crsexp017scheme.jpg

Researcher

Cuepil Choi

Objective

To restudy the kinetics of hemiacetal formation from 4-chlorobenzaldehyde and ethanol at 55 C. Restudy conducted with a different, cleaner stock bottle of 4-chlorobenzaldehyde because CRSEXP013 had 4-chlorobenzoic acid in the stock bottle.

Procedure

A small amount of 4-chlorobenzaldehyde was added to a 5 dram vial along with an excess amount of ethanol and was retriturated before pipetting into an inner NMR tube. HNMR spectra were taken with an outer tube containing deuterated water at 55 C.

Results

HNMR 1 - 66 minutes, 25 C
HNMR 2 - 84 minutes, 55 C
HNMR 3 - 88 minutes, 55 C
HNMR 4 - 99 minutes, 55 C
HNMR 5 - 102 minutes, 55 C
HNMR 6 - 121 minutes, 55 C
HNMR 7 - after 24 hrs, 25 C

Discussion

It is strange that the acetal would make such a complicated pattern in the 3.5 to 4 ppm range. Although the multiplets with approximately 16 peaks seems more suitable for the acetal, it does not make sense that the hemiacetal to aldehyde ratio would change so drastically with heating. Also there are a set of doublets in the aromatic region that maintains its ratio with the aldehyde, pointing strongly towards the hemiacetal. It may be that perhaps wer are seeing neither the hemiacetal or the acetal with the multiplet peaks coming out.

Conclusion

Unlike the conclusion for CRSEXP013, this kinetic study suggests that acetals do form when ethanol and 4-chlorobenaldehyde are heated. The multiplet peaks in the 3.5-4 range that is often seen next to the ethanol quartet does not seem to be from the hemiacetal but from the acetal. The growing benzylic peaks point strongly that the growing doublets in the aromatic region and the multiplets in the 3.5-4 ppm region is part of acetal. [give rates/ratios [cc]]

Log

2013-08-08

16:15 mass of 5 dram vial 1 11.8559 g
16:17 0.1339 g 4-chlorobenzaldehyde added to vial 1
16:18 2.0102 g of ethanol added to vial 1
16:19 retriturated mixture then pipetted into NMR tube and capped
17:24 HNMR 1 taken at 25 C
17:32 NMR set 20 C
17:35 NMR taking too long to cool down, temperature at 23.8 C, NMR set to 55 C
17:42 HNMR 2 taken at 55 C
17:46 HNMR 3 taken at 55 C
17:57 HNMR 4 taken at 55 C
18:00 HNMR 5 taken at 55 C
18:11 NMR temperature set to 25 C
18:17 temperature at 25 C
18:19 HNMR 6 taken at 25 C

2013-08-09

10:02 HNMR 7 taken