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Chemspider Links: salicylaldehyde, methanol, ethanol, salicylaldehyde ethanol acetal, salicylaldehyde ethanol hemiacetal, salicylaldehyde methanol acetal, salicylaldehyde methanol hemiacetal, benzene, propylamine, 2-[(E)-(Propylimino)methyl]phenol, Benzene, 6H,12H-Dibenzo[b,f][1,5]dioxocin
Reaction Attempts

Researcher

Matthew McBride

Objective

To analyze the possible products (acetal or hemiacetal formation) of salicylaldehyde with ethanol, benzene, methanol, and propylamine

Procedure

Approximately 50/50 by volume mixtures of salicylaldehyde with ethanol, benzene, methanol, and propylamine were prepared and analyzed by 500MHz HNMR spectroscopy using the coaxial insert NMR tube system with CDCl3 as the reference solvent. The HNMR spectra were obtained within a half an hour after the initial preparation of the mixtures (0 hours) and after 24 hours at room temperature.

Results

HNMR Spectra of Reagents
1. CRSEXP035_1_0hours: Salicylaldehyde: 11.11 ppm (1H, s), 9.704 ppm (1H, s), 7.37 ppm (2H, t), 6.87 (2H, t).
2. Ethanol (Obtained from CRSEXP032): 1.728 PPM (3H, t), 4.159 PPM (2H, m), 5.890 (1H, t)
3. CRSEXP035_3_0hours: Benzene: 7.157 ppm (6H, s).
4. Methanol (Obtained from CRSEXP032): 4.100 PPM (3H, s), 5.660 PPM (1H, s).
5. CRSEXP035_5_0hours: Propylamine: 3.094 ppm (2H, t), 1.915 ppm (2H, m), 1.738 ppm (2H, s), 1.403 ppm (3H, t).

HNMR Spectra of mixtures (approximately 50/50 by volume): 0 hours
6. CRSEXP035_6_0hours: Salicylaldehyde and ethanol: Hemiacetal peak at 6.530 ppm (1H, s), Acetal peak forms at 5.884 ppm (1H, s) - increases after 24 hours.
Mole Fraction Spreadsheet
7. CRSEXP035_7_0hours: Salicylaldehyde and benzene: Formation of two new doublet peaks at 7.075 ppm and 6.849 ppm. Integration indicates that these peaks are part of the salicylaldehyde and not formation of new product.
Mole Fraction Spreadsheet
8. CRSEXP035_8_0hours: Salicylaldehyde and methanol: Hemiacetial peak at 6.634 ppm (1H, s), Acetal peak at 5.894 ppm (1H, s) - has a 1:6 ratio with new methyl peak (6H, s) forming at 3.615 ppm.
Mole Fraction Spreadsheet
9. Salicylaldehyde and propylamine (one drop): Caused an insolubility event to take place, so no HNMR spectrum was obtained.

HNMR Spectra of mixtures (approximately 50/50 by volume): 24 hours
6. CRSEXP035_6_24hours: Salicylaldehyde and ethanol: Hemiacetal peak at 6.515 ppm (1H, s), Acetal peak forms at 5.868 ppm (1H, s) - increases from 0 hours.
Mole Fraction Spreadsheet
7. CRSEXP035_7_24hours: Salicylaldehyde and benzene: No new product formed
Mole Fraction Spreadsheet
8. CRSEXP035_8_24hours: Salicylaldehyde and methanol: Hemiacetial peak at 6.590 ppm (1H, s), Acetal peak at 5.850 ppm (1H, s) - has a 1:6 ratio with new methyl peak (6H, s) forming at 3.570 ppm.
Mole Fraction Spreadsheet

Discussion

The mixture of salicylaldehyde and benzene did not result in any new product forming within 24 hours at room temperature. The mixture of salicylaldehyde and propylamine caused a precipitate to form upon the addition of a single drop of propylamine, so the composition of the mixture was not further examined by HNMR due to the insolubility event.

Salicylaldehyde and benzene: None of the 6H,12H-Dibenzo[b,f][1,5]dioxocin product, formed by two salicylaldehyde molecules reacting together, was observed in the NMR analysis.

Salicylaldehyde and ethanol: At the zero hour time point, the mole fraction of the acetal was 0.0025 and the mole fraction of the hemiacetal was 0.0036. The mole fraction of the salicylaldehyde present was 0.4173. This means at zero hours, the ratio of aldehyde to acetal was 168:1 and the ratio of aldehyde to hemiacetal was 116:1. After 24 hours, the mole fraction of acetal was 0.0227 and the mole fraction of the hemiacetal was 0.0040. The mole fraction of the salicylaldehyde present was 0.4233. This means at 24 hours, the ratio of aldehyde to acetal was 19:1 and the ratio of aldehyde to hemiacetal was 106:1. With time, the amount of acetal forming was increasing, but the amount of hemiacetal was staying close to constant.

Salicylaldehyde and methanol: At the zero hour time point, the mole fraction of the acetal was 0.0155 and the mole fraction of the hemiacetal was 0.0027. The mole fraction of the salicylaldehyde present was 0.2310. This means at zero hours, the ratio of aldehyde to acetal was 15:1 and the ratio of aldehyde to hemiacetal was 86:1. After 24 hours, the mole fraction of acetal was 0.0500 and the mole fraction of hemiacetal was 0.0025. The mole fraction of salicylaldehyde present was 0.2294. This means that at 24 hours, the ratio of aldehyde to acetal was 5:1 and the ratio of aldehyde to hemiacetal was 92:1. The amount of acetal was increasing with time, but the hemiacetal level was not changing/had reached an equilibrium. One possible reason for the greater aldehyde to acetal ratio with methanol is due to less steric hinderance of the alcohol molecule (methanol is smaller than ethanol) and also that this mixture had a large excess of methanol compared to the ethanol/aldehyde mixture. The methanol to aldehyde was about 75:25 by mole fraction and the ethanol to aldehyde was about 60:40 in each of the original mixtures.

Conclusion

After 24 hours, a 5:1 ratio of aldehyde to acetal was obtained in the mixture of salicylaldehyde and methanol. For this mixture with methanol, the aldehyde to hemiacetal ratio remained around 90:1. After 24 hours, a 19:1 ratio of aldehyde to acetal was obtained in the mixture of salicylaldehyde and ethanol. For this mixture with ethanol, the aldehyde to hemiacetal ratio remained around 110:1. This showed that a good aldehyde to hemiacetal ratio is not required to obtain a good aldehyde to acetal ratio.

Log

2013-10-23

14:00 Prepared samples of pure salicylaldehyde (#1), ethanol (#2), Benzene (#3), methanol (#4), propylamine (#5), approximately 50/50 mixture of salicylaldehyde and ethanol (#6), approximately 50/50 mixture of salicylaldehyde and benzene (#7), approximately 50/50 mixture of salicylaldehyde and methanol (#8), and one drop of propylamine in salicylaldehyde (#9). The solution of #9 caused an insolubility event to take place. The HNMR spectra of these samples were obtained using the 500MHz NMR spectrometer within 15 minutes after they were prepared using the coaxial insert system. The samples were placed in the inner coaxial insert and the CDCl3 reference solvent was placed in the outer NMR tube. The spectra obtained are CRSEXP035_1_0hours, CRSEXP035_3_0hours, CRSEXP035_5_0hours, CRSEXP035_6_0hours, CRSEXP035_7_0hours, and CRSEXP035_8_0hours.

2013-10-24

16:05 The samples of approximately 50/50 mixture of salicylaldehyde and ethanol (#6), approximately 50/50 mixture of salicylaldehyde and benzene (#7), and approximately 50/50 mixture of salicylaldehyde and methanol (#8) were analyzed by 500MHz HNMR using the coaxial insert to hold the sample and CDCl3 as the reference solvent in the outer tube. The spectra obtained are CRSEXP035_6_24hours, CRSEXP035_7_24hours, and CRSEXP035_8_24hours.