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I'm just going to put the questions first and the explanation after in case y'all don't have the patience.

I want to know if it's reasonable to think that :

  1. Using an ultrasonic bath on something like a rotovap would prevent bumping, with the cavitation effects serving as basically the ultimate boiling chip.

  2. Whether ultrasound could be used to degas an organic solution while a reaction is occurring, in order to definitely confirm that a gas is not supersaturating the reaction mixture.

  3. Does it make any sense whatsoever that hydrogen iodide could stay in solution in toluene?

I'm considering strapping an ultrasonic transducer onto a metal pan we use as our oil bath. Is there a potential reason that this wouldn't be effective for 1) and 2)?

Context: working on a mild cannabinoid conversion (at a Canadian university, definitely not sketchy) via the following method: https://pubs.acs.org/doi/10.1021/acs.jnatprod.7b00946

Long story short, we're investigating why side products are being produced and halving the yields when any larger amounts are used in the reaction. I'm seeing brown residue (immiscible with the reaction solvent of Toluene) collect and return down the condenser into the mixture, formed via this reaction:

4 HI + O2 → 2 H2O + 2 I2

Of which the HI and H2O then form concentrated hydroiodic acid droplets which return to the mixture. I think this means that purging with nitrogen and otherwise degassing the solution is necessary. I think HI should basically boil out as it is formed due to very low boiling point and negligible solubility in toluene, so just doing it under nitrogen flow should be fine. Supervisor thinks some is sticking around in solution (which is why larger volumes at identical reagent concentrations also lower yields, as the smaller volumes means higher surface:volume and takes less time for the entire volume to boil/recondense/cycle compared to larger volumes), so basically what I'm trying to do is go so ham on degassing this solution that we can diagnose whether this is accurate.

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    $\begingroup$ Could you react the HI somehow to remove it? Long time since organic chemistry but would cleaving an ether work? $\endgroup$ – MaxW Jan 30 at 0:56
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    $\begingroup$ I can't view the full reaction procedure you are using as it is behind a paywall but if your system is generating water due to the presence of oxygen then running under nitrogen/argon should help. Can you remove the HI by running in the presence of a basic resin? $\endgroup$ – Waylander Jan 30 at 8:01
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In short, to answer your question "Why side products are being produced", you appear to have ignored all possible radical activity!

Per this source: Free radical formation from sonolysis of water in the presence of different gases, for example, to quote:

$\ce{H2O + Sonolysis -> .H + .OH}$

Here, replacing H2O with HI likely results similarly in:

$\ce{HI + Sonolysis -> .H + .I}$

Some possible further reactions:

$\ce{.H + .H -> H2 (g)}$

$\ce{.I + .I -> I2 (s)}$

And, in the presence of an organic (RH):

$\ce{.H + RH -> .R + H2 (g)}$

$\ce{.OH + RH -> .R + H2O (l)}$

$\ce{.R + .I -> RI }$

$\ce{.R + .R -> R2 (g)}$

Also, with any dissolved oxygen (or even nitrogen, see cited reference), expect even more, as for example:

$\ce{.H + O2 -> .OOH}$

$\ce{.HO2 + .HO2 -> H2O2 + O2}$

$\ce{.R + .OOH -> ROOH}$

....

As such, expect a range of products, as would occur, by the way, if you performed photolysis in lieu of sonolysis. However, there are related reactions, like in the presence of ammonia, where the final photolysis products can display a high degree of product selectivity.

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