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chemoleo
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Civility? Do you speak it?
Sauron's last post just above was deleted as it amounted to nothing but an utterly pointless flame war Blitzkrieg, totally unnecessary and out of
proportion.
I'm not even going to apologise for taking such a step.
This is out of order and has no place in this forum.
Please let's get back ON TOPIC.
A shame such measures are necessary given the quality of the posts here, including those of the originating author.
I recommend taking the 'E' out of the 'EGo'!
Thank you.
[Edited on 5-4-2008 by chemoleo]
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Sauron
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I have deleted as many of my posts as possible in this thread because a forum moderated in so biased a manner does not deserve good chemistry.
I'm sure chemoleo will delete this as well.
I will communicate developments in this area (CCl4/CHCl3 preps) to such members as are capable of carrying them out safely.
The hysterical overreaction of some disgusts me.
[Edited on 5-4-2008 by Sauron]
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chemoleo
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Good chemistry hardly goes amiss here, Sauron, and as you know no-one will debate that.
Picking on minute issues such as the detailed toxicity and war gas capability of SCCl2 is not (welcome), particularly if it erupts in animosity EVERY
time when someone happens to contradict YOU ever so slightly.
It's a pattern I observe every single time.
Bias is not the issue here, as I wholeheartedly appreciate your *scientific* efforts here, as well as your knowledge.
But if your knowledge and effort comes at the expense of online fighting/insulting/cursing/judging/confrontation every single time someone dares to
disagree or contradict, I feel we'd rather be deprived of that knowledge and live in something resembling peace.
As I said in the U2U (which I'm sure you aren't going to read), there are ways of dealing with disagreements with any members that don't automatically
result in arguments, name-calling etc. Please try, you'll see yourself how truly friendly this forum is once you get the hang of it ....
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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Sauron
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Your absurd distortion of my statements and demeanor simply underscores your inability to be impartial.
THAT is bias, personal bias in regard to me, and unbecoming of a moderator, a position to which you should never have been appointed.
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LSD25
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Sauron,
If you suggest that CWC type agents are of some use to you in a tropical climate - I'm fucked if I see any reason why I shouldn't point out the
problems with that approach. I am on shaky ground here, 'cos of the fact that Sauron is involved and I'm just gunna get slapped down, so I'll shut the
fuck up NOW
Whhhoooppps, that sure didn't work
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Sauron
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What CWC type agents?
Thiophosgene is not on CWC and I said so. It is a commercially available reagent used for making thiocyanates.
If you want to characterize it as a CWC type agent for your own reasons, then I am here to say you are wrong, and question your agenda.
Tropical climate is pertinent to what? The inside of my fume hood is not tropical.
Thiophosgene preparation is described in Org.Syn., q.v. Their method is clumsy and low yield. Their apparatus is too large to fit in a 2 meter long, 1
meter high, 1 meter deep hood.
I have a nice review on the useful synthetic chemistry of thiophosgene from Synthesis, which I will post here in the possibly futile hope that this
compound be seen to be useful for something other than flinging at one's enemies. It is pretty useless for that.
In short you are either misinformed or mendacious, which is it?
This thread was about alt routes to CHCl3 and CCl4.
Thiophosgene came up only as an intermediate in one of the three reactions, and need not have been isolated. By continued chlorination, both
intermediates were converted quantitatively to CCl4. The only other product was TCT and that is a sought after material for many members. The sulfur
chlorides produced are mostly a nuisance but can be converted to more useful reagents. This is the same dilemna faced by every industrial maker of
CCl4: what to do with all the SCl2/S2Cl2?
If someone wishes to stop at the intermediate stage and fractionate off the thiophosgene, before continuing chlorination of the other intermediate
(CSCl4)
[Edited on 5-4-2008 by Sauron]
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LSD25
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What, who me? What? Never...
Next thing you'll be suggesting I'm sarcastic
Whhhoooppps, that sure didn't work
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Sauron
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Ah. Mendacity then, it is.
Jokes belong in Whimsy.
However, as promised,
"Thiophosgene in Organic Synthesis"
from SYNTHESIS.
[Edited on 5-4-2008 by Sauron]
Attachment: s-1978-24896.pdf (1.3MB)
This file has been downloaded 4249 times
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Sauron
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To resume the topic of this thread:
Conventional wisdom is that chloroform is best prepared by the haloform reaction, and CCl4 by chlorination of CS2,
The haloform reaction requires very large scale apparatus if the yield is to be more than 50-100 ml. The reaction can be hazardous and is always
laborious.
The chlorination of CS2 has its own drawbacks. CS2 is rather costly, and very very flammable. Chlorination produces a toxic intermediate, CSCl4, and a
nasty byproduct, SCl2 admixed with S2Cl2. The difficulties in separating and purifying CCl4 from these are pretty well known and discussed in the
chemical and technological literature.
So I went looking for alternatives.
One such is chlorination of methyl thiocyanate. Like CS2, MeSCN is rather expensive. But unlike CS2, it is amenable to synthesis. See downthread.
The first stage of MeSCN chlorination produces cyanuric chloride as acrystalline precipitate. This is separated easily by filtration. The liquid
mixture remaining contains the following components
CSCl2 thiophosgene
CSCl4 trichloromethyl sulfenyl chloride (same as in CS2 chlorination)
CCl4
SCl2 (same as in CS2 chlorination)
Continued chlorination of this mixture gives CCl4 and SCl2. It is possible if desired to seperate out the thiophosgene but not mandatory.
So to summarize, MeSCN can be economically synthesized as below, and gives CC (TCT) on chlorination as well as thiophosgene and products identical to
those from CS2 chlorination. Ultimately the products can be as few as three (TCT, CCl4 and SCl2).
This is more interesting than CS2 chlorination but still contains the problem of separating CCl4 and SCl2, so let's move on to the other alternative.
Chlorination of trichloroacetic acid to trichloroacetyl chloride was reported by H.C.Brown to result in a significant amount of decomposition of the
acid chloride to CCl4 and some CHCl3.
To a lkesser extent this also occurs when preparing the acyl chloride of dichloroacetic acid by Brown's method, benzotl chloride.
Glacial acetic acid is an inexpensive starting material and its chlorination through chloroacetic acid is well known. It is also available
commercially at rather low cost.
I reasoned, it is also possible to chlorinate ethanol to chloral (trichloroacetaldehyde, which unlike acetic acid is a process that does not require
UV. Chloral can be converted to dichloroacetic acid, see Org.Syn. The trichloroacetyl chloride process can be entered at that point advantageously.
Things turn out to be even simpler than that.
A number of researchers studied the chlorination of chloral and chloral hydrate under UV and found that trichloroacetyl chloride is formed and at
ordinary temperatures decomposes by a radical process to CCl4 and gaseous products (CO, HCl) quantitatively.
At -50 C it was possible to recover 55% trichloroacetyl chloride.
At -10 C only 7.5%
At 10 C to 90 C, no acid chloride was recovered and only CCl4 remained.
This represents the conversion in two stages of ethanol (anhydrous) to CCl4 quantitatively. In first stage, to chloral by chlorination first at 0 C
and ultimately at 90-100 C. The procedure is described in a Chem.Rev. article as well as in a number of patents. Anhydrous ethanol is cheap and
ubiquitous. Yields are high 70-85%).
The second stage requires UV photolysis. Unless you rely on sunlight, photolytic reactions require special equipment and impose safety hazards (eye
protection), and this is the downside of this method. However, this is compensated for by the highest economy of any of the methods and by the absence
of noxious sulfur-containing intermediates. hose who are unwilling, unprepared or unequipped to deal with CSCl2, CSCl4 and sulfur chlorides should
employ this method. The CCl4 product will be devoid of ill smelling impurities.
[Edited on 6-4-2008 by Sauron]
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Sauron
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Apologies for double post.
The preparation of methyl thiocyanate can be conducted by two methods.
Per Merck Index, but without references, MeSCN is prepared from barium thiocyanate and dimethyl sulfate according to the equation
Me2SO4 + Ba(SCN)2 => BaSO4 + 2 MeSCN
We are left to presume that solvent choices are, per Ullmann's, ethanol or DMF.
As garage chemist pointed out, PainKilla has furnished a method of preparing DMS for those who cannot purchase it. BE WARNED! Dimethyl sulfate is a
proven human carcinogen, specifically a brain carcinogen. I personally do not relish its use and would not prepare it.
Barium thiocyanate is prepared per a procedure in Inorganic Syntheses vol 3, p 24, from ammonium thiocyanate and barium hydroxide. This procedure
looks a little tedious and the commercially available barium thiocyanate is horribly expensive, almost $900/Kg from Alfa.
Ammonium thiocyanate is also a little expensive, but can be itself prepared from less dear starting materials.
The other methos is more advantageous.
An alkyl halide such as MeBr or MeI is reacted per Vogel, in 95% ethanol with potassium or sodium thiocyanate.
Methyl iodide (iodomethane) like DMS is a hazardous methylating agent, but less dangerous than DMS. It is not too expensive commercially, and can also
be prepared, per Org.Syn., from DMS and potassium iodide.
I have on hand dimethyl sulfate, potassium iodide, and potassium thiocyanate. Therefore I can make my own MeI and from that, MeSCN. To me this appears
better than the longer and more laborious NH4SCn to Ba(SCN)2 to MeSCN method.
But others may have different priorities.
The productivity of chlorination of MeSCN is extraordinary and due to the large amount of chlorine absorbed.
Overall equation is
3 CH3SCN + 15 Cl2 -> C3N3Cl3 + 3 CCl4 + 3 SCl2 + 9 HCl
The yield of TCT is 70% according to James (J.Chem.Soc.)
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Sauron
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Once again mea culpa for double post. In my defense I am restoring in a more concide form the content of my posts in this thread which I gutted
earlier today. Hopefully the logic of my remarks will be more apparent than previously.
The chlorination of dry ethanol does not require photolysis and is not improved by it. This is quite unlike the chlorination of glacial acetic acid.
Chlorine initially oxidizes ethanol to acetaldehyde and monochlorinates that. This phase of the reaction needs to be chilled hard () C). As
chlorination progresses the temperature can be raised and at the end is in the 90-100 C range. Yields are typically 70-85%.
CH3CH2OH + 3 Cl2 -> Cl3C-CHO
Thus 46 g ethanol will typically produce more than 100 g chloral.
The further and photolytic chlorination of chloral is quantitative.
C2HOCl3 + Cl2 -> Cl3CCOCl + HCl
And the trichloroacetyl chloride falls apart via the radical
Cl3CCOCl -> Cl3CCO. + Cl. => CCl4 + CO
So the overall conversion is Cl3COCl -> CCl4 + CO + HCl
I should point out that Cl2 in presence of CO is likely to combine to phosgene. Indeed, one of three investigators of this reaction as cited in the
Chem.Rev. article on chloral's chemistry, observed phosgene among the products. Appropriate precautions need to be taken against CO and COCl2 as well
as Cl2 of course.
I suppose I should mention nin passing that trichloroacetaldehyde (chloral) and its hydrate and alcoholates are controlled substances in USA and
probably other countries. Chloral hydrate as an intoxicant really ceased to be a problem more than a century ago despite its ease of preparation, and
lingered only as "mickey finn" knockout drops. So if you reside in a jurisdiction of concern, and wish to proceed, I'd advise processing the chloral
into CCl4 immediately rather than storing it. Chloral is not the most stable of compounds anyway.
Remember, trichloroacetic acid, upon conversion to its chloride, in absence of photolysis still fell apart in the same manner, doubtless by same
radical mechanism. The expected yield of trichloroacetyl chloride was 85-90%, but only 56% was obtained. (Brown, JACS.) Therefore it is reasonable to
assume that trichloroacetic acid, upon photolytic chlorination, or chlorination in presence of a radical initiator, would give CCl4 in same fashion.
This is probably practical, but would never be as economical as starting with ethanol except in terms of time saved.
[Edited on 6-4-2008 by Sauron]
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Nicodem
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Thanks for reviewing this topic. Being one of those lucky bastards that can just take a CCl4 bottle of the shelve, I don't have any interest in
preparing it, but these reactions are new to me and quite interesting.
Anyway, if you are into discovering new things I have an idea you could try. Theoretically there is chance it might even work, though I would not bet
on it.
Trichloroisocyanuric acid (TCCA) can be used in the Hell-Volhard-Zelinsky reaction (the relevant paper is uploaded at least in two posts: here and there). This reaction requires the enolization of the carboxylic carbonyl group which is done by having the acid equilibrate with a small amount
of acid chloride (or bromide) which enolize without troubles. The small amount of acid chloride required is usually prepared in situ with any method
of choice (red phosphorous, POCl3, another acid chloride, etc.).
So to keep it short, perchlorination of acetic acid with TCCA in the presence of an acid chloride generating reagent (for example cyanuric chloride,
TCT), and possibly some catalytic amount of AlCl3 to speed up the decomposition of Cl3CCOCl, might give off CCl4 and CO as products distilling from
the reaction mixture.
The drawback, if it works at all, would be the possible runaway due to highly exothermic reactions and the other is in the in the necessity of an
inert and nonvolatile solvent since one would need at least 1 mol TCCA : 1 mol AcOH : 1/3 mol TCT : ~0.05 mol AlCl3 (an obviously impossible slurry to
deal with, and furthermore one that can just become a small volcano). As for an appropriate solvent, there are only few choices and most are
chlorinated alkanes which is a bit unreasonable for a reaction that is supposed to be used for the preparation of CCl4. But if anyone motivated enough
wants to try it solventless on a small scale and report what happened…
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Sauron
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That is indeed interesting, thanks, Nicodem.
As it happens I had occasion to study the HVZ reaction a while back in connection with the alpha bromination of caproic acid, on the way to preparing
racemic Norleucine for resolution via an enzyme to L-Nle.
The classical method is just Br2 with a little kicker from red P or in my case PBr3 (which I can get).
Clearly the P or P halide generates as you said, a little acid halide and that reacts, this process repeats and so on.
A slightly more au current variation is to formally prepare the acid chloride, and then a-brominate that with NBS (in CCl4!) to the a-bromoacid
chloride, then liberate the acid.
My question is, does the HVZ method work beyond the mono-a-halo stage? Because I have not heard of any instance of such. Perhaps my interest in too
narrow, as I was only looking for preparative routes to a-amino acids.
But I have no doubt at all that TCCA (a chloramide after all) would be a suitable alternative to N-bromosucconimide (a chloroimide).
Beware of trying to utilize all three chlorines on CC (TCT) because the final chlorine has a very different pKa and is far less labile. This usually
requires higher temperature.
Therefore, I would advise that more than 1/3 equivalent TCT be used.
Better would be to preform the acid chloride by whatever means. Start with acetyl chloride. Then see if TCCA in the right solvent (whatever that might
be) will go beyond the chloroacetyl chloride state. If it does, then indeed there ought to be stage set for radical decomposition to CCl4 and CO.
I would hesitate to try to go for broke with a one-pot gambit, and son't really see why AlCl3 is required.
Another reagent besides TCCA and the N-halosuccinimides that would be a candidate is yhe dihalogenated 5,5-dimethylhydantoin family. Like TCCA, cheap
and ubiquitous.
Can you point me at the TCCA/HVZ article? The FSE and I often fail to have a meeting of the minds.
Again, thanks for the idea. By coincidence - I have to prepare chloroacetyl chloride sometime in not too distant future. This is for cyclization with
1,2-ethanediol on the way to BEDT-TTF, the tetrathiafulvalene. Chloroacetyl chloride is commercially available but very hard to ship, has to go by
ocean. Only one company has a license to import it, and they don't want to bother, Apparently it has to be refrigerated in transit. The MOD here is
paranoid about it, I had a hard time figuring why, but it turns out it is because they are afraid of chloroacetophenone! Oh well.
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not_important
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| Quote: | Originally posted by Sauron
...
My question is, does the HVZ method work beyond the mono-a-halo stage? Because I have not heard of any instance of such. Perhaps my interest in too
narrow, as I was only looking for preparative routes to a-amino acids.
... |
Actually it can be difficult to stop at the mono-substituted stage in many cases. Chlorine is more likely to go further than bromine, because of
crowding, but then acetic acid will have the least crowding issues.
Ah, March Advanced Org Chem 2-5
| Quote: | | When there are two alpha-hydrogens, one or both may be replaced, although it is often hard to stop with just one. |
[Edited on 5-4-2008 by not_important]
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Nicodem
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The two posts where the Synthetic communication paper using TCCA for the alpha-monochlorination of carboxylic acids are linked in my above post.
Di- and trichlorination of acetic acid by the Hell-Volhard-Zelinsky reaction is possible, at least when using Cl2. Using TCCA would require acidic
catalysis or prolonged heating though.
The proposition of adding some ~5mol% AlCl3 is for catalyzing all the processes involved:
- enolization of (chloro)acetyl chlorides, thus catalyzing the di- and trichlorination of chloroacetyl chloride (every new alpha-chlorine group
reduces the reactivity of the enolized form via inductive effect);
- the activation of TCCA (TCCA gets much, much more electrophilic when activated by acids);
- the activation of TCT (protonated TCT should be more reactive toward carboxylic acids and might give off the last chlorine more readily; essentially
you can act in two ways: increasing the nucleophilicity of AcOH by deprotonation with Et3N which is unfortunately not applicable in this case, or
increasing the electrophilicity of TCT which is applicable);
- Cl3COCl should be easily decomposed by AlCl3 (just guessing, should check the literature but today I'm bored enough to make a lot of guessing).
Anyway, forget AlCl3. I remembered of an acid that would work as a great catalyst and a solvent at the same time. Sulfuric acid. TCCA is well soluble
in it and it makes it incredibly electrophilic (there is a paper in J. Braz. Chem. where they actually did DFT calculations about it).
Edit: Damn, forgot that CCl4 decomposes to COCl2 in conc. H2SO4.
[Edited on 6/4/2008 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Sauron
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March did'nt happen to cite references for such reactions, did he? I just can't recall ever seeing a halogenation of acetic acid other than photolytic
and usually with a "halogen carrier" as well.
But per March, it ought to be hard to stop at chloroacetyl chloride, or bromoacetyl bromide. You'd expect the dihalo product to predominate or at
least be a major contaminant.
There ought to be a review of the Hell-Volhard Zellinski reaction in OR or Chem Rev and Merck would be where I'll look first in the named-reactions
section. If unproductive, next the ACS search engine.
Thanks, Nicodem, for that Synth.Comm. paper. They got an 88% yield of chloroacetic acid using excess TCCA at 130 C for 19 hours. The acetyl chloride
was generated first with PCl3 to the extent of about 2%. Purity by GC, 99.4% so no indication of dichlorination.
So far it sounds like a good cheap replacement for NCS and no one ought to be amazed that a chloamide can do the job of a chlorimide. I want to hit
the lit looking for di- and trichlorination examples under HVZ conditions.
I found four reviews cited by Merck. Two in Chem Rev. and two in JACS. I've requested them and when they appear we will see what we will see.
---------------------
So far I have obtained and read two of the four HVZ reviews cited in Merck Index. Neither of these makes any mention of poly-a-halogenation of
carboxylic acids or acid halides. I will await the other two reviews which may be more pertinent.
[Edited on 6-4-2008 by Sauron]
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Nicodem
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I checked the literature about catalysts for decomposing CCl3COCl into CCl4 and only found two references at all about such decomposition:
- one is a thermolysis:
| Quote: | Decomposition of Trichloroacetyl Chloride.-Several passages of this material through the furnace at 600°C caused about one-third to react. Carbon
tetrachloride and hexachloroethane were formed in the ratio of about ten to one. Carbon monoxide and some phosgene were also produced.
From: J. Am. Chem. Soc., 61 (1939), 435-436. DOI: 10.1021/ja01871a061 |
- the other, even older, is the mechanistically already logical decomposition by AlCl3 (Unfortunately I don’t have access to this journal and the
reaction conditions are not mentioned in the abstract, neither is this reaction the main topic of the paper.):
| Quote: | The Modifications of Metachloral and the Decomposition of Chloral by Aluminium Chloride. Perchlorobutanal: CCl3CCl2CCl2CHO.
Boeseken, J.; Schimmel, A.
Recueil des Travaux Chimiques des Pays-Bas et de la Belgique, 32 (1913) 128-133. |
I also checked for the preparation of trichloroacetic acid by the Hell-Volhard-Zelinsky reaction and found this patent US2613220 where 3mol% acetic anhydride is used as a reagent/source for enolization. I could find no other electrophilic chlorination, but besides
the HVZ reaction there is also the radical chlorination of AcOH which does not require additions of reagents promoting the enolization (since the
mechanism is completely different), yet it requires UV light for the homolytic dissociation of Cl2 (one such example is patent US2674620).
I guess it would be much better to start with chloroacetyl chloride which is relatively easily prepared from trichloroethylene (probably the most
common chlorinated solvent that can be found OTC all over the world). With the appropriate corrosion resistant autoclave it is a quite easy
preparation (I know there is a thread about it with the patent numbers and all somewhere on the forum). Chloroacetyl chloride could then be hopefully
directly perchlorinated with TCCA/AlCl3 to CCl4 and CO (with all due safety requirements due to phosgene and other nasties).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Sauron
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Better, don't you think, to chlorinate ethanol (anhydrous) to chloral? This does not require, nor is it promoted by UV.
It's high yield.
Once in the trichloroacetaldehyde form, only the final chlorination step to trichloroacetyl chloride needs photolysis. Surely preferable to
irradiating it all the way from GAA?
As it happens one of my suppliers has a second hand Ace power supply for a Hanovia immersion lamp for sale. I will have price in next 24-36 hours. The
special joint on Ace's photoreactor flasks is 60/40. Other glass companies sell 60/50 joints that will certainly work so I can have a flask made up
locally to accept an Ace immersion well (quartz) and lamp to match the power supply.
Ethanol to CCl4.
Who'd have figured?
Here's the Chem.Rev. paper on chloral chemistry, its preparation, its photolytic halogenation, and a lot more.
Yes, Rec.Trav.Chim. is unavailable online so far. Too bad. The reference for decomposition on trichloroacetyl chloride in Brown's paper (JACS) is same
one you cite and I have never been able to lay hands on it. Brown made no mention of AlCl3, so your efforts are not without reward. We have more
information than before.
[Edited on 6-4-2008 by Sauron]
[Edited on 6-4-2008 by Sauron]
[Edited on 7-4-2008 by Sauron]
Attachment: cr60295a001.pdf (1MB)
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chemoleo
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I thought it worth noting that according to the excellent review, Chloral can also be produced by electrolysis of ethanol and NaCl or CaCl2 at 110-115
deg C, and yields of chloral rise to 61% in the presence of cyanuric acid as catalyst.
Even simpler and cheaper than straight chlorination, the only caveat being the temperature - the electrolysis vessel would be pressurised (EtOH BP: 78
deg C).
Then of course chloral can be decomposed to chloroform and formate with strong alkalis.
(THis is off topic but quite interesting - chloral also reacts with phenol to parahydroxy benzaldehyde and other goodies, see p 14)
[Edited on 6-4-2008 by chemoleo]
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not_important
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| Quote: | Originally posted by Sauron
March did'nt happen to cite references for such reactions, did he? I just can't recall ever seeing a halogenation of acetic acid other than photolytic
and usually with a "halogen carrier" as well.
[Edited on 6-4-2008 by Sauron] |
No, not a single ref given in that paragraph. Several surveys, which you seem to be tracking down. But much of the original HVZ stuff seems to fall
into the category of Really Old Chemistry, where stones axes were used to carve flasks out of tree trunks, and the nearest thing to a reference is a
collection of lists of surveys.
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Sauron
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No, chemoleo, not OT at all. Chloroform is in the thread title, and my intent, given a facile route to CCl4, was to turn part of that into chloroform
anyway (with wet Fe filings, one Cl is pulled off.)
So a direct transformation of chloral to chloroform is certainly of interest With formate for a bonus. I like it.
It looks like there is paydirt in the Sonntag review of aliphatic acid chloride chemistry (Chem.Rev. vol.52). In this long and rather comprehensive
paper, halogenation of acid chlorides is buried in the middle and I almost overlooked it. But, indeed, it seems that acetyl chloride is chlorinated to
dichloroacetyl and trichloroacetyl chlorides in absence of any powerful light source, by the addition of a small amount of iodine. If this reaction is
carried out at too high a temperature (200 C) then hexachloroethane is produced. Clearly, although Sonntag makes no mention of CCl4 being formed, the
hexachloroethane is resulting from the union of two CCl3 radicals rather than that of one CCl3 radical and a Cl radical. We will have to have
recourse to Sonntag's references.
Attached is p 359 from Sonntag, the reaction he is talking about it chlorination of acetyl chloride with PCl3 at 190 C. which gives a mixture of
ClCH2COCl, Cl2CHCOCl, and Cl3CCOCl. However, a mere 10 degree increase in reaction temperature is reported to yield instead hexachloroethane.
Three references are given, all accessible fortunately, in the 19th century German primary literature. One from Ber., one from Ann., and one from
J.Prakt.Chem. Sounds like a job for References to me. I will go ferret out the DOIs.
While this helps save March's face, it is unlikely to provide a practical alternative to the chlorination of ethanol to chloral and the decomposition
of that material to CCl4. The major product would have to be the trichloroacetyl chloride, TCCA or some other cheap reagent would have to replace
PCl3 which is now so politically incorrect. But I will follow through and see where this takes us.
[Edited on 7-4-2008 by Sauron]
Attachment: Pages from Sonntag.pdf (84kB)
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Sauron
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I got the first of the references from Gallica (BNF)
Attached below
He is proposing to prepare trichloroacetyl chloride from acetyl chloride and PCl5 (3 mols) according to the equation
CH3COCl + 3 PCl5 -> Cl3CCOCl + 3 PCl3 + 3 HCl
Three mols PCl5 is more than 500 g, to treat one mol acetyl chloride? It must have been nice in those days to be so extravagent. This method may be
noteworthy as a method of obtaining PCl3 from PCl5 and therefore from red P.
As for the main thrust of the paper, : m-nitro-p-trichloroacetoluid is presumably N-trichloroacetyl-3-nitro-p-toluidine.
]
Trichloroacetyl chloride was also prepared conventionally by trating trichloroacetic acid with PCl5. In this case the byproduct is of course POCl3.
No discussion of details, yields, analysis is given, the prep of the Cl3CCOCl is merely mentioned in passing as a preliminary matter.
[Edited on 7-4-2008 by Sauron]
Attachment: Ber11_1970.pdf (276kB)
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Nicodem
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Iodine is indeed an excellent Lewis acid for certain reactions, perhaps just because it so mild as to prevent certain side reactions that would
otherwise occur with such strong acids like AlCl3 (for example, direct chlorination of AcCl to CCl4 ).
But otherwise acyl chlorides enolize so easily that for monochlorination you don't even need any iodine or other acid catalysts. However, if you will
want to use TCCA for alpha-perchlorination of AcCl you will probably have to add an acid catalyst to get it go to CCl3COCl at some acceptable
conditions, but only experiments can tell.
The mention of PCl3 as a chlorinating reagent is probably a mistake. PCl5 is the reagent used in such HVZ reactions as a replacement for Cl2 (PCl3 is
generally not an oxidant). We'll see what the original references say.
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scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
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Sauron
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Yes, well, at least the sole reference that I have so far used
-- preformed acetyl chloride
-- stoichiometric PCl5 (3 mols) for the alpha-perchlorination
So Sonntag's entry is a little off.
But I have yet to see the other two references.
To my mind, ethanol is the better feedstock and chloral the more versatile intermediate.
Treat it with strong base and get chloroform
Hit it with UV and Cl2 and get CCl4.
And there's still the Boeseker report of decomposition by AlCl3.
So acetyl chloride, more precious than ethanol, is a less attractive feedstock. It might be interesting to establish the conditions under which TCCA
would chlorinate chloroacetyl chloride to dichloroacetyl chloride. And that to trichloroacetyl chloride. In presence of and absence of catalysts. But
looking at boiling points, and the time and temperature at which excess TCCA only formed the monochloroacetyl chloride, I suspect we may be looking at
conditions of autogenous pressure in an autoclave.
Also easy enough to work on the conditions for decomposition of trichloroacetyl chloride. We already are taught that 200 C results in
hexachloroethane, and we can safely assume that this is a competing reaction involving the same Cl3C, radical as formation of CCl4. So this
represents a ceiling. We don't want hexacloroethane. Anyway we are told in the Sonntag review that CCl4 on its own at a certain temperature spits off
a tenth of a mol per hour Cl2 and forms hexachloroethane. So that compound is always available easily if you have ample CCl4.
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Nicodem
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Chloral can also be a source to CCl3COCl possibly by chlorination with TCCA directly (I posted about the relevant patent in the thread dealing with benzoyl chloride preparation. I think chloral was not among the examples but I can't see any reason why it would not work as well.).
| Quote: | Originally posted by Sauron
Also easy enough to work on the conditions for decomposition of trichloroacetyl chloride. |
I think the best preparative option is to decompose it with AlCl3 since this should result in less side products, given that it is about a simple and
well documented carbocation fragmentation (not involving radical species and no radicals can diffuse to couple into undesired side products like C2Cl6
and similar).
[Edited on 7/4/2008 by Nicodem]
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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