Using MICROWAVE REACTOR

1. Using MICROWAVE REACTOR Krystyna R. Brzezinska Materials Research Laboratory

2. 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 bar20 bar = 290 psi, 250 psi = 17 bar Microwave

3. Mechanism of Microwave Heating Dipolar oscillation Ionic conduction Molecular Orientation = Molecular Friction = Heat

4. Speed Up Chemical Reaction? • Temp. up to 250 oC and pressure up to 20 bars • Heat much faster than the conventional reaction. Vials: 0.2-0.5 ml, 0.5-2 ml, 2-5 ml, 10-20 ml

5. Polar Solvents • 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! • Decrease initialpower use: • ‘Sample Absorption’ - High or Very High. • Dilute reaction mixture.

6. Less Polar Solvents Less polar solvents (e.g. toluene, dioxane, THF) • Heat poorly • Concentrate the reaction mixture • - speeds workup • - lower cost of ‘waste’ solvent removal • Add polar co-solvent • Increase ionic concentration

7. Solvent polarity Effect of a co-solvent Set temp: 200 °C 4.5 mL Toluene 4.0 Toluene + 0.5 mL DMF

8. Reaction rate? Arrhenius Equation: K = A e–DG/RT Reaction rate ~ doubles for every 10 oC temperature increase

9. Using the 10o Rule to determine a starting point K = A e–DG/RT

10. Prepare Three Vials 180oC 5 min 160oC 5 min 140oC 5 min First Choice

11. Temperatures and pressures measured* with some common organic solvents _______________________________________________________________________________________________ Solvent BP Temp Pressure** (°C) (°C) (bar) _______________________________________________________________________________________________ N,N-Dimethylformamide (DMF) 153 250 5 Water 100 220 16 Ethanol 78 180 16 Methanol 65 160 17 N-Methylpyrrolidinone (NMP)202 220 5 Ammonium hydroxide (28%) - 15019 Dimethylsulfoxide (DMSO)189 250 5 Pyridine 115 220 8 1,2-Dimethoxyethane (DME)85 200 6 Dichloromethane 40 140 15 Acetonitrile 86 200 10 o-Dichlorobenzene 190 250 2 1,4-Dioxane 101 200 4 Acetone 56 150 5 Tetrahydrofuran (THF) 65-67 180 12 Xylene 137-138 150 2 1,2-Dichloroethane 83 170 2 Toluene 110 170 4 Diethyl 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 using different reaction conditions and compositions. Red indicates good microwave absorption, while Blue indicates less good**Volume = 2.5 mL

12. Reaction is not proceeding at all or not going to completion: • Increase temp. (limit is pressure buil-up in the vial and security max = 250 oC). • Extend reaction time. • Increase initialpower ‘Sample Absorption’ – Normal, High or Very High • Increase concentration. • Use more polar solvent (water at high temp become less polar). • Add polar co-solvent

13. Decomposition: • Lower temperature. • Increase initialpower ‘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.

14. Questions? Please contact Krystyna (kbrzez@mrl.ucsb.edu) -------------------------------------------------------------------------- Login: Faces Scheduling System Group: MRLPOLY User name: kkk@ Password: system will generate for you Account: 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.