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Acetophenone

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Acetophenone is the organic compound with the formula C6H5C(O)CH3. It is the simplest aromatic ketone. This colorless, viscous liquid is a precursor to useful resins and fragrances.[1]

Production

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Acetophenone is formed as a byproduct of the cumene process, the industrial route for the synthesis of phenol and acetone. In the Hock rearrangement of isopropylbenzene hydroperoxide, migration of a methyl group rather than the phenyl group gives acetophenone and methanol as a result of an alternate rearrangement of the intermediate:

C6H5C(CH3)2O2H → C6H5C(O)CH3 + CH3OH

The cumene process is conducted on such a large scale that even the small amount of acetophenone by-product can be recovered in commercially useful quantities.[1]

Acetophenone is also generated from ethylbenzene hydroperoxide. Ethylbenzene hydroperoxide is primarily converted to 1-phenylethanol (α-methylbenzyl alcohol) in the process with a small amount of by-product acetophenone. Acetophenone is recovered or hydrogenated to 1-phenylethanol which is then dehydrated to produce styrene.[1]

Uses

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Precursor to resins

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Commercially significant resins are produced from treatment of acetophenone with formaldehyde and a base. The resulting copolymers are conventionally described with the formula [(C6H5COCH)x(CH2)x]n, resulting from aldol condensation. These substances are components of coatings and inks. Modified acetophenone-formaldehyde resins are produced by the hydrogenation of the aforementioned ketone-containing resins. The resulting polyol can be further crosslinked with diisocyanates.[1] The modified resins are found in coatings, inks and adhesives.

Niche uses

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Acetophenone is an ingredient in fragrances that resemble almond, cherry, honeysuckle, jasmine, and strawberry. It is used in chewing gum.[2] It is also listed as an approved excipient by the U.S. FDA.[3] More common as a fragrance is the closely related 4-methylacetophenone.[4]

Laboratory reagent

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In instructional laboratories,[5] acetophenone is converted to styrene in a two-step process that illustrates the reduction of carbonyls using sodium borohydride and the dehydration of alcohols:

4 C6H5C(O)CH3 + NaBH4 + 4 H2O → 4 C6H5CH(OH)CH3 + NaOH + B(OH)3
C6H5CH(OH)CH3 → C6H5CH=CH2 + H2O

A similar two-step process is used industrially, but reduction step is performed by hydrogenation over a copper chromite catalyst:[1]

C6H5C(O)CH3 + H2 → C6H5CH(OH)CH3

Being prochiral, acetophenone is also a popular test substrate for asymmetric hydrogenation experiments.

Drugs

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Acetophenone is used for the synthesis of many pharmaceuticals.[6][7]

Natural occurrence

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Acetophenone occurs naturally in many foods including apple, cheese,[8] apricot, banana,[9] beef, and cauliflower.

Pharmacology

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In the late 19th and early 20th centuries, acetophenone was used in medicine.[10] It was marketed as a hypnotic and anticonvulsant under brand name Hypnone. The typical dosage was 0.12 to 0.3 milliliters.[11] It was considered to have superior sedative effects to both paraldehyde and chloral hydrate.[12] In humans, acetophenone is metabolized to benzoic acid, carbonic acid, and acetone.[13] Hippuric acid occurs as an indirect metabolite and its quantity in urine may be used to confirm acetophenone exposure,[14] although other substances, like toluene, also induce hippuric acid in urine.[15]

Toxicity

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The Template:LD50 is 815 mg/kg (oral, rats).[1] Acetophenone is currently listed as a Group D carcinogen indicating that there is no evidence at present that it causes cancer in humans.

References

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  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Template:Ullmann
  2. ↑ Burdock, George A. (2005), Fenaroli's Handbook of Flavor Ingredients (5th ed.), CRC Press, p. 15, ISBN 0-8493-3034-3, archived from the original on 2014-09-25
  3. ↑ "Inactive Ingredient Search for Approved Drug Products". Archived from the original on 2013-05-04.
  4. ↑ Panten, Johannes; Surburg, Horst (2016). "Flavors and Fragrances, 3. Aromatic and Heterocyclic Compounds". Ullmann's Encyclopedia of Industrial Chemistry. pp. 1–45. doi:10.1002/14356007.t11_t02. ISBN 978-3-527-30673-2.
  5. ↑ Wilen, Samuel H.; Kremer, Chester B.; Waltcher, Irving (1961). "Polystyrene—A multistep synthesis: For the undergraduate organic chemistry laboratory". J. Chem. Educ. 38 (6): 304–305. Bibcode:1961JChEd..38..304W. doi:10.1021/ed038p304.
  6. ↑ Sittig, Marshall (1988). Pharmaceutical Manufacturing Encyclopedia. pp. 39, 177. ISBN 978-0-8155-1144-1.
  7. ↑ Gadamasetti, Kumar; Tamim Braish (2007). Process Chemistry in the Pharmaceutical Industry, Volume 2. Taylor & Francis. pp. 142–145. ISBN 978-0-8493-9051-7.
  8. ↑ Engels, W.J.M.; Dekker, R.; De Jong, C.; Neeter, R.; Visser, S. (1997). "A comparative study of volatile compounds in the water-soluble fraction of various types of ripened cheese". International Dairy Journal. 7 (4): 255–263. Bibcode:1997IntDJ...7..255E. doi:10.1016/S0958-6946(97)00003-4.
  9. ↑ Pino, Jorge A.; Febles, Yanet (2013). "Odour-active compounds in banana fruit cv. Giant Cavendish". Food Chemistry. 141 (2): 795–801. doi:10.1016/j.foodchem.2013.03.064. PMID 23790849.
  10. ↑ Template:Merck12th
  11. ↑ Bartholow, Roberts (1908). A Practical Treatise on Materia Medica and Therapeutics. Appleton & Co.
  12. ↑ Norman, Conolly (1887). "Cases illustrating the sedative effects of aceto-phenone". Journal of Mental Science. 32: 519. doi:10.1192/bjp.32.140.519.
  13. ↑ "Hypnone – The new hypnotic". Journal of the American Medical Association. 5 (23): 632. 1885. doi:10.1001/jama.1885.02391220016006.
  14. ↑ Template:PubChem
  15. ↑ "The Netherlands Center for Occupational Diseases (NCvB): toluene (Dutch)" (PDF). beroepsziekten.nl. Retrieved 19 April 2018.
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