Benzylideneacetone

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Benzylideneacetone
Benzylideneacetone-2D-skeletal.png
Benzylideneacetone-3D-balls.png
Names
IUPAC name
(E)-4-Phenylbut-3-ène-2-one
Other names
Benzalacetone
Benzylideneacetone
Methyl styryl ketone
Benzylidene acetone
Identifiers
122-57-6 YesY
1896-62-4 (trans) YesY
ChEBI CHEBI:217301 YesY
ChEMBL ChEMBL73639 YesY
ChemSpider 21106584 YesY
Jmol 3D model Interactive image
RTECS number EN0330000
Properties
C10H10O
Molar mass 146.19 g/mol
Appearance pale yellow solid
Density 1.008 g/cm3
Melting point 39 to 42 °C (102 to 108 °F; 312 to 315 K)
Boiling point 260 to 262 °C (500 to 504 °F; 533 to 535 K)
1.3 g/L
Solubility in other solvents nonpolar solvents
Hazards
Main hazards irritant
R-phrases 36/37/38-43
S-phrases 22-26-36/37
Flash point 116 °C (241 °F; 389 K)
Related compounds
Related compounds
Dibenzylideneacetone
cinnamaldehyde
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Benzylideneacetone is the organic compound described by the formula C6H5CH=CHC(O)CH3. Although both cis- and trans-isomers are possible for the α,β-unsaturated ketone, only the trans isomer is observed. Its original preparation demonstrated the scope of condensation reactions to construct new, complex organic compounds.[1]

Preparation[edit]

Benzylideneacetone can be efficiently prepared by the NaOH-induced condensation of the readily available reagents acetone and benzaldehyde:[2]

CH3C(O)CH3 + C6H5CHO → C6H5CH=CHC(O)CH3 + H2O
Reaction schematics

However, the benzylideneacetone formed via this reaction can undergo another Claisen-Schmidt condensation with another molecule of benzaldehyde to form dibenzylideneacetone. Because relatively weak bases such as NaOH make very little of the enolate ion at equilibrium, there is still a lot of unreacted base left in the reaction mixture, which can go on and remove protons from the alpha carbon of benzylideneacetone, allowing it to undergo another Claisen-Schmidt condensation and make dibenzylideneacetone.[3]

If, on the other hand, lithium diisopropylamide (LDA) is used as the base, all of the acetone will deprotonated, making enolate ion quantitatively. Therefore, the most efficient way to make benzylideneacetone is to use equimolar amounts of LDA, acetone, and benzaldehyde. Because LDA is an extremely strong base, the reaction must be done in an inert solvent, such as THF or ether. [4]

BenzalacetonePreparationUsingLDA.png

Reactions[edit]

As with most methyl ketones, benzylidineacetone is moderately acidic at the alpha position, and it can be readily deprotonated to form the corresponding enolate[5]

LiHMDS EnolateFormation.png

The compound undergoes the reactions expected for its collection of functional groups: e.g., the double bond adds bromine, the heterodiene adds electron-rich alkenes in Diels-Alder reactions to give dihydropyrans, the methyl group undergoes further condensation with benzaldehyde to give dibenzylideneacetone, and the carbonyl forms hydrazones. It reacts with Fe2(CO)9 to give (benzylideneacetone)Fe(CO)3, a reagent for transferring the Fe(CO)3 unit to other organic substrates.[6]

References[edit]

  1. ^ Claisen, L. "Über die Einwirkung von Aceton auf Furfural und auf Benzaldehyd bei Gegenwart von Alkalilauge" Berichte der deutschen chemischen Gesellschaft 1881, volume 14, p 2468-2471.
  2. ^ Drake, N. L.; Allen, Jr. P. "Benzalacetone". Org. Synth. ; Coll. Vol. 1, p. 77 
  3. ^ Moya-Barrios, R. CHEM 2402 Lab Manual, Winter 2016. Dalhousie University, Department of Chemistry
  4. ^ Bruice, Paula Yurkanis. Organic Chemistry, 7th Edition. Pearson Education, 2014. ISBN 0-321-80322-1
  5. ^ Danheiser, R. L.; Miller, R. F.; Brisbois, R. G. (1990). "Detrifluoroacetylative Diazo Group Transfer: (E)-1-Diazo-4-phenyl-3-buten-2-one". Org. Synth. 73: 134. ; Coll. Vol. 9, p. 197 
  6. ^ Knölker, H.-J. "(η4-Benzylideneacetone)tricarbonyliron" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. Onlinedoi:10.1002/047084289X.rb058.