Benzylideneacetone

Benzylideneacetone

Names
IUPAC name (E)-4-Phenylbut-3-ène-2-one
Other names Benzalacetone Benzylideneacetone Methyl styryl ketone Benzylidene acetone
Identifiers
CAS Number	122-57-6 Y 1896-62-4 (trans) Y
3D model (Jmol)	Interactive image
ChEBI	CHEBI:217301 Y
ChEMBL	ChEMBL73639 Y
ChemSpider	21106584 Y
ECHA InfoCard	100.004.142
RTECS number	EN0330000
InChI InChI=1S/C10H10O/c1-9(11)7-8-10-5-3-2-4-6-10/h2-8H,1H3/b8-7+ Y Key: BWHOZHOGCMHOBV-BQYQJAHWSA-N Y InChI=1/C10H10O/c1-9(11)7-8-10-5-3-2-4-6-10/h2-8H,1H3/b8-7+ Key: BWHOZHOGCMHOBV-BQYQJAHWBQ
SMILES CC(=O)/C=C/c1ccccc1
Properties
Chemical formula	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)
Solubility in water	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

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

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]

Reactions

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]

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