Sciencemadness Discussion Board - Preparation of Iodomethane

Preparation of Iodomethane

Arrhenius - 5-7-2009 at 20:03

Iodomethane is widely used as an 'active' methylating agent for the methylation of carbon, nitrogen, oxygen, sulfur and phosphorus. It can also be used to prepare the Corey-Chaykovski reagent for cyclopropanation and epoxidation. Published procedures generally utilize phosphorus and iodine, which are generally unavailable to the amateur. I have prepared iodomethane on 400mmol scale in 81% yield by direct halogenation of methanol.

Introduction
Alkyl halides can generally be prepared from the corresponding alcohol by treatment with the hydrogen halide.(ref. 1) The hydrogen halide may be prepared in situ from its salt and a strong acid.(ref. 2) Phosphoric acid was employed to produce HI (Note 1):

H3PO4 + KI → HI + KH2PO3

While this equilibrium does not favor HI, it can be driven by consuming HI in the following dehydration reaction:

HI + ROH → RI + H2O

This reaction is entropically driven by the removal of the alkyl iodide.

Experimental

**Caution! Iodomethane is a probable carcinogen and is highly volatile!**

All reagents used were technical grade. I combined potassium iodide (66.4g, 400mmol), methanol (120ml, 3mol) and 85% phosphoric acid (175ml, 3mol) in a round bottom flask and flushed the apparatus with argon (note 2). I performed a simple distillation at a relatively slow pace over a period of approximately 3 hours (condensor at -5ºC). A clear product with a boiling point of 55-60ºC distilled over when the reaction mixture reached 90-100ºC. - the potassium iodide was entirely dissolved and the reaction mixture was red. I continued heating until the distillate temperature rose to 70ºC, at which point the reaction should be stopped. I dilluted the distillate with 30ml of cold water and transferred it to a separatory funnel (note 3). I removed the lower layer and dried it with anhydrous calcium chloride. A small amount of copper was added to stabilize the product for storage (note 4).

Results
Crude iodomethane (45.83g) was obtained as a light red liquid in 81% of theory based on potassium iodide. Its IR spectrum is consistent with published spectra.

Discussion
The product obtained in this scaled up procedure is of sufficient purity to use in subsequent reactions. The red color may be avoided by promptly stopping the reaction when the distillate temperature rises above 65ºC. Fractional distillation of the product would also improve purity. Analagous procedures may be used to prepare alkyl bromides in excellent yield; procedures are widely available online.(ref. 3)

Notes
1. Sulfuric acid should be avoided in the preparation of hydrogen iodide because it can oxidize the iodide ion.
2. Inert atmosphere is optional, but appears to improve purity and perhaps yield.
3. The obtained organic phase may be washed with sodium thiosulfate and/or sodium bisulfite to remove free iodine from the product.
4. Copper helps to absorb iodine resulting from the slow decomposition of the product. As with other alkyl halides, iodomethane should be stored in the dark.

References
(1) Sidgwick, NV "The Chemical Elements and Their Compounds" p.1183 (available in sciencemadness library)
(2)Organic Syntheses, Coll. Vol. 4, p.323 (1963); Vol. 31, p.31 (1951). Link
(3) http://www.books-about-california.com/Pages/Experimental_Org...

[Edited on 6-7-2009 by Arrhenius]

CMOS - 6-7-2009 at 03:16

nice work, i'm waiting for more.
why condenser is green??

DJF90 - 6-7-2009 at 04:10

PC coolant in recirculating system I suspect. Nice work Arrhenius. Perhaps a short fractionation column would help rid the orange/red colour?

[Edited on 6-7-2009 by DJF90]

Sedit - 6-7-2009 at 05:42

I was thinking that it was antifreeze.

Arrhenius is the H3PO4 lab grade or otherwise? I have been looking for an over the counter source but so far either highly dilute H3PO4 or navel jelly(worthless) is all I have been able to find.

Nice work. I have been toying with a simular synthesis of Bromoethane but using H2SO4 and NaBr with mixed results due to oxidation of the HBr from H2SO4.

UnintentionalChaos - 6-7-2009 at 05:51

Very nice work. I can get a small quantity of 85% H3PO4 in the near future and will give isopropyl bromide a try by the same route.

Quote: Originally posted by Sedit

Nice work. I have been toying with a simular synthesis of Bromoethane but using H2SO4 and NaBr with mixed results due to oxidation of the HBr from H2SO4.

I was having some spectacular failure at that same reaction using isopropanol. The quality of H2SO4 I have to use can't be helping either.

smuv must be magical: http://www.sciencemadness.org/talk/viewthread.php?tid=10758

[Edited on 7-6-09 by UnintentionalChaos]

Arrhenius - 6-7-2009 at 07:06

All: The condensor is green because I use antifreeze and a circulating cooling bath. It gets to -10C on a good day, and the ethylene glycol won't freeze. Looks high-tech too

DJF90: I suspect a fractional distillation would work quite well (as stated in the 'discussion'), but I'm not worried by the color. A highly pure sample will start to turn redish-brown fairly quickly after the bottle has been opened a few times. I'm going to try some O-methylation shortly, I suppose that'll be a good test.

Sedit: The phosphoric acid is technical grade. I know of one place to get it OTC, which is hydroponics stores. There are pH down products which are conc. phosphoric with some phosphate salts in it. I highly doubt the salts will interfere with the reaction. As for ethyl bromide, I would suggest you follow the prep. in the link at the end of my first post. I've used it to make upwards of 500g of EtBr in one run. Using H2SO4:H2O really mitigates oxidation of bromine. I mean, the reaction is red, but the losses are negligible. I presume NaBr is OTC for you.

Unintentional Chaos: I've made quite a lot of ethyl bromide, and since sodium bromide is OTC (spa bromine source) I would suggest that you use sulfuric acid and water to do the reaction. See the link above for the prep of ethyl bromide and follow that. Keep in mind that elimination to propene may be a competing reaction if you heat too much or use too concentrated an acid catalyst. Purity of the sulfuric acid is not really an issue. I've used brown drain cleaner, no problem.

[Edited on 6-7-2009 by Arrhenius]

Sedit - 6-7-2009 at 09:06

Thank you for the link Arrhenius. Yes NaBr is very over the counter in 52 gram packs for about $1.50 with 99% purity at Wal-Mart. It can be had cheaper but I have yet to find larger containers with equal purity. I have been trying a slow addition of the H2SO4 in an ice bath to try to avoid over oxidation but I feel H2O is a must if for nothing else to help dissolve the NaBr and bring it into solution.

As to not lead such a fine threed astray i'll pm you.

[Edited on 6-7-2009 by Sedit]

Theophrastus_2 - 6-10-2009 at 18:05

Brilliant work arrhenius!

Magpie - 6-10-2009 at 18:38

Sedit: 58 wt% H3PO4 can be made from OTC materials. See
http://www.sciencemadness.org/talk/viewthread.php?tid=2923&a...

Arrhenius: In your top picture you show a tube leading to the RBF in the foreground. Is this for the argon? If so, did you use a continuous purge, or just an initial flush?

[Edited on 7-10-2009 by Magpie]

Arrhenius - 18-10-2009 at 22:03

Magpie: Yes, it's an inert gas (argon) line. I purged it before I began heating, but that was it. On the two runs I made, it didn't seem to effect yield, and perhaps only slightly effected the color of the product. With or without it, I think this is a robust method of preparing good purity iodomethane. I can no longer do chemistry at home, but I sure would like to see someone take a stab at making allyl bromide *hint hint hint*. PM me if you're interested.

If anyone repeats this synthesis, I would appreciate hearing about your yield, etc.

crazyboy - 26-10-2009 at 19:07

How easily can methyl iodide be substituted for other methylating agents such as dimethyl sulfate?

Sedit - 26-10-2009 at 19:18

You are turning methylating reagents into something generic. There are pros and cons of many things and it depends on the reaction at hand you plan on using it for.

crazyboy - 26-10-2009 at 19:51

Quote: Originally posted by Sedit

You are turning methylating reagents into something generic. There are pros and cons of many things and it depends on the reaction at hand you plan on using it for.

2,5-dimethoxybenzaldehyde from 2-hydroxy-5-methoxy benzaldehyde.

http://www.freepatentsonline.com/6670510.html
http://www.usdoj.gov/dea/programs/forensicsci/microgram/jour...

bahamuth - 3-11-2009 at 10:11

My workup.

Methyliodide, Iodomethane.

To a 250ml RB flask in a cold water bath there was added 19g Methanol PA grade, 4.0 grams Phosphorus reagent grade.
Then there was prepared a condenser fit for reflux onto the RB flask and through it there were added 50.0 grams elemental iodine in portions so to not cause boiling, the addition took about 5-7 minutes.
When the addition of the iodine were complete, the flask with the condenser still attached for reflux and cold water running through it, was left stirring for about an hour or so before it was set on a hot water bath for gentle reflux for another half hour or so, before it was taken off the bath to reach RT.
Quickly the flask was set up for simple distillation with the same condenser , with the distillate coming over into a 125ml sep. funnel cooled in a Griffin beaker with icy cold water, again to ensure that no product escapes. The distillation was ended when no more came over to the sep. funnel.
The crude distillate, brown, milky, from iodine and water brought over by the MeI, was washed twice with 0,1M NaOH, top layer removed by decantation, so it was clear and colorless, and once with RO water before it was transferred to a clean, dry RB flask with about 5-10 grams of anhydr. Calcium chloride prills. This was left for 10 minutes or so to ensure all water was removed by the calcium chloride, and then set up for a final distillation on hot water bath, with a brown preweighed flask for receiver. The RB flask was distilled to complete dryness for, yet again, ensuring no loss of product. The product was perfect clear with no color.

This procedure should yield over 80%, my first try I got ≈47.5 grams which is ≈84.9%.
My second run, with three times the amounts listed above, yield rose to ≈89% (149.3 grams), as to why I do not know, perhaps a larger system gives better yields.
Finally the product was stored over around .5 grams powdered Cu metal to act as stabilizer in a brown black painted bottle with Teflon lined cap.
From 200 grams of iodine, 197 grams of MeI came over, with ≈223.7 grams as 100%, giving an overall yield ≈88%.

BTW, red phosphorus can be obtained from vendors who sell "bulk" crystal iodide on ebay, ask if they got a website...

[Edited on 3-11-2009 by bahamuth]

DJF90 - 3-11-2009 at 10:59

Interesting work up. Why do you wash with NaOH? This seems strange to me; I would work up the reaction using a sodium thiosulfate wash followed by a brine wash. This should remove all the residual iodine, and most of the water in your product. Drying can then be commenced over CaCl2, although I would probably use potassium carbonate myself. But nice prep, and nice yeild.

bahamuth - 3-11-2009 at 14:32

I washed with 0.1M NaOH because I found this old student assignment on the net somewhere, cannot remember where now though, but here is the original writeup:

129. Preparation of Methyl Iodide from Methyl Alcohol and Phosphorus Iodide (Sections 49, 204).
- In a 200 cc. round-bottomed flask place 15 grams of methyl alcohol and 3.2 grams of red phosphorus.

Have ready a reflux condenser with cork attached.

Place the flask in cold water and add in small portions at a time 38 grams of iodine;
the addition should take about 10 minutes.

If the contents of the flask begin to boil, attach it to the reflux condenser;
when reaction ceases add more iodine.

Finally attach the flask to the condenser and let it stand for at least 4 hours (preferably over night).

Distil through a condenser from a water-bath, as long as any liquid passes over.

The receiver should be placed in cold water as methyl iodide is very volatile.
Wash the distillate by decantation with a dilute aqueous solution of sodium hydroxide
until the lower layer is colorless, and then once with water.

Separate the methyl iodide carefully from the water using a separatory funnel,
and transfer it to a small distilling flask.

Add about 10 grams of anhydrous calcium chloride.

Stopper the flask, place a cork over the end of the side-arm, and set aside until the liquid is quite clear.

Place a thermometer in the flask, connect the latter with a condenser, and distil from a water-bath.

Note the boiling-point and weight of the methyl iodide.

Calculate the theoretical yield from the iodine used (why iodine?),
and the percentage of this obtained.

Methyl iodide boils at 44°, and has the specific gravity 2.27 at 15°.
The yield in the experiment should be about 80 per cent of the theory.

Note. - An excess of the alcohol is usually taken in preparing alkyl halides by the method illustrated above.
The phosphorus and iodine are used in the proportions necessary to form phosphorus tri-iodide, PI3.

Also did this workup synthesizing propyliodide with a little less yield, I think, could not find my papers just now to confirm.

[Edited on 3-11-2009 by bahamuth]

entropy51 - 3-11-2009 at 17:25

Nice job bahamuth, but for some of us that would be a waste of iodine and phosphorus, both of which are watched, especially on ebay. MeI can be made using NaI and H3PO4 or gaseous HCl, which are more accessible and safe to order or make. www.hms-beagle.com was also selling MeI recently.

Arrhenius - 6-11-2009 at 22:18

That procedure using NaOH is in Reference 3 from my initial post. In my opinion, the phosphoric acid method still represents the safest, most economical way to prepare iodomethane.

Anders Hoveland - 19-6-2010 at 21:15

Iodomethane is known to react with anhydrous AgClO4 dissolved in benzene to make AgI precipitate and methyl-perchlorate, which is likely to spontaneously explode if separated from a solvent. Using IodoEthane would, then give Ethyl Perchlorate, which is discussed elsewhere on this forum. The precipitation reaction is rather slow, and AgClO4 hydrate is impossible to dry by heating (AgClO4 will explode).

crazyboy - 17-10-2010 at 13:21

How should one go about disposing of the reaction mixture and cleaning the distillation equipment in a safe way?

EDIT: never mind, sending it to HazMat disposal.

[Edited on 18-10-2010 by crazyboy]

Arrhenius - 21-10-2010 at 20:28

Whoa really? I would just chuck it down the drain.... frankly. There's not much alkyl iodide in it, and the acid will be diluted to harmless concentrations, and the methanol has a very short environmental half life.

crazyboy - 21-10-2010 at 21:37

Quote: Originally posted by Arrhenius

Whoa really? I would just chuck it down the drain.... frankly. There's not much alkyl iodide in it, and the acid will be diluted to harmless concentrations, and the methanol has a very short environmental half life.

Honestly I dilute just about everything and toss it down the drain. But methylating agents are something else, wouldn't want to mutate the sea life and all.

peach - 1-1-2012 at 20:35

Quote:

Carcinogenicity in mammals:

Methyl iodide is listed under California Proposition 65 (1986) as a chemical known by the state to cause cancer or reproductive toxicity based on evaluative studies performed in the 1970s.[18] It is considered a potential occupational carcinogen by the U.S. National Institute for Occupational Safety and Health (NIOSH), the U.S. Occupational Safety and Health Administration and the U.S. Centers for Disease Control and Prevention.[19] The International Agency for Research on Cancer concluded based on studies performed after methyl iodide was Proposition 65 listed that: “Methyl iodide is not classifiable as to its carcinogenicity to humans (Group 3).” As of 2007 the Environmental Protection Agency classifies it as "not likely to be carcinogenic to humans in the absence of altered thyroid hormone homeostatis," i.e. it is a human carcinogen but only at doses large enough to disrupt thyroid function (via excess iodide).[20] However this finding is disputed by the Pesticide Action Network which states that the EPA’s cancer rating "appears to be based solely on a single rat inhalation study in which 66% of the control group and 54-62% of the rats in the other groups died before the end of the study". They go on to state: "The EPA appears to be dismissing early peer-reviewed studies in favor of two nonpeer-reviewed studies conducted by the registrant that are flawed in design and execution."[21] Despite requests by the U.S. EPA to the Pesticide Action Network to bring forth scientific evidence of their claims, they have not done so.

I have phosphoric, phosphorus, KI and iodine, but noted the wiki article mentioning;

Quote:

Methyl iodide can also be prepared by the reaction of methanol with potassium iodide, catalyzed by acid:

CH3OH + KI + H2SO4 → CH3I + K2SO4 + H2O

The reaction is carried out at low temperature and the water generated in the reaction is trapped by excess sulfuric acid so the reaction is not reversible. The generated methyl iodide can be distilled from the reaction mixture.

I have also seen this appearing elsewhere.

There a few oddities about the wiki article, such as;

The acid in the formula is not a catalyst, it's a reactant.
Also from the formula, the sulphuric is not acting as a drying agent. On the contrary, it and the methanol are the source of the water on the right hand side.

Adding concentrated sulphuric to iodide salt and warming the two up was the route by which iodine it's self was first isolated. I posted photos of me rerunning this original isolation in this thread, when I accidentally made iodoacetone towards the end of it.

I suspected the wiki note was edited based on hearsay.

Arrhenius has already demonstrated the preparation with phosphoric acid, and bahamuth has shown it with phosphorus. The other method is with DMS, not a healthy thing to be using. Even if the yields were quantitative, I would still prefer the phosphoric option.

So I thought I'd try this supposed sulphuric mention.

I carried it out in much the same manner as Arrhenius, but swapping phosphoric for 98% sulphuric.

Quote: Originally posted by DJF90

Interesting work up. Why do you wash with NaOH? This seems strange to me; I would work up the reaction using a sodium thiosulfate wash followed by a brine wash. This should remove all the residual iodine, and most of the water in your product. Drying can then be commenced over CaCl2, although I would probably use potassium carbonate myself. But nice prep, and nice yeild.

Any moisture around the PI3 method will cause it to decompose, with one of the products being hydrogen iodide; a gas down to -34C. Any that escapes may, in some percentage, end up in the resulting distillate.

I don't think a column is all that worthwhile if it causes much extra effort. To ensure all of the product is over, it's best to allow it to go up to the BP of methanol, as Arrhenius suggests.

If there is any iodine in the hot flask, enough of that will make it's way over, column or not, that it'll benefit from a thiosulphate rinse.

Which I did, and it does a great deal to clean the result up.

I also rinsed with brine.

Quote:

In my opinion, the phosphoric acid method still represents the safest, most economical way to prepare iodomethane.

Agreed. The only real competition for it is with phosphorus. Which is a lot more effort to get hold of and adds some potential health risks that are not present with phosphoric. It also means measuring out iodine it's self; much messier than KI.

----------------------------------------------------------------------------

Experimental:

I took the copypasta equation from wiki and scaled it to 25ml.

The methanol and KI were combined and cooled in the freezer, with the sulphuric sat next to them. I prepared a salt / ice bath and sat the flask in there, adding a squirt of the acid and giving them a swirl until it was all in, then set up a simple distillation.

Distillation began with a colourless, low viscosity liquid coming over at the BP for methyl iodide. The temperature was gradually rising in a continuous band towards that of methanol.

After approximately 1 to 1.5ml of colourless liquid had been collected, a dark brown began appearing within the still and was soon crossing over. I continued the distillation until the temperature fell back down from around 70C - all volatiles removed.

I had started with 5.8g (approx. 7ml) of methanol. The theoretical yield of methyl iodide would therefore be 24.8g (approx. 10.9ml). My actual volume was 7.3ml of something blatantly contaminated.

Retaining the volatiles in the distillation tube and using a disposable pipette, I washed with 3ml x 2 water to remove the methanol. Then again with 3ml x 2 of thiosulphate, making the second more concentrated as it did not seem to be budging the staining too quickly as it was. The second wash entirely removed the stain. I finished by washing with 3ml of brine.

The layers separate very nicely throughout, but I left this to stand for approximately an hour whilst I tidied up and preweighed a test tube (14.24533g). Returning, I noted the volume of the suspect iodide as being 2.7ml. I then withdrew the base layer, placing it into the preweighed tube and noting that less approx. 0.1ml remained in the distillation tube.

I remeasured the mass of the storage tube and found it to be 19.68300g. Giving a mass change of 5.43767g for a volume of 2.6ml, and so a density of 2.09g/ml, with that of methyl iodide being 2.28g/ml. The density obtained would be correct if the volume was 2.8ml. As I made no attempt to standardize the temperature and the graduations on those tubes are likely not super accurate, that's reasonably close (8% off). My sample may also have a trace of moisture or methanol left in it.

The yield from methanol (using sulphuric in place of phosphoric) is a terrible 22%.

I cleaned a small length of copper wire in sulphuric, then under a running tap, gave it a dry and dropped it in with the methyl iodide. Which shall live in the fridge for now until I can find something more suitable to store it in.

Tidying up:

The sulphuric has oxidised most of the iodide to iodine. The glass is full of it. I knocked and rinsed it back out, removed the (rock solid) lump of potassium sulphate from the flask, dumped it all into a big beaker, filled it up with water, stirred it all to get the sulphate dissolved, then ran it all through a filter paper to recover the (so large it's actually useful) mass of iodine.

Yep

It does work. It works badly.

There is probably some way to increase the yield with sulphuric but I doubt it's worth it.

I have made ethyl iodide in the past and found mentions of preferably leaving it to reflux overnight (bahamuth has posted an example including that). When I tried ethyl iodide by PI3, only refluxing for a few hours, I did note a low yield. With the method described by Arrhenius, similarly, it may increase the yield a little if it's left to go overnight.

For anyone else preparing it, the point Arrhenius made to distill up to the BP of methanol is important. As you can see, I had just over 1ml of colourless methyl iodide prior to the brown beginning to appear and the temperature rising, yet I have double that after washing by allowing the distillation to continue upwards.

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That's the phosphoric, phosphorus and sulphuric variations tried. And some sweet team action. Hands up who's doing DMS?

[Edited on 3-1-2012 by peach]

entropy51 - 2-1-2012 at 15:11

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.

Sedit - 2-1-2012 at 15:58

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

peach - 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

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]

UnintentionalChaos - 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]

Scr0t - 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.

Quatro - 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?

S.C. Wack - 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)

JJay - 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.

Amos - 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.

JJay - 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.

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.

alimonium - 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 ?

Chemi Pharma - 12-8-2017 at 19:45

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)
This file has been downloaded 1262 times

NaK - 16-4-2020 at 10:06

Quote: Originally posted by alimonium

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 ?

I tried it stichiometricly and almost didn't work at all. I got like 5 grams from expected 60 grams of iodomethane.
That makes sense as there are two equilibrium reactions going on:
KI + H3PO4 <-> KH2PO4 + HI
HI + CH3OH <-> CH3I + H2O

The more water and the less phosphoric acid, methanol and iodide are in there the slower the reaction will proceed, to a point where it's basically just methanol coming over.

I didn't have a flask big enough matching the destillation setup i wanted to use so instead of having a large methanol excess I added magnesium sulfate as drying agent to the mixture. Removing water will also drive the equilibrium. Worked pretty well and I got liquid coming over at 50C.

That also implies to use the highest concentration of phosphoric acid you can find, 85% is common. As concentrated phosphoric acid is pretty hygroscopic having a concentration even higher might improve the yield.

A good indicator how well this reaction works is the temperature of the distillate. If it rises to 70C too early you can be pretty sure that something is wrong.

[Edited on 16-4-2020 by NaK]

Cou - 3-7-2020 at 22:11

very nice i might try this x)

Tsjerk - 12-8-2020 at 02:37

Very nice and easy preparation! I'm running it at the moment. I did notice however there are copious amounts of methanol coming over with the distillate even when running at such a pace the distillation head is kept at around 43 degrees. The product is coming over with a drop every 2/3 seconds at this temperature. Okay... I don't use a fractionating column and the ambient temperature at the moment is 31 degrees, so little to no reflux going on, but still.

Why I noticed is the following: I'm collecting over a column filled with CaCl2 and the methanol is dissolving the CaCl2. In the collection vessel it is salted out (solubility of CaCl2 in methanol is 20/100 gr/gr at 0 degrees...). Not a problem, as it will be easy to separate, but be aware. I'm preparing the MeI for a grignard, in which methanol would be quite a pain.

NaK - 1-9-2020 at 13:38

That's why you need such a large excess of MeOH

[Edited on 1-9-2020 by NaK]

DReed123 - 3-9-2020 at 20:51

I'll just mention that the linked study in the above post regarding 95% phosphoric acid is legit. In it the authors found insane increases in yield with the 10% increase in phosphoric acid concentration. This follows from thermodynamics because water is a product of the reaction. It's probably a good idea to toss a dessicant like mag or sodium sulfate in the reaction vessel to help drive the reaction towards the right as well.

[Edited on 4-9-2020 by DReed123]

[Edited on 4-9-2020 by DReed123]

clearly_not_atara - 4-9-2020 at 06:09

I think the phosphoric acid is the desiccant. Using an excess of phosphoric acid makes sense -- you want to maximize the efficiency of utilizing iodide, which is far more expensive than the phosphoric acid or your alcohol, most likely.

What I don't understand is why we are concentrating 85% phosphoric acid by adding P2O5 rather than just heating it. It will eat away at glass but it should be fine to dehydrate phosphoric acid in stainless steel.

Sulfates, I think, would not be good desiccants here because they are (weakly, but still) basic and a little oxidizing.

DReed123 - 7-9-2020 at 16:04

Phosphorus Pentoxide is the anhydride of phosphoric acid. You can safely add it in small portions if you put the phosphoric acid in the freezer first. Toslyic acid would likely be ideal as well. Good point on using the sulfates. That's actually why phosphoric acid is used instead of sulfuric acid..too oxidizing for iodide. For some of the alkyl halides the authors found yield doubled in switching from 85% to 95%, which is pretty insane.

[Edited on 8-9-2020 by DReed123]

[Edited on 8-9-2020 by DReed123]

Mateo_swe - 7-5-2022 at 07:04

Is it possible to use NaI instead of the KI (same mol%) in the original procedure (first post) without changing any other parameters?
If one adds some phosphorus pentoxide to OTC 75% phosphoric acid, can the increased concentration of the phosphoric acid be determined by some simple means like density measurement or must a titration be made?

SuperOxide - 7-5-2022 at 15:26

Quote: Originally posted by Mateo_swe

If one adds some phosphorus pentoxide to OTC 75% phosphoric acid, can the increased concentration of the phosphoric acid be determined by some simple means like density measurement or must a titration be made?

Yeah, you should be able to. If you add too much then it just starts to turn into PPA (Polyphosphoric Acid), which I could be wrong but I don't think that would be too big of a deal. PPA just turns back into phosphoric acid once you add some water to it.

You could get pretty close to 100% just by adding the proper molar amount though. That's what I would do (then maybe just use density to verify the concentration, roughly)

Keras - 8-5-2022 at 02:57

IINM, 100% H₃PO₄ is a solid with m.p. around 40 °C.
It cannot be obtained from commercially available grades (75, 85%) because the acid ‘polymerises’ before being entirely dehydrated. In any case, it boils away before reaching the anhydride form.

So you can probably reach 100% phosphoric acid by addition of phosphorus pentoxide, but be warned that:
1. P₂O₅ is hard to work with, especially because the phosphoric acid that forms tends to form a syrupy layer covering the unreacted material and preventing it to react further
2. The resulting material will be solid and very difficult to stir

Now, I’m a bit skeptical about this, because lately I tried to get HBr out of a mix of phosphoric acid and NaBr that I heated. Any evolved gas was led into a bubbler full of water. I heated quite a bit (but not high enough to endanger the glass), got dew on the flask, and quite a lot of bubbles, but they turned out to be only air, since the water in the bubbler was only very slightly acidic when I stopped the ‘reaction’ (pH ~ 6). So far, for me, phosphoric acid is not strong enough to evolve HBr in appreciable quantities from NaBr. Now I agree in this experiment the few molecules of HI produced are consumed right away in the substitution reaction, which drives it forward, but I’m still surprised it works so well.

Boffis - 8-5-2022 at 12:09

Do you really need such strong acid? If the acid is merely a catalyst and the product is exceedingly volatile you can probably us a large excess of rather dilute phosphoric acid and K or NaI and add a small excess of methanol, heat to 70 C and continually fractionate off the methyl iodide. See Fery's thread on the reactive distillation of ethyl formate. I have tried this and found that you can distil ethyl formate out of the mixture until the formic acid content is only 5%!! The only advantage of high strength acid is that it increases the reaction rate. If you distil it very slowly you can get ethyl formate at even this low concentration of acid as I report in Fery's thred.

clearly_not_atara - 8-5-2022 at 14:35

Quote: Originally posted by Keras

IINM, 100% H₃PO₄ is a solid with m.p. around 40 °C.
It cannot be obtained from commercially available grades (75, 85%) because the acid ‘polymerises’ before being entirely dehydrated. In any case, it boils away before reaching the anhydride form.

Unless there's some way to stabilize it that I haven't heard of, any phosphoric acid exists in equilibrium with its oligomers:

2 H3PO4 <> H2O + H4P2O7

H3PO4 + H4P2O7 <> H2O + H5P3O10

etc, see for example https://link.springer.com/content/pdf/10.1007/BF00648228.pdf

This equilibrium is the same regardless if the phosphoric acid is dehydrated by heating or by adding anhydrides. I stand by my original supposition that adding P2O5 to phosphoric acid is just wasting P2O5. But I think Boffis may be right about the concentrated acid being unnecessary.

You could also use TsOH so that you never worry about damaging glassware.

Keras - 8-5-2022 at 21:41

Quote: Originally posted by clearly_not_atara

Unless there's some way to stabilize it that I haven't heard of, any phosphoric acid exists in equilibrium with its oligomers:

2 H3PO4 <> H2O + H4P2O7
H3PO4 + H4P2O7 <> H2O + H5P3O10
etc, see for example https://link.springer.com/content/pdf/10.1007/BF00648228.pdf

This equilibrium is the same regardless if the phosphoric acid is dehydrated by heating or by adding anhydrides. I stand by my original supposition that adding P2O5 to phosphoric acid is just wasting P2O5. But I think Boffis may be right about the concentrated acid being unnecessary.

You could also use TsOH so that you never worry about damaging glassware.

I would have to read the article you provide a link to, but from what I gathered from the article in attachment, the equilibrium is not reached unless the temperature is raised. Besides, true orthophosphoric acid doesn’t seem to etch glass. The effect is caused by hot polymerised acid.

I wonder if protecting the glassware with a silver mirror would be an effective treatment against etching, both in hot phosphoric acid and fused NaOH cases, such as in the decarboxylation of benzoic acid to get benzene.

Also this free article.

Attachment: Phosphoric Acid on Glass.pdf (321kB)
This file has been downloaded 207 times

Boffis - 10-5-2022 at 04:23

I have been thinking about this a bit more and I checked up on the pKa values for various acid. For practical purposes the value for HI is 0 but the first base of phosphoric acid is 2.15 and pKa2 is 7.2 so the concentration of free HI in the mixture of KI and phosphoric acid is going to be very low. The only way this reaction is going to work is to continually remove the methyl iodide as it forms and this may also explain why the acid concentration needs to be so high. Tosylic acid is a much stronger acid but if you were to use it to replace the phosphoric acid you would have to add more than one molar equivalence to the KI use to liberate the HI as the reaction proceeds.

Keras - 10-5-2022 at 06:46

AFAIK, TsOH has pKa -2.7, so definitely the reaction KI + TsOH → TsOK + HI should be next to complete.

Texium - 10-5-2022 at 07:11

Quote: Originally posted by Keras

AFAIK, TsOH has pKa -2.7, so definitely the reaction KI + TsOH → TsOK + HI should be next to complete.

Not sure what’s leading you to that conclusion, considering HI has a pKa of -9.3.

[Edited on 5-10-2022 by Texium]

clearly_not_atara - 10-5-2022 at 08:12

Quote: Originally posted by Keras

Ah, yes, refutation by "I don't feel like reading it", the highest form of argument.

While you apparently don't want to read my articles, I am quite capable of reading yours. Of course, it doesn't say anything about the stability of orthophosphoric acid at temperatures below 300 C. But it does refer to the original source by van Wazer, which you also didn't read. That's okay, because van Wazer just references earlier work by Bell, which is attached. Here's the last sentence of the article:

"No difference in composition was found between strong phosphoric acids prepared by heat and those prepared by the addition of phosphorus pentoxide"

So, as I previously emphasized, you are simply telling people to waste P2O5 for no good reason whatsoever.

While pure orthophosphoric acid cannot be prepared under standard conditions, Bell also finds that (nearly) pure crystalline pyrophosphoric acid apparently can, by dehydrating to just the right composition and cooling. This may have advantages for storing and measuring?

Attachment: bell1948.pdf (564kB)
This file has been downloaded 231 times

Boffis - 11-5-2022 at 04:48

Looking at the strength of HI I now understand the problem of liberating it from an alkaline iodide with acids.

This immediately raises the obvious question of "why not reduce iodine to HI in the presence of methanol". This is essentially the red phosphorus route. The well known problem of obtaining red phosphorus is the reason it is little used. There are, however, other reducing agents such as hydrogen sulphide and possibly organic compounds like ascorbic acid that might work. Hydrogen sulphide certainly does and since the liberated sulphur is not volatile and the product can be easily distilled out of the reaction mixture how about this idea:

Dissolve iodine in excess cold methanol and pass in hydrogen sulphide until the iodine has been decolourised and the mixture turned milky yellow. Warm slowly to reflux for say a couple of hours and then fractionate. The excess methanol can be recovered by simply filtering, neutralize and distill. The low boiling distillate should be neutralized too and then fractionated again.

Keras - 11-5-2022 at 05:20

Quote: Originally posted by Texium

Quote: Originally posted by Keras

AFAIK, TsOH has pKa -2.7, so definitely the reaction KI + TsOH → TsOK + HI should be next to complete.

Not sure what’s leading you to that conclusion, considering HI has a pKa of -9.3.

Well, the preceding message quoted a pKa of 0, I didn't bother to check (though I must admit I was a bit surprised because of all the halogen acids, HI is reputedly the strongest. But the wording of the message made me think that this theoretical consideration was just, like, theoretical.)

[Edited on 11-5-2022 by Keras]

Keras - 11-5-2022 at 05:27

Quote: Originally posted by clearly_not_atara

Ah, yes, refutation by "I don't feel like reading it", the highest form of argument.

Lol. No, don’t worry. I was just a bit busy when I answered. And then I moved on and forgot about it. My bad.

Quote: Originally posted by clearly_not_atara

"No difference in composition was found between strong phosphoric acids prepared by heat and those prepared by the addition of phosphorus pentoxide"

So, as I previously emphasized, you are simply telling people to waste P2O5 for no good reason whatsoever.

Oh, no. Quite the contrary in fact, since 100% ‘phosphoric’ acid would be quite impossible to handle anyway, being solid.

And PS: This time I promise I’ll read your reference!

[Edited on 11-5-2022 by Keras]

clearly_not_atara - 11-5-2022 at 08:16

Keras: Crystals of H3PO4 can indeed be obtained by various means, as described e.g. by Ross and Durgin 1925:
https://pubs.acs.org/doi/pdf/10.1021/ie50190a031

However, in all cases they are prepared by simply cooling and/or seeding a solution, and when the crystals melt, an equilibrium mixture is quickly established. Phosphoric acid and diphosphoric acid exist as (sort of) pure substances in the solid state, but not as liquids.

Quote: Originally posted by Boffis

Looking at the strength of HI I now understand the problem of liberating it from an alkaline iodide with acids.

It's true that TsOH is about a million times weaker than HI, and H3PO4 another hundred thousand times weaker still, but this doesn't completely preclude distilling HI for a couple of reasons. For one thing, when you use concentrated acid, the solvent isn't water anymore, and all of the dissociation constants change. For another thing, vapor pressures are roughly exponential with temperature, so HI will be more than a million times as volatile as TsOH.

It should also be noted that the diphosphoric acid, H4P2O7, has a pKa1 of about 0.97, making it more than ten times as strong as orthophosphoric acid (pKa1 = 2.12). Obtained from (using pKa = -log(Ka) / log(10)):
https://cdnsciencepub.com/doi/pdf/10.1139/v54-024

[Edited on 11-5-2022 by clearly_not_atara]

Keras - 11-5-2022 at 09:24

Quote: Originally posted by clearly_not_atara

Keras: Crystals of H3PO4 can indeed be obtained by various means, as described e.g. by Ross and Durgin 1925:
https://pubs.acs.org/doi/pdf/10.1021/ie50190a031

However, in all cases they are prepared by simply cooling and/or seeding a solution, and when the crystals melt, an equilibrium mixture is quickly established. Phosphoric acid and diphosphoric acid exist as (sort of) pure substances in the solid state, but not as liquids.

I wonder if you can obtain pure phosphoric acid as a byproduct of, say, bromination of ethanol using phosphorus and TsOH.

Quote: Originally posted by clearly_not_atara

It's true that TsOH is about a million times weaker than HI, and H3PO4 another hundred thousand times weaker still, but this doesn't completely preclude distilling HI for a couple of reasons.
[…]

As I said before, I tried to make HBr out of NaBr and 85% phosphoric acid and despite heating to circa 200 °C and eliminating a lot of water vapour, I didn't get an ounce of acid, even if it should have distilled at 122 °C.

clearly_not_atara - 11-5-2022 at 09:53

^Theory is worse than practice

But I think you'd have a better shot with TsOH. You can, for example, produce HCl (g) from hydrochloric acid and CaCl2, and the latter is barely even acidic.

Keras - 11-5-2022 at 10:45

Quote: Originally posted by clearly_not_atara

^Theory is worse than practice

But I think you'd have a better shot with TsOH. You can, for example, produce HCl (g) from hydrochloric acid and CaCl2, and the latter is barely even acidic.

You mean by dehydrating it?

TBH, when I dismantled the flask I heated, there was a strong indication of some acidic gas floating over the phosphoric acid. It was just too thin to make it to the wash bottle. Do you think a silver mirror made out of silver nitrate and Fehling's solution could protect the glass and allow pushing the temperature higher?

I have small quantities of KI and tosylic acid over here. I can try at least qualitatively to validate the process, using xylene as solvent (for high boiling point).

[Edited on 11-5-2022 by Keras]

Keras - 13-5-2022 at 08:29

I just happened to mix TsOH and KI in a beaker on a back of an envelope today. Experiment was made with max. a dozen of milligrams of both TsOH and KI.
First try in xylene. Bad choice. Neither TsOH nor KI seems to be soluble in it. I was not expecting KI to dissolve, but TsOH stubbornly stayed solid. Nevertheless, the crystals slowly took on a brown tinge, and the xylene a slight pink tinge (dissolved iodine?).

I discarded the xylene and carried on with acetone. TsOH dissolved at once in it. KI didn't, or even-so-slightly, considering my acetone is technical and must contain water. The solution slowly turned orange and then brown. I let the acetone evaporate and was left with a deep ochre goo. I was expecting iodoacetone to form (H⁺ action on the enol form of acetone). There was an unmistakable lacrimatory compound in there, in very small quantities, though I can’t say if it’s simply HI or iodoacetone. But it definitely was eye-watering.

In both cases, I⁻ appeared to be oxidised to some extent. Whether it is by air oxygen or TsOH, I don’t know. But betting on TsOH as a non-oxidising strong acid seems risky.

clearly_not_atara - 13-5-2022 at 19:26

Interesting. HI is a very strong reductant. It can actually reduce benzene to cyclohexane (which rearranges to methylcyclopentane).

Bis(oxalato)boric acid is very strong and non-oxidizing. It is prepared by combining boric acid and oxalic acid in a 1:2 ratio. This patent says it has a pKa of -0.2 in DMSO, making it stronger than HBr (compare the Bordwell table)

https://patents.google.com/patent/DE10108608C2/en
https://organicchemistrydata.org/hansreich/resources/pka/#ka...

I don't think xylene will be a good solvent for any of this, it is very nonpolar. Acetone, maybe, though self-condensation is still a possibility. I don't know if mesityl oxide is lachrymatory, but it could have formed under your conditions.

I think acetonitrile might be ideal. Even HI has a pKa of just 2.8 in MeCN:

https://d-nb.info/1227454171/34

[Edited on 14-5-2022 by clearly_not_atara]

Keras - 13-5-2022 at 23:33

Quote: Originally posted by clearly_not_atara

Interesting. HI is a very strong reductant. It can actually reduce benzene to cyclohexane (which rearranges to methylcyclopentane).

Darn, to reduce an aromatic compound, it must be quite strong indeed. And why would cyclohexane rearrange to a five-member cycle?

What I can hardly figure is how you can actually produce HI out of KI and H₂SO₄ given than sulphuric acid’s pKa is actually less than HI’s.

Quote: Originally posted by clearly_not_atara

Bis(oxalato)boric acid is very strong and non-oxidizing. It is prepared by combining boric acid and oxalic acid in a 1:2 ratio. This patent says it has a pKa of -0.2 in DMSO, making it stronger than HBr.

Interesting. I have both oxalic and boric acid, though not at hand r.n. I might have a crack at it later this month, though.

Quote: Originally posted by clearly_not_atara

I don't think xylene will be a good solvent for any of this, it is very nonpolar. Acetone, maybe, though self-condensation is still a possibility. I don't know if mesityl oxide is lachrymatory, but it could have formed under your conditions.

You’re right. I discounted aldol condensation, because I considered it being promoted by base rather than acid, but it seems both work as catalyst. The compound clearly tickled the eye and the smell was pungent. That’s all I can say. I will probably order a microscale glass kit later this year, so as to be able to carry out small experiments with more quantitative results.

Quote: Originally posted by clearly_not_atara

I think acetonitrile might be ideal. Even HI has a pKa of just 2.8 in MeCN.

Then I’ll try with MeCN. Same deadline. I’ll let you know, if you or someone else don’t do it before.

And big thanks for all the reference material I never had heard of, and which is now safe and sound on my hard disk!

[Edited on 14-5-2022 by Keras]