Tuesday, March 28, 2006

Exp 005

Purpose: To synthesize 3,4-dihydroxyphenylacetaldehyde from adrenaline. How this fits into the synthesis of anti-malarials is explained here. In a prior attempt using glacial acetic acid as the main solvent, monitoring by TLC and IR was problematic. In this attempt benzene will be added and samples drawn from the top benzene layer should be easier to chromatograph and follow by IR. Also since benzene boils near 80C it will be convenient to reflux at a lower temperature.

Procedure: Benzene (12 mL), glacial acetic acid (12mL), 6M sulfuric acid (1.5mL) and adrenaline (51.7 mg, 0.282mmol) are stirred and refluxed in a 50mL flask under nitrogen.

Discussion and Conclusion

The video after 60 minutes shows that a small brown layer separates at the bottom of the flask, suggesting that it contains only the aqueous sulfuric acid dissolving the adrenaline. Since the point of adding the benzene was to extract out the resulting aldehyde from the acetic and sulfuric acids, this didn't work. The acetic acid is clearly favoring the benzene layer. The heavy streaks in the TLCs are consistent with this.



12:15) Mixed chemicals and turned on heating mantle at 80 degrees C. A sample of 1mL, t=0 (5A) was taken and as expected there was some separation. The bottom layer was brownish in color while top layer was clear.

12:46) Sample 5B or t= 30 min was taken. Still under N2, the flask was allowed to cool to take the sample. The solution did not separate in the amount of time lotted in any visible way. Sample does not separate. TLC of 5A(t0) vs 5B (30 min) with methylene chloride (MC) as eluent was put in iodine chamber.

13:15) Sample 5C (t=60 min) was taken. Still no clear separation in the solution, although the solution itself is clear except for the adrenaline which has not dissolved. Video at this time shows that a small brown layer settles at the bottom of the flask when stirring stops.

13:35) Sample 5D (t=80min) was taken. Reflux solution remains the same, samples turn somewhat cloudy in atmosphere. After a while cloudiness dissipates and sample is clear. Pic of TLC 5A (t0) vs 5C (60min) and 5D(80min) (5D plate is on the left and on each plate 5A is on the left).

14:20) TLC of 5A vs 5B, 5C and 5D was made in 1:1 (MC/hexanes) and is similar to pure MC

14:45) Sample 5E taken t=2.5hrs. Refluxed stopped and solution saved. UV lamp is needed. TLC's reveal after several minutes in iodine chamber what would be a moving streak surrounded by the iodine coating. Streaks of 5B-E against 5A are higher.


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