dba scheme .png

Researcher

Matthew McBride

Objective

To synthesize trans-dibenzalacetone from benzaldehyde and acetone.

Procedure

This experiment used the guidance provided by the following article to complete the experiment. A 10% potassium hydroxide solution was created. Ethanol was added to this solution and the solution was cooled in an ice bath. Benzaldehyde was added to the solution and then acetone was added. The solution was allowed to mix for 30 minutes. The solution was cooled on an ice bath and then the product was filtered off using suction filtration. The product was then recrystallized using ethanol.

Results

This Reaction Preparation Spreadsheet was used to prepare the experiment and shows the molar amounts of each reactant as well as the theoretical yield. 0.5036g of the brown crystal product was obtained and shown in picture #3.

Picture #1: The solution while the reaction was taking place
ONSEXP274Picture#1.png

Picture #2: The recovered product from the reaction, but prior to the recrystallization in ethanol
ONSEXP274Picture#2.png

Picture #3: The product recovered from the second recrystallization, after all of the product passed through the filter during the first recrystallization
ONSEXP274Picture#3.png


Discussion

From observations alone, it seems that trans-dibenzalacetone was obtained from the reaction. The crystals had a yellow-orange color (picture #2) consistant with the known appearance of trans-dibenzalacetone. However, when it was attempted to recrystallize the product, none of the product was captured by the filter and entered the solution contained in the suction flask. The suction flask was not cleaned out between each filtration and consequently the product was mixed in with the mother liquor from each filtration. This was a mistake and for each future experiment, the suction flask will be rinsed with acetone and then dried before the next filtration so the mother liquor can be obtained without contamination. Some crystals were obtained from the mother liquor, but when it was attempted to recrystallize those crystals, they became a brown solid (picture #3) that showed no visible similarity to trans-dibenzalacetone crystals.

Conclusion

It does not seem that any trans-dibenzalacetone was obtained from this experiment. But once HNMR has been used to examine the brown crystals ultimately obtained, it will be known for sure whether any product was obtained. It is believed that the desired product was obtained from the reaction, but was lost during the recrystallization in ethanol.

This synthesis was successfully completed in EXP279

Log

2012-04-02

11:39 6.150g of potassium hydroxide pellets were placed in a 50mL Erlenmeyer Flask with a stir bar.
11:45 18mL of distilled water was added to the flask and the flask was placed on the stir plate. The solution was stirred and the pellets were observed to quickly dissolve into solution.
11:47 7.5mL of ethanol was added to the flask. The flask continued to be stirred on the stir plate.
11:53 The flask was placed on ice to cool.
12:05 1mL of benzaldehyde was added to the falsk and the flask was placed back on the stir plate. The benzaldehyde was allowed to throughly mix into solution.
12:12 0.5mL of acetone was added to the flask. The solution turned a pale yellow color. Picture #1 was taken. The solution was stirred on the stir plate for 30 minutes.
12:42 The flask was removed from the stir plate and placed in the ice bath to cool.
12:50 A small piece of circular filter paper was cut out and placed in the Hirsch funnel. The piece of filter paper was large enough to cover all the holes in the filter, but small enough to lay flat along the surface so that nothing could pass underneath the filter paper. The filter was placed in a suction flask and the flask was attached to the vacuum. The vacumm was turned on and the solution was removed from the ice bath and poured through the filter. The product captured by the filter was washed once with distilled water. The product was yellow and had the consistency of "mush" or clay, not of completely dried crystals. Picture #2 was taken.
13:02 To recrystallize the product, the product captured by the filter was placed in a 25mL Erlenmeyer flask. 5mL of ethanol was added to the flask. The flask was swirled and placed on the hot plate set to 150C.
13:07 All of the solid was observed to have dissolved into the ethanol. The ethanol was not observed to have reached boiling (78C).
13:12 The flask was removed from the hot plate and placed in the ice bath to recrystallize.
13:17 The weight of the empty 1-dram vial was 4.7069g.
13:41 The crystals were observed to have formed in the solution in the ice bath. The solution was filtered through the Hirsch funnel. All of the solution passed through and no crystals were captured. The mother liquor was filtered, but the suction flask had not be cleaned out before use for the second filtration and so the mother liquor contained the starting material as well as the recrystallization material. The solution in the suction filter was removed and filtered and yellow crystals were obtained.
13:47 The recovered crystals were dissolved in 3mL of ethanol to re-attempt the recrystallization. One all of the solid had dissolved in ethanol, the flask was placed in the ice bath.
13:52 The crystals formed in the solution in the ice bath were observed to be a brown color. The solution was filtered to recover the recrystallized product.
13:55 Picture #3 was taken. The weight of the flask with the brown crystal product was 5.2105g. This means there was 0.5036g of the brown crystal product.