Pre-lab preparation

In your lab notebook, prepare the following (see lab notebook guide for details):

1. Write all procedures required for this experiment. Prepare it so that it can be used as a sole source of your experimental procedures.

2. Write detailed reaction mechanism. You must include arrows, electron flow and lone pairs.

3. Construct table of chemicals that include physicochemical data for all chemicals used (see chapter 6).

4. Provide theoretical yield calculations.

5. Perform analysis of IR spectra for acetone and benzaldehyde. Report data in table format.

6. Read chapter 5 instructions and watch video tutorials on how to work with micropipettes.

In the laboratory

The essential reactants for dibenzalacetone synthesis are provided in Table 1.

Table 1.

To a 4 mL conical vial add 2mL of 10% of sodium hydroxide solution and a magnetic spin vane. Next, add 1.5 mL mL of 95% ethanol and stir it on a magnetic stirrer. After that, add 212 uL of benzaldehyde and keep stirring. The benzaldehyde initially insoluble will go into solution and a clear (pale yellow) solution is obtained. Next, add 74 L of acetone and continue to stir. At some point, a yellow solid should form. Continue stirring the reaction mixture vigorously for another 20 min. At the end of that time, yellow, flaky crystals should be observed. After that time, cool the reaction mixture in an ice bath and isolate the product by vacuum filtration using Hirsch funnel. Wash it 2 times with ice-cold water (using Pasteur pipette). Weigh and record the amount of your crude product.

Synthesis and characterization of dibenzalacetone

Purpose

this experiment you will synthesize dibenzalacetone by using aldol condensation reaction. The product will then be recrystallize and characterized by m.p. and IR analysis.

Background information

The reaction of an aldehyde with a ketone is the aldol condensation reaction. The reaction between an aldehyde/ketone and an aromatic carbonyl compound lacking an alpha-hydrogen is called the Claisen-Schmidt condensation.

In this laboratory exercise, you will synthesize dibenzalacetone by condensation of two equivalents of benzaldehyde with one equivalent of acetone. The aldehyde carbonyl is more reactive than that of the ketone and therefore reacts rapidly with the anion of the ketone to give b- hydroxyketone, which easily undergoes base-catalyzed dehydratation (Figure 36). By varying the amounts of the reactants in this Claisen-Schmidt reaction it is possible to obtain either the mono- or di-substituted benzalacetone. We will prepare dibenzalacetone, which is easier to isolate from reaction mixture.

In the present experiment, sufficient amount of ethanol is present as a solvent to dissolve the starting material, benzaldehyde and it's intermediate benzalacetone. The benzalacetone undergoes second condensation reaction forming final product - dibenzalacetone. 2 HC CHE NaOH benzaldehyde acetone dibenzalacetonoe