Pyridinium

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Pyridinium
Pyridinium.svg
Pyridinium-3D-balls.png
Names
Preferred IUPAC name
Pyridin-1-ium
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
UNII
  • InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1 Yes check.svgY
    Key: JUJWROOIHBZHMG-UHFFFAOYSA-O Yes check.svgY
  • InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1
  • InChI=1S/C5H5N/c1-2-4-6-5-3-1/h1-5H/p+1
    Key: JUJWROOIHBZHMG-UHFFFAOYSA-O
  • c1cc[nH+]cc1
Properties
[C5H5NH]+
Molar mass 80.110 g·mol−1
Acidity (pKa)~5 [1] [2]
Conjugate base Pyridine
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Pyridinium refers to the cation [C5H5NH]+. It is the conjugate acid of pyridine. Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines. They are prepared by treating pyridine with acids. [3]

Contents

As pyridine is often used as an organic base in chemical reactions, pyridinium salts are produced in many acid-base reactions. Its salts are often insoluble in the organic solvent, so precipitation of the pyridinium leaving group complex is an indication of the progress of the reaction.

Pyridinium cations are aromatic, as determined through Hückel's rule. [4] They are isoelectronic with benzene.

N-Alkylpyridinium cations

Nicotinamide adenine dinucleotide is a N-alkylpyridinium cation that occurs widely in life. NAD+ phys.svg
Nicotinamide adenine dinucleotide is a N-alkylpyridinium cation that occurs widely in life.

When the acidic proton is replaced by alkyl, the compounds are called N-alkylpyridinium. A simple representative is N-methylpyridinium ([C5H5NCH3]+). These pyridinium intermediates have been used as electrophiles in synthetic organic chemistry to build dearomatized congeners called dihydropyridines, as demonstrated in one example from Smith in 2021. [5] Earlier, the same research group also delineated the rules surrounding regioselectivities associated with adding nucleophiles to pyridinium electrophiles with varying substituents. [6] From a commercial perspective, an important pyridinium compound is the herbicide paraquat. [7]

See also

References

  1. ↑ Linnell, Robert (1960). "Notes – Dissociation Constants of 2-Substituted Pyridines". Journal of Organic Chemistry. 25 (2): 290. doi:10.1021/jo01072a623.
  2. ↑ Pearson, Ralph G.; Williams, Forrest V. (1953). "Rates of Ionization of Pseudo Acids.1V. Steric Effects in the Base-catalyzed Ionization of Nitroethane". Journal of the American Chemical Society. 75 (13): 3073. doi:10.1021/ja01109a008.
  3. ↑ George A. Olah; Michael Watkins (1978). "Fluorinations With Pyridinium Polyhydrogen Fluoride Reagent: 1-Fluoroadamantane". Org. Synth. 58: 75. doi:10.15227/orgsyn.058.0075.
  4. ↑ "Aromatic Compounds" (PDF). Alex Roche, Rutgers University.
  5. ↑ Grigolo, Thiago A.; Subhit, Ariana R.; Smith, Joel M. (2021-09-03). "Regioselective Asymmetric Alkynylation of N-Alkyl Pyridiniums". Organic Letters. 23 (17): 6703–6708. doi:10.1021/acs.orglett.1c02276. ISSN   1523-7060. PMID   34474575. S2CID   237401193.
  6. ↑ Knight, Brian J.; Tolchin, Zachary A.; Smith, Joel M. (2021-03-11). "A predictive model for additions to N-alkyl pyridiniums" . Chemical Communications. 57 (21): 2693–2696. doi:10.1039/D1CC00056J. ISSN   1364-548X. PMID   33595047. S2CID   231945207.
  7. ↑ Shimizu, Shinkichi; Watanabe, Nanao; Kataoka, Toshiaki; Shoji, Takayuki; Abe, Nobuyuki; Morishita, Sinji; Ichimura, Hisao (2007). "Pyridine and Pyridine Derivatives". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a22_399. ISBN   978-3-527-30673-2.
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