Researcher

Rani Saba

Objective

To recrystallize trans-cinnamic acid from the high boiling point solvent 1-octanol and washing with the low boiling point solvent pentane at concentrations of 0.25 M, 0.74 M, and 1.48 M.

Procedure

Began by creating three different trans-cinnamic acid in 1-octanol solutions, with concentrations of 1.5 M, 0.75 M, and 0.25 M. Inserted the three labeled tubes into a 400 mL ethylene glycol bath in a 500 mL beaker, while on a hot plate set to 315°C. Once the solute dissolved in all three tubes, they were removed from the hot bath and placed into a water and ice bath in a 500 mL beaker. While test tube #3 did not crystallize, tubes #1 and #2 were removed from the ice bath and centrifuged for 5 minutes. After initial centrifuging, the tubes were analyzed for 1-octanol separation. The centrifuging was repeated 2 more times, for a total of 15 minutes. At the 10 minute mark, a noticeable amount of 1-octanol separation was recognized and the excess 1-octanol was carefully micropipeted from the tubes. After removal of the 1-octanol, the test tubes were weighed individually and their masses were recorded. We then proceeded to add 2.5 g of pentane to wash our trans-cinnamic acid sample, and centrifuged the sample for 3 minutes to allow for separation. This process was repeated three times. As the last supernatant was removed, a TLC spotting was performed with the excess pentane to confirm the complete removal of 1-octanol. As the TLC spotting confirmed this, we were able to proceed to the last step - drying of the sample. With our two samples purified, we removed the caps from our tubes and returned them to the ethylene glycol bath at a lowered heat setting of 120°C. After ten minutes, the samples appeared dry and were removed for melting point analysis.

Results

Recrystallization Spreadsheet for Tube 1
Concentration: 1.48 M
Trans-cinnamic acid recovered: 0.2154 g
Percent Yield: 86%
Melting Point: 132°C
Appearance: White crystals

Recrystallization Spreadsheet for Tube 2
Concentration: 0.74 M
Trans-cinnamic acid recovered: 0.1933 g
Percent Yield: 77%
Melting Point: 131°C
Appearance: White crystals

Recrystallization Spreadsheet for Tube 3
Concentration: 0.25 M
Sample did not recrystallize

Discussion

According to the temperature curve, for the solubility of cinnamic acid in 1-octanol, all three of our samples would easily enter the solution over the hot bath at 121°C. This was observed, as our samples dissolved almost instantly, with only a few crystals needing agitation to enter the solution. As the temperature curve suggests, our 0.25 M solution would have entered solution at 4°C, the 0.74 M solution at 35°C, and finally the 1.48 M solution at around 59°C. After all three samples had entered the solution, only the 1.48 M and the 0.74 M samples were able to recrystallize. This was no surprise, as even with an ice bath, it was difficult to overcome the high solubility of cinnamic acid in the 1-octanol, as suggested in the temperature curve. For the two samples that did recrystallize, we experienced a thick gel formation between the cinnamic acid and the 1-octanol. However, multiple washings and centrifuging of the samples allowed for careful removal of the 1-octanol from our samples. Finally, drying our samples in an ethylene glycol bath served to remove any excess pentane from our samples, while ultimately preparing our samples for melting point analysis.

Conclusion

Considering the temperature curve for the solubility of cinnamic acid in 1-octanol, our experiment yielded fairly expected results. With the high solubility of our 0.25 M solution, recrystallization of the cinnamic acid would prove to be difficult. Despite our best efforts using an ice bath, this lower concentration solution did not recrystallize. However, both the 0.74 M and 1.48 M solution recrystallized very quickly and formed thick gels with the 1-octanol. Using multiple pentane washes, and centrifuging our samples made it very easy to remove the 1-octanol and obtain our pure cinnamic acid. For the 1.48 M solution, we were able to recrystallize 0.2154 g of pure cinnamic acid (86% yield) and for the 0.74 M solution, we were able to recrystallize 0.1933 g (77%) yield. Later, we were able to furthest test purity of our samples by performing a melting point analysis of our samples. With our experimental samples and a pure sample in the apparatus, we were able to calculate melting points of 132°C for the 1.48 M solution and 131°C from the 0.74 M solution. This varied less than a couple of degrees from the pure sample, which was observed to have a melting point of 133.5°C, therefore establishing a high level of purity.

Log

2013-01-14

11:55 Weighed three 10 mL test tubes and recorded their weights
12:06 Added 0.2501 g of trans-cinnamic acid into a 10 mL test tube with screw cap. This was labeled as tube #1 and is used for our 1.5 M solution.
12:07 Added 0.2501 g of trans-cinnamic acid into a 10 mL test tube with screw cap. This was labeled as tube #2 and is used for our 0.75 M solution.
12:09 Added 0.2502 g of trans-cinnamic acid into a 10 mL test tube with screw cap. This was labeled as tube #3 and is used for our 0.25 M solution.
12:11 Prepared a 400 mL ethylene glycol hot bath in a 500 mL beaker. With a thermometer in the beaker, set a hot plate below the beaker to 315°C.
12:13 Added 0.7640 g of 1-octanol into tube #1.
12:14 Added 1.6990 g of 1-octanol into tube #2.
12:16 Added 5.4120 g of 1-octanol into tube #3.
12:19 Measured bath temperature to be 121°C and inserted all three test tubes into hot bath
12:21 Solute dissolves in test tubes #1 and #2
12:22 Test tube #3 is removed from the hot bath, inverted, and vortexed for one minute to completion
12:23 All test tubes are removed from hot bath and placed into empty 500 mL beaker
12:28 Ice and cold water are added to beaker to assist in re-crystallization
12:30 Crystals are identified in test tube #1
12:31 Crystals are identified in test tube #2
12:45 Still no evidence of crystals in test tube #3; test tubes #1 and #2 are removed and placed in 4 slot centrifuge.
12:50 Test tubes are removed after 5 minutes of centrifuging . Test tube #1 contains thick gel with little separation of 1-octanol, whereas test tube #2 shows a distinguishable amount of 1-octanol separation. Test tubes are then relocated to 6 slot centrifuge.
12:55 Test tubes are removed after 5 minutes of centrifuging . Test tube #1 shows further evidence of 1-octanol separation , whereas test tube #2 shows an even more distinguishable amount of 1-octanol separation.
13:00 Test tubes are stored away in drawer for future use.

2013-01-16

11:12 Placed test tubes #1 and #2 in centrifuge for 10 minutes.
11:22 Removed test tubes from centrifuge.
11:29 Carefully removed octanol from top of tube #1 and weighed test tube containing remaining crude trans-cinnamic acid.
11:33 Carefully removed octanol from top of tube #2 and weighed test tube containing remaining crude trans-cinnamic acid.
11:59 Added 2.4040 g pentane to tube #1
12:03 Added 2.5900 g pentane to tube #2
12:11 Vortexed tubes #1 and #2 and placed in 6 slot centrifuge for 3 minutes
12:20 Carefully removed pentane from top of tube #1
12:23 Carefully removed pentane from top of tube #2
12:29 Added 2.5519 g pentane to tube #1
12:32 Added 2.4821 g pentane to tube #2
12:37 Vortexed tubes #1 and #2 and placed in 6 slot centrifuge for 3 minutes
12:43 Carefully removed pentane from top of tube #1
12:46 Carefully removed pentane from top of tube #2
12:51 Added 2.4801 g pentane to tube #1
12:54 Added 2.5331 g pentane to tube #2
12:57 Vortexed tubes #1 and #2 and placed in 6 slot centrifuge for 3 minutes
13:04 Tested supernatant in tubes #1 and #2 on TLC plate using a single dot. As evidenced by disappearance of the spot and no residual shadowing on the TLC plate, only pentane is contained in the supernatant.
13:07 Carefully removed pentane from top of tube #1
13:11 Carefully removed pentane from top of tube #2
13:19 With screw caps removed, slowly placed tubes #1 and #2 into the ethylene glycol bath at a measured temperature of 120°C. This is done to boil off any remaining pentane (boiling point 35-37°C) and prepare our trans-cinnamic acid for final purity analysis.
13:29 After ten minutes, the samples appear completely dry and removed from the hot bath.
13:31 Weighed dried test tube #1, recovered sample is calculated as 0.2154 g
13:32 Weighed dried test tube #2, recovered sample is calculated as 0.1993 g
13:35 Took melting point of test tube #1

2013-01-20

11:40 Samples were analyzed using melting point apparatus using both experimental samples and pure cinnamic acid
11:41 Samples melting points are recorded: 1.48 M melting point is recorded as 132°C, 0.74 M melting point is recorded as 131°C, pure sample as 133.5°C