حمض النيتروز

حمض النيتروز
الأسماء
	اسم أيوپاك Nitrous acid
المُعرِّفات
رقم CAS
3D model (JSmol)	Interactive image;
3DMet	B00022;
ChEBI	CHEBI:25567 ;
ChEMBL	ChEMBL1161681 ;
ChemSpider	22936 ;
ECHA InfoCard	100.029.057
رقم EC	231-963-7;
مرجع Gmelin	983
KEGG	C00088 ;
عناوين مواضيع طبية MeSH	{{{value}}}
PubChem CID	24529;
UNII	T2I5UM75DN ;
CompTox Dashboard (EPA)	DTXSID7064813 ;
	InChI InChI=1S/HNO2/c2-1-3/h(H,2,3) Key: IOVCWXUNBOPUCH-UHFFFAOYSA-N ;
	SMILES O=NO;
الخصائص
الصيغة الجزيئية	HNO2
كتلة مولية	47.013 g/mol
المظهر	Pale blue solution
الكثافة	Approx. 1 g/ml
نقطة الانصهار
الحموضة (pKa)	3.15
المخاطر
NFPA 704 (معيـَّن النار)	0 4 2 OX
نقطة الوميض	Non-flammable
مركبات ذا علاقة
أنيونات أخرى	Nitric acid
كاتيونات أخرى	Sodium nitrite; Potassium nitrite; Ammonium nitrite
مركـّبات ذات علاقة	Dinitrogen trioxide
	ما لم يُذكر غير ذلك، البيانات المعطاة للمواد في حالاتهم العيارية (عند 25 °س [77 °ف]، 100 kPa).
	verify (what is ?)
	مراجع الجدول

Nitrous acid (molecular formula H N O 2) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite (NO−2) salts.^[2] Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

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Structure

In the gas phase, the planar nitrous acid molecule can adopt both a syn and an anti form. The anti form predominates at room temperature, and IR measurements indicate it is more stable by around 2.3 kJ/mol.^[2]

Dimensions of the anti form
(from the microwave spectrum)
Model of the anti form
syn form

Preparation

Nitrous acid is usually generated by acidification of aqueous solutions of sodium nitrite with a mineral acid. The acidification is usually conducted at ice temperatures, and the HNO₂ is consumed in situ.^[3]^[4] Free nitrous acid is unstable and decomposes rapidly.

Nitrous acid can also be produced by dissolving dinitrogen trioxide in water according to the equation

N₂O₃ + H₂O → 2 HNO₂

Reactions

Nitrous acid is the main chemphore in the Liebermann reagent, used to spot-test for alkaloids.

Decomposition

Gaseous nitrous acid, which is rarely encountered, decomposes into nitrogen dioxide, nitric oxide, and water:

2 HNO₂ → NO₂ + NO + H₂O

Nitrogen dioxide disproportionates into nitric acid and nitrous acid in aqueous solution:^[5]

2 NO₂ + H₂O → HNO₃ + HNO₂

In warm or concentrated solutions, the overall reaction amounts to production of nitric acid, water, and nitric oxide:

3 HNO₂ → HNO₃ + 2 NO + H₂O

The nitric oxide can subsequently be re-oxidized by air to nitric acid, making the overall reaction:

2 HNO₂ + O₂ → 2 HNO₃

Reduction

With I⁻ and Fe²⁺ ions, NO is formed:^[6]

2 HNO₂ + 2 KI + 2 H₂SO₄ → I₂ + 2 NO + 2 H₂O + 2 K₂SO₄

2 HNO₂ + 2 FeSO₄ + 2 H₂SO₄ → Fe₂(SO₄)₃ + 2 NO + 2 H₂O + K₂SO₄

With Sn²⁺ ions, N₂O is formed:

2 HNO₂ + 6 HCl + 2 SnCl₂ → 2 SnCl₄ + N₂O + 3 H₂O + 2 KCl

With SO₂ gas, NH₂OH is formed:

2 HNO₂ + 6 H₂O + 4 SO₂ → 3 H₂SO₄ + K₂SO₄ + 2 NH₂OH

With Zn in alkali solution, NH₃ is formed:

5 H₂O + KNO₂ + 3 Zn → NH₃ + KOH + 3 Zn(OH)₂

With N 2H+5, both HN₃ and (subsequently) N₂ gas are formed:

HNO₂ + [N₂H₅]⁺ → HN₃ + H₂O + H₃O⁺

HNO₂ + HN₃ → N₂O + N₂ + H₂O

Oxidation by nitrous acid has a kinetic control over thermodynamic control, this is best illustrated that dilute nitrous acid is able to oxidize I⁻ to I₂, but dilute nitric acid cannot.

I₂ + 2 e⁻ ⇌ 2 I⁻ E^o = +0.54 V

NO−3 + 3 H⁺ + 2 e⁻ ⇌ HNO₂ + H₂O E^o = +0.93 V

HNO₂ + H⁺ + e⁻ ⇌ NO + H₂O E^o = +0.98 V

It can be seen that the values of Eocell for these reactions are similar, but nitric acid is a more powerful oxidizing agent. Base on the fact that dilute nitrous acid can oxidize iodide into iodine, it can be deduced that nitrous is a faster, rather than a more powerful, oxidizing agent than dilute nitric acid.^[6]

Organic chemistry

Nitrous acid is used to prepare diazonium salts:

HNO₂ + ArNH₂ + H⁺ → ArN+2 + 2 H₂O

where Ar is an aryl group.

Such salts are widely used in organic synthesis, e.g., for the Sandmeyer reaction and in the preparation azo dyes, brightly colored compounds that are the basis of a qualitative test for anilines.^[7] Nitrous acid is used to destroy toxic and potentially explosive sodium azide. For most purposes, nitrous acid is usually formed in situ by the action of mineral acid on sodium nitrite:^[8] It is mainly blue in colour

NaNO₂ + HCl → HNO₂ + NaCl

2 NaN₃ + 2 HNO₂ → 3 N₂ + 2 NO + 2 NaOH

Reaction with two α-hydrogen atoms in ketones creates oximes, which may be further oxidized to a carboxylic acid, or reduced to form amines. This process is used in the commercial production of adipic acid.

Nitrous acid reacts rapidly with aliphatic alcohols to produce alkyl nitrites, which are potent vasodilators:

(CH₃)₂CHCH₂CH₂OH + HNO₂ → (CH₃)₂CHCH₂CH₂ONO + H₂O

The carcinogens called nitrosamines are produced, usually not intentionally, by the reaction of nitrous acid with secondary amines:

HNO₂ + R₂NH → R₂N-NO + H₂O

Atmosphere of the Earth

Nitrous acid is involved in the ozone budget of the lower atmosphere, the troposphere. The heterogeneous reaction of nitric oxide (NO) and water produces nitrous acid. When this reaction takes place on the surface of atmospheric aerosols, the product readily photolyses to hydroxyl radicals.^[9]^[10]

المصادر

^ https://pubchem.ncbi.nlm.nih.gov/compound/24529#section=IUPAC-Name&fullscreen=true
^ ^أ ^ب Greenwood, N. N. (1997). Chemistry of the Elements (2nd Edition ed.). Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. {{cite book}}: |edition= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help) p. 462.
^ "Ethyl Glycidate from (S)-Serine: Ethyl (R)-(+)-2,3-Epoxypropanoate". Org. Synth. 75: 37. 1998. doi:10.15227/orgsyn.075.0037. {{cite journal}}: Cite uses deprecated parameter |authors= (help)
^ "Synthesis of 4-, 5-, and 6-methyl-2,2'-bipyridine by a Negishi Cross-coupling Strategy: 5-methyl-2,2'-bipyridine". Org. Synth. 78: 51. 2002. doi:10.15227/orgsyn.078.0051. {{cite journal}}: Cite uses deprecated parameter |authors= (help)
^ Kameoka, Yohji; Pigford, Robert (February 1977). "Absorption of Nitrogen Dioxide into Water, Sulfuric Acid, Sodium Hydroxide, and Alkaline Sodium Sulfite Aqueous". Ind. Eng. Chem. Fundamen. 16 (1): 163–169. doi:10.1021/i160061a031.
^ ^أ ^ب Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 449. ISBN 978-0-13-175553-6.
^ Clarke, H. T.; Kirner, W. R. "Methyl Red" Organic Syntheses, Collected Volume 1, p.374 (1941). "Archived copy" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2007-07-26.{{cite web}}: CS1 maint: archived copy as title (link)
^ Prudent practices in the laboratory: handling and disposal of chemicals. Washington, D.C.: National Academy Press. 1995. doi:10.17226/4911. ISBN 978-0-309-05229-0.
^ Spataro, F; Ianniello, A (November 2014). "Sources of atmospheric nitrous acid: state of the science, current research needs, and future prospects". Journal of the Air & Waste Management Association. 64 (11): 1232–1250. doi:10.1080/10962247.2014.952846. PMID 25509545.
^ Anglada, Josef M.; Solé, Albert (November 2017). "The Atmospheric Oxidation of HONO by OH, Cl, and ClO Radicals". The Journal of Physical Chemistry A. 121 (51): 9698–9707. Bibcode:2017JPCA..121.9698A. doi:10.1021/acs.jpca.7b10715. PMID 29182863.

[1] ttps://pubchem.ncbi.nlm.nih.gov/compound/24529#section=IUPAC-Name&fullscreen=true

[G&E-2] أ ^ب Greenwood, N. N. (1997). Chemistry of the Elements (2nd Edition ed.). Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4. {{cite book}}: |edition= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help) p. 462.

[3] "Ethyl Glycidate from (S)-Serine: Ethyl (R)-(+)-2,3-Epoxypropanoate". Org. Synth. 75: 37. 1998. doi:10.15227/orgsyn.075.0037. {{cite journal}}: Cite uses deprecated parameter |authors= (help)

[4] "Synthesis of 4-, 5-, and 6-methyl-2,2'-bipyridine by a Negishi Cross-coupling Strategy: 5-methyl-2,2'-bipyridine". Org. Synth. 78: 51. 2002. doi:10.15227/orgsyn.078.0051. {{cite journal}}: Cite uses deprecated parameter |authors= (help)

[5] Kameoka, Yohji; Pigford, Robert (February 1977). "Absorption of Nitrogen Dioxide into Water, Sulfuric Acid, Sodium Hydroxide, and Alkaline Sodium Sulfite Aqueous". Ind. Eng. Chem. Fundamen. 16 (1): 163–169. doi:10.1021/i160061a031.

[InorgChem-6] أ ^ب Catherine E. Housecroft; Alan G. Sharpe (2008). "Chapter 15: The group 15 elements". Inorganic Chemistry, 3rd Edition. Pearson. p. 449. ISBN 978-0-13-175553-6.

[7] Clarke, H. T.; Kirner, W. R. "Methyl Red" Organic Syntheses, Collected Volume 1, p.374 (1941). "Archived copy" (PDF). Archived from the original (PDF) on 2007-09-30. Retrieved 2007-07-26.{{cite web}}: CS1 maint: archived copy as title (link)

[8] Prudent practices in the laboratory: handling and disposal of chemicals. Washington, D.C.: National Academy Press. 1995. doi:10.17226/4911. ISBN 978-0-309-05229-0.

[9] Spataro, F; Ianniello, A (November 2014). "Sources of atmospheric nitrous acid: state of the science, current research needs, and future prospects". Journal of the Air & Waste Management Association. 64 (11): 1232–1250. doi:10.1080/10962247.2014.952846. PMID 25509545.

[10] Anglada, Josef M.; Solé, Albert (November 2017). "The Atmospheric Oxidation of HONO by OH, Cl, and ClO Radicals". The Journal of Physical Chemistry A. 121 (51): 9698–9707. Bibcode:2017JPCA..121.9698A. doi:10.1021/acs.jpca.7b10715. PMID 29182863.

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