Appearance pale yellow solid | ||
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Related compounds | ||
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.
Contents
Preparation
Benzylideneacetone can be efficiently prepared by the NaOH-induced condensation of the readily available reagents acetone and benzaldehyde:
CH3C(O)CH3 + C6H5CHO → C6H5CH=CHC(O)CH3 + H2OHowever, 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.
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.
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
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.