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Information about Birch Reduction

The Birch reduction is the organic reduction of aromatic rings with sodium in liquid ammonia to form 1,4-cyclohexadienes. The reaction was reported by the Australian chemist Arthur John Birch (1915–1995) in 1944.[1] [2] This reaction provides an alternative to catalytic hydrogenation, which usually reduces the aromatic ring all the way to a cyclohexane (after the initial reduction to a cyclohexadiene, catalytic reduction of the remaining (nonaromatic) double bonds is easier than the first reduction).

The Birch reduction


Lithium and potassium can substitute for sodium, and alcohol such as ethanol and tert-butanol can be used instead of ammonia.

Several reviews have been published.[3] [4] [5] [6]

Reaction mechanism

A solution of sodium in liquid ammonia consists of the electride salt [Na(NH3)x]+ e-, associated with the intense blue color of these solutions. The solvated electrons add to the aromatic ring to give a radical anion followed by the dianion. These carbanions deprotonate the ammonia to form the cyclohexadiene.

Reaction mechanism of the Birch reduction

Birch alkylation

In the presence of an alkyl halide the carbanion can also undergo nucleophilic substitution with carbon-carbon bond formation. In substituted aromatic compounds an electron-withdrawing substituent, such as a carboxylic acid[7], stabilizes a carbanion and the least-substituted olefin is generated. With an electron-donating substituent the opposite effect is obtained.[8] The reaction produces more of the less thermodynamically stable non-conjugated 1,4-addition product than the more stable conjugated 1,3-diene because the largest orbital coefficient of the HOMO of the conjugated pentadienyl anion intermediate is on the central carbon atom. Once formed, the resulting 1,4-cyclohexadiene is unable equilibrate to the thermodynamically more stable product; therefore, the observed kinetic product is produced. Experimental alkali metal alternatives that are safer to handle, such as the M-SG reducing agent, also exist.

In Birch alkylation the anion formed in the Birch reduction is trapped by a suitable electrophile such as a haloalkane.[9] For example, in the reaction depicted below, 1,4-dibromobutane is added to t-butyl benzoate to form an alkylated 1,4-cyclohexadiene product.[10]:

Enlarge picture
Birch alkylation

References

1. ^ (a) Birch, A. J. J. Chem. Soc. 1944, 430. (b) Birch, A. J. J. Chem. Soc. 1945, 809. (c) Birch, A. J. J. Chem. Soc. 1946, 593. (d) Birch, A. J. J. Chem. Soc. 1947, 102 & 1642. (e) Birch, A. J. J. Chem. Soc. 1949, 2531.
2. ^ Vogel, E.; Klug, W.; Breuer, A. (1974). "1,6-Methano-10-annulene". Organic Syntheses 54: 11. 
3. ^ Birch, A. J.; Smith, H. Quart. Rev. 1958, 12, 17. (Review)
4. ^ Caine, D. Org. React. 1976, 23, 1-258. (Review)
5. ^ Rabideau, P. W.; Marcinow, Z. Org. React. 1992, 42, 1-334. (Review)
6. ^ Mander, L. N. Comp. Org. Syn. 1991, 8, 489-521. (Review)
7. ^ Kuehne, M. E.; Lambert, B. F. (1963). "1,4-Dihydrobenzoic acid". Organic Syntheses 43: 22. 
8. ^ Paquette, L. A.; Barrett, J. H. (1969). "2,7-Dimethyloxepin". Organic Syntheses 49: 62. 
9. ^ Taber, D. F.; Gunn, B. P.; Ching Chiu, I. (1983). "Alkylation of the anion from Birch reduction of o-Anisic acid: 2-Heptyl-2-cyclohexenone". Organic Syntheses 61: 59. 
10. ^ Formation of Benzo-Fused Carbocycles by Formal Radical Cyclization onto an Aromatic Ring Derrick L. J. Clive and Rajesh Sunasee Org. Lett.; 2007; 9(14) pp 2677 - 2680; (Letter) doi:10.1021/ol070849l

See also

Organic reductions or organic oxidations or organic redox reactions are redox reactions that take place with organic compounds. In organic chemistry oxidations and reductions are different from ordinary redox reactions because many reactions carry the name but do not
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Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone.
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Sodium (IPA: /ˈsəʊdiəm/) is a chemical element which has the symbol Na (Latin: natrium), atomic number 11, atomic mass 22.9898 g/mol, common oxidation number +1.
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Ammonia is a compound with the formula NH3. It is normally encountered as a gas with a characteristic pungent odor. Ammonia contributes significantly to the nutritional needs of the planet as a precursor to foodstuffs and fertilizers.
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Arthur John Birch AC (August 3, 1915 - December 8 1995) was an organic chemist from Australia. Birch developed the "Birch reduction" of aromatic rings which is widely used in synthetic organic chemistry. The Birch Reduction enables the modification of steroids.
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19th century - 20th century - 21st century
1880s  1890s  1900s  - 1910s -  1920s  1930s  1940s
1912 1913 1914 - 1915 - 1916 1917 1918

Year 1915 (MCMXV
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19th century - 20th century - 21st century
1960s  1970s  1980s  - 1990s -  2000s  2010s  2020s
1992 1993 1994 - 1995 - 1996 1997 1998

Year 1995 (MCMXCV
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19th century - 20th century - 21st century
1910s  1920s  1930s  - 1940s -  1950s  1960s  1970s
1941 1942 1943 - 1944 - 1945 1946 1947

Year 1944 (MCMXLIV
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catalysis is the acceleration (increase in rate) of a chemical reaction by means of a substance called a catalyst, which is itself not consumed by the overall reaction.
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Hydrogenation is a class of chemical reactions which result in an addition of hydrogen (H2) usually to unsaturated organic compounds. Typical substrates include alkenes, alkynes, ketones, nitriles, and imines.
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Lithium (IPA: /ˈlɪθiəm/) is a chemical element with the symbol Li and atomic number 3. It is a soft alkali metal with a silver-white color.
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Potassium (IPA: /pə(ʊ)ˈtasiəm/, /pə'tæsiəm/) is a chemical element. It has the symbol K (Arabic: al qalja
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alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is CnH2n+1OH.
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Ethanol, also known as ethyl alcohol, drinking alcohol or grain alcohol, is a flammable, colorless, slightly toxic chemical compound, and is best known as the alcohol found in alcoholic beverages.
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tert-Butanol, or 2-methyl-2-propanol, is a tertiary alcohol. It is one of the four isomers of butanol. tert-Butanol is a clear liquid with a camphor-like odor. It is well soluble in water and miscible with ethanol and diethyl ether.
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An electride is an ionic compound in which an electron is the anion.[1] The first electrides to be studied in depth were solutions of alkali metals in ammonia.[2] When sodium metal dissolves in ammonia, the result is a blue solution consisting of [Na(NH
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A radical ion is a free radical species that carries a charge. Radical ions are encountered in organic chemistry as reactive intermediates.

Radical anions

Many aromatic compounds can undergo one-electron reduction by alkali metals.
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haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide.
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A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons [1]. The carbanion exists in a trigonal pyramidal geometry.
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In organic and inorganic chemistry, nucleophilic substitution is a fundamental class of substitution reaction in which an "electron rich" nucleophile selectively bonds with or attacks the positive charge of a group or atom called the leaving group; rarely referred to as an
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A carbon-carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond – a bond composed of two electrons, one from each of the two atoms.
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For polar effect in genetics, see .
The Polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby reaction center.
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Carboxylic acids are organic acids characterized by the presence of a carboxyl group, which has the formula -C(=O)OH, usually written -COOH or -CO2H. [1] Carboxylic acids are Bronsted acids — they are proton donors.
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A carbanion is an anion in which carbon has an unshared pair of electrons and bears a negative charge usually with three substituents for a total of eight valence electrons [1]. The carbanion exists in a trigonal pyramidal geometry.
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alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond. The simplest alkenes, with only one double bond and no other functional groups, form a homologous series of hydrocarbons with the general formula
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For polar effect in genetics, see .
The Polar effect or electronic effect in chemistry is the effect exerted by a substituent on modifying electrostatic forces operating on a nearby reaction center.
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conjugated system is a system of atoms covalently bonded with alternating single and multiple (e.g. double) bonds (e.g., C=C-C=C-C) in a molecule of an organic compound. This system results in a general delocalization of the electrons across all of the adjacent parallel aligned
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In M-SG an alkali metal is absorbed into silica gel at elevated temperatures. The resulting black powder material is an effective reducing agent and safe to handle as opposed to the pure metal.
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In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.
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haloalkanes (also known as halogenoalkanes or alkyl halides) are a group of chemical compounds, consisting of alkanes, such as methane or ethane, with one or more halogens linked, such as chlorine or fluorine, making them a type of organic halide.
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