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Researcher

Matthew McBride

Objective

To synthesize dibenzalacetone from acetone and benzaldehyde using NaOH as the catalytic base in a 1:1 water/ethanol solvent using a modification of the procedure described in Hawbecker78. The Hawbecker procedure describes using 6.0 equivalents of benzaldehyde, but this procedure uses 2.9 equivalents.

Procedure

(1E,4E)-1,5-Diphenyl-1,4-pentadien-3-one: A solution of NaOH (0.902 g, 22.55 mmol, 1.6 eq) in distilled water (40 mL) at room temperature was added to a stirred solution of benzaldehyde (4.361 g, 41.13 mmol, 2.9 eq) in ethanol (40 mL). Acetone (0.833 g, 14.36 mmol, 1.0 eq) was added to the reaction mixture. The reaction mixture was then stirred at room temperature for 30 minutes. The precipitated product was recovered by suction filtration, washed 1x with 2-3mL of 1:1 ethanol/water, dried over suction for 25 minutes, and recovered (3.044 g, 90.6%) as yellow crystals (mp 103-104°C).

Results

Reaction Preparation Sheet
Characterization of Product 284A
Amount: 3.044 g
Appearance: Bright yellow crystals
Melting Point: 103-104°C (lit mp 110-112°C Hawbecker78)
HNMR Spectrum of UCEXP284_A
1H NMR (500 MHz, CDCl3) δ 7.72 (d, J = 16.3 Hz, 2H), δ 7.58 (m, 4H), δ 7.38 (m, 6H), δ 7.06 (d, J = 15.5 Hz, 2H)
Second HNMR Spectrum of UCEXP284_A2
Purity: Very pure sample of trans-dibenzalacetone by NMR

Discussion

This procedure produced pure trans-dibenzalacetone without having to recrystallize. The two characteristic doublets of trans-dibenzalacetone had coupling constants of 16.25Hz (located at 7.7ppm) and 15.5Hz (located at 7.1ppm). These coupling constants of near 15Hz indicates that the trans product was recovered.

The limiting reagent was the acetone (0.833 g, 14.36 mmol) and the precent yield of this reaction was 90.6%. An excess of benzaldehyde (2.87 equivalent) was used and the benzaldehyde was dissolved into the ethanol prior to being introduced into the reaction mixture. The was a major modification from the Hawbecker78 synthesis procedure, which used 6.0 equivalents of benzaldehyde and only listed yields of 40-60%. Additional modifications include that no scratching was needed to form crystals in the reaction mixture. The yellow crystals formed in the mixture immediately as they were formed. A second crop of crystals did not need to be recovered from the filtrate, but were recovered from the first filtration. The most important modification is that the product was recovered from the reaction mixture pure and did not need to be recrystallized. The Hawbecker78 procedure recrystallized the crystals from ethanol using water to crash the crystals out of solution. Product 284A was not recrystallized and was determined to be pure by HNMR.

The measured melting point of the product (103-104°C) is less than other recorded melting point values. The melting point has been recorded to be around 110°C and the melting point measured in this experiment was 6-7°C less.

Conclusion

3.044 g of pure trans-dibenzalacetone was produced in a yield of 90.6%

Log

2012-07-17

14:28 0.902 g of NaOH pellets were placed in a 250 mL [[#|Erlenmeyer flask]] (#1).
14:30 Added 40 mL of distilled H2O to the flask and placed on stir plate with stir bar to dissolve the pellets.
14:33 Added 40 mL of ethanol to a separate flask (#2).
14:35 Added 4.3614 g of benzaldehyde to flask #2 with the ethanol. Stirred the solution.
14:39 The ethanol and benzaldehyde solution in flask #2 was added to the aqueous NaOH solution in flask #1 and the solution was stirred.
14:41 Added 0.8332 g of acetone to the reaction mixture in flask #1. The solution was stirring and had a clear yellow color.
14:43 Solution became a pale yellow and was no longer clear.
14:44 Solution is a darker yellow and crystals are visible in the solution. A small amount of liquid was noticed on the walls of the flask as if heat was present, but no heat had been applied to the reaction mixture.
15:15 The solution was removed form the stir plate and filtered using a Buchner funnel and suction filtration. Bright yellow crystals were captured on the filter paper (Product 284A). The crystals were washed with 2-3mL of 1:1 ethanol/water. The crystals were spread out over the filter paper using a spatula and left over the suction to dry.
15:40 The suction was removed from the flask and a piece of paper towel was placed over the Buchner funnel.

2012-07-18

9:28 A small amount of yellow crystals were visible in the filtrate in the filtration flask.
9:31 0.0801 g of Product 284A was added to a 1-dram snap cap vial.
9:35 Approximately 0.4 mL of CDCl3 was added to the vial with Product 284A. The crystals dissolved into the solution immediately. The solution was transfered to NMR Tube 1.
10:15 The sample was analyzed 500MHz HNMR and the file of the spectrum was saved as UCEXP284_A.
10:34 The weight of an empty 5-dram snap cap vial (with no cap) was 11.9516 g.
10:41 The weight of the 5-dram vial with Product 284A was 14.9956 g. The weight of the recovered product was 3.044 g.
11:15 The melting point of Product 284A was measured to be 103-104°C.

2012-07-19

16:12 0.0625 g of Product 284A was placed in a 5-dram snap cap vial. Approximately 0.4 mL of CDCl3 was added to the vial and the sample was transferred to NMR Tube 2. The sample was analyzed by 500MHz HNMR and the file of the spectrum was saved as UCEXP284_A2.

2012-08-28

10:55 The melting point of Product 284A was measured to be 104-105°C. The melting point of a benzoic acid sample measured at the same time was 129-130°C.