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Author: Subject: Iodomethane prep.
sakshaug007
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I was researching methods of making methyl iodide a couple months ago, particularly safe methods using readily available chemicals. What I found and ultimately wanted to try was a Kolbe electrolysis method using a solution of sodium acetate and potassium iodide. I would assume the yields would be low (due to side ethane, iodine, and oxygen byproducts) but it would be cheap and safe to do. Would anyone with the materials and equipment be willing to try this and report on its success/failure?

Thanks

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woelen

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I did the experiment with making CH3I again and my result was not very different from my previous attempt. I again dissolved some P4O10 in CH3OH and added a solution of NaI in CH3OH. Used amounts: 3 grams of P4O10, 5 grams of NaI and approximately 25 ml of CH3OH.

Now I did not have charring. I added the P4O10 much more carefully and more slowly. The solution, however, was not completely clear. It was a mobile liquid (not viscous, nor flocculent), but it was opalescent. When this is added to the solution of NaI, then nothing seems to happen at first, but over time, some flocculent precipitate is formed (is this some phosphate salt of sodium and methyl?).

Distilling gives a perfectly clear and colorless liquid, boiling over at a quickly increasing temperatur. The temperature just before the gas mix goes into the cooler starts at around 50 C but it increases to well over 60 C. I get the impression that the CH3I is not easily separated from CH3OH by simple distillation.

The clear liquid collected in the receiving flask gives a white liquid when a small amount of water is added. Two layers are formed, but only a very small amount of lower liquid (the heavier CH3I).

Again, I have the feeling that the result is not really good, but I have learned quite a few things now. Most important is that the distillation needs to be done VERY carefully and really slowly, but for me this is not that easy to do. I do have a (non-isolated) vigreux column, but the losses (vapor and droplets on the glass) with such a long column are too large with such small quantities as I use and there is the problem of wind around the column, which makes the flow of gas into the cooler unpredicatable. I do not want to do this experiment on a larger scale.

Another interesting observation is that the mixture really needs to be distilled. The distillation drives off CH3I (together with CH3OH), which lets the reaction go to completion. I also did an experiment in which I simply dissolved NaI and P4O10 in methanol, let it reflux for a while and then add a small amount of water. This does not give any white precipitate and no CH3I separates from the liquid. Only by distilling away the CH3I the reaction can be brought to completion, but it is not that easy.

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Klute
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Why not forming trimethylphosphate by pyrolysis of the P4O10/MeOH mixture? I guess TMP and NaI will forming MeI easily, but you could just aswell use TMP for most methylation needs! There is a patent on forming TMP in the TMP thread I started a while ago...

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smuv
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Azeotrope

http://www.chemeng.ed.ac.uk/people/jack/azeotrope/II.html#Io...

As a rough rule compounds that are rather different in polarity form azeotropes; as well, compounds with bp's close to one another are also more likely to form azeotropes.

You can remove the methanol with calcium chloride or maybe even by standing over P2O5.

Glad to see you do some organic reactions btw.

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Mush
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Quote: Originally posted by Nicodem
 Quote: Originally posted by Sauron I have not found any other lit on prep of MeSCN, so f you run across any, please call them to my attention.

Alkylation of KSCN with alkyl idodides, bromides or tosylates is the most standard method for preparing alkyl thiocyanates. I have no idea why would one want to use the barium salt. Maybe it used to be comercialy available in the ancient times. KSCN is well soluble in acetonitrile as solvent and the reaction with primary alkyl bromides/iodides/tosylates is rapid (with methyl iodide or dimethyl sulfate it should be over in a couple of hours at <40°C). Methanol, ethanol, DMF and other solvents where KSCN is soluble can also be used. There are plenty of references in the literature.
Here are a few outputs from Beilstein regarding the MeSCN synthesis:

Methylation of KSCN with (MeO)2SO2:
Walden, Chemische Berichte, 40 (1907) 3215 (and/or 4301?)
Kaufler, Pomeranz, Monatshefte fuer Chemie, 22 (1901) 495.
Rybin, Zil'berman, Trachenko, J. Gen. Chem. USSR (Engl. Transl.), 50 (1980) 1702-1705.

Methylation of KSCN with MeI:
Hassanein, Akelah, Selim, El-Hamshary, Indian Journal of Chemistry, Section B: Organic Chemistry Including Medicinal Chemistry, 29 (1990) 763-765.
Jaworski, International Journal of Chemical Kinetics, 35 (2003) 61-66 (DOI: 10.1002/kin.10105) nonpreparative, kinetics study

Methylation of KSCN with Ca(MeOSO3)2:
Muspratt, Justus Liebigs Annalen der Chemie, 65 (1848) 253,257.
Cahours, Justus Liebigs Annalen der Chemie, 61 (1847) 96.

MeSCN from S-methylisothiourea hydrochloride thermolysis at 160-200°C:
Arndt, Chemische Berichte, 54 (1921) 2242.

Preparation and synthetic applications of
poly(vinylbenzylphosphonium)-bound thiocyanate,
nitrite and borohydride reagents

Hassanein, Akelah, Selim, El-Hamshary,

Indian Journal of Chemistry, Section B: Organic Chemistry Including Medicinal Chemistry, 29 (1990) 763-765.

Attachment: Indian Journal of Chemistry, Section B Organic Chemistry Including Medicinal Chemistry, 29 (1990) 763-765.pdf (2.4MB)
Chemi Pharma
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I have a study that claims the better way to produce alkyl iodides from alcohols, ethers or even alkenes is using an alkaline iodide (sodium/potassium), with 95% phosphoric acid, giving 90-95% yield.

Since 95% phosphoric acid isn't an easy reagent to find and buy at the market, the study teaches how to produce it from the comercial and cheap 85% phosphoric acid and P2O5.

You know that P2O5 added to phosphoric acid increase it's concentration up to more than 100% and means the way to produce even polyphosphoric acid, widely used in organic cyclizations and acylations.

Here's the paper:

Attachment: Iodides from clevage of ethers or iodination of alcohols and alkenes with KI + H3PO4.pdf (328kB)
Melgar
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 Quote: Originally posted by Chemi Pharma I have a study that claims the better way to produce alkyl iodides from alcohols, ethers or even alkenes is using an alkaline iodide (sodium/potassium), with 95% phosphoric acid, giving 90-95% yield.

The 95% yield is with respect to the alcohol/ether though. I don't really care about how much $5/kg methanol I'd use though, I care much more about the$100/kg potassium iodide. In that paper, the iodide was used 2-3 times in excess.

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Chemi Pharma
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But you can't deny Melgar, it's a better way then use methanol, red phosphorous and iodine, don't you think that? The classic sinthesis use much more expensive and watched reagents. Instead, I'm offering (I think) an economic, high yielding and secure way to sinthesize alkyl iodides using unsuspected reagents.
Corrosive Joeseph
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"Crystalline Orthophosphoric Acid

According to Simon and Schulze, very pure, crystalline H3PO4 may be prepared by evaporating 83% phosphoric acid in
high vacuum to crystallization.

A Platinum-Gold alloy dish is fastened by melting in a glass flask. The dish is filled with 83% phosphoric acid,
which is then concentrated to 99% at 80degreesC and 1mm.

The procedure takes one week."

Taken from - "Orthophosphoric Acid" in Handbook of Preparative Inorganic Chemistry, 2nd ed., G. Brauer (ed.),
Academic Press, NY. Vol. 1. page 543. (1963)

http://gen.lib.rus.ec/book/index.php?md5=9E06458DD73B42C60B0...

/CJ
Melgar
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 Quote: Originally posted by Chemi Pharma But you can't deny Melgar, it's a better way then use methanol, red phosphorous and iodine, don't you think that? The classic sinthesis use much more expensive and watched reagents. Instead, I'm offering (I think) an economic, high yielding and secure way to sinthesize alkyl iodides using unsuspected reagents.

Yeah, although the method you're mentioning is nothing new; it's actually the standard way to prepare methyl iodide. It'd be preferable to optimize the reaction conditions to conserve KI, though, so saying the yield is 95% is a bit misleading.

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clearly_not_atara
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Perhaps thermal decomposition of tetramethylammonium iodide could be utilized? The Wikipedia page for the analogous tetraethylammonium iodide claims decomposition at 280 C.

The tetramethylammonium iodide can then be prepared from potassium iodide and Me4NCl in dry methanol. KI has very good solubility in methanol and KCl has very low solubility in the same.

And I know I'm adding a lot of steps but I'm pretty sure that methylsulfuric acid -- easily prepared -- can quaternize ammonia to Me4NSO4H, tetramethylammonium bisulfate. The rxn of this compound with CaCl2 should convert it to the chloride, which can then be used in the double displacement with KI.

Metacelsus
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 Quote: Originally posted by clearly_not_atara Perhaps thermal decomposition of tetramethylammonium iodide could be utilized? The Wikipedia page for the analogous tetraethylammonium iodide claims decomposition at 280 C.

I expect decomposition of the tetraethylammonium salt to proceed by an elimination to produce ethylene, not ethyl iodide. The analogous process would not be possible for tetramethylammonium salts.

As below, so above.
JJay
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I wonder if potassium methyl sulfate and potassium iodide would form methyl iodide if heated together. Prepchem lists a procedure using dimethyl sulfate and potassium iodide that produces "nearly the theoretical amount," but it uses approximately equimolar quantities: http://www.prepchem.com/synthesis-of-methyl-iodide/

S.C. Wack
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No

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JJay
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Good to know. I guess the side reactions at elevated temperatures would obliterate the yield.

S.C. Wack
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I would not think the thermal stability while mixed with stuff is all that great, even if it works. IIRC the original lit (I noted after scanning Vanino) did this and indicated same, with better luck with KBr and best with KCl.

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JJay
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I just took a look at Vanino, and it says that the yield is only 93%.

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 Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » Iodomethane prep. Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues