Sodium methoxide

Sodium methoxide is a chemical compound with the formula CH3ONa. This white solid, which is formed by the deprotonation of methanol, is a widely used reagent in industry and the laboratory. It is also a dangerously caustic base.

Sodium methoxide
The sodium cation
Ball-and-stick model of the methoxide anion
Names
IUPAC name
Sodium methoxide
Other names
Sodium methylate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.004.273
UNII
Properties
CH3NaO
Molar mass 54.02 g/mol
Appearance White solid
Melting point 127 °C (261 °F; 400 K)
Boiling point 350 °C (662 °F; 623 K)[1] (decomposition)
Reacts with water
Solubility Soluble in ethanol, methanol
Insoluble in hydrocarbons
Structure
Hexagonal
Hazards
Safety data sheet Sigma[2]
GHS pictograms
GHS Signal word Danger
H251, H302, H314[2]
P235+410, P280, P305+351+338, P310[2]
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

Preparation and structure

Sodium methoxide is prepared by treating methanol with sodium:

2 Na + 2 CH
3OH → 2 CH
3ONa + H
2

The reaction is so exothermic that ignition is possible. The resulting solution, which is colorless, is often used as a source of sodium methoxide, but the pure material can be isolated by evaporation followed by heating to remove residual methanol. The solid hydrolyzes in water to give methanol and sodium hydroxide. Indeed, samples of sodium methoxide are often contaminated with sodium hydroxide. The compound absorbs carbon dioxide (and water vapor) from the air, thus diminishing the alkalinity of the base.

2 CH
3ONa + CO
2 + H
2O → 2 CH
3OH + Na
2CO
3

In the solid form, sodium methoxide is polymeric, with sheet-like arrays of Na+ centers, each bonded to four oxygen centers.[3]

The structure, and hence the basicity, of sodium methoxide in solution depends on the solvent. It is a significantly stronger base in DMSO where it is more fully ionized and free of hydrogen bonding.[4]

Applications

Organic synthesis

Sodium methoxide is a routinely used base in organic chemistry, applicable to the synthesis of numerous compounds ranging from pharmaceuticals to agrichemicals.[4] As a base, it is employed in dehydrohalogenations and various condensations.[5] It is also a nucleophile for the production of methyl ethers.[6]

Industrial applications

Sodium methoxide is used as an initiator of anionic addition polymerization with ethylene oxide, forming a polyether with high molecular weight. Biodiesel is prepared from vegetable oils and animal fats, that is, fatty acid triglycerides, by transesterification with methanol to give fatty acid methyl esters (FAMEs). This transformation is catalyzed by sodium methoxide.

Stability

Solid sodium methoxide has significant air instability, and can degrade into a variety of other sodium salts when exposed to air. This instability can be prevented by storing sodium methoxide under an inert (N2) atmosphere. It was reported that newly obtained commercial batches of sodium methoxide show variable levels of degradation, and were a major source of irreproducibility when used in Suzuki reactions.[7]

Safety

Sodium methoxide is highly caustic and reacts with water to give methanol, which is toxic and volatile.

NFPA 704

The ratings for this substance vary widely.

Rating
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 3: Capable of detonation or explosive decomposition but requires a strong initiating source, must be heated under confinement before initiation, reacts explosively with water, or will detonate if severely shocked. E.g. hydrogen peroxideSpecial hazards (white): no code
4
3
3
Flammability code 4: Will rapidly or completely vaporize at normal atmospheric pressure and temperature, or is readily dispersed in air and will burn readily. Flash point below 23 °C (73 °F). E.g. propaneHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
4
3
2
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g. gasolineHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
3
3
2
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 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
2
3
2
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 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazards (white): no code
2
2
2
Source State of Connecticut[8] DuPont[9] Pharmco AAPR[10] ScienceLab[11](Both ratings on same sheet)

See also

References
  1. Chandran, K.; Kamruddin, M.; Ajikumar, P.K.; Gopalan, A.; Ganesan, V. (2006). "Kinetics of thermal decomposition of sodium methoxide and ethoxide". Journal of Nuclear Materials. 358 (2–3): 111–128. Bibcode:2006JNuM..358..111C. doi:10.1016/j.jnucmat.2006.07.003. ISSN 0022-3115.
  2. Sigma-Aldrich Co., Sodium methoxide. Retrieved on 2018-05-24.
  3. E. Weiss (1964). "Die Kristallstruktur des Natriummethylats" [The Crystal Structure of Sodium Methylate]. Zeitschrift für Anorganische und Allgemeine Chemie (in German). 332 (3–4): 197–203. doi:10.1002/zaac.19643320311.
  4. Y. El-Kattan; J. McAtee; B. Bessieres (2006). "Sodium Methoxide". Encyclopedia of Reagents for Organic Synthesis. New York: John Wiley & Sons. doi:10.1002/047084289X.rs089m.pub2. ISBN 0471936235.
  5. O. E. Curtis, Jr., J. M. Sandri, R. E. Crocker, H. Hart (1958). "Dicyclopropyl ketone". Organic Syntheses. 38: 19. doi:10.15227/orgsyn.038.0019.CS1 maint: multiple names: authors list (link); Collective Volume, 4, p. 278
  6. F. Reverdin (1927). "3,5-Dinitroanisole". Organic Syntheses. 7: 28. doi:10.15227/orgsyn.007.0028.; Collective Volume, 1, p. 219
  7. 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
  8. "The Code Officials Perspective" (PDF).
  9. "DuPont Material Safety Data Sheet" (PDF).
  10. "Pharmco AAPR Material Safety Data Sheet" (PDF).
  11. "ScienceLab Material Safety Data Sheet".
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