Ryszard Kapuściński, Krystyna Strączek, "Rwący nurt historii"
Using MICROWAVE REACTOR Krystyna R. Brzezinska Materials Research Laboratory.
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Transcript of Using MICROWAVE REACTOR Krystyna R. Brzezinska Materials Research Laboratory.
Microwave
• Collective name for electromagnetic irradiation with frequencies in the range of 0.3-300 GHz.• To avoid interferences between applications - 2.45 GHz corresponding to wavelength 12.2 cm.• temp: 60-250 °C, temp increase: 2-5 °C/sec• Power: 0-300 W at 2.45 MHz Pressure: 0-20 bar• Pressure: 0-20 bar 20 bar = 290 psi, 250 psi = 17 bar
Dipolar oscillation Ionic conduction
Mechanism of Microwave Heating
Molecular Orientation = Molecular Friction = Heat
Temp. up to 250 oC and pressure up to 20 bars Heat much faster than the conventional reaction.
Speed Up Chemical Reaction?
Vials: 0.2-0.5 ml, 0.5-2 ml, 2-5 ml, 10-20 ml
Polar solvents (e.g. DMF, DMSO, ROH etc.) Heat rapidly. Same concentration as conventional reaction.
Polar solvent with high ionic content (e.g. DMF + K2CO3 etc)Heat VERY rapidly and may overshoot set temperature.
Temp too high!
Polar Solvents
• Dilute reaction mixture.
• Decrease initial power use: ‘Sample Absorption’ - High or Very High.
Less polar solvents (e.g. toluene, dioxane, THF)
Less Polar Solvents
• Concentrate the reaction mixture- speeds workup- lower cost of ‘waste’ solvent removal
Heat poorly
• Add polar co-solvent
• Increase ionic concentration
Reaction rate?
Arrhenius Equation: K = A e–G/RT
Reaction rate ~ doubles for every 10 oC temperature increase
Temperatures and pressures measured* with some common organic solvents
______________________________________________________________________________________________
_Solvent BP Temp Pressure**
(°C) (°C) (bar)______________________________________________________________________________________________
_
N,N-Dimethylformamide (DMF) 153 250 5Water 100 220 16Ethanol 78 180 16Methanol 65 160 17N-Methylpyrrolidinone (NMP) 202 220 5Ammonium hydroxide (28%) - 150 19Dimethylsulfoxide (DMSO) 189 250 5 Pyridine 115 220 8 1,2-Dimethoxyethane (DME) 85 200 6Dichloromethane 40 140 15Acetonitrile 86 200 10o-Dichlorobenzene 190 250 21,4-Dioxane 101 200 4Acetone 56 150 5Tetrahydrofuran (THF) 65- 67 180 12Xylene 137-138 150 21,2-Dichloroethane 83 170 2Toluene 110 170 4Diethyl ether 35 135 4*This is a general table with data generated under various reaction conditions. The actual temperature and pressure achieved with a given solvent might differ significantly usingdifferent reaction conditions and compositions. Red indicates good microwave absorption, while Blue indicates less good **Volume = 2.5 mL
• Increase temp. (limit is pressure buil-up in the vial and security max = 250 oC).
• Extend reaction time.
• Increase initial power ‘Sample Absorption’ – Normal, High or Very High
• Increase concentration.
• Use more polar solvent (water at high temp become less polar).
•Add polar co-solvent
Reaction is not proceeding at all or not going to completion:
• Lower temperature.
• Increase initial power ‘Sample Absorption’ – Normal, High or Very High
• Shorten reaction time. Product is actually formed, but then decomposes rapidly at elevated temperatures.
• Decrease concentration.
• Change reagents.
Decomposition:
Please contact Krystyna ([email protected])--------------------------------------------------------------------------Login: Faces Scheduling SystemGroup: MRLPOLYUser name: kkk@Password: system will generate for youAccount: please send request to Krystyna by E-MAIL----------------------------------------------------------------------------Go to: http://microwave.mrl.ucsb.edu/ Instrument options: status, results, online help, print etc from your office Please clean memory of the Microwave R.
Questions?