neptunium
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x rays activated reactions
hello SciMad,
i was wondering if some chemical reaction that normaly wouldnt happen could go on if irradiated with UV light or X rays?
for example,
i am trying to attach an Iodine atom to a methyl radical from a disolution of iodine in methanol to get iodomethane.
the C-O bond (weakest one in CH3OH) has an energy of 360Kj/mol or 2.24e24 ev
1 bond (divide by A) is 3.72ev or 5.96e-19J
so theoraticaly e=h/v hence e/h=v
5.96e-19/h= 8.99e14 Hz somewhere in the high UV
but i am worry that it will come to an equilibrium as other bond gets brocken and radicals reattached themselves.
i tried with a UVC lite for an hour but nothing noticeable happened
i do have a fully fonctionnal Xray machine working at 40Kv
but that might be too much ?
any thoughts?
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entropy51
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I don't know about your specdific application, but there are chemical reactions that can be driven by ionizing radiation. For example, the Fricke
dosimeter employs free radical mediated oxidation of ferrous to ferric iron to give a color that can be measured spectrophotometically and is used to
calibrate radiation fields for radiotherapy.
I don't know what doses your x-ray can deliver, but I think more than a few Gray would be needed for a practical application on the preparative scale.
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watson.fawkes
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Quote: Originally posted by neptunium  | | i was wondering if some chemical reaction that normaly wouldnt happen could go on if irradiated with UV light or X rays? |
There's a whole industry of UV-driven polymerization reactions. For example, the fancy apparently-seamless acrylic display cases you
see both in museums and perfume counters are mostly fabricated with UV-curing resins these days. Solvent-based glues usually generate at least some
bubbles in the seam.
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AndersHoveland
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Iodomethane could be prepared by simply exposing a mixture of methane gas and iodide vapor to sunlight for several hours. These types of reactions
proceed through a radical cascade mechanism. A note of warning, iodomethane is a poisonous alkylating agent.
[Edited on 31-1-2012 by AndersHoveland]
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unionised
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" iodine in methanol to get iodomethane"
Where do you think the oxygen goes?
Xrays will tend to smash up molecules, rather than give nice well defined reactions.
I'm not sure that the reaction of iodine with methane will work because I think the CH bond is too strong- the HI and IC bonds produced are not very
robust and I'm not certain that they will offset the energetic cost of breaking the CH bond.
In particular, I don't think this gives the cascade mechanism that Cl2 + methane does.
Your UV lamp quite possibly produces less intense UV than ordinary sunlight.
The number of Xray photons per second from a typical Xray source is much smaller than the number of photons per second in sunlight.
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neptunium
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that UVB lamp has a photon output by far much less than the sun has no questions here,
but the energy spectrum of this lamp ( used to kill germs and desinfect and produces ozone in a few seconds) is a different order of magnitude than
what we get on the ground after atmosphere filtration..
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AndersHoveland
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Reaction between CH4 and I2 catalysed by 183.4 nm (uv) light.
http://pubs.acs.org/doi/abs/10.1021/ja01500a005
but I think even vissible light is sufficient, because Br2 molecules can be broken apart by blue light. also see
http://www.sciencemadness.org/talk/viewthread.php?tid=14063
[Edited on 2-2-2012 by AndersHoveland]
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neptunium
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Bromine and chlorine are always easier to react with anything than iodine, thats why i chose I2.
thats too bad you have to pay for the full article the first page was interesting ..Thanks Anders! much apreciate it
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AndersHoveland
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but radical cascade reactions are easier to initiate with bromine or iodine than chlorine. The bond between two iodine atoms is especially weak. Once
the bond is broken, an iodine radical could (presumably) proceed to attack methane.
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madscientist
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If the goal is methyl iodide, perhaps you could toss some red phosphorus or hypophosphorous acid in there with the methanol and iodine? It should
generate HI in situ...
Simply hitting methanol and I<sub>2</sub> with UV light will, if anything, probably just oxidize the methanol (I<sub>2</sub>
is an oxidizer, after all), producing formaldehyde, HI, formyl iodide, and carbonyl iodide, the latter two most likely degrading to iodine,
HI, and carbon monoxide. You'd see some methyl iodide from whatever HI was formed.
I hope you know how nasty methyl iodide is - it is a very potent carcinogen and really, you should work with this in a glovebox if at all possible.
I've smelled enough stenches making their way out of very functional fumehoods to know that you still get considerable exposure when working in one.
[Edited on 2-2-2012 by madscientist]
I weep at the sight of flaming acetic anhydride.
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AndersHoveland
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Apparently sulfur dioxide and iodine can be reacted with methanol to form sulfuric acid and methyl iodide, which separate into two separate liquid
layers.
Dokiya, Kameyama, Fukuda (1979)
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madscientist
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That is potentially a very interesting reaction, do you have a more specific citation? A procedure would be helpful.
I weep at the sight of flaming acetic anhydride.
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neptunium
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yes indeed ! i would use red phosphorus if had any !
i know how toxic CH3I is i was just using this reaction as an example .
but the SO2 bubbling in methanol/I2 sounds like a great idea...
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unionised
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Did you look at the paper?
The quantum yield is quoted as bad to awful.
Whereas the quantum yield for a free radical chain mechanism is typically >>1
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ScienceSquirrel
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Thread Pruned
13-3-2012 at 05:14 |
Texium
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Thread Moved
20-11-2023 at 12:05 |
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