Researcher

Matthew McBride

Objective

To determine the recrystallization yield of trans-dibenzalacetone from n-hexane

Procedure

Add approximately 0.5 g of trans-dibenzalacetone to a Erlenmeyer flask. Add 2-3 mL of n-hexane to the flask and place the solution on the hot plate to boil. Once the solution is boiling, add small amounts of boiling n-hexane to the boiling solution until all of the crystals have entered the solution. Allow the solution to cool to room temperature and filter the solution to recover the product.

Results

Characterization of Product 285A
Amount: 0.3498
Recrystallization Yield: 64%
Melting Point: 100-101°C
Appearance: Yellow Crystals
HNMR Spectrum
Purity: Pure, dry sample
Calculation Sheet

Discussion

Based on the temperature curve, the solubility at boiling was predicted to be 0.35M. The measured solubility at boiling was 0.1M, so the predicted solubility at boiling was high. The temperature curve also predicted that the recrystallization yield would be 97% and the ONS Mobile Web App predicted 91%. The actual recovery yield was 64%. One reason for this lower yield is that when the crystals formed in the n-hexane solution, the crystals formed on the bottom and sides of the glass flask. The crystals had to be scrapped off the sides and bottom and were difficult to remove from the flask. This difficulty in removing the crystals caused some of the product to be lost, because the crystals remained in the flask. This limitation of n-hexane and the fact that it is not miscible with water, causes n-hexane to be an undesirable solvent for recrystallizing trans-dibenzalacetone.

Conclusion

Trans-dibenzalacetone was recrystallized from n-hexane in a yield of 64% and the solubility at boiling was measured to be 0.1M

Log

2012-07-25

15:05 The weight of the 25 mL Erlenmeyer flask with the loose fit cap was 40.4048 g.
15:07 The weight of the flask with the cap and the trans-dibenzalacetone crystals (recovered product from EXP321 and synthesized as Product 284A in UCEXP284) was 40.9519 g. This is 0.5471 g of crystals.
15:11 Added approximately 2 mL of n-hexane to the flask with the crystals and placed the flask on the hot plate to boil.
15:21 Have added a few mL of n-hexane to the boiling solution but crystals are still visible.
15:25 A total of approximately 15 mL of n-hexane has been added to the flask, but crystals are still visible.
15:36 The weight of an empty 50 mL Erlenmeyer flask with a cap was 50.9487 g. The hot solution in the 25 mL flask was transferred to this flask and placed on the hot plate.
15:46 Hexane was added to the solution until all of the crystals were observed to have entered the solution. The flask was removed and weighed 66.926 g (flask, cap and content). The flask was placed on the lab counter to cool to room temperature (the temperature of the lab was at 24°C). Crystals were observed to form in the solution. The weight of the flask with parafilm was 67.231 g.
16:09 The crystals that were forming were sticking to the bottom and sides of the flask.

2012-07-26

9:28 The weight of the flask with parafilm was 67.094 g.
9:34 The crystals were sticking to the bottom and sides of the flask. The crystals had to be scrapped off the sides and bottom into the solution. The solution was then filtered using a Buchner funnel and suction filtration. Yellow crystals were captured on the filter paper. The crystals were spread across the filter paper over the suction to dry.
10:31 The weight of an empty 5-dram snap cap vial was 12.0028 g.
10:34 The weight of the vial with the product was 12.3778 g. This is a total of 0.3498 g.
13:16 Took the melting point of the product and it was 100-101°C.