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Researcher

Cuepil Choi

Objective

To study the kinetics of acetal and hemiacetal formation in ethylene glycol by observing the mixture at room temperature over time.

Procedure

4-chlorobenzaldehyde was mixed into ethylene glycol so that there was 0.1M of 4-chlorobenzaldehyde. Stirring bar was added to mixture to mix solution for several minutes. NMR samples were taken over a period of time.

Results

HNMR spectrum 1 - 1 hr 3 min
HNMR spectrum 2 - 1 hr 18 min T@75 C
HNMR spectrum 3 - 1 hr 25 min T@75 C
HNMR spectrum 4 - 1 hr 33 min T@75 C
HNMR spectrum 5 - 1 hr 42 min T@75 C
HNMR spectrum 6 - 1 hr 50 min T@75 C
HNMR spectrum 7 - Day 2 T@25 C
HNMR spectrum 8 - Day 3 T@25 C

Discussion

This experiment raises questions about the stability of the hemiacetal and how quickly it equilibrates. This experiment suggests that separating the hemiacetal may be possible.

Conclusion

The ratio between hemiacetal and 4-chlorobenzaldehyde stayed the same mostly during the controlled study at 75 C. Strangely, almost all of the 4-chlorobenzaldehyde became hemiacetal and acetal overnight. This may mean that the equilibrium for the hemiacetal is slow or even that the hemiacetal is stable in certain conditions because HNMR spectrum clearly shows hemiacetal without any aldehyde.

Log

12:18 mass of 50 mL erlenmeyer flask 1 40.5531 g
12:26 0.4869 g 4-chlorobenzaldehyde added to flask 1
12:36 29.1029 g of ethylene glycol added to flask 1
12:38 stirring bar added to flask 1 and set to 280 rpm
13:20 most crystals went in
13:28 filtered solution with kimtech in small pasteur pipette
13:31 NMR tube filled up with outer tube with D2O
13:39 HNMR 1 taken at 25 C D2O set to 4.8
13:44 NMR machine temperature set to 75 C
13:52 NMR machine reached 75 C
13:53 HNMR 2 taken at 75 C
14:00 HNMR 3 taken at 75 C
14:08 HNMR 4 taken at 75 C
14:17 HNMR 5 taken at 75 C
14:25 HNMR 6 taken at 75 C
14:35 NMR machine temperature set to 25 C
14:42 temperature reaches 25 C, HNMR 7 taken

08-08-2013

16:28 HNMR 7 taken at 25 C 32 scans and split D2O peak set to 4.8

08-09-2013

9:55 HNMR 8 taken at 25 C 8 scans and no more split D2O peak (peak set to 4.8)