Melgar
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What exactly is the reaction between methylene chloride and aluminum?
I found a bunch of references warning against the chemical incompatibility of aluminum and methylene chloride, but other than anhydrous AlCl3, there
was no mention of any reaction products. It certainly evolves gas, although the gas is odorless. That made me think it was hydrogen, but then
where's the carbon going? There's no oxygen for it to attach to. Unless perhaps it's methane? But then, the equations don't work; not enough
hydrogen. It could be ethylene, I suppose, in which case it'd be a nice way for any of us to produce both anhydrous AlCl3 and ethylene at once, from
fairly easily-obtained precursors.
Note that my CH2Cl2 may have had up to 5% methanol, since it was distilled from paint stripper. Not enough to generate the massive volumes of gas I
was seeing, or the AlCl3, but possibly a catalyst or solubilizing agent.
[Edited on 4/3/17 by Melgar]
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Melgar
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I don't think it's producing ethylene. Most likely, it's a mixture of products, including radicals. Possibly dichlorocarbene and/or methylene?
Anyone have any idea what's going on here?
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RosarioHeis
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Something i've asked my self a long time. Some papers use this combination for friedel crafts alkylation. It's said that this gives less byproducts.
If you evaporate the solvent would you get dry alcl3?
[Edited on 9-4-2017 by RosarioHeis]
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BromicAcid
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Failing at remembering if it's a aluminum or zinc - copper couple that is reacted with chloromethane to give chloromethyl compounds of the metal. The
copper was necessary for a quick reaction, I remember that much. Basically you could be ending up with organometallic aluminum compounds and not
necessarily neat aluminum chloride. I will check into it more tomorrow if it crosses my mind.
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Praxichys
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The abstract of this paper shows that silver sitting in CCl4 generated predominantly tetrachloroethylene, hexachlorobutadiene, and hexachloroethane.
A2 Aluminium
Chlorinated Hydrocarbons - Chloromethanes
DOI: 10.1002/9783527610433.chb08105
It mentions Aluminum but I don't have access to the full article.
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Amos
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Well, I was going to distill dichloromethane today anyway. May as well reflux some with aluminium and shoot it on a GC tomorrow to see what the
reaction products are.
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Boffis
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Quote: Originally posted by Praxichys  | The abstract of this paper shows that silver sitting in CCl4 generated predominantly tetrachloroethylene, hexachlorobutadiene, and hexachloroethane.
A2 Aluminium
Chlorinated Hydrocarbons - Chloromethanes
DOI: 10.1002/9783527610433.chb08105
It mentions Aluminum but I don't have access to the full article.
|
@Praxichys, this is interesting; the presence of a significant amount of hexachlorobutadiene in the reaction products from Ag with CCl4 seems to
suggest that the tetrachlorethylene is reacting with the silver to produce the C4 compound. I have tried to produce hexachlorobutadiene via similar
reactions previously without much success. I had never though that silver would have been reactive enough. The significance of hexachlorobutadiene is
that it can be used to prepare squaric acid and squarates (C4O4)2-.
Since "perc" (tetrachloroethylene) is stil available it might be possible to use it as a source of the butadiene drivative.
In the abstract you give they give a reference [25] but the reference section is not viewable. Can anyone see the whole document and fish out the
reference, please!
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Melgar
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I found some literature hinting that one potential product may be 1,2 dichloroethylene, probably both isomers. Since pulling an HCl molecule from DCM seems the energetically favorable route, that'd leave HCCl**
which would probably form 1,2 dichloroethylene on recombination, unless the hydrogen got involved somehow. Either way, it's all speculation until
some test can be done.
If anyone has the ability to test the products, I believe that a better reaction results when there are trace amounts of alcohol in the DCM, and if
the aluminum is alloyed with galinstan or eutectic gallium and indium, the reaction proceeds much faster. Literature indicates that with pure DCM and
aluminum, the reaction is only very slow, because the AlCl3 that's formed is insoluble in DCM and adheres to the aluminum.
edit: also, if anyone has the ability to test the products of this reaction, I would happily mail you a sample of Al/Ga/In/St alloy (within the US) in
a ratio that is strongly reactive with both water and DCM, if it would help.
[Edited on 4/13/17 by Melgar]
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DFliyerz
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Hmm, sounds like an interesting way of making some harder-to-get compounds, whatever those may be. Also, I'm now realizing that I probably shouldn't
be storing DCM waste in an aluminum bottle, although nothing has happened over the past few months.
[Edited on 4-14-2017 by DFliyerz]
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NEMO-Chemistry
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I dont know if that reference was for the full article or not? But I have put the paper in ref section under DOI: 10.1002/9783527610433.chb08105 title
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halogen
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Olefiant gas was't that the name given to ethylene? A bromine water decolorization is a simple test (the simplest?) for unsaturation, and if there are
higher alkenes jointly responsible would probably be minor and in addition to C2. You would want to look up whether cyclopropane reacts positively: I
don't, though I'll regret this, see other likely possibilities, for an abundant gas.
[Edited on 15-4-2017 by halogen]
F. de Lalande and M. Prud'homme showed that a mixture of boric oxide and sodium chloride is decomposed in a stream of dry air or oxygen at a red heat
with the evolution of chlorine.
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kmno4
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Even simple calculations for reaction:
Al+CH2Cl2 -> AlCl3 + ethylene (or methane +C, etc...)
shows that it is strongly exothermic reaction.
However, without proper catalyst, such reaction have too high activation energy to happen under standard conditions.
Here is googled paper, describing reacion of Al and CH2Cl2 to give some organometallic compound(s):
J. Org. Chem., 1988, 53 (12), pp 2829–2835
[Edited on 16-4-2017 by kmno4]
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Melgar
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I read that article, then looked through the articles it references, regarding the reaction products, and found this:
From Morris R. Ort, Edward H. Mottus, Methylene bis(aluminum dihalides), Journal of Organometallic Chemistry, Volume 50, Issue 1, 1973
| Quote: | | During the course of the reaction a sample of the by-product off-gases was obtained and analyzed by mass spectroscopy. The following analysis was
obtained (mole %): C2H4 55.30, C3H6 31.20, CH3Br 9.40, C2H3Br 1.63, C6H12 1.87 and C4H8 0.43. The C3H6 was identified as cyclopropane by comparing the
GLC retention time with known samples of cyclopropane and propylene using a 3 m Poropak Q column at 100C. |
Another major product is methylene bis(aluminum dibromide), which remains dissolved. (AlBr2 connected with a methylene bridge) Apparently this
reaction only occurs in methylene chloride when a catalytic amount of bromine is present, in a form that's reactive with aluminum. However, there is
obviously CH2: radical formation, as well as plenty of ethylene formation, cyclopropane formation, (@halogen: cheers!), and even some monohalide
formation. For anyone wanting to exhaustively methylate an amine to get a quaternary ammonium salt, bubbling the gas from this reaction into an amine
solution seems like it'd do it, and considering the higher volatility of CH3Cl, there would likely be more of it.
The products are actually a lot more interesting that I expected them to be, and for the most part, seem like they'd be easy to separate based on
reactivity. Looking forward to testing this reaction further.
[Edited on 4/16/17 by Melgar]
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kmno4
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Sorry for late response, I just forgot about it.
Forgotten references in attachment.
Attachment: al.txt (7kB)
This file has been downloaded 512 times
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clearly_not_atara
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1,2-dichloroethylene is pretty cool too: it should react with dienes to generate benzenes with loss of 2 HCl.
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AJKOER
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| Quote: Originally posted by Melgar | I found a bunch of references warning against the chemical incompatibility of aluminum and methylene chloride, but other than anhydrous AlCl3, there
was no mention of any reaction products. It certainly evolves gas, although the gas is odorless. That made me think it was hydrogen, but then
where's the carbon going? There's no oxygen for it to attach to. Unless perhaps it's methane? But then, the equations don't work; not enough
hydrogen. It could be ethylene, I suppose, in which case it'd be a nice way for any of us to produce both anhydrous AlCl3 and ethylene at once, from
fairly easily-obtained precursors.
Note that my CH2Cl2 may have had up to 5% methanol, since it was distilled from paint stripper. Not enough to generate the massive volumes of gas I
was seeing, or the AlCl3, but possibly a catalyst or solubilizing agent.
[Edited on 4/3/17 by Melgar] |
As you have noted also in another comment, the creation of radicals including .CH2.
If there is an O2 presence, a possible radical pathway with some C2H4O formation (which would be my guess as to why a stern warning).
Please review the Wikipedia comments on this compound.
Normally, I would not speculate on possible paths as even radical disproportionation may be occurring (see https://en.m.wikipedia.org/wiki/Radical_disproportionation).
-----------------------------------------------------------------------------
But, in the event that someone asks me to speculate, my guess would be:
O2 + e- = .O2-
H+ + .O2- = .HO2 (superoxide/water vapor as aerosols in the atmosphere is said to be present as .HO2)
.CH2 + .CH2 = C2H4
C2H4 + .HO2 = C2H4O + .OH (See equation 51 at https://books.google.com/books?id=FHtgXjd73QEC&pg=PA207&... )
.......
[Edited on 24-6-2017 by AJKOER]
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Melgar
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That's the thing though, the bubbles are evolving far too fast for oxygen from the air to be a significant component. Sure, there may be an
occasional methanol molecule, but methanol is only 5% of the composition at most, and oxygen would preferentially attach to aluminum. Also, when a
single carbon with chlorine and hydrogen attached to it loses atoms to become a radical, it usually loses a hydrogen and a chlorine to become HCl,
then the rest is a radical. Reason being, the hydrogen is pulled off by a base as a proton, leaving the rest with a negative charge. But it's much
easier for a chlorine atom to detach as chloride, than it is for the rest of the molecule to carry that charge, so that happens, leaving the
three-atom radical.
The first step in the process of learning something is admitting that you don't know it already.
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chornedsnorkack
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Could a reaction
CH3OH+CH2->CH3OCH3
be among the options?
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Melgar
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Probably not. To form that, you'd have to pull an entire hydrogen atom off of an oxygen, including its electron, in order to have the rearrangement.
Oxygen only forms radicals when it's attached to another oxygen, or sometimes a halogen. The more polar a bond is, the less likely that either of the
atoms will participate in a free-radical reaction.
The first step in the process of learning something is admitting that you don't know it already.
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chornedsnorkack
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| Quote: Originally posted by Melgar |
Probably not. To form that, you'd have to pull an entire hydrogen atom off of an oxygen, including its electron, in order to have the rearrangement.
Oxygen only forms radicals when it's attached to another oxygen, or sometimes a halogen. The more polar a bond is, the less likely that either of the
atoms will participate in a free-radical reaction. |
Yet O-H insertion is a typical reaction for carbenes. Mechanism descriptions claim an intermediate with three bonds on O.
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Melgar
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Oh, so then the carbon briefly has a lone pair, and the hydrogen becomes acidic and migrates there? I guess I should have thought harder about the
answer, but if more reasons are needed that it wouldn't happen, then CH2 would be unlikely to be formed in large quantities because the typical
radical-forming reaction would be dehydrohalogenation, leaving a CHCl radical. Also, the radicals would be far more likely to attach either to other
radicals or to something with a group that can provide more stabilization of the intermediate radical/ion than a methyl group. And that would include
just about everything.
The first step in the process of learning something is admitting that you don't know it already.
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chornedsnorkack
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| Quote: Originally posted by Melgar |
Oh, so then the carbon briefly has a lone pair, and the hydrogen becomes acidic and migrates there? I guess I should have thought harder about the
answer, but if more reasons are needed that it wouldn't happen, then CH2 would be unlikely to be formed in large quantities because the typical
radical-forming reaction would be dehydrohalogenation, leaving a CHCl radical. |
It´s not clear to me that the prevalent abstraction would be HCl abstraction. An alternative is Al abstracting Cl2, producing carbene
CH2.
Coupling methylenes to form C2H4 could be a prevalent reaction in an inert solvent... and would keep CH2
concentration low. In presence of an appreciable concentration of a reactive compound, like CH3OH, the insertion reaction might be
prevalent.
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clearly_not_atara
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| Quote: Originally posted by chornedsnorkack | | Quote: Originally posted by Melgar |
Probably not. To form that, you'd have to pull an entire hydrogen atom off of an oxygen, including its electron, in order to have the rearrangement.
Oxygen only forms radicals when it's attached to another oxygen, or sometimes a halogen. The more polar a bond is, the less likely that either of the
atoms will participate in a free-radical reaction. |
Yet O-H insertion is a typical reaction for carbenes. Mechanism descriptions claim an intermediate with three bonds on O. |
Can you link a source? I had been searching for ways to make alkyl dichloromethyl ethers by reacting light alcohols with dichlorocarbene, but all of
the reports I found suggested that carbenes insert to the CH bond of alcohols.
The dichloromethyl ether moiety is useful because it reacts with carboxylate salts to liberate the acyl halide with expulsion of the alkyl formate.
Some orgsyn procedures use methyl dichloromethyl ether for this.
[Edited on 27-6-2017 by clearly_not_atara]
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chornedsnorkack
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This:
http://www.massey.ac.nz/~gjrowlan/adv/lct7.pdf
page 4, claims that X-H insertion is faster than C-H insertion
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