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Advanced Organic Chemistry/ Organic Synthesis – CH 621
Ultrasound Assisted Organic Synthesis (Sonochemistry)
Bela TorokDepartment of Chemistry
University of Massachusetts BostonBoston, MA
1
Ultrasonics/Sonochemistry - Historical Overwiev
Ultrasonics
- Ultrasounds (20-10 000 kHz)
- 1880 Piezoelectricity (Curie brothers)
- 1893 Galton
- 1912 TITANIC
- 1912 Behm (Echo technique)
- 1917 Langevin (Ultrasonic variation,Icebergs, Submarines)
- 1945 Application in chemistry
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Ultrasonics/Sonochemistry – Basics
Frequency ranges of sound
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Ultrasonics/Sonochemistry – Basics
Sound transmission through a medium
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Ultrasonics/Sonochemistry – Acoustic Cavitation
Formation of an acoustic bubble
Bubble size and cavitationdynamics
Transient cavitation
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Ultrasonics/Sonochemistry – Acoustic Cavitation
Acoustic cavitation in a homogeneous liquid
Suslick - ~ 4-5000 K
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Ultrasonics/Sonochemistry – Acoustic Cavitation
Acoustic cavitation in solid/liquid system
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Acoustic cavitation in solid/liquid system
Ultrasonics/Sonochemistry – Acoustic Cavitation
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Ultrasonics/Sonochemistry – Acoustic Cavitation
Acoustic cavitation in liquid/liquid system
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Ultrasonics/Sonochemistry – Sonochemical Effect
Specific ultrasonic effect ? Yes and No
No - another internal heating approach
Yes - The temperature dependence of EA of different reactionscould be significantly different – change in selectivities
- Very effective mixing- Cavitation- Surface cleaning
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Ultrasonics/Sonochemistry – Experimental Parameters
1. Acoustic frequency
Increasing frequency – increasing energy
Theory - usually higher reaction rate
Real life – optimum frequency as we have to balance reactivity/selectivity
The effect is different for every reaction and general rule can not bemade.
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Ultrasonics/Sonochemistry – Sonochemical Effect
2. Acoustic power
Similar as frequency, however, the extent of increase is limited
Optimum
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Ultrasonics/Sonochemistry – Sonochemical Effect
3. Temperature
Cavitation bubbles – energy of collapse
Pressure inside the bubble
In general lower temperature is better, but again there is an optimum
as higher temperature increases the probability of the cavitation
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Ultrasonics/Sonochemistry – Sonochemical Effect
4. External (static) pressure
Not quite clear, but in general higher pressure is better.
Role of particles (ultrafiltration)
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Ultrasonics/Sonochemistry – Sonochemical Effect
5. Gas
Polytrop ratio (γ= Cp/Cv), thermal conductivity, and solubility
Usually inert gases are the best (noble gases)
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Ultrasonics/Sonochemistry – Sonochemical Effect
6. Solvent
Should be as inert as possible, and stable toward ultrasounds
Sonolysis of the solvent
Usually high bioling point is preferred, but it is controversial as diethylether is a good solvent in many applications.
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Ultrasonics/Sonochemistry – Experimental Parameters
Intesity of collapseLimit of transient cavitationPrimer and secondary reactions
Vapor pressureSurface tensionViscosityChemical reactivity
Solvent
Intesity of collapsePrimer and secondary reactionsThe content of bubbles
Politrop ratioThermal conductivityChemical reactivitysolubility
Gas
Intesity of collapseThe content of bubbles
Total pressureSolubility of gas
Static pressure
The content of bubbles, the intensity of collapseSecondary reactions
Vapor pressure of liquidThemal activation
Temperature
The number of cavitationphenomena in a unit volume
Size of the reaction zoneAcoustic power
Change in the size of the bubblesPeriod of bubble collapseAcoustic frequency
EffectPhysical parameterExperimental parameter
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Ultrasonics/Sonochemistry – Transducers
Galton whistle (physical)Liquid whistle (physical)
Piezoelectric sandwich transcducer Magnetostrictive transcducer
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Ultrasonics/Sonochemistry – Reactors
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Ultrasonics/Sonochemistry – Applications
- Electronics industry (coating with metals)
- Therapy (surgery with ultrasounds), diagnostics
- Food industry
- Materials (metallurgy)
- Synthesis
- Environmental applications
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Ultrasonics/Sonochemistry – Synthesis
Applications in Organic Synthesis
1. Homogeneous Sonochemistry- Aqueous medium- Non-aqueous media
2. Heterogeneous Sonochemitsry- Phase Transfer Catalysis- Reactions with metals- Heterogeneous Catalysis
3. Enzyme reactions
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Ultrasonics/Sonochemistry – Synthesis
H2OH + OH2 H2 OH2 OH2 O0,5 O2 + 2 H
H + OHH2OH2
H2O2
O + H2OO2
H2O
1.1. Aqueous sonochemistry
2 BrBr2)))
(2.8)HOOC
COOH
COOH
COOH
(2.9)
OH
COOH
)))
COOH
1. Homogeneous sonochemistry
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Ultrasonics/Sonochemistry – Synthesis
1.2. Non-Aqueous sonochemistry
1. Homogeneous sonochemistry
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Ultrasonics/Sonochemistry – Synthesis
N
R'
+I-
R
Cl3CCOONa, CH3CN
R
N
R'
CCl3
+N
R'
CCl3
R (2.14)
70-100 %
)))
(2.15)
R
I-+N
Me
tBuOK
R
N
Me
OtBu
R
N
Me
O
85-98 %
) ))
91 - 98 %
R+CH3COCH3, NaOH
))) N
Me
CH2
C CH3
O
N
Me
CH2
CCH3O
R
N
Me
+I-
R
(2.16)
1.2. Non-Aqueous sonochemistry
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1.2. Non-Aqueous sonochemistry
Ultrasonics/Sonochemistry – Synthesis
NMe
PO
OEtEtOH +
90 C, tolueneo
NHMe
PO
EtOEtO
Yield (%)15 min 30 min 60 min 120 min
stirring 0 0 <5 37sonication 12 32 67 82
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1.2. Non-Aqueous sonochemistry
Ultrasonics/Sonochemistry – Synthesis
Yield (%)
stirring 10-53sonication 57-93
R R' R"
OO
+
R"R'R
OO
+
O
O
R"R'R
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1.2. Non-Aqueous sonochemistry
Ultrasonics/Sonochemistry – Synthesis
)))
Mo(CO)6O
OHOOH + +
+ +OOHOO
O2+
+ H
OO
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Ultrasonics/Sonochemistry – Synthesis
2. Heterogeneous sonochemistry
2.1. Phase transfer catalysis
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Ultrasonics/Sonochemistry – Synthesis
2.1. Phase transfer catalysis
NaOH + CHCl3 :CCl2
Cl
Cl
74-99%0.7-5h
+ CHCl3NaOH
TEBAH CCl2H H CCl2H
stirring 9 h 15%sonication, 3h 83%
4.3 1
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Ultrasonics/Sonochemistry – Synthesis
2.1. Phase transfer catalysis
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Ultrasonics/Sonochemistry – Synthesis
2.2. Reactions with metals
R
R'O + R"-Cl
Li
)))
R
R'R" OH
10-40 min 68-99%
+ R'-ClLi, THF
)))
72-99%
RO
OLi
R
R'O
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Ultrasonics/Sonochemistry – Synthesis
2.2. Reactions with metals
EtOOCCOOEt
K, toluene
))), 5 minO
COOEt
83%Zn, DMF
)))RF-X + CO2 RF COOH
35-77%
Zn, AcOH
))), 10 minO
H
Me
Me C8H17
H
Me
Me C8H17
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Ultrasonics/Sonochemistry – Synthesis
2.3. Heterogeneous catalysis
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Ultrasonics/Sonochemistry – Synthesis
2.3. Heterogeneous catalysis
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Ultrasonics/Sonochemistry – Synthesis
2.3. Heterogeneouscatalysis
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Microwaves/Sonochemistry – References
- http://www.shiga-med.ac.jp/chemistry/sonochemRes.html
- Luche, J. L., Synthetic Organic Sonochemistry, Plenum Press, 2001
- Suslick, K. S., Ultrasound: Its Chemical, Physical, and Biological Effects; VCH, 1988.
- Mason, T. J., Sonochemistry: Current Uses and Future Prospect in Chemical and Industrial Processing, RSC, 1999
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