azo dyes.
Physical Properties
Pale blue solution; stable only in solution; weak acid, Ka 4.5x10-–4.
Thermochemical Properties |
|
∆Ηƒ° (gas) |
–19.00 kcal/mol |
∆Gƒ° (gas) |
–10.99 kcal/mol |
S° (gas) |
60.73 cal/degree mol |
Cρ |
10.90 cal/degree mol |
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¯ → HNO2
Reactions
Nitrous acid is unstable. It decomposes to form nitric acid and nitric oxide:
3HNO2 → NO3¯ + H3O+ + 2NO
Strong oxidizing agents, such as permanganate, readily oxidize nitrous acid to nitric acid.
Nitrous acid is an effective oxidizing agent. It oxidizes hydrogen sulfide to sulfur forming either nitric oxide or ammonia, depending on the acidity of the solution:
2HNO2 + H2S → S + 2NO + 2H2O
HNO2 + 3H2S → 3S + NH3 + 2H2O
In acid medium it oxidizes iodide ion to iodine:
HNO2 + I¯ + 6H+ → 3I2 + NH3 + 2H2O
Analysis
Nitrous acid in solution can be analysed by measuring the nitrite ion, NO2¯, by ion chromatography, or a colorimetric method. The colorimetric test sees the reddish purple azo dye produced at pH 2.0 to 2.5 by coupling diazotized sulfanilamide with N-(1-naphthyl)ethylenediaminedihydrochloride (APHA, AWWA and WEF. 1998. Standard methods for the Examination of Water and Wastewater, 20th ed. Washington, DC: American Public Health Association). In addition to tests for nitrite ion, other tests should confirm that the NO2¯ is from nitrous acid and not any metal nitrite. This can be done by oxidizing iodide ion in acid medium and measuring the liberated iodide by titrating against a standard solution of sodium thiosulfate using starch indicator, and
664 NITROUS OXIDE
also by measuring ammonia liberated with an ammonium ion selective electrode. (See Reactions).
NITROUS OXIDE
[10024-97-2]
Formula: N2O; MW 44.013; a diamagnetic molecule.
Synonyms: dinitrogen oxide; nitrogen monoxide; dinitrogen monoxide; hyponitrous acid anhydride; laughing gas.
History and Uses
Nitrous oxide was discovered by Priestley. It is found in the atmosphere in trace concentrations. The gas is used as an anesthetic, especially in dentistry and minor surgery. It produces mild hysteria and laughter preceding the anesthetic effect, for which reason it also is called “laughing gas.” It is used as an aerosol propellant, an aerating agent for whipped cream, and an oxidizing agent at high temperatures. Nitrous oxide also is used in the preparation of nitrites and as a flame gas in flame atomic absorption spectrometry of metals.
Physical Properties
Colorless gas with faint sweet odor and taste; heavier than air, density in air 1.53 (air=1); gas density 1.977 g/L at 0°C; noncombustible gas; supports combustion; liquefies to a colorless liquid at –88.5°C; liquid density 1.226 g/mL at –89°C; freezes to a cubic crystalline solid at –90.8°C; dipole moment 0.166 ; critical temperature 36.5°C; critical pressure 71.7 atm; solubility in water: 130 mL gas dissolves in 100mL water at 0°C and 56.7 mL in 100 mL water at 25°C; soluble in alcohol, ether and sulfuric acid.
Thermochemical Properties |
19.61 kcal/mol |
∆Ηƒ° |
|
∆Gƒ° |
24.90 kcal/mol |
S° |
52.52 cal/degree mol |
Cρ |
9.19 cal/degree mol |
Preparation
Nitrous oxide may be prepared by heating molten ammonium nitrate carefully. Rapid and strong heating can cause explosion:
250°C
NH4NO3 → N2O↑ + 2H2O
Any nitric oxide produced in small amounts may be removed by passage through FeSO4 solution.
Alternatively, the gas may be obtained by warming a solution of ammonium nitrate in nitric acid containing a small amount of hydrochloric acid.
Pure nitrous oxide may be prepared by treating a solution of sodium nitrite, NaNO2 with that of hydroxyl amine hydrochloride, NH2OH•HCl: