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]

Anisole
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 checkY
    Key: RDOXTESZEPMUJZ-UHFFFAOYSA-N checkY
  • 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)
NFPA 704 four-colored diamond
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).
checkY verify (what is checkY☒N ?)
Infobox references

It can be prepared by the Williamson ether synthesis; sodium phenoxide is reacted with a methyl halide to yield anisole.

Reactivity

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 + CH3COOH

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 hydroiodic acid:

CH3OC6H5 + HI → HOC6H5 + CH3I

Birch reduction of anisole gives 1-methoxycyclohexa-1,4-diene.[5]

Preparation

Anisole is prepared by methylation of sodium phenoxide with dimethyl sulfate or methyl chloride:[6][7]

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

Applications

Anisole is a precursor to perfumes, insect pheromones, and pharmaceuticals.[7] For example, synthetic anethole is prepared from anisole.

Safety

Anisole is relatively nontoxic with an LD50 of 3700 mg/kg in rats.[8] Its main hazard is its flammability.[8]

See also

References
  1. Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: The Royal Society of Chemistry. 2014. pp. 702–703. doi:10.1039/9781849733069-00648. ISBN 978-0-85404-182-4. Anisole, C6H5−O−CH3, is the only name in the class of ethers which is retained both as a preferred IUPAC name and for use in general nomenclature. For preferred IUPAC names, no substitution is allowed; for general nomenclature substitution is allowed on the ring and on the side chain under certain conditions (see P-34.1.1.4).
  2. Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 978-0-471-72091-1
  3. I. Thomsen; K. Clausen; S. Scheibye; S.-O. Lawesson (1984). "Thiation with 2,4-Bis(4-Methoxyphenyl)-1,3,2,4-Dithiadiphosphetane 2,4-Disulfide: N-Methylthiopyrrolidone". Organic Syntheses. 62: 158. doi:10.15227/orgsyn.062.0158.
  4. E. Peter Kündig (2004). "Synthesis of Transition Metal η6-Arene Complexes". Topics Organomet Chem. Topics in Organometallic Chemistry. 7: 3–20. doi:10.1007/b94489. ISBN 978-3-540-01604-5.
  5. A. J. Birch and K. B. Chamberlain (1977). "Tricarbonyl[(2,3,4,5-η)-2,4-Cyclohexadien-1-one]Iron and Tricarbonyl[(1,2,3,4,5-η)-2-Methoxy-2,4-Cyclohexadien-1-yl]Iron(1+) Hexafluorophosphate(1−) from Anisole". Organic Syntheses. 57: 107. doi:10.15227/orgsyn.057.0107.
  6. G. S. Hiers and F. D. Hager (1929). "Anisole". Organic Syntheses. 9: 12. doi:10.15227/orgsyn.009.0012.
  7. Helmut Fiege; Heinz-Werner Voges; Toshikazu Hamamoto; Sumio Umemura; Tadao Iwata; Hisaya Miki; Yasuhiro Fujita; Hans-Josef Buysch; Dorothea Garbe. "Phenol Derivatives". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_313.
  8. MSDS Archived July 1, 2010, at the Wayback Machine
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