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Author: Subject: Preparation of Iodomethane
peach
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[*] posted on 2-1-2012 at 19:30


Quote: Originally posted by entropy51  
Methyl iodide can also be made by gassing a saturated solution of KI in methanol with HCL gas.

I've not been able to find the ancient reference in which I found this method, but I have used it and it does work. I'd been thinking that I should post something on it since it does not seem to be generally known.


It'd be worth putting that up here, as I expect it works better than the sulphuric idea.

The wiki page needs editing to swap sulphuric for phosphoric, preferably with a note about sulphuric giving a much lower yield and a redirect to the HI page.

The hydrogen chloride method could also go on there.

Quote: Originally posted by Sedit  
Peach if you do not have phosphoric acid perhaps you could use your Sulfuric and react it with Toluene to make TsOH. This is a non-oxidizing acid that should work rather well in this synthesis. Its solid so its easy to weigh and handle.

Its funny this thread was just brought up because I just came in from setting up an electrochemical cell with EtOH, NaBr and NaOAc to see if I can do a Kolbe coupling to produce Methyl bromide. Just another day of me tossing things together and playing around. Once of these days I swear I will take chemistry seriously :P


Part of the reason for me not immediately trying all of the methods (such as the hydrogen chloride) for methyl iodide was that I was interested in making all of the iodides rather than looking at just the one - as per the pokemon mantra, catching them all.

So I've been busy making some iodoform today, but I should have sublimated the iodine I recovered from the above post, as the resulting iodoform wasn't too nice to look at. I'll probably redo that tomorrow.

And methylene iodide is up next. One option being to use HI with the iodoform or the Finkelstein swap with DCM. Got two tubs of KI, but NaI would be better. I've either got to make some or buy it.

I do have phosphoric and phosphorus, but your TsOH suggestion for methyl iodide is good for those who don't. I started trying to make benzene sulphonic acid two weeks ago or so, but that needs redoing too as the first try was a mess. I obtained black as my primary product.

[Edited on 3-1-2012 by peach]




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[*] posted on 17-6-2014 at 23:26


Repetition of procedures is always welcome, right?

I ran this prep, but with 500mmol (83.00g) of KI instead of 400mmol and identical amounts of other reagents. Distillation flask was a 500ml RBF. Condenser and recieving flask were chilled with/in ice water. Recieving flask contained 50ml of ice water from the start to help slow evaporation. Distillation was slow and took 1hr, 40 minutes. The stillpot was maintained at ~85-90C until the end when it rose to 100C. Distillation was stopped when the stillhead reached 67C.

A reciever was swapped and for interest, distillation was maintained for an additional 20 minutes. A few drops of extremely dark material collected under the water. The vast majority of the distillate was miscible (methanol, I would assume).

The biphasic distillate was placed in a 250ml seperatory funnel and a chilled solution of 2.04g of anhydrous CaCl2 in 10ml of distilled water was added to speed clearing of the aqueous phase. The upper phase was discarded and the lower, pale red organic phase was washed with 50ml of ice-cold distilled water containing ~1g of NaCl and a spatula tip of sodium metabisulfite. On shaking, the red color immediately vanished and the lower phase became colorless. The organic layer was transferred to a 50ml RBF and allowed to stand over anhydrous CaCl2 for a few hours in a fridge. Gravity filtration through a tiny plug of cotton afforded 56.73g of methyl iodide as a dense, colorless, volatile liquid. This is a 79.9% yield from KI.

This is an extremely reliable and easy procedure. The yield is great, provided you take steps to avoid evaporative losses, and it needs no phosphorus or iodine.

Storage is preferably at -20C or in ampoules. A tiny amount of precipitated copper powder will keep it colorless for months/years at these temps. I made mine with acidified CuSO4 solution and zinc granules. I've had a considerable amount of MeI evaporate from tightly-sealed teflon-lined vials (at -20C!) when stored for several months/years. Make as needed to avoid having money evaporate on you...

[Edited on 6-18-14 by UnintentionalChaos]




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[*] posted on 18-6-2014 at 13:12


It's even more tolerant than that!

You don't need to monitor temperature and you can just distill until it stops (still pot <=200'C) and it can be distilled more quickly too with no significant impact on yield i.e. +80%.
It can be done with 75% P2O5 that's solid at room temperature with the same yields.
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[*] posted on 10-11-2015 at 20:58


Does anyone have experience making MeI by gassing a saturated solution of KI in MeOH with HCL gas?

Or how about refluxing Methanol, Phosphoric Acid, and Sodium Iodide?

NaI + H3PO4 → NaH2PO4 + HI
CH3OH + HI → CH3I + H2O
CH3OH + H3PO4 + NaI → CH3I + H2O + NaH2PO4

(Not sure if that other equation is correct, but the key point is that HI can be made with Phosphoric acid and sodium Iodide. HI and Methanol form Methyl Iodide)

Anyone have suggestions?




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[*] posted on 11-11-2015 at 17:51


Sur la préparation des éthers iodhydrique, bromhydrique et méthyliodhydrique.
Par J. E. de Vrij, professeur de chimie à Rotterdam.

Quoique le procédé de M. E. Soubeiran pour la préparation de l’éther iodhydrique publié dans ce Journal, t. XXX, p. 5, donne des résultats très-satisfaisants, il ne sera peut-être pas sans quelque intérêt de connaître le procédé dont je me sers depuis plus de trois ans, dont le principal mérite consiste en ce qu’on n’emploie pas le phosphore et qu’on peut préparer des kilogrammes d’éther à la fois sans le moindre danger. Pour préparer l’éther iodhydrique, on commence par saturer l’alcool de gaz acide hydrochlorique sec. Si l’alcool est privé d’eau, autant que possible et bien refroidi il peut dissoudre entre 0,5 à 0,6 de son poids de gaz acide hydrochlorique. Après avoir constaté la quantité d’acide hydrochlorique contenu dans l’alcool, on introduit une quantité déterminée d’iodure de potassium pulvérisé dans une cornue, et on y verse une quantité d’alcool contenant assez d’acide hydrochlorique pour former avec le potassium du chlorure de potassium. Le lendemain on distille et on obtient une quantité d’éther équivalente à la quantité d'iodure de potassium employé. Cet éther qui ordinairement ne retient pas du tout ou très-peu d’iode libre, est ensuite lavé et rectifié comme dans tous les autres procédés. La seule condition pour obtenir un résultat satisfaisant, c’est de faire absorber par l’alcool la plus grande quantité possible de gaz acide hydrochlorique, ce qui se fait plus facilement en hiver, ou en plaçant l’alcool dans un mélange réfrigérant pendant qu’on y introduit le gaz.

Éther méthyliodhydique. — Cet éther s’obtient de la même manière et encore plus facilement. Aussitôt qu’on ajoute l’esprit de bois saturé de gaz acide hydrochlorique sur l’iodure de potassium, la réaction commence immédiatement et le mélange s’échauffe, de sorte que si on prépare de grandes quantités de cet éther il sera prudent de verser le liquide par parties sur l’iodure alcalin, afin de prévenir une trop grande élévation de température. L’esprit de bois bien purifié, d’une densité de 0,798, peut absorber 0,6 de son poids de gaz acide hydrochlorique.

Éther bromhydrique. — Cet éther s’obtient aussi très-facilement en distillant à une douce chaleur 4 parties de bromure de potassium pulvérisé avec 5 parties d’un mélange de 10 parties d’acide sulfurique concentré et de 5 parties d’alcool de 96° G. L.

Journal de pharmacie et de chimie 169 (1857)




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[*] posted on 12-11-2015 at 01:33


Entirely out of academic curiosity - is it possible to make MeI by reacting aluminum, methanol, and elemental iodine? I assume you'd need a really cold reflux column.
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[*] posted on 12-11-2015 at 09:47


Quote: Originally posted by JJay  
Entirely out of academic curiosity - is it possible to make MeI by reacting aluminum, methanol, and elemental iodine? I assume you'd need a really cold reflux column.


Actually, I have done this, and it would've been much more successful if I had taken more steps to prevent evaporation or MeI escaping from my reflux apparatus. I got about a 25% yield but was able to recover over half of the starting iodine, so I can probably attribute the biggest drop in yield to problems with the equilibrium, such as not using anhydrous reagents. If you want to know more, Chem Player on YouTube has a video on making ethyl iodide in a pretty good yield using ethanol instead of methanol. This is what I was basing my methyl iodide synth on.




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[*] posted on 12-11-2015 at 15:17


Quote: Originally posted by Amos  
Quote: Originally posted by JJay  
Entirely out of academic curiosity - is it possible to make MeI by reacting aluminum, methanol, and elemental iodine? I assume you'd need a really cold reflux column.


Actually, I have done this, and it would've been much more successful if I had taken more steps to prevent evaporation or MeI escaping from my reflux apparatus. I got about a 25% yield but was able to recover over half of the starting iodine, so I can probably attribute the biggest drop in yield to problems with the equilibrium, such as not using anhydrous reagents. If you want to know more, Chem Player on YouTube has a video on making ethyl iodide in a pretty good yield using ethanol instead of methanol. This is what I was basing my methyl iodide synth on.


I saw Chem Player's video... its pretty interesting. I was considering making some EtI or EtBr last week. The yields in the video aren't that bad but are too low for my purposes given the high cost of iodine.

Using anhydrous reagents and a drying tube is often the difference between a low yield with lots of side products and a quantitative yield... but I don't think the yields would be that much higher than Chem Player's even if everything was anhydrous.
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[*] posted on 3-5-2016 at 18:12


I'm curious why such an excess of phosphoric acid is used ? I'm thinking the extra ethanol helps the iodide distill instead of sitting at the bottom of the flask, but why so much acid? Would yields suffer if stoichiometric amounts were used ?
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