Author Topic: Heretical point of view?  (Read 193 times)

Prepuce

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Heretical point of view?
« on: July 21, 2010, 07:00:04 AM »
I believe that this is a new twist on an old discussion, and hope it's not entirely incorrect.

Maybe those of you who were tired of this particular type of thread five years ago will find something fresh to fume about here.  >:(

Just kidding. Or am I?  :)

There's an interesting discussion on WD started by iknowit on a faster way to reduce PSE with phosphorous acid. It interested me because I started looking at the reaction in a different way than I had before, and several points have come up that lead me to wonder if any of the old explanations for this reaction are correct.

Every reference I've seen says that iodoephedrine is formed by the action of HI on ephedrine. However, it was noted long ago that an exothermic reaction between PSE and I2 takes place with no more provokation than stirring the mixture, which quickly melts. This mixture reduces in a reaction with RP just as expected. I can't imagine that anything other than the formation of iodoephedrine is taking place in what was observed, but if that's true then HI isn't needed for this part of it.

In researching the matter, one author that seemed to be talking about the same thing mentioned that an SN2 was ordinarily the way this kind of thing takes place, as did one of the posters to the WD threads. The carbon attached to the OH is highly acidic, the article said, and the OH, being highly basic, doesn't come off easily. However, a characteristic of SN2 is molecular inversion, since in this the halogen acid attacks from the back side. I'm no chemist but I don't see that a reversal takes place. But even if it does, what reaction takes place between PSE and I2 alone?

Another tidbit from the thread was the suggestion that using the HCl salt of PSE wastes HI, because it must be expended in freeing HCl from the molecule prior to the reduction. It was difficult to find a molecular model that showed PSE HCl, but I finally did find one, and it showed HCl bonded ambiguously to the whole molecule. I don't know if that's correct, but see no reason why HCl would bond with the carbon we want to manipulate, and as long as that's not the case, see no reason why the HCl needs to bother about it at all. Wouldn't it be fine, wherever it is, right up until the end of the reaction, at which point the mixture is based? It does make sense that at that point the base would be both removing the HCl as well as oxidizing the iodoamphetamine.

Then again, that last makes no sense because it would imply the entire reduction occurs when the mixture is based, and that sounds very unlikely. Could it be that this is one of the functions of the phosphorus, in whatever form it may be used, to oxidize the HI from the iodoephedrine,leaving a proton and completing the reduction?

My thinking is probably wrapped around the axle somewhere in this. Any insights are much appreciated!

Thanks,
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Sedit

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Re: Heretical point of view?
« Reply #1 on: July 21, 2010, 02:02:05 PM »

Another tidbit from the thread was the suggestion that using the HCl salt of PSE wastes HI, because it must be expended in freeing HCl from the molecule prior to the reduction. It was difficult to find a molecular model that showed PSE HCl, but I finally did find one, and it showed HCl bonded ambiguously to the whole molecule. I don't know if that's correct, but see no reason why HCl would bond with the carbon we want to manipulate, and as long as that's not the case, see no reason why the HCl needs to bother about it at all. Wouldn't it be fine, wherever it is, right up until the end of the reaction, at which point the mixture is based? It does make sense that at that point the base would be both removing the HCl as well as oxidizing the iodoamphetamine.

There is nothing to suggest that the HCl will interfere with the reaction. It is bound loosely to the amine part of the molecule and should in no way affect the reduction of the alcohol. When I2 is added to H2O you get an equilibrium as with all halogens in water in the formation of (HO)I<---->(H)I. I dont know how well this holds true for iodine but it may help explain the exothermia experianced as it melts into the mixture.

I can't say much more because I have my doubts as well as to the mechanics of the reaction and I find it odd that Cl2 forms chloramines in presence of amines yet no one ever mentions there formation in the reduction of ephedrine when adding raw I2 to an amine substrate.
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Re: Heretical point of view?
« Reply #2 on: July 21, 2010, 04:40:45 PM »
I once saw an alcohol oxidation wherein iodide and iodine were used in tandem to form I3, which is electrophilic enough to be attacked by the alcohol. Alpha-deprotonation (I believe this particular paper used carbonate) will oxidize the substrate to the ketone, but attack of iodide on the benzylic carbon could cause this iodo-oxygen species to leave (presumably via SN-1 since the carbon is benzylic). I know next to nothing about PSE but my guess is that the mechanism is similar.
« Last Edit: July 22, 2010, 03:39:18 PM by Vanadium »

Naf1

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Re: Heretical point of view?
« Reply #3 on: July 22, 2010, 02:25:18 AM »
Sedit is right about the HCl apart from it being bound loosely, as it is bound at the catonic nitrogen [RNH+] by an ionic bond with an anionic chloride [-Cl] ion. So is stronger than the covalent bonds that make up the compound in question!

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I can't say much more because I have my doubts as well as to the mechanics of the reaction and I find it odd that Cl2 forms chloramines in presence of amines yet no one ever mentions there formation in the reduction of ephedrine when adding raw I2 to an amine substrate.

Any N-Iodamine formed would be extremely unstable and would hydrolyze upon making the conditions extremely acidic. It could only be a potential problem with some of the more stable chloro and bromo compounds and reacting the halide with the amine first. In the cases where you dont have HI and only I2 and RP ideally you would want to follow the OrgSyn method;(but really does not matter that much).

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In a 1-l. round-bottomed flask are placed 250 cc. of glacial acetic acid, 15 g. of red phosphorus, and 5 g. of iodine. The mixture is allowed to stand for fifteen to twenty minutes until the iodine has reacted, and then 5 cc. of water (Note 1) and 100 g. (0.44 mole) of benzilic acid (p. 89) are added. A reflux condenser is attached, and the mixture is boiled continuously for at least two and one-half hours.
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0224

A good example of protonation of the amine hindering N-bromoamine formation would be;

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1-Phenyl-2-amino-3-bromopropane Hydrobromide(I)-
dl-Phenylalanine ethyl ester was converted to dl-Phenylalaninol, m.p.67-68*, by reduction with lithium aluminum hydride.
  A sealed tube containing 1.0 g.(0.006 mole) of dl-phenylalaninol and 25ml. of 48% hydrobromic acid was heated at 170-175* for five hours. The dark colored reaction mixture, in which some carbonized material was present, was diluted with 100ml of water and was decolorized with charcoal (Nuchar). The resulting water-white, strongly acid solution was taken to dryness under reduced pressure on the steam bath. The dry residue after crystallization from absolute alcohol weighed 1.27g (65%) and melted at 173-176*. A second crystallization (from 3ml of absolute alcohol) afforded 0.97 g (49%) of pure 1-phenyl-2-amino-3-bromopropane hydrobromide, m.p. 174-175*.
  When the reaction was carried out at 100* instead of 170*, the hydrobromide of dl-phenylalaninol was the only material isolated. This salt was prepared in a separate experiment by evaporating a mixture of 1.0 g (0.0066 mole) of dl-phenylalaninol and 25 ml of 48% hydrobromic acid under reduced pressure, and crystallizing the dry residual solids from ethyl alcohol. The hydrobromide obtained in this way (1.21 g or 79%) melted at 148-149*, and showed no change in meting point after admixture with the material (m.p. 148-149) obtained from the reaction at 100*
http://pubs.acs.org/doi/abs/10.1021/ja01137a505

(HI can also be made from Iodine salts and Mineral acid)

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Prepuce
Every reference I've seen says that iodoephedrine is formed by the action of HI on ephedrine. However, it was noted long ago that an exothermic reaction between PSE and I2 takes place with no more provokation than stirring the mixture, which quickly melts. This mixture reduces in a reaction with RP just as expected. I can't imagine that anything other than the formation of iodoephedrine is taking place in what was observed, but if that's true then HI isn't needed for this part of it.

Thats right the iodoephedrine is formed, the hydroxyl group is protonated by HI (step 1). The ROH is converted to ROH2+, effectively the alcohol OH has been turned into H2O and water is a much better leaving group than OH. Which then forms water and a secondary carbocation. The reaction you noted was most probably the reversible reaction at the amines nitrogen forming the unstable N-iodamine, that regenerates the starting compounds upon adding RP and water.

http://www.arkat-usa.org/get-file/18759/

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In researching the matter, one author that seemed to be talking about the same thing mentioned that an SN2 was ordinarily the way this kind of thing takes place, as did one of the posters to the WD threads. The carbon attached to the OH is highly acidic, the article said, and the OH, being highly basic, doesn't come off easily. However, a characteristic of SN2 is molecular inversion, since in this the halogen acid attacks from the back side. I'm no chemist but I don't see that a reversal takes place. But even if it does, what reaction takes place between PSE and I2 alone?

The reaction does not proceed via the SN2 mechanism and the OH is not highly basic, SN2 mechanism would be applicable for primary alcohols (not sec or tert alcohols). Sec and tert alcohols react via a carbocation intermediate in a SN1 reaction, primary alcohols connot form carbocations as they are too unstable so have to react via a SN2 mechanism (where the halide forms a partial bond to the carbon before the alcohol function can leave, thereby avoiding the primary carbocation and has to approach from behind). So with pseudo there will be no inversion.

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Another tidbit from the thread was the suggestion that using the HCl salt of PSE wastes HI

On the contrary, HI is a strong acid, no? What do you think adding 40% HI to freebase will do? Maybe the same thing as 35% HCl! It does not waste PSE as the nitrogen is already protonated so little if any N-haloamines are going to form with it, it will just hasten the protonation of the alcohol (Step 1). Honestly the differences would be so trivial as not to be worth worrying about, if anything you would need more HI to first protonate the nitrogen (which will be protonated first, before the mildly acidic alcohol).
« Last Edit: July 22, 2010, 02:29:36 AM by Naf1 »

Prepuce

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Re: Heretical point of view?
« Reply #4 on: July 25, 2010, 09:13:32 PM »
Naf1, just about everything you're written that I can understand agrees with what I've been finding. Very little is written on using HI, the dynamic is usually illustrated using Cl, as is the example you used.

The reason that some believed that HI would be wasted when reacting the HCl salt was the mistaken impression that the ephedrine would first have to be converted to the freebase before the reaction could proceed. It's now obvious that this was a mistake.

I will take small issue with one minor issue--that HI can be made from mineral acid. Well, you didn't say which mineral acid, but in fact HI cannot be made from H2SO4 because it's oxidized as soon as it's produced. It doesn't work with HCl either, for reasons that I no longer recall. I've tried to look it up but haven't been able to find a reference one way or the other. I want to say it's because the Cl holds more strongly to the proton than I2, but I'm not sure about that. I do know that Cl oxidizes KI when in solution.

HI can be made using phosphoric acid, however, as well as a variety of other organic acids, HS, etc.

Another aspect to this discussion is in understanding why RP/I reactions are never 100% efficient. I ran into something of an analysis of this question, and here's the relevant section. It's from A Study of Impurities Found in Methamphetamine Synthesized From Ephedrine, by T.S. Cantrell et. al., Forensic Science international 39, 39-53 (1988)

============================================
"The halo compound may undergo an internal substitution reaction, whereby nitrogen replaces iodine to give an aziridine which can decompose to give the compounds

      A (N-methylbenzylamine),
      B (benzaldehyde),
      C (propiophenone) and
   -->   D (phenyl-2-propanone).

Due to the extreme acidity of the reaction mixture, only routes C and D are viable considerations.

The protonated nitrogen of the aziridine controls retro ring-opening to produce an zwitterion intermediate. The rational choice of route D, based on the highly favored zwitterion intermediate with resonance overlap to the aromatic ring, is borne out with experimental fact. The product of retro ring-opening, followed by hydrolysis of 1,2-dimethyl- phenyl-aziridine is P-2-P [6]. Thus, P-2-P is a common impurity in these clandestine laboratory preparations of (+)methamphetamine. This anomaly has puzzled a number of forensic investigators where the clandestine synthesis was known to start from ephedrine and not the popular route P-2-P/methylamine Schiff base reduction via aluminium foil.

From the selected number of clandestine methamphetamine samples screened for the presence of trace impurities, we have found that the major portion of P-2-P produced in this reaction undergoes self-condensation (aldol) to afford hydrocarbon impurities. These impurities are

      1-benzyl-3-methyl-naphthalene (E) and
      1,3-dimethyl-2-phenylnaphthalene (F).

Both compounds incorporate two molecules of P-2-P as result of an aldol condensation, followed by dehydration, followed by a second internal condensation and dehydration."
=================================

So it looks like the primary contaminant is likely to be P-2-P. What could be done to minimize this? From observation alone it appears that it depends upon the type of phosphorus being used, but in the case of a phosphonic acid reaction it seems to be the case that a significant excess of the acid helps.

PP
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Naf1

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Re: Heretical point of view?
« Reply #5 on: July 26, 2010, 01:33:53 AM »
Note;
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a SN1 reaction

Not to be confused with chlorination with Thionyl Chloride for example it becomes somewhat more complicated and can proceed via three different mechanisms! SNi (retains configuration), or two concentric SN2 reactions (first one proceeds with inversion of configuration the second one returns the stereochemistry to the original so proceeds with retention of configuration)  or SN2 (inversion). All three can happen at once some retaining their original stereochemistry some being inverted depending on the reaction it undergoes.
http://www.lycaeum.org/rhodium/chemistry/meth.impurities2.html

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I will take small issue with one minor issue--that HI can be made from mineral acid. Well, you didn't say which mineral acid, but in fact HI cannot be made from H2SO4 because it's oxidized as soon as it's produced. It doesn't work with HCl either, for reasons that I no longer recall. I've tried to look it up but haven't been able to find a reference one way or the other. I want to say it's because the Cl holds more strongly to the proton than I2, but I'm not sure about that. I do know that Cl oxidizes KI when in solution.

Thanks for the correction! You are right about sulphuric acids oxidation abilities. In theory HCl and the mineral acids work but maybe not so well in practice? (but is not HCl used to prepare HI from iodine, then H2O2 added to oxidize the iodine to I2 and can be filtered out? I have done that several times!).

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So it looks like the primary contaminant is likely to be P-2-P. What could be done to minimize this?

Your problem, is with the vulnerability of the newly formed haloamine (iodoephedrine) to undergo an intramolecular nucleophilic substitution resulting in cyclization to produce an aziridine. Once the hydroxyl has been converted to a good leaving group (Iodine), the ability for the amine to displace it is increased greatly. As you will see in the paper you quoted above this is common to all methods that proceed via a haloephedrine or halopseudoephedrine, for example even using very mild conditions with thionyl chloride. Once the haloamide is formed the aziridine follows. The named reaction to go with this would be, but obviously proceeds with hydroxide catalyst;
Gabriel Ethylenimine Method (Gabriel-Marckwald Ethylenimine Synthesis)

S. Gabriel et al., Ber. 21, 1049 (1888); W. Marckwald et al., ibid. 32, 2036 (1899); 33, 764 (1900); 34, 3544 (1901).

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The reaction mechanism for the reduction of ephedrine with Hl/red P is summarized as follows. Ephedrine reacts with HI to form iodoephedrine (iodomethamphetamine) which is predominately reduced to methamphetamine. Iodoephedrine can undergo a ring closure to form 'aziridines'. The 'aziridines' (cis and trans-1,2-dimethyl- 3-phenylaziridine, mol wt 147) could also be formed directly from ephedrine by acid dehydration [9]. However, formation from iodoephedrine is more likely. The 'aziridines' can be reduced to methamphetamine or react to form the impurities found in the reaction. The 'aziridines' can undergo a ring opening acidic hydrolysis to form phenyl-2-propanone. The P2P forms an aldol condensation product with subsequent dehydration to form the 'naphthalene' impurities, 1,3-dimethyl-2-phenylnaphthalene and 1-benzyl-3-methylnaphthalene [10]. The non-acidic reduction of chloroephedrine produces the 'aziridines' but no P2P [11,12]. The transient existence of iodoephedrine was detected indirectly by the total 'aziridines'. The analogous chloroephedrines undergo thermal decomposition to the 'aziridines' in the injection port of the gas chromatograph (Martin, W., pers. comm.).
http://designer-drugs.com/pte/12.162.180.114/dcd/chemistry/meth.hi-rp.html

The red text shows that a lot of that P2P produced will end up as useless napthalene compounds, but the P2P ultimately comes from the aziridine 'ring opening hydrolysis'. Regarding halogenation with thionyl chloride at room temp then a neutral hydrogenation (reduction) generally with palladium on charcoal or raney nickel;

"The non-acidic reduction of chloroephedrine produces the 'aziridines' but no P2P"

So the extremely acidic enviroment that HI creates, produces P2P by hydrolysis of the aziridine before it gets reduced to meth, once in situ the P2P quickly produces napthalene compounds via aldol condensation.

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we have found that the major portion of P-2-P produced in this reaction undergoes self-condensation (aldol) to afford hydrocarbon impurities. "

"The protonated nitrogen of the aziridine controls retro ring-opening to produce an zwitterion intermediate. The rational choice of route D, based on the highly favored zwitterion intermediate with resonance overlap to the aromatic ring, is borne out with experimental fact."
http://www.lycaeum.org/rhodium/chemistry/meth.impurities.html

Seeing this, one can start to understand why someone would say, it would be better off using the freebase as the nitrogen is not protonated and subsequent aziridine ring opening is not favored as highly as the intermediate zwitterion will not be formed because without a protonated nitrogen the number of resonance structures available that overlap into the pi system of the ring for the intermediate compound is reduced thus are much less stable. And can be seen by the non-acidic reduction that does not produce P2P in the example above. But as stated the HI will protonate the nitrogen and form that ionic bond producing a salt (Ephedrine Iodide). Heat will allow the hydrolysis to happen at a greater rate (more heat = more hydrolysis), so the most gentle conditions possible will obviously help. An easily removed protecting group on the amine would stop that completely, protection with a benzoyl group followed by halogenation followed by reduction which would remove the halogen and benzoyl protection in one pot ??? More to come!

Prepuce

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Re: Heretical point of view?
« Reply #6 on: July 26, 2010, 03:41:01 AM »
Great discussion, Naf1. It's a big help to have someone explain some of this in English. Your teaser at the end will have me checking for the follow-on.

One other thing that I wanted to consider is the fact that the quantity of contaminants produced by the same type of reaction will vary from one to the next. From what you've said it's obvious that too much heat would be a contributor, but there must be other things as well. Observations suggest that excess phosphonic acid helps, although what actually takes place as a result may be an entirely different process than formation of aziridines.

The quoted article also mentions that aziridines "can be reduced to MA or react to form impurities", but of course the means of pushing the reaction in one direction or the other is not mentioned. What might be a likely influence?

On producing HI using HCl, to get iodine to dissolve in water you would probably use KI either by itself or with additional I2. So you'd have hydrogen, chlorine, potassium and iodine ions swimming around together. In an ionic solution like that could you say that you had HI in there? Could it be used as such? If you could pull this off in something that would dissolve all of the above but not HI or HCl, I'm still thinking that you'd get HCl, just because chlorine is so much more reactive than iodine.

PP

PP
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Re: Heretical point of view?
« Reply #7 on: July 26, 2010, 05:34:08 AM »
Answering my own question--Of course a solution with HCL, KI and I2 dissolved in it would have hydriodic acid in it, but also hydrochloric acid. It seems to me that anything that might like to have a proton and a halogen ion or two would almost certainly take the chlorine. I'm not sure how to quantify it's higher reactivity, but (as an indicator?) the ion is over twice as electronegative than that of iodine.

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Re: Heretical point of view?
« Reply #8 on: July 26, 2010, 05:47:46 AM »
Vanadium, I3 sounds like a possibility to me. I ran across something yesterday that suggested that allowing the I2 to combine with pse "ahead of time", so to speak, might not be a good thing, and causes the formation of something undesirable. Of course I lost track of the reference almost as soon as I found it, and am still searching to find it again.

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Sedit

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Re: Heretical point of view?
« Reply #9 on: July 26, 2010, 05:18:21 PM »
Java uploaded the paper in the interesting papers thread in the reference section that shows the mechanism of the alcohol reduction as HI halogenating the alcohol and further being reduced by the HI to the alkane and presumably I2. This is where the Phosphorus comes into play converting the I2 back into HI making sure the levels of acid are not lowered thruout the reaction progress. It also states alternative means of reducing the halo alkane as well.

Make your acid first then add the amino alcohol.

Slight suggestion that the HCl salt may just not be the greatest thing since Cl ions decompose HI.
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This substance is a condensable gas; at a temperature of 59.8°, it solidifies into a transparent, colorless mass; and water absorbs a large quantity. The strongest liquid hydriodic acid has a specific gravity of 1 7/10, when it boils at a temperature between 257° and 262°. It is not a stable com pound; oxygen from the air is absorbed, and iodine is liberated and dissolved by it. Chlorine and bromine decompose it.

Mechanism of HI formation.
Quote
Phosphorus combines very vividly with iodine, and the iodide of phosphorus, when it comes in contact with water, is decomposed into hydriodic acid and phosphoric acid.

I have always woundered about feeding SO2 in as the reaction progresses as a means of doing away with P all together but it could prove much more troublesome then phosphorus as Sulfur precipitates from the reaction.

http://albumen.conservation-us.org/library/monographs/sunbeam/chap10.html
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Re: Heretical point of view?
« Reply #10 on: August 30, 2010, 08:15:51 AM »
Hmmmm.  Well, I believe there is a report in an old "Microgram" about agents finding some dead Mexican-type meth cook guys, who had succumbed to hydrogen sulphide poisoning.  Had a cylinder of Hydrogen Sulphide Gas.  Must have been using it for something.

These guys might have been using that hydrogen sulphide, to produce HI without the benefit of Phosphorus.  There's always more than one way to skin a cat, and the reduction might be do-able without red phosphorus. 

One thing is for sure though, if the aforementioned fellers were doing it, they ain't doing it anymore.   Playing with hydrogen sulphide, without taking the proper precautions, is terminally unhealthy.
« Last Edit: August 30, 2010, 11:32:01 AM by Buzzoff »

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Re: Heretical point of view?
« Reply #11 on: August 30, 2010, 05:19:48 PM »
Its scary stuff H2S, numbs your olfactory nerve at moderate concentrations, so once you think hey the stench has gone, the danger is passed, lets let my hair down...then it gets you.

Has the potential for extremely fast kills in high concentrations too, remember it acts on the same cytochrome oxidase portion of the electron transport chain that cyanide and azide do, which makes it just as able to inhibit cellular respiration and spleen-fuck you lovingly with a broken bottle as cyanide, maybe its worse, even, due to its being a volatile gas, a pile of KCN will sit there until its messed with, H2S has the capacity to come up in a huge cloud in your face and KO you instantly, preventing escape.
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