Sodium methoxide
Encyclopedia
Sodium methoxide is a chemical compound, with formula CH3ONa. This colourless 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.
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 sodium hydroxide, and commercial samples are significantly contaminated with the hydroxide. The solid and especially solutions absorb carbon dioxide
from the air, thus diminishing the effectiveness of the base.
In the solid form, sodium methoxide is polymer
ic, with a sheet-like arrays of Na+ centers, each bonded to four oxygen centers.
The structure, and hence its basicity, of sodium methoxide in solution depends on the solvent. It is significantly stronger base in DMSO
where it is more fully ionized and free of hydrogen bonding.
s. As a base, it is employed in dehydrohalogenation
s and aldol condensation
s. It is also a nucleophile
for the production of methyl ether
s.
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 ester
s (FAMEs). This transformation is catalyzed by sodium methoxide.
gives methanol
, which is toxic and volatile.
Deprotonation
Deprotonation is the removal of a proton from a molecule, forming the conjugate base.The relative ability of a molecule to give up a proton is measured by its pKa value. A low pKa value indicates that the compound is acidic and will easily give up its proton to a base...
of methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, is a widely used reagent
Reagent
A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction, or added to see if a reaction occurs." Although the terms reactant and reagent are often used interchangeably, a reactant is less specifically a "substance that is consumed in the course of...
in industry and the laboratory. It is also a dangerously caustic base.
Preparation and structure
Sodium methoxide is prepared by carefully treating methanol with sodium :- 2 Na + 2 → 2 +
The reaction is so exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
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 sodium hydroxide, and commercial samples are significantly contaminated with the hydroxide. The solid and especially solutions absorb carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
from the air, thus diminishing the effectiveness of the base.
In the solid form, sodium methoxide is polymer
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
ic, with a sheet-like arrays of Na+ centers, each bonded to four oxygen centers.
The structure, and hence its basicity, of sodium methoxide in solution depends on the solvent. It is significantly stronger base in DMSO
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
where it is more fully ionized and free of hydrogen bonding.
Organic synthesis
Sodium methoxide is a routine base in organic chemistry, applicable to the synthesis of numerous compounds, ranging from pharmaceuticals to agrichemicalAgrichemical
Agrochemical , a contraction of agricultural chemical, is a generic term for the various chemical products used in agriculture. In most cases, agrichemical refers to the broad range of pesticides, including insecticides, herbicides, and fungicides...
s. As a base, it is employed in dehydrohalogenation
Dehydrohalogenation
Dehydrohalogenation is an organic reaction from which an alkene is obtained from an alkyl halide . It is also called a β-Elimination reaction and is a type of elimination reaction....
s and aldol condensation
Aldol condensation
An aldol condensation is an organic reaction in which an enol or an enolate ion reacts with a carbonyl compound to form a β-hydroxyaldehyde or β-hydroxyketone, followed by a dehydration to give a conjugated enone....
s. It is also a nucleophile
Nucleophile
A nucleophile is a species that donates an electron-pair to an electrophile to form a chemical bond in a reaction. All molecules or ions with a free pair of electrons can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases.Nucleophilic describes the...
for the production of methyl ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
s.
Industrial applications
Sodium methoxide is used as an initiatorInitiator
An initiator can refer to:* A person that takes an initiative in making something happen.* Modulated neutron initiator, a neutron source used in some nuclear weapons...
of anionic addition polymerization
Anionic addition polymerization
Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups. This polymerization is carried out through a carbanion active species. Like all addition polymerizations, it...
with ethylene oxide
Ethylene oxide
Ethylene oxide, also called oxirane, is the organic compound with the formula . It is a cyclic ether. This means that it is composed of two alkyl groups attached to an oxygen atom in a cyclic shape . This colorless flammable gas with a faintly sweet odor is the simplest epoxide, a three-membered...
, forming a polyether with high molecular weight. Biodiesel is prepared from vegetable oils and animal fats, that is, fatty acid triglycerides, by transesterification
Transesterification
In organic chemistry, transesterification is the process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst...
with methanol to give fatty acid methyl ester
Fatty acid methyl ester
A fatty acid methyl ester can be created by an alkali catalyzed reaction between fats or fatty acids and methanol. The molecules in biodiesel are primarily FAMEs, usually obtained from vegetable oils by transesterification....
s (FAMEs). This transformation is catalyzed by sodium methoxide.
Safety
Sodium methoxide is highly caustic, and the hydrolysisHydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
gives methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, which is toxic and volatile.