Reflux under pressure

Ok so I refured to the tech of refluxing under pressure a few times these past few days and since I am no chemist
But sure that this helps with higher yields I would like to hear the pro s and con s of this tech espesialy from chemist and those that know more of the how and why
The concept is simple take a cls terpenator style cls rig and use the collection pot as your boiling flask and a sleeved biomass tube as your condensor
Have some prv installed and for internal agitation I place the cls rig on a magnetic storing heat plate
I place my compounds inside pull a vac depending of solvents till boiling let some boiling take place to make sure all air is out then backfill with argon or nitrogen to 60 psi up to 90 psi
Have had pressure surges of 140 psi
Sort of like bumps at times but in general pressure stays stable


So who s got info as to why isomerization reactions work better under pressure
@Photon_noir @davidb @qga @richpel @Krative @ScoobyDoobie

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Very cool but I’m wondering how you could regulate temp in the vessel.

Do you think it would be possible to use some kind of custom triclamp metal thermowell?

Yes you can use a termo well the small sight glass on this rig I use as the termowell with a din coupling
I am using this rig for it s base plate is of thinner steel than the welded version hence the stirbar functions properly
You can. Barely see it but that’s a spinning stirbar in the center

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What temp do you keep the condenser at?

Dri ice slurry acetone

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Good question, my initial response was going to be that when you increase the pressure you are reducing the volume of the reactants but after thinking about it I dont think that this concept really applies here since we’re working with solid and liquid reactants not gasses.

@RockSteady is another good head to bring in. @eyeworm too

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I am defenatly rising boiling points
Have had heptane well over 120C dead flat

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by work better do you mean the speed or the overall yield of the reaction? (or both)

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The dielectric constant of a given solvent is dependent upon pressure so maybe that’s got something to do with it? Wish I could help you more but that’s just not something I’ve read about yet. Might as well start now I guess :man_shrugging:

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Both but mostly yield
Making d9 from cbd gets me 93% thc and 4% cbn a very few minors
Time seems shorter to but haven t fine tuned that

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That’s a good lead thx
@Photon_noir reveal yourself please :hugs:

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Have you noticed the yields change significantly between a higher pressure reflux and a lower pressure reflux?

If a reactant were to be a gas then adding pressure would be as simple as pushing the reaction forward, but that’s not the case here. Are your temps remaining constant between high pressure and low pressure reflux? Because that would also be am obvious factor

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Yes
On cbd >d8 full conversion
On cbd>d9 as posted
On thc9>cbn 92%
On thc remediation the stuburn last 0.4% is gone under pressure

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Yes I yust follow same sop as under normal pressure with same temps

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At a fixed volume, pressure is directly proportional to the temperature. p/T is a constant.

Heat applied to a system of chemical reactants will speed up the motion of molecules within that system; this increases the frequency and force with which the molecules collide.

Increasing the pressure on a system has the same effect.

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That’s what I was thinking, the pressure has to be somehow increasing the frequency of significant collisions between reactants

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You could repeat the experiment in octane at ambient pressure at reflux (125 C) and see if youre JUST realizing the gains of increasing the reaction temperature (the assumption being that octane is just high boiling heptane in terms of its role in this reaction, which I think is a fair assumption). I dont think the pressure itself is doing any sort of chemistry, both because its a gas above a liquid (the chemistry takes place in the solution, not above the solution) and because youre pressurizing gas is inert. My best guess is youre just running the reaction hotter by raising the boiling point of heptane (if you are indeed at reflux).

I’m doing my best to get details from the comments but I’m getting conflicting information, or misunderstanding. You’re comparing a room temperature heptane reflux reaction (by definition of reflux, the reaction in heptane must be a temperature of ~98 C at 1 atm) versus the SAME reaction run at reflux under pressure (if this is indeed at reflux, the temperature of the solution must be hotter than 98C). So the question is, are you actually running both reactions here at 98C or are both reactions being run at reflux (one at 98C and one at a temperature greater than 98C)? This detail is sort of the heart of your inquiry as reaction temperature has everything to do with rate and the products formed.

Also, I dont know what your actual reagents, quantities and conditions are here - they aren’t specified. Obviously CBD in some volume of heptane, but surely there is some reagent? I know some folks heat their oil in the presence of carbon and call that a process - is that the case here?

Last thing, to do a TRUE comparison you need to define a control by running the exact same reaction with the exact same lot of reagents/solvents side-by-side. Even different lots of heptane for instance could confound your results.

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Pretty sure the liquid is also under pressure thus packing molecules closer to one an other etc etc
And also pretty sure that by lowering bp deu to pressure
The reaction benefits
Good example is with the cbd>d9 reaction using dried methanol instead of heptane
Able to push the reaction at 100C at 160 psi ( please don t try need at least 48" sleeved jacket )

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Liquids aren’t known to be particularly compressible. Many fluid flow calculations assume densities to be constant under a pretty wide range of pressures (assuming constant temperature), for instance. If you were miraculously compressing the solution by a factor of 10 (effectively upping the concentration from 100 mg/mL to 1000 mg/mL, for example) then sure maybe that’s impacting the reaction by making it less dilute and increasing probability/frequency of collisions. But you aren’t doing that here - you aren’t even compressing that liquid by a factor of 2. I would be surprised if you were compressing the reaction mixture by a factor of 1.05.

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