Researcher

Rani Saba

Objective

To recrystallize caffeine using a sintered glass funnel to allow for the removal of 1-octanol and a 50% trans-cinnamic acid contamination in a 0.73 M solution

Procedure

Created a 0.73 M caffeine solution with a 50% trans-cinnamic acid contamination using 0.2509 g of caffeine in a test tube. Once the solution was created, it was heated evenly with a heat gun and stirred until the crystals went completely into the solution. The solution was then set in an ice bath to expedite crystallization. Once crystallization completed, the recovered crystals were then filtered through the sintered glass funnel and washed twice with 1-octanol. One final filtration and wash was completed with pentane. The sintered glass funnel containing the crude product was weighed for yield calculation. Finally, the recovered crystals were analyzed by HNMR to determine purity.

Results

Recrystallization Spreadsheet
Caffeine recovered: 0.2173 g
Percent Yield: 86.60%
Melting Point: 235 C
Appearance: White crystals
HNMR Spectrum of Sample 1
Purity: A very pure sample of caffeine with trace amounts of 1-octanol from sample washings

Discussion

Overall, the performed experiment resulted in both a tremendous yield and level of purity. In our 0.7287 M solution, the process of recrystallizing caffeine using the experimental method was both easy, efficient, and time conservative. Using both HNMR and melting point analysis, we were able to obtain desirable purity results, with the level of purity within the 90% interval with a near exact melting point. In addition, due to the use of a sintered funnnel, we were able to maintain a high yield, that which we calculated to be 86.60%. The heat gun also served its purpose of dissolving the caffeine terrifically, allowing for an even and complete mixture of the solution, which assisted in both the purity and yield results that we obtained. Special attention and detail was also paid to ensuring that our recrystallized caffeine was properly filtered, with none of the crystals being lost during the transfer from the test tube to our funnel.

Conclusion

After completion of the experiment, we saw that the method above allows for a tremendous percent yield and level of purity. The HNMR analysis above suggested above a 90% purity, whereas the weighing of our product showed an 87% yield. Most importantly, the HNMR analysis shows no trans-cinnamic acid, suggesting that this method was extremely successful in purifying the caffeine and removing the experimental contamination. Lastly, our melting point analysis resulted in a reading of 235°C for the recrystallized caffeine. This is only a few degrees off from the accepted literature value of 237.16°C which supports our HNMR analysis regarding the purity of our substance.

Log

2013-02-06

11:35 The weight of a sintered glass funnel was measured to be 16.1650 g
11:37 .2509 g of anhydrous caffeine added to a 10 mL test tube
11:38 0.0961 g trans-cinnamic acid added to the test tube
11:39 1.2531 g 1-octanol added to the test tube
11:50 Clamped the test tube to a stand in the hood, with a spatula seated in the tube to help avoid boiling
11:51 Began to heat the test tube with a heat gun at low setting to allow the crystals to enter the solution
11:55 When less activity was recognized, the heat setting was adjusted to high
11:57 All of the crystals had entered the solution, while little boiling was observed
11:58 Heat gun was turned off, spatula was removed, test tube capped, and crystallization allowed to begin
11:59 Solution was put on ice bath to allow for crystallization to complete
12:06 Test tube was removed from ice bath
12:10 Sinter funnel was placed above a Buchner flask and connected to vacuum for filtration
12:11 Sample was added to funnel, allowing for octanol to pass through to the flask
12:16 Crystals were washed with 1.2951 g of octanol
12:25 Crystals were washed again with 1.2300 g of octanol
12:35 Vacuum was momentarily released and crystals were washed with 1.3375 g of pentane
12:36 Vacuum was reapplied and left on to allow for further filtration and drying of the caffeine
12:55 Sample appeared dry and was removed
12:58 Sintered funnel containing product was removed and weighed
12:59 Weight of sintered funnel containing product is recorded as 16.3823 g
13:02 Sample was carefully scraped from sintered funnel into 5-dram vial
13:05 Drum vial containing product was set aside for future NMR analysis

2013-02-11

11:25 0.0257g of dried anhydrous caffeine placed in vial and dissolved with 0.5 ml of chloroform
11:30 Solution prepared in previous step is prepared for NMR analysis by transfer to NMR tube
11:42 NMR analysis completed by 500MHz HNMR and file saved as ONSEXP348_Sample1

2013-03-20

11:52 Sample was analyzed using melting point apparatus using both sample and pure caffeine
12:02 Sample's melting point is recorded as 235°C.