Sodium ethoxide

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Sodium ethoxide
Sodium ethoxide.png
Identifiers
CAS number 141-52-6 YesY
PubChem 2723922
ChemSpider 8516 YesY
Jmol-3D images Image 1
Properties
Molecular formula C2H5ONa
Molar mass 68.05 g/mol
Appearance white or yellowish powder
hygroscopic
Density 0.868 g/cm^3
Melting point 260 °C (500 °F; 533 K)
Solubility in water Reacts
Solubility miscible with ethanol and methanol
Acidity (pKa) 15.5[1]
Hazards
MSDS Oxford MSDS
EU classification Extremely Flammable F+ Harmful Xn Corrosive C
NFPA 704
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 fuel Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calcium Special hazard W: Reacts with water in an unusual or dangerous manner. E.g., cesium, sodiumNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
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Infobox references

Sodium ethoxide is the organic compound with the formula C2H5ONa. It is a colourless solid that dissolves in polar solvents. It is commonly used as a strong base.[2]

Preparation[edit]

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 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. The salt product may be purified by precipitation in a solution of anhydrous acetone[4]

Reactions[edit]

The solid gradually turns dark on storage in dry air because of oxidation.[5] In moist air, it hydrolyzes rapidly to sodium hydroxide. The conversion is not obvious and typical samples of NaOEt are contaminated with NaOH.

Sodium ethoxide is commonly used in the Claisen condensation and malonic ester synthesis. 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.

Safety[edit]

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

References[edit]

  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", Org. Synth. 6: 40 ; Coll. Vol. 1: 328 
  4. ^ US patent 1978647, Olson, E. & Twining, R. H., "Method for Making Alkali Metal Alcoholates", issued 1934-10-30 
  5. ^ M. Eagleson "Concise encyclopedia chemistry" p.997.

See also[edit]