Sodium ethoxide

Sodium ethoxide, commonly referred to as sodium ethylate, is the organic compound with the formula C2H5ONa. It is a white solid, although impure samples appear yellow or brown. It dissolves in polar solvents such as ethanol. It is commonly used as a strong base.[2]

Sodium ethoxide
Names
IUPAC name
Sodium ethoxide
Other names
Sodium ethanolate, sodium ethylate (obsolete)
Identifiers
3D model (JSmol)
3593646
ChEBI
ChemSpider
ECHA InfoCard 100.004.989
EC Number
  • 205-487-5
UNII
Properties
C2H5ONa
Molar mass 68.05 g/mol
Appearance white
hygroscopic
Density 0.868 g/cm^3 (of a 21 wt% solution in ethanol)
Melting point 260 °C (500 °F; 533 K)
Reacts
Solubility ethanol and methanol
Acidity (pKa) 15.5[1]
Hazards
Safety data sheet Oxford MSDS
GHS pictograms
GHS Signal word Danger
H228, H251, H302, H314, H318
P210, P235+410, P240, P241, P260, P264, P270, P280, P301+312, P301+330+331, P303+361+353, P304+340, P305+351+338, P310, P321, P330, P363, P370+378, P405, P407, P413, P420, P501
NFPA 704 (fire diamond)
Flammability code 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelHealth code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g. chloroformReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acid
2
2
1
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 ?)
Infobox references

Preparation

Few procedures have been reported to the anhydrous solid. Instead the material is typically prepared in a solution with ethanol. It is commercially available and as a solution in ethanol. It is easily prepared in the laboratory by treating sodium metal with absolute ethanol:[3]

2 C2H5OH + 2 Na → 2 C2H5ONa + H2

An alternative, cheaper route involves the reaction of sodium hydroxide with anhydrous ethanol. This reaction suffers from incomplete conversion to the alkoxide, but for less stringent applications, full conversion is unimportant.

Structure

The crystal structure of sodium ethoxide has been determined by X-ray crystallography. It consists of layers of alternating Na+ and O− centres with disordered ethyl groups covering the top and bottom of each layer. The ethyl layers pack back-to-back resulting in a lamellar structure. The reaction of sodium and ethanol sometimes forms other products such as the disolvate NaOEt·2EtOH. Its crystal structure has been determined, although the structure of other phases in the Na/EtOH system remain unknown.[4]

ball-and-stick model of layer stacking
in the crystal structure of NaOEt
coordination geometry at Na
coordination geometry at O

Reactions

Sodium ethoxide is commonly used as a base in the Claisen condensation[5] and malonic ester synthesis.[6] Sodium ethoxide may either deprotonate the α-position of an ester molecule, forming an enolate, or the ester molecule may undergo a nucleophilic substitution called transesterification. If the starting material is an ethyl ester, trans-esterification is irrelevant since the product is identical to the starting material. In practice, the alcohol/alkoxide solvating mixture must match the alkoxy components of the reacting esters to minimize the number of different products.

Many alkoxides are prepared by salt metathesis from sodium ethoxide.

Stability

Solid samples of sodium ethoxide gradually turn dark on storage in dry air because of oxidation.[7] In moist air, it hydrolyzes rapidly to sodium hydroxide. The conversion is not obvious and typical samples of NaOEt are contaminated with NaOH. Beyond clearly visible degradation, solid sodium ethoxide also has significant air instability without clear changes in physical appearance, e.g. degrading into a variety of other sodium salts when exposed to air. This instability can be prevented by storing sodium ethoxide under an inert (N2) atmosphere. It was reported that newly obtained commercial batches of sodium ethoxide show variable levels of degradation, and were a major source of irreproducibility when used in Suzuki reactions.[8]

Safety

Sodium ethoxide is a strong base, and is therefore corrosive.

See also

References
  1. disassociation constant of ethanol, referenced in the CRC Handbook of Chemistry and Physics 87th edition.
  2. K. Sinclair Whitaker, D. Todd Whitaker, "Sodium Ethoxide" Encyclopedia of Reagents for Organic Synthesis 2001.doi:10.1002/047084289X.rs070
  3. C. S. Marvel and E. E. Dreger (1926). "Ethyl Acetopyruvate". Organic Syntheses. 6: 40.; Collective Volume, 1, p. 328
  4. M. Beske, L. Tapmeyer, M. U. Schmidt (2020). "Crystal structure of sodium ethoxide (C2H5ONa), unravelled after 180 years". Chem. Commun. 56 (24): 3520–3523. doi:10.1039/C9CC08907A. PMID 32101200.CS1 maint: uses authors parameter (link)
  5. Clayden, Jonathan; Greeves, Nick; Warren, Stuart (2012). Organic chemistry (2nd ed.). New York: Oxford University Press. p. 645. ISBN 978-0-19-927029-3.
  6. Wang, Zerong (15 September 2010). Comprehensive organic name reactions and reagents. John Wiley. pp. 1811–1815. ISBN 9780471704508.
  7. M. Eagleson "Concise encyclopedia chemistry" p.997.
  8. Wethman, Robert; Derosa, Joseph; Tran, Van; Kang, Taeho; Apolinar, Omar; Abraham, Anuji; Kleinmans, Roman; Wisniewski, Steven; Coombs, John; Engle, Keary (2020-08-19), An Under-Appreciated Source of Reproducibility Issues in Cross-Coupling: Solid-State Decomposition of Primary Sodium Alkoxides in Air, American Chemical Society (ACS), doi:10.26434/chemrxiv.12818234.v1
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