sonochemistry.pdf

7/28/2019 sonochemistry.pdf

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Sonochemistry


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Introduction, background

How it works

Specific reactions

others are not


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Enhances reaction rates up to a million times

Believed to be due to small cavities (100microns) which implode, creating tremendousheat and pressure, shock waves, and particle

accelerations. This process is calledcavitation

Started gaining attention for organic chemists

formed cavities


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Name of sound with frequency above

normal human hearin 20kHz BTW, sound is waves of compression and


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arms

Dog whistles Tooth brushes

Cleaners

Medical uses Allows bats to hunt insects

Cell phone ring tones for teenagers (old peoplecant hear the hones rin in

Detecting submarines


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Sonochemistry, destroyer of

destroyers During the testing of torpedo boats in 1894

the British noticed severe vibrations of theships along with erosion of the propellers

,cavities, from spinning propellers

Simple solution: larger propellers and


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oa s go gger, an e pro em go

worse Lord Rayleigh (NP 1904) was asked to

investi ate

He confirmed bubbles imploding on the.

also blamed bubbles for the sound a tea

The effect was named cavitation


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-

Shiny new Francis turbine Turbine destroyed by cavitation


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1927-beginning of intercontinental

flight and sonochemistry Loomis reported beneficial uses of

ultrasound to chemistr such as Ever so slightly depressing boiling points

Expulsions of supersaturated dissolvedgasses

Increases in the rate of hydrolysis of dimethylsulfate

J ACS 49, 3086


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Sonochemistry involves high energies and

ressures on a short time scale Photochemistry interacts with chemicals

,thermochemistry interacts on a long timescale at lower energies


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Tensile strengths of liquid important

strength of liquid, cavities form

uc ea e process; w ou wea po n s,ultrasound could not form cavities

Dissolved gasses often help for cavities,

Every solvent forms cavities, not just water

J. Phys. Chem. A 2006 110, 10720


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Black: bulk li uid, ambient tem erature

Cavity Imploding cavity

Red: supercritical fluid 1900 KWhite: cavity with some gas 5000 K


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More void the cavity, the hotter it becomes

u on colla se Vapor pressure important

ower vapor pressure so ven s ea o o ercavitation

Lower temperature solvents foster hotter

cavitation


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Aqua blue: bulk liquidBlue: supercritical fluidWhite: cavity

Magenta dots in cavity: gas


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Do your sonication experiments cold

,the higher boiling

you wan o supe -c arge your reac on,bubble some Xe through the solution, as ittransfers heat fairly terribly


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With solids present, collapsing bubbles

chan e No longer symmetric, they deform,

towards the solid

Effects: removes oxidized outer layer


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J et of hot liquid shooting towards a

metal


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e a par c es on e or er o u es

wont produce hot jets Shock waves propel metals at really fast

s eeds which can collide with other

metals

pchem, Suslick and coworkers determined

temperatures of 3,000k


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J ACS 102, 7926


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J ACS 104, 6879


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J OC 71, 5179


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-

J ACS 126, 24 J ACS 125, 13624

D ti d ti i hi d d


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Dramatic reduction in hindered

Mitsunobu reaction rate

J OC 68, 8261

A t US ff t i h l t d


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Apparent US effect in halogenated

solvents actually not that cool

When HCl gas bubbled in, results were identical to sonication

J OC 61, 2547


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Nature, 446, 423


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mechanical forcebiases reaction

pathway to products thates re eve n uce s ra n


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. . . .

Chanon published a paper in 1985

accordin to which sonication should beable to modify significantly electron

Two possibilities of Barbier


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Two possibilities of Barbier

coupling


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Tet. Lett. 31, 7619; Tet. Lett. 29, 4125

Luche develops a new


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Luche develops a new

interpretation uc e c ass e organc sonoc emca

reactions by types Heterogeneous reactions were sped updue to mechanical effects of the sound

waves (agitation, cleaning effects)

due to generation of radicals

rue sonoc emca reac ons are osewhich involve a SET

Tet. Lett. 29, 4125


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ro e omogeneous reac ons nown o averadical character with US and without

and ionic mechanism. Termed sonical switching

If he is correct he would have opened a door toimproving many reactions HWE

Cope

Testing US with known anionic


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Testing US with known anionic

reactions

Known to react purely via anionic mechanism

Ultrasound had no effect on rate or yield (score one for Luche)

Tet. Lett. 29, 4129


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Tet. Lett. 29, 4129


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,

Coll. Czech. Chem. Comm 47, 1334: Tet. Lett. 31, 4125


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Tet. Lett. 29, 2183; J OC, 51, 271; J OC51, 271


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Luche argued carbohydratechemistry enhanced with US

mixing


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Luke, Timmy


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Me, today in lab


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US accelerates reactions due to cavitation

Can also be due to promotion of SET


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ow ey e ermne e empera ure:

J ACS 126, 13890; Science 247, 1067;Science 253, 1397; J ACS 105, 5781;J ACS 105, 6042; J ACS 106, 6856

Bubble dynamics: Am. J . Phys. 68, 211

Energy Chemistry 38, 135

va sonoc ems ry: , ;J ACS 104, 3987

Special thanks to Dee and Mark

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