Advanced Organic Chemistry/ Organic Synthesis –...

Advanced Organic Chemistry/ Organic Synthesis – CH 621

Ultrasound Assisted Organic Synthesis (Sonochemistry)

Bela TorokDepartment of Chemistry

University of Massachusetts BostonBoston, MA

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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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