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Nitrous acid

Nitrous acid (molecular formula HNO
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] It was discovered by Carl Wilhelm Scheele, who called it "phlogisticated acid of niter". Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

Nitrous acid
Names
IUPAC name
Nitrous acid[1]
Identifiers
  • 7782-77-6 Y
3D model (JSmol)
  • Interactive image
3DMet
  • B00022
ChEBI
  • CHEBI:25567 Y
ChEMBL
  • ChEMBL1161681 Y
ChemSpider
  • 22936 Y
ECHA InfoCard 100.029.057
EC Number
  • 231-963-7
983
KEGG
  • C00088 N
MeSH Nitrous+acid
  • 24529
UNII
  • T2I5UM75DN Y
  • DTXSID7064813
  • InChI=1S/HNO2/c2-1-3/h(H,2,3) Y
    Key: IOVCWXUNBOPUCH-UHFFFAOYSA-N Y
  • O=NO
Properties
HNO2
Molar mass 47.013 g/mol
Appearance Pale blue solution
Density Approx. 1 g/ml
Melting point Only known in solution or as gas
Acidity (pKa) 3.15
Conjugate base Nitrite
Hazards
NFPA 704 (fire diamond)
Flash point Non-flammable
Related compounds
Other anions
Nitric acid
Other cations
Sodium nitrite
Potassium nitrite
Ammonium nitrite
Related compounds
Dinitrogen trioxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N verify (what is YN ?)

Structure edit

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]

Preparation edit

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 or concentrated solutions are unstable and decompose rapidly.

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

N2O3 + H2O → 2 HNO2

Reactions edit

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

Decomposition edit

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 edit

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
2
H+
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   Eo = +0.54 V
NO
3
+ 3 H+ + 2 e ⇌ HNO2 + H2O   Eo = +0.93 V
HNO2 + H+ + e ⇌ NO + H2O   Eo = +0.98 V

It can be seen that the values of Eo
cell
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 edit

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 edit

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]

DNA damage and mutation edit

Treatment of Escherichia coli cells with nitrous acid causes damage to the cell’s DNA including deamination of cytosine to uracil, and these damages are subject to repair by specific enzymes.[11] Also, nitrous acid causes base substitution mutations in organisms with double-stranded DNA.[12]

See also edit

References edit

  1. ^ "Nitrous Acid".
  2. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8. p. 462.
  3. ^ Petit, Y.; Larchevêque, M. (1998). "Ethyl Glycidate from (S)-Serine: Ethyl (R)-(+)-2,3-Epoxypropanoate". Org. Synth. 75: 37. doi:10.15227/orgsyn.075.0037.
  4. ^ Smith, Adam P.; Savage, Scott A.; Love, J. Christopher; Fraser, Cassandra L. (2002). "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. doi:10.15227/orgsyn.078.0051.
  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.
  6. ^ a b Housecroft, Catherine E.; Sharpe, Alan G. (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. (1922). "Methyl Red". Organic Syntheses. 2: 47. doi:10.15227/orgsyn.002.0047.
  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.
  11. ^ Da Roza, R.; Friedberg, E. C.; Duncan, B. K.; Warner, H. R. (1977-11-01). "Repair of nitrous acid damage to DNA in Escherichia coli". Biochemistry. 16 (22): 4934–4939. doi:10.1021/bi00641a030. ISSN 0006-2960. PMID 334252.
  12. ^ Hartman, Z.; Henrikson, E. N.; Hartman, P. E.; Cebula, T. A. (1994). "Molecular models that may account for nitrous acid mutagenesis in organisms containing double-stranded DNA". Environmental and Molecular Mutagenesis. 24 (3): 168–175. doi:10.1002/em.2850240305. ISSN 0893-6692. PMID 7957120.

nitrous, acid, confused, with, nitric, acid, hono, redirects, here, place, sweden, hönö, molecular, formula, hno2, weak, monoprotic, acid, known, only, solution, phase, form, nitrite, salts, discovered, carl, wilhelm, scheele, called, phlogisticated, acid, nit. Not to be confused with nitric acid Hono redirects here For the place in Sweden see Hono Nitrous acid molecular formula HNO2 is a weak and monoprotic acid known only in solution in the gas phase and in the form of nitrite NO 2 salts 2 It was discovered by Carl Wilhelm Scheele who called it phlogisticated acid of niter Nitrous acid is used to make diazonium salts from amines The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes Nitrous acid Names IUPAC name Nitrous acid 1 Identifiers CAS Number 7782 77 6 Y 3D model JSmol Interactive image 3DMet B00022 ChEBI CHEBI 25567 Y ChEMBL ChEMBL1161681 Y ChemSpider 22936 Y ECHA InfoCard 100 029 057 EC Number 231 963 7 Gmelin Reference 983 KEGG C00088 N MeSH Nitrous acid PubChem CID 24529 UNII T2I5UM75DN Y CompTox Dashboard EPA DTXSID7064813 InChI InChI 1S HNO2 c2 1 3 h H 2 3 YKey IOVCWXUNBOPUCH UHFFFAOYSA N Y SMILES O NO Properties Chemical formula HNO2 Molar mass 47 013 g mol Appearance Pale blue solution Density Approx 1 g ml Melting point Only known in solution or as gas Acidity pKa 3 15 Conjugate base Nitrite Hazards NFPA 704 fire diamond 402OX Flash point Non flammable Related compounds Other anions Nitric acid Other cations Sodium nitritePotassium nitriteAmmonium nitrite Related compounds Dinitrogen trioxide Except where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa N verify what is Y N Infobox references Contents 1 Structure 2 Preparation 3 Reactions 3 1 Decomposition 3 2 Reduction 3 3 Organic chemistry 4 Atmosphere of the Earth 5 DNA damage and mutation 6 See also 7 ReferencesStructure editIn 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 nbsp Dimensions of the anti form from the microwave spectrum nbsp Model of the anti form nbsp syn formPreparation editNitrous 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 or concentrated solutions are unstable and decompose rapidly Nitrous acid can also be produced by dissolving dinitrogen trioxide in water according to the equation N2O3 H2O 2 HNO2Reactions editNitrous acid is the main chemophore in the Liebermann reagent used to spot test for alkaloids Decomposition edit See also Dinitrogen trioxide 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 edit 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 N2 H 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 Eo 0 54 V NO 3 3 H 2 e HNO2 H2O Eo 0 93 V HNO2 H e NO H2O Eo 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 edit 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 a 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 H2OAtmosphere of the Earth editNitrous 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 DNA damage and mutation editTreatment of Escherichia coli cells with nitrous acid causes damage to the cell s DNA including deamination of cytosine to uracil and these damages are subject to repair by specific enzymes 11 Also nitrous acid causes base substitution mutations in organisms with double stranded DNA 12 See also edit nbsp Wikimedia Commons has media related to nitrous acid Demjanov rearrangement Nitric acid HNO3 Nitrosyl O hydroxide Tiffeneau Demjanov rearrangementReferences edit Nitrous Acid a b Greenwood Norman N Earnshaw Alan 1997 Chemistry of the Elements 2nd ed Butterworth Heinemann ISBN 978 0 08 037941 8 p 462 Petit Y Larcheveque M 1998 Ethyl Glycidate from S Serine Ethyl R 2 3 Epoxypropanoate Org Synth 75 37 doi 10 15227 orgsyn 075 0037 Smith Adam P Savage Scott A Love J Christopher Fraser Cassandra L 2002 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 doi 10 15227 orgsyn 078 0051 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 a b Housecroft Catherine E Sharpe Alan G 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 1922 Methyl Red Organic Syntheses 2 47 doi 10 15227 orgsyn 002 0047 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 amp Waste Management Association 64 11 1232 1250 doi 10 1080 10962247 2014 952846 PMID 25509545 Anglada Josef M Sole 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 Da Roza R Friedberg E C Duncan B K Warner H R 1977 11 01 Repair of nitrous acid damage to DNA in Escherichia coli Biochemistry 16 22 4934 4939 doi 10 1021 bi00641a030 ISSN 0006 2960 PMID 334252 Hartman Z Henrikson E N Hartman P E Cebula T A 1994 Molecular models that may account for nitrous acid mutagenesis in organisms containing double stranded DNA Environmental and Molecular Mutagenesis 24 3 168 175 doi 10 1002 em 2850240305 ISSN 0893 6692 PMID 7957120 Retrieved from https en wikipedia org w index php title Nitrous acid amp oldid 1217241986, wikipedia, wiki, book, books, library,

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