Author Topic: Etard reaction and safety  (Read 210 times)

badger

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Etard reaction and safety
« on: March 12, 2010, 03:09:05 PM »
I have access to reasonably pure toluene, potassium dichromate, and 90% sulfuric acid. I've been reading about the Etard reaction and am thinking about synthesizing some chromyl chloride to oxidize toluene to benzaldehyde. There's a youtube video (http://www.youtube.com/watch?v=D9qEmaiYSPk) that demonstrates the K2Cr2O7 + 4NaCl + 6H2SO4 >>> 2 CrO2Cl2 + 2KHSO4 + 4NaHSO4 + 3H2O reaction, and it seems pretty straightforward; the chromyl chloride in the vial seems to want to climb up the sides, but I was thinking maybe a long-necked volumetric flask might be one way to contain the fumes a bit.

I'm concerned about the concentration of the sulfuric acid, though, because chromyl chloride releases HCl and hexavalent chromium on contact with water, neither of which I am super keen on the idea of. How difficult is it to dry sulfuric acid? The idea of distilling H2SO4 gives me the willies but could I add some CaCl2 or MgSO4 or CaO to suck out the water? Or does it actually even matter given that water is a reaction product?

Now of course all that said, http://www.sciencemadness.org/talk/viewthread.php?action=printable&fid=10&tid=2223 discusses another route from toluene involving MnO2 (look for "Patent DE102221 from 1897"), and immediately below, a description of the preparation of chromyl chloride and that its use is similar to the MnO2. Which is now making me wonder whether one could simply prepare chromyl chloride in a long-necked flask to minimize fume escaping, then add toluene and H2SO4 into the flask with the CrO2Cl2 (and some sodium/potassium bisulfite). What would happen to the aqueous bisulfites?

Also, a little farther down the SM page there is a mention of using CCl4 as the solvent -- I assume that is for a liquid-liquid extraction during workup?

Any advice is appreciated -- btw, benzaldehyde is commonly used in soap making to give the soap the smell of almonds, several hundred mL are needed for a one-kilogram batch of soap. Saponification reactions are cool to do at home ;) and soap making is a very good reason to have sodium hydroxide in bulk ...

Evilblaze

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Re: Etard reaction and safety
« Reply #1 on: March 13, 2010, 11:13:54 AM »
Sorry, but you should learn chemistry first.

"How difficult is it to dry sulfuric acid? The idea of distilling H2SO4 gives me the willies but could I add some CaCl2 or MgSO4 or CaO to suck out the water?"

The H2SO4 can be distilled until it forms an azeotope with water, this will contain 98,3% H2SO4, this is enough good for this synthesis.
To "dry" it out there is two ways what can be used: add sulfur trioxide to it or add phosphorus pentoxide. Both are dangerous chemicals, don't play with them.
If you add CaCl2 CaSO4 and HCl will be produced, but the acid won't dry out.
MgSO4 will dissolve in the H2SO4, but it wont dehydrate it.
CaO will form CaSO4 and one mole of water.

"Which is now making me wonder whether one could simply prepare chromyl chloride in a long-necked flask to minimize fume escaping, then add toluene and H2SO4 into the flask with the CrO2Cl2"

What do you want to make exactly? If you add the toluene directly to the chromyl chloride it will burn or if you are unlucky, than it will explode, this is why they use the CrO2Cl2 in CCl4 solutions. The reaction is still very violent, but the large excess of the CCl4 prevents the reaction from fire. A brownish/reddish sludge will form what should be hydrolyzed by water and distilled to obtain the benzaldehyde.

"benzaldehyde is commonly used in soap making to give the soap the smell of almonds"

Yes, it is used for several things. It is not so hard to buy a bottle from it at the local chem supply shop. And it is really cheap (cheaper than the chromyl chloride and the CCl4).

But is you want to make your own benzaldehyde, than I suggest you should make it with a KMnO4 or MnO2/H2SO4 oxidation. It is less hard to make, less dangerous and less carcinogen than the chromyl chloride.....
« Last Edit: March 13, 2010, 11:16:07 AM by Evilblaze »

badger

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Re: Etard reaction and safety
« Reply #2 on: March 13, 2010, 04:11:25 PM »
Sorry, but you should learn chemistry first.

That would be why I'm asking n00b questions on a forum rather than haring off into the basement to try every idea that comes to mind. I know enough to know that there are a lot of things I need to learn fast.

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The H2SO4 can be distilled until it forms an azeotope with water, this will contain 98,3% H2SO4, this is enough good for this synthesis.

It's "what constitutes 'good enough'" that I'm really curious about. In particular, since the reaction already forms 3 moles of water for every 2 of chromyl chloride, I wonder how much damage some additional initial water will do.

However I've now found a local OTC source of 98% sulfuric acid, so if I do decide to go ahead and make chromyl chloride I can just use the purer material, then later find out if more dilute H2SO4 will still work.

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What do you want to make exactly? If you add the toluene directly to the chromyl chloride it will burn or if you are unlucky, than it will explode, this is why they use the CrO2Cl2 in CCl4 solutions. The reaction is still very violent, but the large excess of the CCl4 prevents the reaction from fire. A brownish/reddish sludge will form what should be hydrolyzed by water and distilled to obtain the benzaldehyde.

This is exactly the kind of information I was looking for; thank you. I had not yet found a source describing the setup and reaction conditions for the Etard, and your explanation led me to this paper: http://article.pubs.nrc-cnrc.gc.ca/ppv/RPViewDoc?issn=1480-3291&volume=36&issue=4&startPage=667

Carbon tetrachloride is pretty difficult to get, but Org Syn seems to suggest that dichloromethane can be used instead for terminal olefins in general:

http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV6P1028

So now what I'm wondering is whether I can follow the description in the SM thread, setting up a 3-neck RBF with NaCl and K2Cr2O7 dry in the flask, condenser leading out the side to a receiving flask already containing cold dichloromethane (maybe put the receiver in an ice bath), and add the H2SO4 with an addition funnel, thereby distilling directly into DCM. I'd weigh the DCM flask before and after distillation of chromyl chloride to determine yield. Then I could immediately use the product in the Org Syn procedure.

I seem to recall seeing people somewhere on the net asking whether anyone had tried it with DCM; it seems worth a stab.

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It is not so hard to buy a bottle from it at the local chem supply shop. And it is really cheap (cheaper than the chromyl chloride and the CCl4).

I cannot get it at my local chem supply shop. I have one, but they don't do special orders. They're sort of like a hardware store from the 1940s.

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But is you want to make your own benzaldehyde, than I suggest you should make it with a KMnO4 or MnO2/H2SO4 oxidation. It is less hard to make, less dangerous and less carcinogen than the chromyl chloride.....

The problem there is the KMnO4 or the MnO2. My supplier doesn't carry either. I've heard of retrieving MnO2 from Li/MnO2 batteries, but that sounds like an annoying task, and people here have said it doesn't work very well.

I might be able to get my hands on some KMnO4 but my understanding is that it is a vicious oxidizer and might very well oxidize the product beyond benzaldehyde (is that benzoic acid?), whereas the benefit of the Etard reaction is that it stops at the aldehyde. Please correct me if I'm mistaken here.

Vesp

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Re: Etard reaction and safety
« Reply #3 on: March 13, 2010, 09:09:14 PM »
Pretty sure KMnO4 will not produce Benzaldehyde... I'd love to see a reference for it doing that!

MnO2 I don't think works well... The best methods around AFAIK is the manganese persulfate...Mn(SO4)2 or the chlorination of toluene via Cl2 and UV light to produce benzyl chloride, which reacts via the somnolent reaction with hexamine to produce benzaldehyde. There is much talk about these methods on the forum already, and on Douchermanns FTP account.
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badger

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Re: Etard reaction and safety
« Reply #4 on: March 13, 2010, 09:35:33 PM »
The best methods around AFAIK is the manganese persulfate...Mn(SO4)2 or the chlorination of toluene via Cl2 and UV light to produce benzyl chloride, which reacts via the somnolent reaction with hexamine to produce benzaldehyde. There is much talk about these methods on the forum already, and on Douchermanns FTP account.

I've also seen len1's really excellent article on SM, which describes and depicts the benzyl chloride route quite well. Part of why I'm interested in chromyl chloride is the fact that it doesn't seem like a lot of amateur investigation has been done along that route yet. The real concerns, I think, are materials availability and safety ... if DCM works as a replacement for CCl4, and if the apparatus can be made vapor-tight enough to avoid exposure to the dangerous reagents.

The Org Syn writeup mentions using zinc "to reduce the higher valence chromium salts, thereby eliminating overoxidation and double bond cleavage" -- this sounds like it would help control losses to benzoic acid, which as I recall were still an issue with the benzyl chloride route. Zinc powder isn't too hard to get or make.

Evilblaze

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Re: Etard reaction and safety
« Reply #5 on: March 15, 2010, 04:16:27 PM »
Pretty sure KMnO4 will not produce Benzaldehyde... I'd love to see a reference for it doing that! 

KMnO4 oxidation works. Actually one of my friends used it with 18-20% yield. Dilute KMnO4 + dilute H2SO4 and it worked. Just need a distillation after the synth to get "pure" benzaldehyhe. I agree, this method is really bad, but it is cheap and easy.
This method was on SM.

The other way by KMnO4 is from benzyl alcohol. Solventfree KMnO4 oxidaton with good yields (+75%).
This method is described here: http://www.erowid.org/archive/rhodium/pdf/solventfree.kmno4.oxidation.pdf

badger

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Re: Etard reaction and safety
« Reply #6 on: March 15, 2010, 05:48:57 PM »
Turns out I can get KMnO4 (and 98% H2SO4) locally, although I will have to show them my ID for the KMnO4. I don't mind though ... if anyone wants to come investigate I'm happy to show them my soap-making equipment, and even send them home with a bar of almond scented soap :D

I'll give this a try and report back. I seem to recall that the yields for chromyl chloride aren't that great either, so 18-20% yield is worth a stab. (Although parachlorotoluene apparently gives 100% yield!)

Do you think extracting into DCM, filtering or distilling, then evaporating the solvent might work better than simple distillation?

Vesp

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Re: Etard reaction and safety
« Reply #7 on: March 16, 2010, 02:12:07 AM »
Distillation may not be needed -- one could form an adduce with the bisulfite or make the hydrobenzamide with ammonia, filtering out the solids and than returning it into benzaldehyde ought to give you a toluene free substance. While distillation might give some problems.

That is good to know the KMnO4 can do that, Benzoic acid isn't a useless side product either.
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badger

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Re: Etard reaction and safety
« Reply #8 on: March 16, 2010, 06:48:01 AM »
I've seen a few references to bisulfite adducts of aldehydes, but hadn't really looked into it until now. http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv5p0437 describes forming the adduct with a 1:1 molar ratio of bisulfite to benzaldehyde; does it matter if there's an excess of bisulfite?

I was initially wondering whether the bisulfite could be added in solution at the start to capture the benzaldehyde as it's formed and prevent conversion to benzoic acid, but it sounds like the bisulfite reduces MnO4-, so that wouldn't help.

I'd really like to see a cite on this dilute KMnO4 thing, because every reference I've found talks about toluene + KMnO4 >>> benzoic acid as a common classroom demonstration. Evilblaze, how dilute were the solutions your friend used? Molarity would be nice to know.

lugh

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Re: Etard reaction and safety
« Reply #9 on: March 27, 2010, 10:05:38 PM »
This article might help in gaining understanding:
Chemistry is our Covalent Bond

jon

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Re: Etard reaction and safety
« Reply #10 on: March 29, 2010, 01:04:46 PM »
initially i thought this was something out of the urban dictionary u know just refer to some of my previous posts for Ex: of what an etard is.
another factor in kmno4 oxidations is temp.
concetration is importante but wit proper thermodynamic control you can master what mno4- does in a system.
i'm etarded and i know that

oh by the way i get so emotional when i listen to brittney spear's music.

Tsathoggua

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Re: Etard reaction and safety
« Reply #11 on: June 11, 2011, 10:00:29 PM »
Bear in mind also the dangers of carbon tet....it is exceedingly hepatotoxic, used to be used as dry-cleaning fluid but got banned (and for general consumer use, as opposed to [clandestine] chemist purposes, with good reason where safety is concerned) Much, much more so than dichlor, and even more so than chloroform*

*which, very surprisingly is actually still used to a limited extent in the UK medicinal arsenal, several brands of codeine linctus are available, although very very hard to get, most pharmacies not stocking it anymore, and those that do, refusing to sell in a fair few cases, one of the brands, carex I think its called, comes in a white labelled bottle, is flavoured with chloroform, soluabilized with EtOH, and contains enough CHCl3 for it to be percievable as an oily blob when a bottle of the linctus is dissolved in a nonalcoholic soft drink...yummy with tesco brand limeade...it tastes strongly of chloroform when drank either neat or dissolved in a fizzy drink..I am very surprised they allow it to be in something that is consumed, especially a product for oral ingestion...the codeine linctus product in question tastes very strongly of chloroform, much like dichlor smells-sweetish and pungent, although without the 'bite' carried in the scent of an accidental whiff of methylene chloride vapor.

C-tet though is another matter, it has been banned for consumer use nearly worldwide, even in chemistry labs it is nearly forbidden entirely, alternate solvents are demanded near universally, save for when carbon tet is actually the reactant needed, or an alternate suitable solvent cannot be found/used for some specific practical reason.

I think quite such an extensive reaction is a bit of an overreaction, given how some things are still used when alternatives are available without quite such fervour to eliminating their use.

As for production of chromyl chloride....well....93% H2SO4 will produce chromyl chloride when added to a mixture of a dichromate salt and salt, it fumes on exposure to atmospheric moisture, as said, to give hexavalent Cr, and HCl, the boiling point is a little over that of water, 117 degrees C. Dark red liquid, looks not that different from elemental bromine, its a very powerful oxidizer, and will go for most inorganic structural materials such as plastics, rubber seals etc and corrode the crap out of them. Use a perfluroalkane grease for the glassware to avoid attack.

Tsathoggua once had a mishap with this stuff....he was distilling some, in his bedroom at the time, not the best idea of course, but he had nowhere else, much younger in his days, many centuries ago, and the glass broke. That was pretty friggin' well hairy...spilled conc. H2SO4 (thankfully mostly reacted...he thinks thankfully...maybe...at any rate..) and let the CrO2Cl2 loose all over the damn place along with a bit of H2SO4, but due to the lack of structural damage that the wooden surface the distillation went awry over, he thinks it was almost entirely Cr2Cl2 and residual acid/salt.

Left green stains all over the wooden surface, this is the color signifying presence of hexavalent Cr. After legging it out of the room to get a safe breath of air, then back in to grab his gas mask, and mount an immediate containent operation, he left the house after this was done and the mopped up nasties disposed of, for a long time, not coming back for hours, until dark, leaving the room to ventilate.

Lets just say, that night, the inexperienced young toad-deity actually slept wearing a gas mask. One of only two times he ever has...and certainly the last time he will ever have to.

So, from his experience, 93% sulfuric is good enough and will produce CrO2Cl2, and lots of it, when added to dichromate and salt.

Trivia-chlorides can be tested for by addition of the test substrate to a dichromate and the addition of conc. H2SO4, if the red fumes/liquid of chromyl chloride evolve, then a chloride was present in the test sample, this reaction does not do the same thing if a bromide, fluoride, iodide, or the pseudohalogens cyanide, and I am fairly sure, azide, are present instead (although bugger me if I, or tsathoggua would dare try that on an azide...danger of explosion, and addition to azide of acid liberates the deadly hydrazoic acid...which is an unstable explosive gas, forms a solution, like HCN, and is a rapid acting and highly lethal poison just as HCN is)

Vesp-By the way, it is a 'sommelet' reaction you refer to, not a 'somnolent' rxn, the word 'somnolent' refers to sleepyness or sedation, from 'Somnus', the Roman counterpart of the greek god of sleep, Hypnos, the adjective for the state of being so affected being 'somnolent'
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