Sodium ethoxide

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Sodium ethoxide
Ball-and-stick model of the sodium cation
Sodium-ethoxide-xtal-layer-view-1-Mercury-3D-bs.png
Names
Other names
Sodium ethanolate, sodium ethylate (obsolete)
Identifiers
  • 141-52-6 checkY
3D model (JSmol)
3593646
ChEBI
ChemSpider
ECHA InfoCard 100.004.989 Edit this at Wikidata
EC Number
  • 205-487-5
UNII
  • InChI=1S/C2H5O.Na/c1-2-3;/h2H2,1H3;/q-1;+1 checkY
    Key: QDRKDTQENPPHOJ-UHFFFAOYSA-N checkY
  • InChI=1/C2H5O.Na/c1-2-3;/h2H2,1H3;/q-1;+1
    Key: QDRKDTQENPPHOJ-UHFFFAOYAQ
  • [Na+].[O-]CC
Properties
C2H5ONa
Molar mass 68.05 g/mol
Appearance white
hygroscopic
Density 0.868 g/cm3 (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 labelling:
GHS02: FlammableGHS05: CorrosiveGHS07: Exclamation mark
Signal word
 Danger
H228, H251, H302, H314
P210, P235+P410, P240, P241, P260, P264, P270, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P370+P378, P405, P407, P413, P420, P501
NFPA 704 (fire diamond)
2
2
1
W
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N  (what is checkY☒N ?)
Infobox references

Sodium ethoxide, also referred to as sodium ethylate, is the organic compound with the formula C2H5ONa, or NaOEt. 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]

Preparation[]

Few procedures have been reported to prepare 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]

2C2H5OH + 2Na → 2C2H5ONa + 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]

Sodium-ethoxide-xtal-layer-stacking-Mercury-3D-bs.png Sodium-ethoxide-xtal-Na-coordination-Mercury-3D-bs.png Sodium-ethoxide-xtal-O-coordination-Mercury-3D-bs.png
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[]

Sodium ethoxide is prone to reaction with both water and carbon dioxide in the air.[7] This leads to degradation of stored samples over time, even in solid form. The physical appearance of degraded samples may not be obvious, but samples of sodium ethoxide gradually turn dark on storage. It has been reported that even newly-obtained commercial batches of sodium ethoxide show variable levels of degradation, and responsible as a major source of irreproducibility when used in Suzuki reactions.[7]

  • New bottle of sodium ethoxide from Sigma-Aldrich

  • Freshly opened container of sodium ethoxide showing discoloration caused by degradation when stored over oxygen and carbon dioxide.

In moist air, NaOEt hydrolyses rapidly to sodium hydroxide (NaOH). The conversion is not obvious and typical samples of NaOEt are contaminated with NaOH.

In moisture-free air, solid sodium ethoxide can form sodium ethyl carbonate from fixation of carbon dioxide from the air. Further reactions lead to degradation into a variety of other sodium salts and diethyl ether.[7]

This instability can be prevented by storing sodium ethoxide under an inert (N2) atmosphere.

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 (2001). "Sodium Ethoxide". In Charette, André B. (ed.). Encyclopedia of Reagents for Organic Synthesis. John Wiley & Sons. doi:10.1002/047084289X.rs070. ISBN 9780470842898.
  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. S2CID 211523921.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. ^ a b c 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, S2CID 242420220
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