Microwave Synthesis Anton Paar

44 Pages·2011·3.27 MB·English

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A Success Story
of more than 85 Years
1922 The one-man business Anton Paar is founded
1957 Production of Kratky small-angle X-ray scattering camera
1963 † Anton Paar; Ulrich Santner joins the company
Presentation of the first digital density meter based on the
1967
oscillating U-tube principle
1997 Dr. Friedrich Santner becomes CEO
2004 New ownership: The charitable Santner Foundation
2010 Establishment of the 13th subsidiary, AP Switzerland AG
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Microwave-Mediated Heating Process
Dipolar Rotation Ionic Conduction
(cid:1) (cid:1)
Dipoles align in Electromagnetic Field Ions oscillate in Electromagnetic Field
(cid:1) (cid:1)
Rotation (cid:1) Friction Rapid movement (cid:1) Friction
(cid:1) (cid:1)
Heat transfer Heat Transfer
(cid:1) (cid:1)
Effectiveness is a function of Effectiveness is a function of
Dipole moment Concentration
(cid:1)
direct „in-core“ heating (generated from within the sample)
(cid:1)
Interaction with MW determined by Loss Tangent (cid:2)(cid:2)(cid:2)(cid:2)tan (cid:3)(cid:3)(cid:3)(cid:3) (cid:4)(cid:4)(cid:4)(cid:4) (cid:5)(cid:5)(cid:5)(cid:5)‘‘ (cid:6)(cid:6)(cid:6)(cid:6)(cid:5)(cid:5)(cid:5)(cid:5)‘(cid:7)(cid:7)(cid:7)(cid:7)
= Measure for conversion of electromagnetic energy into heat
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Loss Tangents of Different Solvents
(2.45 GHz, 20 °C)
Loss tangent, tan (cid:3)(cid:3)(cid:3)(cid:3)
(cid:2)
defines ability of materials to convert electromagnetic energy into heat energy
at given frequency and temperature
“High“ (> 0.5) “Medium“ (0.1-0.5) “Low“ (< 0.1)
Solvent tan (cid:3)(cid:3)(cid:3)(cid:3) Solvent tan (cid:3)(cid:3)(cid:3)(cid:3) Solvent tan (cid:3)(cid:3)(cid:3)(cid:3)
ethylene glycol 1.350 2-butanol 0.447 chloroform 0.091
EtOH 0.941 dichlorobenzene 0.280 MeCN 0.062
DMSO 0.825 NMP 0.275 EtOAc 0.059
2-propanol 0.799 acetic acid 0.174 acetone 0.054
formic acid 0.722 DMF 0.161 THF 0.047
MeOH 0.659 dichloroethane 0.127 DCM 0.042
nitrobenzene 0.589 water 0.123 toluene 0.040
1-butanol 0.571 chlorobenzene 0.101 hexane 0.020
from “Microwave Synthesis“, Hayes, B., CEM Publishing, Matthews, NC, 2002 Chapter 2
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Conventional Heating by Conduction
(cid:3)
Conductive heat
(cid:3)
Heating by convection current
(cid:3)
Slow and energy inefficient process
Temperature on the outside surface is far higher than the real internal temperature
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”Direct” Heating by Microwave Irradiation
(cid:3)
Solvent/reagent absorbs MW energy
(cid:3)
Vessel wall transparent to MW
(cid:3)
Direct in-core heating
(cid:3)
Instant on-off
Inverted temperature gradients !
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Benefits of MW-Assisted Synthesis
Boiling over night
Controlled reactions within a few minutes
300 30
C] ar]
° b
er [W]ature [ 200 20 sure [
wr s
Pompe 100 10 Pre
e
T
0 0
0 150 300 450 600 750 900
Time [s]
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Benefits of MW-Assisted Synthesis
Arrhenius Equation :
(cid:1)
Rule of thumb:
–E /RT
a 10 °C temperature increase
k = A*e
= 2-fold rate acceleration
Increasing temperature
80 °C 90 °C 100 °C 110 °C 120 °C 130 °C 140 °C 150 °C 160 °C
8 h 4 h 2 h 1 h 30 min 15 min 8 min 4 min 2 min
Decreasing reaction time
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Benefits of MW-Assisted Synthesis
(cid:1)
Energy efficient direct “in core heating”, rapid energy transfer
(cid:1)
no temperature gradients (possibility of wall effects excluded)
(cid:1)
Enhanced temperatures, rapid superheating of solvents in sealed vessels
(cid:2)
easy access to high pressures (autoclave-like)
(cid:1)
Faster reactions, higher yields (less byproducts), pure compounds
(cid:1)
Rapid reaction screening and optimization of conditions
(cid:2)
ideally suited for automation and parallel synthesis
(cid:1)
Selective heating (activation of catalysts), specific effects
(cid:1)
Excellent control over reaction parameters (instant on/off)
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Microwaves in Organic Synthesis
1986 first relevant publications
“The Use of Microwave Ovens for Rapid Organic Synthesis”
Gedye, R. N. et al. (Laurentian University, Canada)
Tetrahedron Lett. 1986, 27, 279.
“Application of Commercial Microwave Ovens to Organic Synthesis”
Giguere, R. J. (Mercer Univ) and Majetich, G. (Univ Georgia)
Tetrahedron Lett. 1986, 27, 4945.
up to 1000 fold rate increases for several reactions reported !
Earlier Patent Literature
“Carrying Out Chemical Reactions Using Microwave Energy”
Vanderhoff, J. W. (Dow Chem Co), US 3,432,413 (1969)
see also: US 4,210,593 (1981), DE 3,018,321 (1981)
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