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18th August 2011 @ 04:05
Partial formation, microwave issues.

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See also:

Paal-Knorr Synthesis of 1-aryl-2,5-dimethyl Pyrrole Core (PMY 1-1)
Paal-Knorr Synthesis of 1-aryl-2,5-dimethyl Pyrrole Core (PMY 1-2)


Reaction Scheme PY13.png

Experiment start time: 11.55 EST 18/08/2011
4-fluoroaniline (94.7 μL, 1 mmol, 1 equiv.) and 2,5-hexanedione (117.3 μL, 1 mmol, 1 equiv.) were mixed in a microwave tube and heated in a CEM Discover microwave. Target temperature 160 °C for 20 minutes (10 minute ramp time). Measured 124 °C, 5-6 psi. Condensation observed (see image). After cooling the reaction was diluted with diethyl ether (5 mL) and dried (MgSO4). The solvents was removed under reduced pressure to obtain a brown oil (190 mg). Crude 1H NMR consistant with pyrrole, 4-fluoroaniline, and 2,5-hexanedione (46:25:29 respectively by NMR). After overnight at room temperature, brown oil now contains small amount of off-white crystalline solid.

TLC (10% EtOAc/petrol) visualised with UV and vanillin (right spot):
Crude product TLC

Notes
Microwave temperature calibration suspected to be out. Matter under investigation.

Condensation in reaction

1H NMR spectra
1HNMRcrude


Hazard and Risk Assessment:
As for Paal-Knorr Synthesis of 1-aryl-2,5-dimethyl Pyrrole Core (PMY 1-1), except no solvent.
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Attached Files
Reaction Scheme
completed reaction
1HNMRcrude
Comments
Re: Paal-Knorr Synthesis of 1-aryl-2,5-dimethyl Pyrrole Core (PMY 1-3) by Matthew Todd
18th August 2011 @ 06:17
What makes you think the temp calibration is out?
Re: Paal-Knorr Synthesis of 1-aryl-2,5-dimethyl Pyrrole Core (PMY 1-3) by Paul Ylioja
19th August 2011 @ 00:15
The microwave is using the full 300W and it is only reaching 124 °C. In experiment PY 1-1 the sample only heated to 96 °C but reached a pressure of 50 psi. The solvent mixture should have no trouble reaching 170 °C from previous experience. Also, the lab who run the microwave have reported that there are problems with it. However, if the microwave is using full power, the reaction should have no problem going to completion and possibly "past" completion.