05-24-02 13:22
No 313715
Since Swim has one last time decided to break out the ol hydrogenator for a final hurrah. Since swim has not seen any info here on this method Swim has decided to post it for all.
Hydrogenation of MDP2P to MDMA.hcl via hydrogenation with Rainey Nickel Catalyst.
Preperation of Rainey Nickel catalyst.
* Caution-Rainey Nickel is pyroforic meaning it will explode in air so this must be done in an inert atmosphere.
All Rainey Nickel Swim has recieved has been shipped stored in Water. This water must be removed for even microscopic levels will cause this reaction to fail.
The Rainey Nickel is strained off then soaked in Anhydrous MeOH. This is to pick up any H20 and also strip off any extra electrons that might lessen its activity during hydrogenation.
The MeOH is strained and dried off then once again soaked in MeOH. This time the mix is flushed with Iodine in a 1.5% in wieght of Cat to Iodine ratio. This is to buffer the molecules we want during the reaction. The MeoH is strained off and Cat is dried and is now ready for use.
Preperation of Ma.hcl to Liquid to Gas
Into a 22L vessel
4600g Ma.hcl
3000ml DH20
7000g KOH pellets (60% volume to H20)
Stirred via Overhead stiirer till it starts to thicken.
4000ml DH20 added and stirring continued
After most gas has been released then 2L 50% Noah solution is added via sep funnel to liberate the last of the gas.
The solution is heated to boiling (100C)
The gas now created is now passed through a first a friedrich condensor then through a coil submerged in a bucket of dry ice. The now liquid Ma.hcl is now collected in a recieving tank.
After the last of gas is formed it the vessel is slowly purged with Argon to liberate the last of the gas and the recieving tank is vented and closed.
You should have 30-50 lbs/psi a 20C.
The tank is now heated to 100C to produce 400psi/lbs.
You should have about 2000g of gas from this.
Ma Bleed In.
The tank containing your gas is submerged in a warm bath. The gas is then slowly let of through a packed vessel containing KOH and glass to a vessel containing Anhydrous MeOH in an ice water bath. This vessel should be on a tared scale to measure absorption of gas.
You should bleed in at a rate of 1g a minute and should shake MeoH every 5 minutes or so to move around the gas.
HIGH PRESSURE HYDROGENATION
In a 25L Hydrogen Bomb Rated at: 304 stainless steel tank with 1/2 inch walls, working pressure of 1500psi and a burst rating of 6000psi place in this order:
-Load 392.5g of Cat
-Load 3002g of MDP2P
-Load a chilled solution of 7515g Anhdryous Meoh and 672.5g of Ma gas
2. Close your tanks
3. Fill up tanks with 350psi of hydrogen. No heat or rotation yet. Purge of Hydrogen slowly. This is to remove O2 in tanks. Submerse your bleed off into a bucket of water to disperse hydrogen. No sparks or flame here.
4. Fill tanks to 700psi. Set rockers to Medium Swish. Set heating devices to full. AFter 1 hour Your internal heat should rise to 125psi. The pressure should build to 1200psi due to heat and expansion. The reaction presure should then fall to 900psi as the hydrogen is taken up so manually bring it back to 1200 psi. The reaction will continue to eat up hydrogen till it reaches 150psi so you will have to adjust level of hydrogen to maintain 1200psi. Level off heat at 155C. Once it heats to 155C let it rock for 5 hours then take of heat. Let it cool to room temperature while barelly rocking. While on cool down shut off hydrogen on tanks but leave pressure alone. Once cool slowly bleed off hydrogen.
-The contents were poured into a 50L jug and tanks rinsed 3x500ml MeoH.
-Strained though filters to remove Cat
-Contents acidified to PH 3-4
-Vaped down to leave you with a dark cherry colored liquid
-Washed 3x3l tolune
-Basified to Ph 11-12
-Extracted 3x3.5L tolune
-Washed 2x saturated Brine solution
-Dried with 5lbs Sodium sulfate
-Then Vac distilled to get product oil
-Oil taken up in 20L MeOH
-MeOH submerged In a dry ice bath and 37% Hcl added to Ph6
-MeOh is Vaped off and Crystals left are washed once with dry ice cold acetone and dried
-TOTAL YIELD 2980g of Snow white MDMA.hcl
(Chief Bee)
05-24-02 16:20
No 313771
Nice writeup, but due to your not-so-perfect english (as well as frequent factual errors) I wonder if this procedure is authentic - have you actually performed this?
If it is authentic, and you clarify the write-up by answering the questions below and incorporate them into a rewitten procedure, I'll gladly post it on my page. Do you have any literature references for the reaction?
Rainey Nickel is pyroforic meaning it will explode in air so this must be done in an inert atmosphere.
It's spelled Raney Nickel, and pyrophoric. Inert atmosphere is good, but a bit overkill, as pyrophoric only means spontaneously inflammable, not that the catalyst will explode. As long as the catalyst is kept wet (with either water or methanol), there is no danger of ignition.
The Rainey Nickel is strained off then soaked in Anhydrous MeOH. This is to pick up any H20 and also strip off any extra electrons that might lessen its activity during hydrogenation.
I can understand that you rinse the water off the catalyst with MeOH, but what do you mean with "stripping off electrons"?
This time the mix is flushed with Iodine in a 1.5% in wieght of Cat to Iodine ratio. This is to buffer the molecules we want during the reaction.
This is very unclear. Do you rinse the catalyst with an 1.5% solution of I2 (how much solution, what solvent?), or do you mean that every gram of catalyst is treated with 15mg I2 (if so, how is this performed?).
What actual chemical process does "buffering molecules" correspond to, what is the purpose of doing it, and what molecule is buffered?
Can the catalyst be reused with similar activity? If so, how many times, and is it regenerated in the same fashion as above between the runs, or is there any special treatment necessary?
Into a 22L vessel
4600g Ma.hcl
3000ml DH20
7000g KOH pellets (60% volume to H20)
Stirred via Overhead stiirer till it starts to thicken.
Mixing all that at once will result in a huge cloud of methylamine gas evaporating right in the face of the chemist. Describe the order of addition, and detail the equipment/apparatus used for liquefying the gas without expelling it into the atmosphere. What kind of tank can hold 400psi? What was used as coolant in the Friedrich condenser, and what's its purpose - just to pre-cool the MeNH2? The coil between the Friedrich and the tank, is that a Graham condenser cooled with a dry ice solution pumped through, or a vertical unjacketed glass coil submerged in the cooling bath (if so, how long was it)?
The now liquid Ma.hcl is now collected in a recieving tank.
I assume you mean liquid MeNH2 freebase?
You should bleed in at a rate of 1g a minute and should shake MeoH every 5 minutes or so to move around the gas.
In the MeNH2 freebase preparation step, you made 2000g MeNH2, and in the reduction step below, the concentration of MeNH2 in MeOH is 12.2% - that is the concentration we are aiming for here, or? Making a 12.2% solution from 2000g MeNH2 equals a volume of 16.4 LITERS - how are you supposed to shake that, especially inside an ice-bath? I guess overhead stirring should be better, or to run 5 or more smaller batches, using magnetic stirring. Did you use a fritted glass gas disperser or just a thin tube when bubbling the MeNH2 through the MeOH?
Load 3002g of MDP2P
How pure was the ketone (analytical assay, or distillation range/color)? Prepared using what method?
In a 25L Hydrogen Bomb Rated at: 304 stainless steel tank with 1/2 inch walls, working pressure of 1500psi and a burst rating of 6000psi
Is this an item of commerce? What kind of valves are used? If not a commercial hydrogenator, how do you determine the working/burst ratings? Does it come with an emergency valve, and what rating should that have?
Submerse your bleed off into a bucket of water to disperse hydrogen.
Why? Hydrogen is not especially soluble in water. Is it to absorb MeNH2 gas? Is a water trap in order, due to the high solubility of MeNH2?
-Load a chilled solution of 7515g Anhdryous Meoh and 672.5g of Ma gas
About how cold should the methanolic MeNH2 be? Shouldn't the hydrogenator apparatus also be chilled, so that the added MeNH2 doesn't evaporate prematurely?
Set rockers to Medium Swish. Set heating devices to full.
Could you express "medium swish" and "full heat" in metric units, as in RPM and Watts? How is the hydrogenator heated? Internal coils (oil or electric), heating tape or something else?
Once cool slowly bleed off hydrogen.
Again bleed by bubbling through water? With a water trap?
Strained though filters to remove Cat
Gravity or suction filtration? Does regular filter paper work here, or does it plug up due to the finely powdered catalyst? Did you use any filter aid like Celite, Florisil etc?
Contents acidified to PH 3-4, Evaporated down to leave you with a dark cherry colored liquid
What concentration of which acid do you suggest? Evaporated at atmospherical pressure, or with vacuum? What is the approximate target volume after evaporating?
Washed 2x saturated Brine solution
Suggested volume of the brine washes?
-Oil taken up in 20L MeOH
-MeOH submerged In a dry ice bath and 37% Hcl added to Ph6
-MeOh is Vaped off and Crystals left are washed once with dry ice cold acetone and dried
This is not good laboratory practice, you should at least recrystallize your product (from minimum amount of boiling methanol, IPA or Acetonitrile), alternatively dissolve your freebase in 10L IPA, acidify with ~1300ml 37% HCl and then slowly crash out the MDMA.HCl by adding 15L diethyl ether, one liter at a time with good stirring, followed by cooling of the solution and filtering. Distilling off the ether for reuse, and evaporating the IPA gives an additional 10% of crude product which can be purified by recrystallization as mentioned earlier.
TOTAL YIELD 2980g of Snow white MDMA.hcl
12.97 mol MDMA.HCl from 16.85 mol MDP2P equals 77% yield - pretty good. What was the yield/weight of the freebase before the crystallization step?
(Hive Bee)
05-26-02 00:51
No 314343
Sorry Rhodium about the grammar and like. Currentlly Swim has limited access to a computer and speed of connection is 56K. This was attempted 3x after bieng frustrated with bieng booted because of dialup hurried the writeup along. Swim thought of perhaps emailing it first to a mod but did not know when Swim would be able to reply to any questions. Swim is surprised by no other posts here about high pressure hydrogenation. There has been talk about using Raney nickel as cat for hydrogenations but have not seen any writeups on it but this was the way Swim learned step by step years ago. Didnt have any real interest in pursuing any other aspects of chemistry back then but just followed instructions and simple basics. I would edit it with the corrections needed but for some reason it is not giving me that option on my screen.
But to answer your questions.
The Raney Nickel I was told had to have the activity lessoned. When shipped It is Activity level around 10 the activity level has to be around 6 for the hydrogenation. The soaking in MeOH apparentlly lessons its activity for the reaction.
The Iodine is added to the Cat soaking in the MeOH. The Ratio is for every gram of Cat used add 15mg of I2.
The buffering of the Cat is something that I do not know is needed or not. This was the way I shown and have always done so. I do not know if it is needed or not.
The Cat can be reused but for swim he never has due to had a large supply.
The Apparatus for the MeNH2 gas collecting is a 22l vessel. Conected to it is a Friedrichs for the very purpse of precooling the gas bieng generated. Connected to the friedrich is a hose and this is connected to a 3ft coil submerged in an dry ice bath. The friedrich is cooled with ice cold water. This is mounted atop of the recieving vessel.
The recieving tank is a prepared cylinder. In this case an empty 02 medical cylinder that has been modified a for this purpose.
The KOH pellets are first placed into vessel. The methylamine is mixed with the DH20 and added via sep funnel.
The vessel with the gas bieng bubled into the MeOH can be stirred Via overhead stirrer. The purpose is to just help the gas bieng absorbed so a little shake works. The gas was bubled in with a tube but it will work with a gas diffuser.
The Ketone was prepared Via Performic. Not buffered. It had a amber color with green tints.
This is a commercial Hydrogenator. As far as obtaining one that would be extremelly dificult nowdays. But I believe similar can be made.
The bleed off is the hydrogen. It is meant so as not to flood your space with hydrogen. A heavy duty sparkproof fan moving the air is heavilly recommended.
The hydrogenator does not have to be cooled. The MeOH is only needed to be cooled for the prep work. It should already be cooled from the addition of the gas.
The Hydrogenator Rocker devices are set to Medium. The Swish is to descibe the motion that they perform.
The heating devices are pads controlled by Variacs. They are turned first to 100%(2800 watts). They are turned down to about 30% to steady the temp at 155C.
The Cat is gravity filtered via 3 filter papers in a buchner funnel.
Acidify with a 5.5L solution of 37% Hcl.
Simple distillation to distill of the MeOH. Some not all of the H20 will be vap off.
Wash 2x with 3.5L of a saturated brine solution.
Swim hurried typing when finishing the writeup so the end was rushed.
My apologies for the rushed writeup. An additional 308g was obtained after cleanup of solvents.
This is the last time for Swim doing this. Am curentlly breaking apart the hydrogenator and calling it retirement.
This is not an easy method and it does require special equipment and skill. Most Bees would not be not be able to do this mainly due to the hydrogenator. But at least if any does it can at least give them some options on going about it.
I will rewrite this with the clarifications needed.
(Stranger)
05-26-02 03:49
No 314383
Donīt take this the wrong way, but this write-up has too many errors in it to make it trust worthy.
1.Caution-Rainey Nickel is pyroforic meaning it will explode in air so this must be done in an inert atmosphere.
Raney nickel is pyrophoric yes. This menas it will ignite in the presence of air when it is dry. When it is water soaked it takes a long time for it to dry enough to ignite. When it has been used in a reaction with another solvent, like in this case MeOH, just wash it with the same solvent and finally pour water over it again. Just keep it covered with some solvent at all times and you are going to be just fine.
2.This water must be removed for even microscopic levels will cause this reaction to fail.
The very reaction forms water, 1 mol water/mol ketone, so if it was as sensitive towards water as the writer suggests.... Hell, you can even run a reductive alkylation like this in a 60/40 water/MeOH enviroment without complications. Check Freifelder for "wet" reductive alkylations.
3. The iodine-thing....
Here we can see the traveling of another myth. The reason for adding the iodine cannot be given by the author. He just "knows" that it has to be added...
Well try and run the reaction without it and behold, it works just fine without iodine.
4. The slow purging of the reactor with hydrogen.
The author does not say for how long this "slow" purging has to be done. He starts with pressurising the reactor to 350 psi(24.1 bar). The slowly releses the pressure to remove the oxygen. Depressurise to what pressure? And for how long? If you have all this equipment, reactor, stirring assembly with a magnetic coupling, ex-proof motor(hopefully), hydrogen gas tank, then why not get yourself a tank of nitrogen or argon? Both gases are more easily avalible and cheaper than hydrogen, and you can purge the reactor with a inert gas.
Pressurising a reactor with a hydrogen/air mixture is a BAD procedure. The range within a mixture of hydrogen/air can burn(and explode)is ridiculously wide, 4,1-74,2 vol% in dry air. So you better make damn sure your equipment is properly grounded if you want to use the procedure.
5. The very need for a pressure of 1200 psi(82,7 bar)@ 155 deg C implies that you have a extremly bad stirring and a close to dead catalyst, or that you have only read about these reactions and actually never performed them.
6. The yield of amine should be way higher with that equipment and those conditions. It should be in the range of 85-95%, calculating for losses in workup.
(Old P2P Cook)
05-26-02 10:40
No 314467
I second everything Barium has said.
Except for the iodine part it sounds like blaztoff is badly paraphrasing a probably bogus write-up that I have seen before, perhaps somewhere in Rhodium's archives.
One of the many pieces of erroneous information in that writeup is that the hydrogenation requires Raney Nickel and high pressure. In fact, this hydrogenation runs very well at atmospheric pressure using platinum or palladium catalyst and gives near 100% yields.
(Chief Bee)
05-26-02 11:29
No 314485
erroneous information in that writeup is that the hydrogenation requires Raney Nickel and high pressure.
I'd say that the hydrogenation would require higher pressure just because Raney Ni is used. To the best of my understanding, all of the Pd/Pt catalysts are more active on a weight basis.
I think we all agreed that the reduction of nitrostyrenes at STP gives either very low yields, or requires catalyst loads of nearly the same weight as the substrate. Because time is money, and Pd/Pt is even more money, I guess some people prefer to use heaps of a cheaper catalyst and run it hotter and under higher pressure than what actually is necessary.
Myself I rather take the bike when I need to transport myself a few blocks, rather than renting a Ferarri and driving in 150 km/h for 500m. The goal is to actually get to your target, not doing it as fast and flashy as possible.
Rather use one of the more common "chemical" reduction pathways, and perform it several times instead, each time changing one of the reaction parameters just a little and recording the exact procedure and yield after each step. That way you aquire loads of experience along the way, you don't need to buy a huge reaction setup, just an ordinary lab glassware setup and you can spend the money on buying quality or perhaps some other chemicals you didn't actually need in the beginning, but you could have use for when wanting to try out a 2C-B, meacaline or TMA-2 synthesis for example.
By being one of those who performs several reactions of the same sort, and at the same time investigating small variations, you will eventually discover something nobody else had thought bof earlier (or had, but was too lazy/broke/careful to try it out). Then post about it at the Hive and earn eternal fame - just look at Methyl Man, Bright Star and Placebo - they all have their own little reaction or procedure named after them, just like in the real academic world when someone has accomplished something everybody else want to make use of.
(Old P2P Cook)
05-26-02 13:21
No 314529
I think we all agreed that the reduction of nitrostyrenes at STP gives either very low yields, or requires catalyst loads of nearly the same weight as the substrate. Because time is money, and Pd/Pt is even more money, I guess some people prefer to use heaps of a cheaper catalyst and run it hotter and under higher pressure than what actually is necessary.
Agreed, but this thread so far has been about the reduction of the n-methylimine of P2P and methylamine.
(Stranger)
05-27-02 05:37
No 314740
There are so many myths around about which conditions are needed when using Raney Nickel as the catalyst. First of all, there are MANY types of raney nickel. The name raney nickel is a bit misguiding, since it contains more than just nickel. When it is made of nickel/aluminum only it will of course contain only nickel and aluminum. But diffrent digestion times and temperatures will leave more or less aluminum in it. And this aluminum content together with a high or low hydrogen content will give a wide range of activity. Some types of catalyst will be almost dead unless you have conditions like 100-250 bar @ 100-300 deg C, others will kick the living shit out of a poor reducible group at 1-5 bar @ 10-40 deg C.
To make it even worse(better actually) you can add diffrent promotors, Cr, Mo, Cu, Co, Fe and so on, to the Ni/Al alloy. This will greatly affect the activity and selectivity of the catalyst.
One of the main reasons for needing those high loadings of noble metals catalysts when reducing nitrostyrenes directly to amines is that the researchers have the wrong kind of reactors for this type of reductions. The old Parr shaker is NOT the way to go here. Why? Well you cannot saturate the catalyst with enough hydrogen in a parr shaker, or in a reactor with a magnetic stiring bar spinning at the bottom. The Parr shaker is actually only really useful for stuff like O- or N-debenzylations, and in such cases you can make your own Brown hydrogenator way way cheaper then buying a Parr.
(Hive Addict)
05-27-02 06:41
No 314755
Barium. When you put the RaNi into the basic solution all the Al will react with the basic solution and produce H2 (The solo point of the Al in the RaNi). Usual both homemade and Aldric RaNi is werrye reactive.
For the Parr thing, I don't agree. The problem is that at 5-8bar there is not enough energy to let the reacton run. Cat. reduction of nitrostyren's is simply not the way to go.
(Stranger)
05-27-02 08:04
No 314786
The aluminum content affects the catalytic activity, it really does. It is not only there to saturate the nickel during the digestion. If it was like you said, then please explain the diffrence in activity you can get by digestion of the alloy at various temperatures. Diffrent digestion conditions gives diffrent percentages of aluminum left.
But there are other promotors as well as I said earlier.
Get yourself a couple of books about heterogenous catalysts and read what there is to know about skeletal catalysts(raney). I can assure you itīs a very worthwhile reading.
The biggest barrier in hydrogenation is this: Molecular hydrogen has to dissolve in the solvent and then be ripped apart to form a sort of metal hydride on the catalyst surface. You can very well run a catalytic hydrogenation of a nitrostyrene to an amine if you chose the right solvent, have an acidic enviroment, and saturate the catalyst with hydrogen. The Parr shaking style is not a good way to saturate a heterogenous catalyst unless you are doing a really easy hydrogenation/hydrgenolysis like a O- or N-debenzylation.
Why using a high pressure? Well this is a easy way to actually PRESS the hydrogen into the solvent and carry it to the catalyst surface. Can this be done by other means? Yes it can!! Get your self a better stirring device than a stirbar at the bottom of the reactor. You should get a "hollow shaft stirrer". This is a simple device but with a tremendous effect for your hydrogenations.
It works by allowing the hydrogen above the liquid surface to pass through the stirrer shaft and coming out just where the stirrer blades are spinning. When those blades are spinning at a rate of 800-1500 rpm, the gas bubbles are divided into very fine bubbles which dissolves very easily in the solvent. Any hydrogen that is not dissolved simply bubbles up to the surface again only to get sucked back into the shaft again soon. By recirculating your hydrogen like this you will keep your catalyst saturated at all times, and thus give you the product you want with a minumum of unwanted crap. You can in most cases actually reduce the amount of catalyst needed by between 50-90%.
The main problem in hydrogenation of nitrostyrenes to amines is that the partially reduced intermediates of the nitrostyrenes are given time to react in a unwanted fashion. How do you prevent that then? By keeping the catalyst properly saturated with hydrogen you do not give those intermediates enough time to do freaky shit. Instead they do what you want them to do, which is to transform into amines.
(Hive Addict)
05-27-02 09:05
No 314802
I thought that the solubiliti of hydrogen into (any) solvent was ekstreem small. Thats why you need the shaking, to let the catalyst flow through the hydrogen atmospher and then down the solvent. My personal ekspiriense with the hydrogenation of nitrostyren is that you only get's the oxime. This reaction takes from 5 to 10min and then nothing more happens (atleast not for 12-24houers).
Iff you have some sugestions (or referens) I hope you will share the with the hive.
(Stranger)
05-27-02 15:33
No 314929
what conditions did you use in the reduction (catalyst solvent temperature pressure) I have a dream that the reduction of recrystalised 3,4,5 tmns in absolute Ethanol saturated with HCl and using pd/c with hydrogen at 1 atm and chilling to 5 oC in an external bath works.
(Hive Addict)
05-28-02 04:12
No 315139
The post is at the hive somevere.
I tryet with methanol, ethanol, ethylacetat and acetic acid as the solvent. I used HCL in Methanol or sulfuric acid as strong acid.
I tryet on trimethoxy-nitro-ETHEN, trimethoxy-nitro-ETHAN, 1-phenyl-2-nitro-PROPEN and 1-phenyl-2-nitro-PROPAN. ended up with the oxime (and one time a tiny amount of amphetamin (GCMS)) The temp was 25°C and the presure 6-8 bar
The cat. was RaNi or Pd/C (3 diff. batches from Aldrich)
(Master Whacker)
05-28-02 12:18
No 315275
(Rated as: excellent)
Barium mentioned:
The old Parr shaker is NOT the way to go here. Why? Well you cannot saturate the catalyst with enough hydrogen in a parr shaker
SWIM has extensive experience working with Parr shakers. I must speak up here and let it be known that a few of your statements, although logical in theory simply are not true in practice. SWIM has reduced everything from 17-hydroxycodeinone(alkene), imines, enamines, oximes , azides, mandelonitriles and of course the common N-debenzylation reactions in good to outstanding yields with his precious Parr. PM me if you want to know about other projects using hydrogenation. Since the topic of this thread is reductive amination, I'll relate some theoretical experiences from manufacturing MDE with a Parr 500ml shaker. 100g ketone and 75ml 70% ethylamine(aq.) were charged into the reactor bottle and qs'd with methanol to the 2/3 full mark- about 100-150ml is required(qs is an old apothecary term which means to add an ingredient to increase the total volume of a solution to a designated volume). 1.5g Pt black(fresh) is weighed into a small beaker and CAREFULLY dampened with a few ml methanol then added to the Parr bottle. After purging the bottle headspace of O2, shaking is started and the reduction is run no higher than 35psi/room temp for a special reason which I will explain in a moment. The bottle is continuously recharged to 35 psi after pressure bottoms out at 10-20psi. I have found that the rxn tends to absorb 5% more H2 than the theoretical value, however I'm not too worried about it because the yield is consistently amazing (98%crude, 94%distilled) and thats no bullshit. Even though this high of a yield is typical for this reduction, I actually thought twice about posting those yields because I know the other experienced folks here tend to call bullshit on most outrageous high yielding claims. I even tend to dismiss these claims myself until I've run the rxn. and proved it myself.
The reduction takes 2.5-3 hours and a single charge of Pt Black can be reused 4-6 times before poisoning. 500g of honey from 1.5g catalyst in 14 hours is amazing! Now if that isn't proof enough that Parr shakers effectively transfer hydrogen to the catalyst then I just dont know what to tell you! Perhaps I missed your point entirely.
Repetitive experience working with Adams Catalyst (PtO2) in place of Pt black has proven this catalyst is not as reliable or predictable as the pre-reduced form (Pt black). Numerous experiments with varying parameters were used to isolate the variable which determined the activity of the final catalyst. It turns out that the method for reducing the PtO2 to Pt black completely determines the activity of the catalyst. Many refs say to just add the PtO2 to the substrate and allow it to be reduced in situ. It has been found that catalyst prepared by pre-reducing the Adams Catalyst in plain distilled water at low pressure (15-20psi) before adding to the substrate produces a superior catalyst. By "superior" I am referring to the rate at which H2 absorption commences and the amount of times the catalyst can be reused before poisoning sets in. If PtO2 is simply added to the above MDE reagents and hydrogenation started, the reduction will take about 6-8h for theoretical H2 uptake resulting in a 85% yield. When the catalyst is recovered it is only good for about 1.5-2 additional reductions.
As you see Barium, Parr reductions work just fine. I can provide multiple high yielding refs using these devices to reduce a whole cornucopia of compounds upon request. I do sincerely respect your knowledge and willingness to share such with the Hive and can tell you know what you're talking about when it comes to high PSI hydrogenation equipment. However I am skeptical of how you obtained your information on Parrs and wonder if your knowledge came from something other than personal experience. To be honest, I suspect that you actually have very little experience with Parrs and think the opinion you presented on the inferiority of these devices is actually conjecture extrapolated from experience with high-pressure hydrogenators.(that is not an insult, only my gut feeling
). The reason I make statements like that is that my personal experiences have been nothing short of remarkable, I experience a great deal of satisfaction knowing that I own such a reliable, useful instrument. It has treated me SOOO well over the years! If you still are not convinced that Parr hydrogenations not only work but work efficiently, than what do you have to say about all the literature published over the past fifty years employing this device to successfully produce thousands of compounds?About the 35psi max reduction pressure: I read some info in Freifelder which stated that higher pressures sometimes catalyzed polymerization of product resulting in decreased yields (75%). In all honesty, I have run the reduction at 60psi and 60'C several times and never found a significant difference in yield than the 35psi reduction. Normally it would be very tedious to constantly maintain the pressure in such a tight range(20-35psi) because the absorption occurs so rapidly. To remedy this annoyance I conquered my impatience by designing a micro controller to fully automate the hydrogenator. A set of pressure transducers and solenoid valves constantly automatically adjust the pressure in the reactor bottle and temporary H2 holding tank. The computer will also automatically turn on the hydrogen generator to refill the holding tank if pressure drops below the setpoint. Valuable data is collected by logging pressure changes in real time during the run. Analyses of this data can be used to predict when a reduction is approaching completion and when catalyst will need to be changed.
Quote-Barium:"The Parr shaking style is not a good way to saturate a heterogeneous catalyst unless you are doing a really easy hydrogenation/hydrogenolysis like a O- or N-debenzylation.
I just realized this statement is the route of your personal disposition toward these fantastic instruments. Lets talk some more facts. The shaking motion provided by the Parrs is without question capable of dispersing catalyst particles in an extremely finely divided manner. I have experience with high pressure shaking (not stirred) autoclaves and know for a fact the rocking action does not disperse Ra-Ni particles any better than the small amount of Pt or Pd catalysts employed in Parr shakers. Now you are probably thinking about the solubility of H2 in the solvent at high pressure conditions. I have read more than a few places on the hive that H2 gas actually does not absorb into the solvent with low psi (0-60) pressures. That idea is ridiculous. Ever try disconnecting a Parr bottle from the clamp assembly after bleeding off the overhead pressure? If so, you will notice that a great amount of H2 effervesces from the solvent if the bottles is shaken in anyway. Stirred hydrogenators are a totally different story and off topic for this rant
.Your assumption that Parr reductions are not capable of reducing most substrates because the catalysts can't absorb and release the hydride to the substrate rapidly enough is flawed. Have you ever tried varying the pressure during a reduction to see how pressure affects reaction rate? One particular experience where an isonitroso compound was being reduced to its respective amine left me very humbled. The literature stated the rdxn was to take place at 2atm H2(30psi). A few 50 gram batches were run at this pressure, each run took 2 hours as long as the catalyst was prereduced. One day I decided I needed some more of that compound in a hell of a hurry and figured I could simply accelerate the reduction by cranking the H2 up to 70 PSI. Bad mistake. The reactor immediately started heating increasing the pressure to something over 100psi(the guage was maxed!) before the bottle VIOLENTLY exploded. The explosion was so powerful it drove glass shards through a plate glass window without shattering the window pane! I keep the chart of pressure data vs time from this run on the wall of my lab as a constant reminder of what can happen the second we chemists get sloppy with safety procedures. This mishap proves that heterogonous catalysts in Parr shakers can indeed rapidly absorb H2 and react with a substrate in a rapid manner. It also shows that the reaction rate can (often) be adjusted by modifying the temperature of the reactor. Wrapping a fiberglass heating tape around the bottle and powering it with a powerstat works really well. If you are using reused catalyst, hydrogen uptake may not begin as quickly as with fresh catalyst. If no absorbtion has taken place after 20minutes, jack the H2 presure up to 50psi and start heating the bottle by supplying the heating tape with 20 volts. The bottle will heat up to about 40'C over the next 15-20 minutes and hydrogen absorbtion will begin. Once the reaction is underway, the H2 pressure can be lowered to 35-40psi however the heat should be left on. If absorbtion gets sluggish again after a while, jack the variac up to 27-30 volts.
My experience with Parr's has been overwhelmingly positive. Almost every reduction attempted using that instrument produced a good to excellent yield of product in a timely, predictable and repeatable fashion(except for nitropropenes
). With this in mind, I can't imagine why you prefer working with much more complicated, expensive, and dangerous high pressure equipment. In case you didn't know, the current trend in pilot scale Org. Synth. is to replace when possible the old high pressure hydrogenation equipment with SAFER modern medium pressure units(they dont exceed 80 psi H2) such as the small Buchi pilot-scale 2-4Liter medium pressure mag. coupled paddle-stirred hydrogenator. These units are absolutely beautiful, they are made entirely of glass, have a water jacket surrounding the reactor for cooling and are starting to gain wide acceptance in the scientific community because of their excellent design which is optimized to provide the highest degree of safety possible in case of accident. Ultra-high pressure reactions and autoclaves are being replaced when possible with less dangerous equipment, although high PSI hydrogenation will always be an essential part of industry.Barium, none of the above is meant to insult you so please do not take it that way-thats not my style. My personal experience just doesn't jive with a lot of what you are saying. Perhaps you can clarify my confusion on this matter after reading my post. Anyway, welcome to the hive!!! We've needed a member knowledgeable in your field of expertise for a long time now.
-Ritter
(Distinctive Doe)
05-28-02 18:17
No 315395
Not to disparage the Parr but Barium makes sense.
If the reaction is limited by mass transfer of the hydrogen and hydrogen has a very low solubilty in the solvent then his hollow stir shaft sounds pretty good. It would give the hydrogen a huge surface area and provide mixing thats hundreds of times better than shaking could ever get.
I think the shaker is routed in history not practicality or whats best. 100 years ago it was probably very difficult to contain high pressures and temps and get adequate stirring. Shakers are the EASIEST way to do that, but I would venture to agree that they definately are NOT the BEST.
Just rambling.
Barium
Whats the price tag on your hydrohgention set-up?
I would guess the $ number is painful to hear?
Foxy
Those who give up essential liberties for temporary safety deserve neither liberty nor safety
(Hive Bee)
05-28-02 23:21
No 315517
This reaction does work. Personaly swim has been doing this for 4+ years and the person who taught him developed this over 10 years ago. Some statements were stated for th benifit of newbees who mighty read this and not understand.
As far as the purging of hydrogen the hydrogen is brought down to 50psii from 350 psi. Nitrogen or Argon would work as well but if your going to use Hydrogen later why change tanks. I have performed this reaction and knows this works. Yields are better normally. I will rewrite this with the necessary explanations and added detail in it. Like I said earlier this is an outdated reaction but it works. Its main purpose was only to alow thought for any future bees who might want to explore this in the future. It has always been said that Raney Nickel can be used for MDMA but I have never seen any writeups on it. Swim has ben using this for years and didnt want it to fade away after retirement. Also Swim has seen this for batches wieghing in at 15000g at one time so the implications for large scale production are great.
The hydrogenator used is a commercial hydrogenator. It is not a Parr hydrogenator. It is not easilly available due to restrictions on it. Frankly if any hydrogenation that went to 1200psi goes boom its going to take a hell of a lot with it. The work needed to obtain one is extremlly difficult. BUt if obtained then its a treasure.
(Stranger)
05-29-02 05:54
No 315598
Hi Ritter and everybody else! Thank you for welcoming me here, Iīm sure Iīll enjoy this place. Donīt worry, I just love a good and lively discussion.
First of all, I just love catalytic hydrogenations/dehydrogenations/hydrogen
Parr used a very smart way, shaking, to overcome the mass transfer barrier with the technology they had avalible then. But today we have better materials and technology. The type of reactors most in use today are stirred reactors and the loop reactor. The latter mainly for continous production. We can use a dispersed catalyst or a fixed catalyst. The latter again mainly in continous production.
I could go on the whole day babbling about the advatages/disadvatages between diffrent types of reactors, but letīs go back to the topic.
In a gas/liquid hydrogenation reactor we have to overcome one big obstacle, the mass transfer barrier. Gas-liquid-solid. Those three stops has the hydrogen molecule to pass before it can be utilised to reduce something. Hydrogen has quite low solubility in most used solvents. This means that at every given moment there is only a small amount of hydrogen solvated and avalible to the catalyst. The solubility in water for example is only 1:50, 1ml H2 in 50ml water @ 0 deg C. This is the big barrier. Why? Because hydrogen has to compete with the substrate, and now and then some nasty poisons, for the sites on the catalyst suface. sometimes we even add poisons to moderate the activity of the catalyst, lindlar catalyst for example. Those poisons has higher affinity for the sites of the catalyst than both the substrate and hydrogen. This is very much the same way as drugs are competing with neurotransmittors over receptor sites.
If we have substrates which has to go through a number of intermediate steps to become the product we want, like phenylnitroalkenes, and those intermediates can do freaky shit when they are left alone for a while, then we must minimise then time of their existense. That is by reducing them further as soon as possible.
Now if we have a catalyst which is depraved of hydrogen there is going to be more intermediates present, and freaky shit happens, like as big glob of tar as the product.
If we on the other hand have substrates like imines, enamines, alkenes, alkynes, aromatic nitros, N- and O-benzyls to reduce. Then there is way less of a problem to have a hydrogen depraved catalyst, since none of these forms any particulary kinky intermediates.
What type of reactor gives a hydrogen depraved catalyst then? Any type of reactor where you donīt have the solvent saturated with hydrogen, and lots and lots of finely dispersed hydrogen bubbles ready to go into solution as soon as they are allowed. By increasing the pressure inside the reactor you can get the solvent oversaturated with hydrogen. By increasing the amount of dispersed gas bubbles together with increased pressure(5-200 bar)you can make sure that the catalyst is surrounded by hydrogen at all times. This will speed up the reaction rate and lessen the life-span of the intermediates. The drawback is that you can get a runaway reaction if you donīt keep a close watch on whats going on inside. A very good proof of how big an obstacle the mass transfer barrier really is and how quick the catalyst becomes hydrogen depraved, is what happens when you have a reaction which is about to become a runaway and the temperature is skyrocketing. Just stop the mixing...No more hydrogen gets solvated, and the reaction dies immediately.
Of course one can run almost any kind of hydrogenation in a Parr shaker. The litterature is a good proof of that. But Iīm simply saying that there are better ways to mix the contents and overcome the mass transfer barrier than shaking. This is the hollow shaft stirrer I mentioned earlier. It is not expensive at all, since itīs just a regular stirrer shaft but hollow, and perforated at the upper part, where gas gets sucked in, and at the lower end, where gas gets pressed out, all by the spinning of the shaft.
I have a couple of reactors myself. But the one I use most is a low-pressure(1-8 bar)vessel with a hollow shaft stirrer. With this baby I can run reactions which normally takes 5-24 hours and 5-20% w/w catalyst/substrate loading in a Parr shaker, in 0,5-5 hours and with 0,1-3% w/w catalyst loading only, and it is actually cheaper than a Parr shaker...
I have never done anything illegal nor will I, but letīs just for arguments sake say that I were to perform a reductive alkylation of methylamine with 3,4-MDP-2-P. PtO2 or Pt black are the most used catalysts in the litterature for this type of reduction. The amounts of those expensive catalysts used are almost silly. Ritter told us he were using 1,5g pure Pt(reused 4 times)for the reduction of 100g ketone. With my baby I would use 1 to abso-fucking-lutely-max-2g 5%Pt/C or Pd/C. 50-100mg versus 1,5g pure metal. This may perhaps seem a bit cheap considering the value of 500g product compared to the cost of the catalyst. But it also reflects the efficiency of the reactor(it also has to do with the surface area). My reaction time is also a bit less 1,5-2 hours @ 40-55 deg C versus 2,5-3 hours @ room temp.
I would have the following ratios: 1 mol ketone, 1,05 mol amine and 1,5 mol glacial acetic acid, all in some 200ml EtOH or MeOH. Dump in the catalyst first then the ketone and acetic acid. Mix the alcohol solvent with the aqueous amine and add this in 4-5 portions to the ketone over 4-5 minutes. Purge with argon(my choice) and pressurise to 2 bar with hydrogen. The reaction mixture should have reached 40 deg C by itself, if needed heat in a waterbath to that temperature. Start stirring at 1000 rpm. Keep the pressure constant at 2 bar. Check the progress of the reaction from time to time by closing the hydrogen feed-valve and observe the pressure drop. When the reaction ceases to consume hydrogen itīs done. But donīt do this too early. The very last bit of imine has a hard time to find the catalyst. So the reaction might appear to have ceased. Just let it stir for another 30 min @ 2 bar to reduce the last bit of imine. This last step is the diffrence between a 90-95% yield and a 98-99,9% yield.
Add 4-5-teaspoons celite to the mixture ad give it a good stir. Filter at the water pump through a regular filter paper in a buchner funnel. Re-run the filtrate once again using the same filter cake to get rid of the last catalyst. Strip off the alcohol in a rotovap. There will be a aqueous solution of the amine acetate in some acetic acid. Wash with 500 ml toluene, basify and there will be close to a theoretical yield of amine ready to be crystalised.
(Distinctive Doe)
05-29-02 10:17
No 315648
Nitrogen or Argon would work as well but if your going to use Hydrogen later why change tanks.
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