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Anisole

Organic compound (CH₃OC₆H₅) also named methoxybenzene From Wikipedia, the free encyclopedia

Anisole

Anisole, or methoxybenzene, is an organic compound with the formula CH3OC6H5. It is a colorless liquid with a smell reminiscent of anise seed, and in fact many of its derivatives are found in natural and artificial fragrances. The compound is mainly made synthetically and is a precursor to other synthetic compounds. Structurally, it is an ether (−O−) with a methyl (−CH3) and phenyl (−C6H5) group attached. Anisole is a standard reagent of both practical and pedagogical value.[2]

Quick Facts Names, Identifiers ...
Anisole
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Names
Preferred IUPAC name
Anisole[1]
Systematic IUPAC name
Methoxybenzene[1]
Other names
Methyl phenyl ether[1]
Phenoxymethane
Identifiers
3D model (JSmol)
506892
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.002.615
EC Number
  • 202-876-1
2964
KEGG
RTECS number
  • BZ8050000
UNII
UN number 2222
  • InChI=1S/C7H8O/c1-8-7-5-3-2-4-6-7/h2-6H,1H3 Y
    Key: RDOXTESZEPMUJZ-UHFFFAOYSA-N Y
  • InChI=1/C7H8O/c1-8-7-5-3-2-4-6-7/h2-6H,1H3
    Key: RDOXTESZEPMUJZ-UHFFFAOYAP
  • COc1ccccc1
Properties
C7H8O
Molar mass 108.140 g·mol−1
Appearance Colorless liquid
Density 0.995 g/cm3
Melting point −37 °C (−35 °F; 236 K)
Boiling point 154 °C (309 °F; 427 K)
Solubility Insoluble
−72.79×10−6 cm3/mol
Hazards
GHS labelling:
GHS02: FlammableGHS07: Exclamation mark
Warning
H226, H315, H319
P210, P233, P240, P241, P242, P243, P264, P280, P302+P352, P303+P361+P353, P305+P351+P338, P321, P332+P313, P337+P313, P362, P370+P378, P403+P235, P501
NFPA 704 (fire diamond)
ThumbHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 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 fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
2
0
Lethal dose or concentration (LD, LC):
3700 mg/kg (rat, oral)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Reactivity

Summarize
Perspective

Anisole undergoes electrophilic aromatic substitution reaction at a faster speed than benzene, which in turn reacts more quickly than nitrobenzene. The methoxy group is an ortho/para directing group, which means that electrophilic substitution preferentially occurs at these three sites. The enhanced nucleophilicity of anisole vs. benzene reflects the influence of the methoxy group, which renders the ring more electron-rich. The methoxy group strongly affects the pi cloud of the ring as a mesomeric electron donor, more so than as an inductive electron withdrawing group despite the electronegativity of the oxygen. Stated more quantitatively, the Hammett constant for para-substitution of anisole is –0.27.

Illustrative of its nucleophilicity, anisole reacts with acetic anhydride to give 4-methoxyacetophenone:

CH3OC6H5 + (CH3CO)2O → CH3OC6H4C(O)CH3 + CH3CO2H

Unlike most acetophenones, but reflecting the influence of the methoxy group, methoxyacetophenone undergoes a second acetylation. Many related reactions have been demonstrated. For example, phosphorus pentasulfide (P4S10) converts anisole to Lawesson's reagent, [(CH3OC6H4)PS2]2.[3]

Also indicating an electron-rich ring, anisole readily forms π-complexes with metal carbonyls, e.g. Cr(η6-anisole)(CO)3.[4]

The ether linkage is highly stable, but the methyl group can be removed with strong acids, such as hydroiodic acid or boron trichloride:[5]: 565–566 

CH3OC6H5 + HI → HOC6H5 + CH3I

Birch reduction of anisole gives 1-methoxycyclohexa-1,4-diene.[6]

Synthesis

Anisole was first synthesized in 1841 by Auguste Cahours by barium anisate decarboxylation while heating p-anisic acid he made earlier from the anise essence with barium oxide:[7][8]

2 CH3OC6H4COOH + BaO → (CH3OC6H4COO)2Ba + H2O

(CH3OC6H4COO)2Ba → 2 CH3OC6H5 + BaCO3

It can be prepared by the Williamson ether synthesis from sodium phenoxide and dimethyl sulfate or methyl chloride:[9][5]

2 C6H5O− Na+ + (CH3O)2SO2 → 2 C6H5OCH3 + Na2SO4

Applications

Anisole is a precursor to perfumes, insect pheromones, and pharmaceuticals.[5] For example, synthetic anethole is prepared from anisole.

Safety

Anisole is relatively nontoxic with an LD50 of 3700 mg/kg in rats.[10] Its main hazard is its flammability.[10]

Popular culture

In the board game Scrabble, the word "anisole" is the 39th-most-likely word (out of over 25,000 possibilities) for a "bingo"/"bonus", i.e. the deployment of all seven letters in one's own hand simultaneously.[11]

See also

References

External links

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