[curiouscat]

I've seen a bunch of articles describing sonication / acoustic horns etc. as a  reaction enhancement strategy. Some of the results do seem impressive but  I'm still a bit lost about the big picture.

i.e. Which reactions or classes of reactions are good candidates for this approach? Is there an underlying strategy; the literature seems to be a hodge-podge of various reactions where it just so happened to work.

Also, has this stayed an academic curiosity still or are there any industrial scale applications?

[DrCMS]

From memory of the guy doing a PhD about this on the bench behind me nearly 20 years ago using ultrasonic baths or an ultrasonic probe and Suslick reactors it was solid/liquid reactions or two immiscible liquid reactions that showed the biggest and most consistent improvements.  I think with some other reactions he got some great results, some odd results and some poor results.

[fledarmus]

There were a couple of theories current when I was a grad student and this was a big area of research. One was that it was useful for solid/liquid reactions as DrCMS suggested. The pressure waves from the ultrasound were supposed to break up the solid particles exposing greater surface area for reaction. There may be some truth to this.

The other reactions that it was supposed to work well on were reactions with rates that were increased by increasing pressure. Again, the theory was that the ultrasound created tiny areas of greatly increased pressure, and the rate of reaction would be increased in those areas. I find this reasoning somewhat questionable.

I tried a few sonication reactions at that time but was never able to see any robust effect, even duplicating literature results. I suspect that a substantial portion of the literature of sonication reactions is bogus. Sonication does increase the rate of dissolution of solids in liquids, probably due to micro-mixing and the disruption of solid particles by pressure waves, which makes it useful for cleaning purposes and for preparing colloids, but I haven't seen much use for it in running chemical reactions.

[curiouscat]

Yes, I have my suspicions too whether it is bogus. Which is why I posted here to ask. I'm still undecided.

Also, I thought most liquid-phase reactions were substantially pressure insensitive, so I've a hard time imagining why that'd work.

What I really wish for is a study on Liq-Liq reactions that compared stirring versus sonication.