crsexp010scheme.jpg

Researcher

Cuepil Choi

Objective

To see if the acetals converted from 4-chlorobenzaldehyde in ethylene glycol could be separated by running the solution with methylene chloride through a silica plug.

Procedure

Ethylene glycol 4-chlorobenzaldehyde acetals were created by heating 2 g of 4-chlorobenzaldehyde and 25 g of ethylene glycol to reflux in a 50 mL erlenmeyer flask. Mixture was put in freezer overnight. Mixture was then put into separatory funnel and methylene chloride was added. Bottom layer of methylene chloride was taken into a 5 dram vial. Sample of 2 mL was taken from vial and put into a small pasteur pipette with a kimtech plug and layered with silica and sand. Methylene chloride was used to wash mixture through the column and different fractions were taken in 1 dram vials.

Results

HNMR spectrum 1 - R-5 when reflux was stopped. 5:1 ratio between acetal to aldehyde
HNMR spectrum 2 - W-1 methylene chloride wash with acetal; 9:1 ratio between acetal to aldehyde; 3:1 ratio between acetal to ethylene glycol
HNMR spectrum 3 - W-2 methylene chloride wash with acetal; 10:1 ratio between acetal to aldehyde; almost 1:1 ratio between acetal to ethylene glycol
HNMR spectrum 4 - W-3 ethylene glycol layer with hemiacetal with no aldehyde or acetal
HNMR spectrum 5 - deuterated water outside

Discussion

W-3 has the most bizarre results. All the other experiments we had conducted showed that the hemiacetal formation reaction was incredibly quick to reach equilibrium. It does not make sense that the NMR machine could see the hemiacetal without any trace of aldehyde or acetal. If the equilibrium was quick, the hemiacetal would have reverted quickly to aldehyde, reaching the 1:9 hemiacetal to aldehyde equilibrium ratio we see so often. If the equilibrium is slow, contrary to our previous experiments, it may be able to be isolated. Also, the benzilic peaks for the acetal and hemiacetal flip flop in W-1 and W-2, which is strangle. The peak shift for the ethylene glycol OH is incredibly drastic as well: it shifts from 5.3 ppm to 2.9 ppm.

Conclusion

The experiment showed that almost all of the 4-chlorobenzaldehyde could be converted to acetal. It also showed that the acetal can be extracted by washing the ethylene glycol solution with methylene chloride with fairly low amounts of ethylene glycol dissolving into the methylene chloride. Strangely, W-3 showed almost all hemiacetal with no acetal or aldehyde. There was no aldehyde CHO peak or the mirror imaged CH2 acetal peaks at 3-4 ppm range.

Log

2013-07-23

14:43 mass of erlenmeyer flask 40.5527 g
14:45 2.1597 g 4-chlorobenzaldehyde added to erlenmeyer flask
14:50 24.8972 g ethylene glycol added to flask
14:54 drams labeled in the form CRS010 R-(n) [R for reflux, n for sample number]
14:57 magnetic stirrer added to flask and stirred at 150 rpm
14:58 CRS010 R-1 taken at 25 C
15:00 hot plate settings adjusted to 170 rpm and 290 C
15:07 solution became clear, all crystals went into solution. Vapors are noted
15:07 sample R-2 taken at 75 C
15:13 R-3 acquired at 135 C
15:20 R-4 acquired at 155 C
15:33 hot plate settings adjusted. Temperature raised to 340 C
15:45 hot plate lowered to 300 C
15:45 R-5 acquired
16:41 HNMR 1 of R-5 acquired
17:30 flask taken off of hot plate, allowed to cool and added to freezer with a parafilm on top

2013-07-24

9:40 flask taken out of freezer, whole mixture seems frozen or a very thick slurry.
9:45 contents of flask has melted, clear, oils that are not miscible with solution noted.
11:18 contents added to separatory funnel, approximately 10 mL of methylene chloride added to funnel to extract acetals
11:21 two layers formed with methylene chloride on the bottom. Funnel was shaken and inverted to release gasses.
11:24 bottom layer was taken into 5 dram vial labeled W-1. Noted that significantly less than 10 mL of methylene chloride came out
11:32 10 mL (approximately) wash done again and collected in W-1
11:35 5 mL (approximately) wash done again and collected in W-1
11:37 5 mL (approximately) wash done and collected in W-2
11:50 middle of ethylene glycol layer taken in W-3
11:40 spots taken of W-1 and W-2. Noted that both contained significant amount of aromatics.
13:03 HNMR 2 taken at 26.5 C of W-1 D2O used in outer tube and set to 4.8 ppm
13:22 HNMR 3 taken at 26.6 C of W-2 D2O used in outer tube and set to 4.8 ppm
13:43 HNMR 4 taken at 26.2 C of W-3 D2O used in outer tube and set to 4.8 ppm
14:54 TLC plate test 1 taken with methylene chloride as solvent
14:58 TLC plate test 2 taken
15:25 small pasteur pipette filled with kimtech plug, silica, and sand
15:35 methylene chloride added to column
15:45 approximately 2 mL of W-1 added to column and additional methylene chloride was added to column
15:56 F1 - F21 samples were taken of the column. Noted that a clear band appeared in the silica gel. Started to use 5% methanol in methylene chloride with F13. TCL plates were taken of all fractions.