Vinyl alcohol

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Vinyl alcohol
Displayed formula of ethenol
Ball-and-stick model of ethenol
Names
Preferred IUPAC name
Ethenol
Other names
Hydroxyethene
Hydroxyethylene
Identifiers
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.008.350
Properties
C2H4O
Molar mass 44.053 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Vinyl alcohol, also called ethenol (IUPAC name), is the simplest enol. With the formula CH2CHOH, it is a labile compound that converts to acetaldehyde. It is not a precursor to polyvinyl alcohol.

Tautomerization of acetaldehyde to vinyl alcohol[edit]

Under normal conditions, vinyl alcohol converts (tautomerizes) to acetaldehyde:

Ethanal Ethenol Tautomerie.svg

At room temperature, acetaldehyde (H3CC(O)H) is more stable than vinyl alcohol (H2C=CHOH) by 42.7 kJ/mol:[1]

H2C=CHOH → H3CC(O)H                 ΔH298,g = −42.7 kJ/mol

This keto-enol tautomerization has a high barrier and does therefore not occur near room temperature. The tautomerization can be catalyzed via photochemical process. These findings suggest that the keto-enol tautomerization is a viable route under atmospheric and stratospheric conditions, relevant to a role for vinyl alcohol in the production of organic acids in the atmosphere.[2][3]

It can be formed by elimination of water from ethylene glycol at a temperature of 900 °C and low pressure.[4]

Relationship to polyvinylalcohol[edit]

Because of the instability of vinyl alcohol, the thermoplastic polyvinyl alcohol (PVA or PVOH) is made indirectly by polymerization of vinyl acetate followed by hydrolysis of the ester bonds (Ac = acetyl, HOAc = acetic acid):

n CH2=CHOAc → (CH2−CHOAc)n
(CH2−CHOAc)n + n H2O → (CH2−CHOH)n + n HOAc

As a ligand[edit]

Several metal complexes are known that contain vinyl alcohol as a ligand. One example is Pt(acac)(η2-C2H3OH)Cl.[5]

The industrial synthesis of acetaldehyde ("Wacker process") proceeds via the intermediacy of a vinyl alcohol complex.[6]

Occurrence in interstellar medium[edit]

Vinyl alcohol was detected in the molecular cloud Sagittarius B.[7] Its stability in the (dilute) interstellar medium shows that its tautomerization is not unimolecular.

See also[edit]

References[edit]

  1. ^ R.D. Johnson III. "CCCBDB NIST Standard Reference Database". Retrieved 2014-08-30. 
  2. ^ Heazlewood, B. R.; Maccarone, A. T.; Andrews, D. U.; Osborn, D. L.; Harding, L. B.; Klippenstein, S. J.; Jordan, M. J. T.; Kable, S. H. "Near-threshold H/D exchange in CD3CHO photodissociation." Nat. Chem. 2011, 3, 443−448. doi:10.1038/nchem.1052
  3. ^ Andrews, D. U.; Heazlewood, B. R.; Maccarone, A. T.; Conroy, T.; Payne, R. J.; Jordan, M. J. T.; Kable, S. H. "Photo-tautomerization of acetaldehyde to vinyl alcohol: A potential route to tropospheric acids." Science 2012, 337, 1203−1206. doi:10.1126/science.1220712
  4. ^ Clayden, Jonathan; Greeves, Nick; Warren, Stuart. Organic Chemistry, 2nd edition, pp. 456-57. Oxford University Press, 2012. ISBN 978-0-19-927029-3.
  5. ^ F. A. Cotton, J. N. Francis, B. A. Frenz, M. Tsutsui "Structure of a dihapto(vinyl alcohol) complex of platinum(II)" Journal of the American Chemical Society, 1973, volume 95, p. 2483-6. doi:10.1021/ja00789a011
  6. ^ J. A. Keith, P. M. Henry (2009). "The Mechanism of the Wacker Reaction: A Tale of Two Hydroxypalladations". Angew. Chem. Int. Ed. 48: 9038–9049. doi:10.1002/anie.200902194. 
  7. ^ "Scientists Toast the Discovery of Vinyl Alcohol in Interstellar Space". National Radio Astronomy Observatory. 2001-10-01. Retrieved 2006-12-20.