UCexp261scheme.png

Researcher

Evan Curtin

Objective

To synthesize an imine (benzalaniline) from aniline and benzaldehyde in order to obtain solubility data as explained on the imine project page.

Procedure

Note: The reaction mixture using dichloromethane as a solvent was discarded due to lack of precipitation of the product after attempted recrystallization with added hexane.

Weigh 1.86g (20mmol) aniline and 2.12g (20mmol) benzaldehyde. Measure enough dichloromethane so that the total reaction volume will be 25mL (26.47g) (this will make a .8M solution). Repeat, but instead of dichloromethane use methanol (16.724g). Mix one (20mmol) portion of benzaldehyde in each solvent. Add the 20mmol of aniline slowly to each solution. Cover the reaction vessels with parafilm, and stir using a magnetic stir bar overnight. Roto-vap the solution that had methanol as a solvent. Recrystallize using ethanol. Cool the ethanol/product mixture, then filter. Set the product in a desiccator under high vacuum to dry. Characterize using mp and HNMR.

Results

Exp261plan
Mass of Reactants and Yield calculation

Aniline





Benzaldehyde












Characterization of 261-2C (after 70 min on high vac) (I think you have the wrong NMR here - there was ethanol still at this stage if I recall JCB)[This matches correctly with the one I saved on my computer, is it possible that some of the ethanol evaporated inside the vial and would have been separated from the solid due to the long time between isolation and when I took the NMR? - EC]
appearance: Pale yellow, almost white
amount: 2424.2mg
Melting point: 37C-41 C
H NMR: link and embed




Characterization of 261-2D (dry product after 6 hours on high vac)


appearance: Pale yellow, almost white
amount: 2395.6mg, 66.45%
Melting point: 47C-48C
H NMR: link to jdx file also



Discussion

An equimolar mixture of aniline and benzaldehyde was created in two solvents. (1) was mixed using dichloromethane as a solvent in accordance with previous synthesis methods for benzalaniline. In addition, the same quantity of reactants was mixed in methanol. Ethanol was used as a recrystallization solvent in another procedure for imine synthesis. The product was too soluble in dichloromethane to extract easily. The melting point of the product is slightly lower than literature values of 52-54C. Sigma Aldrich's HNMR matches the one obtained in this experiment, with an imine peak around 8.5. The aromatic peaks also match.

Conclusion

Benzalaniline was successfully synthesized from benzaldehyde and aniline with methanol as the solvent, with a yield of 66.45%. [Wasn't this yield called into question in UC-EXP205 JCB]

Log

2011-02-28 - Day 1

14:10 - Weighed aniline, benzaldehyde, dichloromethane and methanol in separate vials (3mL) and beakers (25mL).
Masses for mixture 1 (dichloromethane as solvent):
Aniline: 1.8558g
Benzaldehyde: 2.1312g
Dichloromethane: 25.0421g
Masses for mixture 2 (methanol as solvent):
Aniline: 1.8637g
Benzaldehyde: 2.1109g
Methanol: 15.8265g
14:36 - Mixed benzaldehyde with dichloromethane (1) and methanol (2).
14:38 - Added aniline dropwise to each solution. No noticeable temperature change in either. Within a minute or two, the dichloromethane mixture became cloudy and opaque. The methanol solution remained clear. Left both samples to stir, covered with parafilm.

2011-03-01 - Day 2

15:05 - Inspected the mixtures from day 1. Both mixtures were clear. Mixture 1 (dichloromethane solvent) had a bubble floating on the top. This is most likely the water byproduct of the reaction.
Mixture 1
15:55 - Dried mixture 1 with sodium sulfate. The bubble at the top disappeared. Filtered the mixture using a sinterglass funnel.
16:01 - Warmed mixture on a hot plate. Added n-hexane slowly to the solution. No precipitate formed. Heated the mixture while adding hexane in installments (~10-20mL hexane). No precipitate formed even after a roughly 4-1 hexane to dichloromethane mixture was made (the mixture was lightly boiling). Left the mixture covered in parafilm in a fume hood.
Mixture 2A
15:13 - Added mixture 2A to a 50mL round bottom flask. Started rotary evaporating. Mass of empty flask is 46.325g
16:30 - Removed (2A) from roto-vap. A non-viscous liquid was at the bottom. Mass of the flask with the mixture is 50.437g.
16:50 - Added ethanol into (2A). No solid precipitated out. Rotary evaporated the mixture. Less than a minute after the vacuum was engaged, a large amount of solid formed. Evaporated off the methanol in the flask. Added ethanol to the flask (roughly 3mL). After warming the mixture in the bath, all of the solid dissolved in the ethanol. Cooled the mixture in an ice bath. Precipitate formed in the flask. Collected the solid via filtration through a scintered glass funnel. Washed solid with cold ethanol (chilled via ice bath). Collected solid benzalaniline (2B) in a vial. Left in a desiccator under house vacuum.

2011-03-02 - Day 3

10:58 - Observed mixture (1) from day 2. No precipitate formed. Discarded mixture (1).
11:02 - Removed (2B) from desiccator, weighed. Total mass of vial and product is 14.3329. Mass of empty vial is 11.9087g.
11:05 - Liquid is visible in the vial containing (2B) after handling.
11:35 - Extracted samples of liquid from (2B) and solid from (2B), as well as samples of the reactants, aniline and benzaldehyde. Put each sample into a separate NMR tube, and added deuterated chloroform to each.
12:31 - Took NMR spectra of each sample using a 300MHz NMR.
14:19 - Added (2B) to desiccator on a high vacuum.
15:29 - Removed (2C) from desiccator - it appeared to be a dry powder.
15:36 - Took melting point for (2C). Melting point is 37-41C.
2011-03-07 - Day 4
12:03 - Put sample in high-vac
16:16 - Removed sample (now 2D) from high vac.