CRSEXP001

=Array transformations in this experiment= Numbers in red are mole fractions for each array and the rest are NMR assignments. Converted from the CRS Array Table. [JCB]

Reaction Attempts for ethanol 4-chlorobenzaldehyde hemiacetal
=Researcher= Cuepil Choi =Objective= To observe the possible products of mixing together 4-chlorobenzaldehyde and ethanol at room temperature over the course of a few hours using a [|co-axial NMR tube] with CDCl3 in the outer compartment. Experiment was prompted by [|UsefulChem post] which hypothesized the role of electron withdrawing groups on aromatic aldehydes and hemiacetal formation. =Procedure= 1.4220g of ethanol was added to 0.1137g of 4-chlorobenzaldehyde crystals in a 1-dram vial then transferred to the inner compartment of an NMR co-axial tube with CDCl3 in the outside compartment. HNMRs were taken starting at 30 minutes after the mixture was prepared. =Results= [|HNMR 1] 30 min, about 10:1 aldehyde/hemiacetal (mole fraction sheet-1) [|HNMR 2] 60 min, about 10:1 aldehyde/hemiacetal (mole fraction sheet2 ) [|HNMR 3] 90 min, about 10:1 aldehyde/hemiacetal (mole fraction sheet3) =Discussion= The small amounts of 4-chlorobenzaldehyde ethanol hemiacetal that was created through the reaction of 4-chlorobenzaldehyde and ethanol was expected. However, comparing the results of ONSEXP033 that tested 4-chlorobenzaldehyde and methanol showed a 4-chlorobenzaldehyde to 4-chlorobenzaldehyde methanol hemiacetal ratio of 2:1 compared to the 10:1 from this experiment. The drastically different ratios between methanol and ethanol reacting with 4-chlorobenzaldehyde may be the result of steric hindrance. In these spectra the hydroxyl group of the hemiacetal (near 7.5 ppm) couples as an expected doublet with the benzylic H (near 6.1 ppm). This can arise when the lack of trace acid or basic impurities slow down H bonding exchange to longer than the NMR timescale. However the same is not observed for the ethanolic OH, which appears as a broad peak instead of a triplet. [JCB] =Conclusion= The reaction of 4-chlorobenzaldehyde with excess ethanol reached equilibrium within 30 minutes and was stable for at least 90 minutes. The aldehyde to hemiacetal ratio was about 10:1. =Log=

2013-07-08
11:38 weight of empty 1-dram vial 1-E was 4.7488g 11:38 0.1137g of 4-chlorobenzaldehyde was put into 1-E 11:39 1.4220g of ethanol was added to 1-E 11:40 mixture was retriturated several times, all the 4-chlorobenzaldehyde crystals went in. 12:08 HNMR spectrum 1 was taken 12:37 HNMR spectrum 2 was taken 13:37 HNMR spectrum 3 was taken