| 词条 | Nitrous acid | ||||||
| 释义 |
| Verifiedfields = changed | verifiedrevid = 462262187 | ImageFile = Nitrous acid acsv.svg | ImageName = Nitrous acid | PIN = Nitrous acid | SystematicName = Hydroxidooxidonitrogen |Section1={{Chembox Identifiers | CASNo = 7782-77-6 | CASNo_Ref = {{cascite|correct|CAS}} | PubChem = 24529 | ChemSpiderID = 22936 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | EINECS = 231-963-7 | KEGG_Ref = {{keggcite|changed|kegg}} | KEGG = C00088 | MeSHName = Nitrous+acid | ChEBI_Ref = {{ebicite|correct|EBI}} | ChEBI = 25567 | SMILES = O=NO | ChEMBL_Ref = {{ebicite|correct|EBI}} | ChEMBL = 1161681 | StdInChI_Ref = {{stdinchicite|correct|chemspider}} | StdInChI = 1S/HNO2/c2-1-3/h(H,2,3) | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = IOVCWXUNBOPUCH-UHFFFAOYSA-N | Gmelin = 983 | 3DMet = B00022}} |Section2={{Chembox Properties | Formula = HNO2 | Appearance = Pale blue solution | MolarMass = 47.013 g/mol | Density = Approx. 1 g/ml | Solubility = | MeltingPt = Only known in solution | ConjugateBase = Nitrite | pKa = 3.398 |Section7={{Chembox Hazards | ExternalSDS = | EUClass = | RPhrases = | SPhrases = | MainHazards = | NFPA-H = 4 | NFPA-F = 0 | NFPA-R = 2 | NFPA-S = OX | FlashPt = Non-flammable |Section8={{Chembox Related | OtherAnions = Nitric acid | OtherCations = Sodium nitrite Potassium nitrite Ammonium nitrite | OtherCompounds = Dinitrogen trioxide }} Nitrous acid (molecular formula HNO2) is a weak and monobasic acid known only in solution and in the form of nitrite ({{chem|NO|-|2}}) salts.[1] Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes. StructureIn the gas phase, the planar nitrous acid molecule can adopt both a cis and a trans form. The trans form predominates at room temperature, and IR measurements indicate it is more stable by around 2.3 kJ mol−1.[1]
PreparationNitrous acid is usually generated by acidification of aqueous solutions sodium nitrite with a mineral acid. The acidification is usually conducted at ice temperatures, and the HNO2 is consumed in situ.[2][3] 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 ReactionsDecomposition{{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:[4] 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 trioxide can subsequently be re-oxidized by air to nitric acid, making the overall reaction: 2 HNO2 + O2 → 2 HNO3 ReductionWith I− and Fe2+ ions, NO is formed:[5] 2 KNO2 + 2 KI + 2 H2SO4 → I2 + 2 NO + 2 H2O + 2 K2SO4 2 KNO2 + 2 FeSO4 + 2 H2SO4 → Fe2(SO4)3 + 2 NO + 2 H2O + K2SO4 With Sn2+ ions, N2O is formed: 2 KNO2 + 6 HCl + 2 SnCl2 → 2 SnCl4 + N2O + 3 H2O + 2 KCl With SO2 gas, NH2OH is formed: 2 KNO2 + 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 {{chem|N|2|H|5|+}}, HN3, and subsequently, N2 gas is 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− {{pad|3em}} Eo = +0.54 V {{chem|NO|3|−}} + 3 H+ + 2 e− ⇌ HNO2 + H2O {{pad|3em}} Eo = +0.93 V HNO2 + H+ + e− ⇌ NO + H2O {{pad|3em}} Eo = +0.98 V It can be seen that the values of E{{su|b=cell|p=o}} 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.[5] Organic chemistryNitrous acid is used to prepare diazonium salts: HNO2 + ArNH2 + H+ → {{chem|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.[6] 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:[7] 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 Atmosphere of the EarthNitrous 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. [8][9]See also{{Commons category|nitrous acid}}
References1. ^1 {{Greenwood&Earnshaw}} p. 462 {{nitrogen compounds}}{{Authority control}}2. ^{{cite journal|title=Ethyl Glycidate from (S)-Serine: Ethyl (R)-(+)-2,3-Epoxypropanoate|authors=Y. Petit, M. Larchevêque|journal=Org. Synth.|year=1998|volume=75|page=37|doi=10.15227/orgsyn.075.0037}} 3. ^{{cite journal|title=Synthesis of 4-, 5-, and 6-methyl-2,2'-bipyridine by a Negishi Cross-coupling Strategy: 5-methyl-2,2'-bipyridine|authors=Adam P. Smith, Scott A. Savage, J. Christopher Love, Cassandra L. Fraser|journal=Org. Synth.|year=2002|volume=78|page=51|doi=10.15227/orgsyn.078.0051}} 4. ^{{cite journal| last1 = Kameoka| first1 = Yohji| last2 = Pigford| first2 = Robert| date=February 1977| title = Absorption of Nitrogen Dioxide into Water, Sulfuric Acid, Sodium Hydroxide, and Alkaline Sodium Sulfite Aqueous | journal = Ind. Eng. Chem. Fundamen.| volume = 16| issue = 1| pages = 163–169| doi = 10.1021/i160061a031}} 5. ^1 {{cite book| title = Inorganic Chemistry, 3rd Edition| chapter = Chapter 15: The group 15 elements| author1 = Catherine E. Housecroft| author2 = Alan G. Sharpe| publisher = Pearson| year = 2008| isbn = 978-0-13-175553-6| page = 449}} 6. ^Clarke, H. T.; Kirner, W. R. "Methyl Red" Organic Syntheses, Collected Volume 1, p.374 (1941). {{cite web |url=http://www.orgsyn.org/orgsyn/pdfs/CV1P0374.pdf |title=Archived copy |accessdate=2007-07-26 |deadurl=yes |archiveurl=https://web.archive.org/web/20070930211221/http://www.orgsyn.org/orgsyn/pdfs/CV1P0374.pdf |archivedate=2007-09-30 |df= }} 7. ^{{cite book | title = Prudent practices in the laboratory: handling and disposal of chemicals | year = 1995 | publisher = National Academy Press | location = Washington, D.C. | isbn = 978-0-309-05229-0 | url = http://books.nap.edu/openbook.php?record_id=4911&page=165}} 8. ^{{cite journal | last1 = Spataro | first1 = F | last2 = Ianniello | first2 = A | date = November 2014 | title = Sources of atmospheric nitrous acid: state of the science, current research needs, and future prospects | journal = Journal of the Air & Waste Management Association | volume = 64 | issue = 11 | pages = 1232–1250| pmid = 25509545 }} 9. ^{{cite journal | last1 = Anglada | first1 = Josef M. | last2 = Solé | first2 = Albert | date = November 2017| title = The Atmospheric Oxidation of HONO by OH, Cl, and ClO Radicals | journal = The Journal of Physical Chemistry A| volume = 121| issue = 51| pages = 9698–9707| doi = 10.1021/acs.jpca.7b10715| pmid = 29182863 }} 4 : Nitrogen oxoacids|Nitrogen cycle|Oxidizing agents|Mineral acids |
||||||
| 随便看 |
|
开放百科全书收录14589846条英语、德语、日语等多语种百科知识，基本涵盖了大多数领域的百科知识，是一部内容自由、开放的电子版国际百科全书。