Researcher

Matthew McBride

Objective

To recrystallize caffeine from toluene with a pentane wash using the sintered glass funnel method to determine whether the pentane wash is able to remove the high boiling point solvent toluene.

Procedure

Caffeine (0.2520 g) was added to a 10 mL screw cap test tube and toluene was added until all of the caffeine went into the solution at the boiling point of toluene (110°C) to create a 0.24 M solution. The solution was cooled on ice for 20 minutes and the transferred to a sintered glass funnel using pentane. The crystals were filtered using suction filtration and washed with an excess of pentane (3x). The crystals were allowed to air dry for ten minutes over the suction and the purity was determined by HNMR.

Results

Recrystallization Sheet
Concentration: 0.24 M
Mass of Product: 0.2007 g
Percent Yield: 80%
HNMR Spectrum
No toluene peaks were visible (no singlet at 2ppm or in the aromatic region)

Discussion

[Is there a reason that you went back to bath to heat the sample? I thought after the 1-octanol experiments that the heat gun was most convenient and fast? JCB] The heat bath was used because our heat gun is not working - it does not warm up at all.

At a concentration of 0.24 M, the temperature curve predicts a yield of 88% and this experiment determined that the yield was 80%. There was some additional lost in yield due to some of the crystals sticking to the test tube and not being transferred to the sintered glass funnel. Consequently, the temperature curve accurately determined the yield of this recrystallization from toluene.

Most importantly, toluene was not present in the recovered crystals. This shows that a higher boiling point solvent, such as toluene, could be used as a recrystallization solvent and be removed by performing a pentane wash.

Conclusion

The recrystallization yield of caffeine from a 0.24 M toluene solution was measured to be 80% and the pentane effectively removed the toluene solvent.

Log

2013-05-24

10:15 Placed ethylene glycol in a Erlenmeyer flask on a hot plate to create a hot bath.
10:23 The weight of the 10 mL screw cap test tube (Tube 1) with the cap was 11.4402 g. 0.2520 g of caffeine and 2.0113 g of toluene were added to the test tube.
10:34 Tube 1 was vortexed and placed in the hot bath at 90°C.
10:42 The solution began to boil at 110°C, but crystals were still visible.
10:54 Toluene was added dropwise to the solution until all of the crystals entered the solution as it was boiling at 110°C. The weight of Tube 1 with the caffeine crystals and the added toluene was 15.5227 g. Tube 1 was removed from the bath and allowed to cool.
10:57 Crystals were visible.
11:01 Tube 1 was placed in an ice bath to cool and mixed with the spatula.
11:20 The tube was removed from the ice bath. The weight of the sintered glass funnel was 33.8783 g.
11:29 The crystals were transferred from Tube 1 to the sintered glass funnel using pentane and filtered using suction filtration. The crystals on the funnel were washed with pentane three times.
11:34 The crystals were allowed to dry over suction.
11:38 Weight of empty 5-dram vial for the product: 11.8061 g.
11:41 Weight of Tube 1 with the crystals that could not be removed: 11.4864 g.
11:44 The funnel was removed from the suction. Weight of the funnel with the recovered crystals: 34.0790 g.
11:48 The vial with the product weighed 11.9769 g.
11:53 0.0176 g of the product (Product A) was dissolved in 1 mL of CDCl3 and placed in an NMR tube. The sample was then analyzed by 500 MHz HNMR. The spectrum is saved as ONSEXP358_A.