Nitroxyl

Last updated
Nitroxyl
Nitroxyl-3D-balls.png
Names
IUPAC name
Azanone
Systematic IUPAC name
Oxidanimine [1]
Other names
Hydrogen oxonitrate(I)

Nitronous oxide
Nitrosyl hydride

Hyponitrous acid monomer
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
MeSH Nitroxyl
PubChem CID
UNII
  • InChI=1S/HNO/c1-2/h1H Yes check.svgY
    Key: ODUCDPQEXGNKDN-UHFFFAOYSA-N Yes check.svgY
  • N=O
Properties
HNO
Molar mass 31.014 g·mol−1
log P 0.74
Structure
Digonal
Bent
Thermochemistry
33.88 J K−1 mol−1
Std molar
entropy (S⦵298)
220.91 J K−1 mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Nitroxyl (common name) or azanone (IUPAC name) [2] is the chemical compound HNO. It is well known in the gas phase. [3] [4] Nitroxyl can be formed as a short-lived intermediate in the solution phase. The conjugate base, NO−, nitroxide anion, is the reduced form of nitric oxide (NO) and is isoelectronic with dioxygen. The bond dissociation energy of H−NO is 49.5 kcal/mol (207 kJ/mol), which is unusually weak for a bond to the hydrogen atom.

Contents

Generation

Nitroxyl is produced from the reagents Angeli's salt (Na2N2O3) and Piloty's acid (PhSO2NHOH). [5] Other notable studies on the production of HNO exploit cycloadducts of acyl nitroso species, which are known to decompose via hydrolysis to HNO and acyl acid. Upon photolysis these compounds release the acyl nitroso species which then further decompose. [6] HNO is generated via organic oxidation of cyclohexanone oxime with lead tetraacetate to form 1-nitrosocyclohexyl acetate: [7]

Nitrosocyclohexyl acetate.png

This compound can be hydrolyzed under basic conditions in a phosphate buffer to HNO, acetic acid, and cyclohexanone.

Dichloramine reacts with the hydroxide ion, which is always present in water, to yield nitroxyl and the chloride ion. [8]

Reactions

Nitroxyl is a weak acid, with pKa of about 11, the conjugate base being the triplet state of NO−, sometimes called nitroxide. Nitroxyl itself, however, is a singlet ground state. Thus, deprotonation of nitroxyl uniquely involves the forbidden spin crossing from the singlet state starting material to triplet state product:

1HNO + B− → 3NO− + BH

Due to the spin-forbidden nature of deprotonation, proton abstraction is many orders of magnitude slower (k = 4.9×104 M−1 s−1 for deprotonation by OH−) than what one would expect for a heteroatom proton-transfer process (processes that are so fast that they are sometimes diffusion-controlled).

The Ka of starting from or ending with the electronic excited states has also been determined. When process of deprotonating singlet state HNO to obtain singlet state NO− has a pKa is about 23. On the other hand, when deprotonating triplet HNO to obtain triplet NO−, the pKa is about −1.8. [9] [10]

Nitroxyl rapidly decomposes by a bimolecular pathway to nitrous oxide (k at 298 K = 8×106 M s): [9]

2 HNO → N2O + H2O

The reaction proceeds via dimerization to hyponitrous acid, H2N2O2, which subsequently undergoes dehydration. Therefore, HNO is generally prepared in situ as described above.

Nitroxyl is very reactive towards nucleophiles, including thiols. The initial adduct rearranges to a sulfinamide: [10]

HNO + RSH → RS(O)NH2

Detection

In biological samples, nitroxyl can be detected using fluorescent sensors, many of which are based on the reduction of copper(II) to copper(I) with concomitant increase in fluorescence. [11]

Medicinal chemistry

Nitroxyl donors, known as nitroso compounds, show potential in the treatment of heart failure and ongoing research is focused on finding new molecules for this task.

See also

Related Research Articles

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6H
5OH. Phenolic compounds are classified as simple phenols or polyphenols based on the number of phenol units in the molecule.

<span class="mw-page-title-main">Nitrous acid</span> Chemical compound

Nitrous acid is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes.

<span class="mw-page-title-main">Dinitrogen pentoxide</span> Chemical compound

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<span class="mw-page-title-main">Cyclobutadiene</span> Chemical compound

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<span class="mw-page-title-main">Nitro compound</span> Organic compound containing an −NO₂ group

In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups. The nitro group is one of the most common explosophores used globally. The nitro group is also strongly electron-withdrawing. Because of this property, C−H bonds alpha (adjacent) to the nitro group can be acidic. For similar reasons, the presence of nitro groups in aromatic compounds retards electrophilic aromatic substitution but facilitates nucleophilic aromatic substitution. Nitro groups are rarely found in nature. They are almost invariably produced by nitration reactions starting with nitric acid.

<span class="mw-page-title-main">Lithium diisopropylamide</span> Chemical compound

Lithium diisopropylamide is a chemical compound with the molecular formula LiN(CH 2)2. It is used as a strong base and has been widely utilized due to its good solubility in non-polar organic solvents and non-nucleophilic nature. It is a colorless solid, but is usually generated and observed only in solution. It was first prepared by Hamell and Levine in 1950 along with several other hindered lithium diorganylamides to effect the deprotonation of esters at the α position without attack of the carbonyl group.

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<span class="mw-page-title-main">Bamford–Stevens reaction</span>

The Bamford–Stevens reaction is a chemical reaction whereby treatment of tosylhydrazones with strong base gives alkenes. It is named for the British chemist William Randall Bamford and the Scottish chemist Thomas Stevens Stevens (1900–2000). The usage of aprotic solvents gives predominantly Z-alkenes, while protic solvent gives a mixture of E- and Z-alkenes. As an alkene-generating transformation, the Bamford–Stevens reaction has broad utility in synthetic methodology and complex molecule synthesis.

<span class="mw-page-title-main">Sulfamic acid</span> Chemical compound

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<span class="mw-page-title-main">Nitroso</span> Class of functional groups with a –N=O group attached

In organic chemistry, nitroso refers to a functional group in which the nitric oxide group is attached to an organic moiety. As such, various nitroso groups can be categorized as C-nitroso compounds, S-nitroso compounds, N-nitroso compounds, and O-nitroso compounds.

<span class="mw-page-title-main">Persistent carbene</span> Type of carbene demonstrating particular stability

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<span class="mw-page-title-main">Nitrosyl chloride</span> Chemical compound

Nitrosyl chloride is the chemical compound with the formula NOCl. It is a yellow gas that is commonly encountered as a component of aqua regia, a mixture of 3 parts concentrated hydrochloric acid and 1 part of concentrated nitric acid. It is a strong electrophile and oxidizing agent. It is sometimes called Tilden's reagent, after William A. Tilden, who was the first to produce it as a pure compound.

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<span class="mw-page-title-main">Nitrolic acid</span>

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References

  1. ↑ "Nitroxyl". PubChem . Retrieved August 24, 2022.{{cite web}}: CS1 maint: url-status (link)
  2. ↑ Doctorovich, F.; Bikiel, D.; Pellegrino, J.; Suárez, S. A.; Larsen, A.; Martí, M. A. (2011). "Nitroxyl (azanone) trapping by metalloporphyrins". Coordination Chemistry Reviews. 255 (23–24): 2764–2784. doi:10.1016/j.ccr.2011.04.012.
  3. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  4. ↑ Wiberg, Egon; Holleman, Arnold Frederick (2001). Inorganic Chemistry. Elsevier. ISBN   978-0-12-352651-9.
  5. ↑ Nagasawa, H. T.; Kawle, S. P.; Elberling, J. A.; DeMaster, E. G.; Fukuto, J. M. (1995). "Prodrugs of Nitroxyl as Potential Aldehyde Dehydrogenase Inhibitors vis-a-vis Vascular Smooth Muscle Relaxants". J. Med. Chem. 38 (11): 1865–1871. doi:10.1021/jm00011a005. PMID   7783118.
  6. ↑ Cohen, A. D.; Zeng, B.-B.; King, S. B.; Toscano, J. P. (2003). "Direct observation of an acyl nitroso species in solution by time-resolved IR spectrocopy". J. Am. Chem. Soc. 125 (6): 1444–1445. doi:10.1021/ja028978e. PMID   12568581.
  7. ↑ Sha, Xin; Isbell, T. Scott; Patel, Rakesh P.; Day, Cynthia S.; King, S. Bruce (2006). "Hydrolysis of Acyloxy Nitroso Compounds Yields Nitroxyl (HNO)". J. Am. Chem. Soc. 128 (30): 9687–9692. doi:10.1021/ja062365a. PMID   16866522.
  8. ↑ White, George Clifford (1986). The handbook of chlorination (2nd ed.). New York: Van Nostrand Reinhold. p. 169. ISBN   978-0-442-29285-0.
  9. 1 2 Shafirovich, V.; Lymar, S. V. (2002). "Nitroxyl and its anion in aqueous solutions: Spin states, protic equilibria, and reactivities toward oxygen and nitric oxide". Proceedings of the National Academy of Sciences of the United States of America. 99, 7340 (11): 7340–7345. doi: 10.1073/pnas.112202099 . PMC   124232 . PMID   12032284.
  10. 1 2 Bianco, C. L.; Toscano, J. P.; Bartberger, M. D.; Fukuto, J. M. (2017). "The chemical biology of HNO signaling". Archives of Biochemistry and Biophysics. 617: 129–136. doi:10.1016/j.abb.2016.08.014. PMC   5318259 . PMID   27555493.
  11. ↑ Rivera-Fuentes, Pablo; Lippard, Stephen J. (2015). "Metal-Based Optical Probes for Live Cell Imaging of Nitroxyl (HNO)". Acc. Chem. Res. 38 (11): 2427–2434. doi:10.1021/acs.accounts.5b00388. hdl: 1721.1/107934 . PMID   26550842.
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