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cnidocyte
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Strong acids
I like this one http://en.wikipedia.org/wiki/Trifluoromethanesulfonic_acid
They call it trifilic acid. This stuff reacts with alcohols to form ethers and alkenes.
Heres a cool one
http://en.wikipedia.org/wiki/Fluoroantimonic_acid
even the molecular structure scares me.
Flourosulfonic acid is a nice one too
http://en.wikipedia.org/wiki/Fluorosulfonic_acid
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peach
Bon Vivant
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Superacid
Superbase
Lewis acid / base theory
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garage chemist
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This reminds me that I've been wanting to prepare fluorosulfonic acid for quite some time.
Brauer gives the method of adding HF gas through a steel capillary to liquid SO3 contained in an aluminium vessel. Simple and quantitative, but I have
no means of generating anhydrous HF gas. Same for the reaction of ClSO3H with HF.
A more convenient method is the reaction of KHF2 (potassium bifluoride) with oleum containing 60% SO3. The FSO3H is distilled off in a glass
apparatus- very convenient.
The problem is that I don't have any KHF2, and only a very small amount of 40%HF that I don't want to use up.
Now, in the FSO3H wikipedia article, it is said that CaF2 may be used instead of KHF2. This would be perfect if it worked.
I also have quite some NaF, which could perhaps also be used if CaF2 turns out to work.
The following reference is given:
Cotton, F.A.; Wilkinson, G. (1980) Advanced Inorganic Chemistry: A Comprehensive Text, 4th Edition, p.246, Wiley-Interscience Publications.
Can anyone with access to this reference provide an excerpt?
I want FSO3H because it can be used to make perchloryl fluoride, FClO3, by simple heating with KClO4 (Brauer p. 166, "Chlorine Trioxide Fluoride").
I read about this compound in the book "Ignition!" (downloadable in the Library), where it is hyped as a major discovery in the field of storable
high-energy liquid oxidisers for liquid-fueled rockets.
It is a remarkably stable and unreactive gas (can be washed with aqueous NaOH, does not decompose in glass at 600°C)
and quite easy to handle compared to other halogen-based rocket oxidisers.
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Fleaker
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I'd trust Cotton and Wilkinson. One's a Nobel laureate, the other certainly deserved it (but was a huge grump!). I'll get you the reference, I have a
copy of the red book.
I'd imagine that you could make FSO3H in much the same fashion as HF (i.e. distillation setup), what with the product being removed.
Here's my question to you, why not heat CaF2 with conc. sulfuric acid and distill the HF into the oleum? Or is the idea to do this all in glass? How
easily does KHF2 lose its HF?
This is mad science at its best.
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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garage chemist
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The idea is to do it in glass, and without generation of gaseous HF as intermediate, and without KHF2.
Looking forward to the reference.
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Jor
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A very crude method not involving any complex apparatus made of materials inert to HF:
Just put NaF in a cheap erlenmeyer and warm it, put a rubber stopper on it with a plastic tube leading into water, and add H2SO4 dropwise. After as
much as possible HF has been absorbed, titrate the acid, and add 0,5 eq. of KOH. The crystallise the KHF2. That's how I would do it. Or use this HF
generator to bubble it straight into oleum, with a plastic drying tube in between (these are cheap).
Yes you will lose your erlenmeyer or it will be severely damaged, but if you do it on a large scale you can get this valuable reagent at the cost of
some cheap glassware.
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woelen
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Are you sure that the HF is of acceptable purity? I expect that quite some SiF4 will be formed as well and this will lead to formation of SiF6(2-)
ions in aqueous solution. The FSO3H formed with the resulting impure KHF2 may contain quite some H2SiF6. I'm not sure how difficult it is to remove
this impurity.
Making HF can be done at much lower cost and does not require the use of the relatively expensive and hard to get NaF. Just use potteries grade CaF2
and gently heat this with conc. H2SO4. HF will distill out. Unfortunately, this most likely also will contain some H2SiF6, because potteries grade
CaF2 almost certainly contains some silica-based material as well.
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peach
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I was wondering if one could build a little still for such purposes using surplus PTFE tubing; or another of the fluoropolymers.
Premade, isostatically pressed teflon bottles and thermoformed PFA/ FEP flasks are extremely expensive, hundreds of dollars a go. However, you can
sometimes find some of the equally expensive tubing going as off cuts from spools. One method I envisaged, for small amounts, would be to use large ID
teflon tubing and fill one end of it with the reactants, and then have the remaining length as the recovery section.
If you have a lathe, or access to someone with one, you could buy a bar of teflon and bore it out to produce the hot flask for larger volumes. You
could do this without a lathe, using a drill press and a tap & die set. Teflon tape or fluoroelastomer could be used as possible thread sealants.
If the fit is tight enough, you could possibly even do away with the threading.
Temperature for CaF2 method: 265C
PTFE decomposition products become detectable: >200C
Recommend service temperature for PTFE: around 250C (e.g. this PTFE clip by Chemglass and this PTFE sleeve from QuickFit)
Melting point of PTFE = 327C
Which brings me on to the suggestion of using teflon it's self as the source of HF, by thermal decomposition. The question then becomes, how the heck
do we contain that and get a pure result if we're melting the teflon in the first place.
After searching around about this idea a month or two ago, I found this handbook guide to resistance, specifically made with HF in mind.
<--- Link
--------------------------------------------------------------------------------------------------------------------------------
Here are some rough ideas.
A desktop furnace built in a thermos flask, with a temperature limit around 480C. <--- Link
And a rough picture of what I'm talking about.
I think the first place to start with such a DIY attempt would be to build the mini oven, bore out a teflon bar, fill it with oil and see how it
behaves at the CaF2 reaction temperature; prior to attempting the HF it's self. The mini oven looks like it could be lots of fun on it's own, even if
not of use here. I decided to ignore the idea of purposefully decomposing PTFE to begin with as, whilst the PTFE it's self is a well known source for
the HF, the need for the other materials to handle it above PTFE's melting point and the possible interactions becomes more complex.
PTFE's sister polymers;
PFA, melts at 305C
FEP, at 260C
ETFE, 260C
^All unsuitable for the hot area and questionable for the tubing. Bottles made from these tend to have fairly thin walls as well, compounding the
problem. If I were making the bottle from PTFE, I would make the walls a good 2 or 3mm+ thick, probably more, to be more sure of it's stability. I
would also be cautious of heating much above the reaction temperature, and opt for more insulation instead.
The reaction temperature is not very far at all over the normal service temperatures. And has the added bonus that the decomposition product is also
the product you're trying to make. As sulphuric can be redistilled to give a reasonably clean acid, this leaves the CaF2 as your only source of
impurity; and there are likely methods for cleaning it up out there.
Take care! 
[Edited on 15-2-2011 by peach]
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entropy51
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HF can be distilled out of the reaction using a retort fashioned from a length of Pb pipe.
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peach
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Nice link.
By a stroke of coincidence, the melting point of both lead and PTFE is 327C.
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garage chemist
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Soldering together a cylindrical retort with lid and side-arm out of roofing lead sheet is probably the best bet, since massive teflon is expensive
and hard to work with.
Or even better, cast the whole retort as one piece...
The lead retort will get attacked somewhat, but it won't contaminate the HF gas, and that's important.
I don't have any CaF2 and pottery suppliers in my country do not stock this.
I know a shop for mineral and gem collectors that offers natural fluorite as large, unpolished rocks of various colors at a very low price. These are
meant to be polished and resold as semi-precious stones.
Purity is, of course, unknown and probably varies drastically from piece to piece.
[Edited on 15-2-2011 by garage chemist]
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ScienceSquirrel
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Hydrogen flouride is an extremely toxic gas, distilling it at home sounds like an excellent way to die.
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peach
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I agree. However I suspect one or two of these boys are also posting on versuchschemie, the origin of the potassium in a flask thread.
Casting it is a nice idea. New roofing lead is also mighty expensive! By casting it, you could start with scrap lead and only buy as much as you need.
I have melted pans full of lead on a counter top oven; and there are enough of those going for free at the tip.
The UK is currently going through a lead replacement scheme, where the old lead water mains are being replaced by blue MDPE whenever there's
significant ground work going on or water pressure problems. As a result, sticks of the very thick walled lead pipe will show up at the scrap yards.
Maybe it's the same in Germany?
I would be concerned about making a large container out of roofing lead for this. As metal researcher demonstrated with his sodium still, metals tend
to fail even when below their melting point if they are not supported or they are under load, and roofing lead is not particularly thick. Giving
another thumbs up to the thick walled cast retort suggestion.
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entropy51
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Yeah, I know but a couple of friends and I used to do it in high school,
before we knew better.
We also distilled ether over a bunsen flame, without any problems.
God watches over fools and teenage boys. Apparently amateur chemistry was a lot safer in the 1950's than it is today.
[Edited on 15-2-2011 by entropy51]
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ScienceSquirrel
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I have distilled ether with a bunsen flame and used a lot of dangerous things in a professional context where you have the kit and the precautions.
God was sleeping on his watch when Fone had a go at APAN in kilo quantities and Myfanwy tried his hand at phosgene.
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Regolith
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Just for accuracy sake his name was Phone. We warned him too. "It was cold where he was" though, so it was safe... God helps those who help themselves
like Kevlar and a blast suit. For the love of god have protection for the above. Damn ( checks texts ) forgot what a scary friken chemical that is
converts to acid on contact with lungs. Eats more substances than Rosie Odonell... Thats something I'd make at somebody else's house.
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Magpie
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I like the idea of casting metal retorts using the lost wax process (or similar). I still want to cast an RBF out of silver. This is a craft that I
hope we can develop on this forum someday.
I think I have mentioned before that I have a 1923 high school lab manual that has an experiment for etching glass with HF. Two cc of CaF2 are placed
in a 5cm lead dish. This is moistened with con sulfuric acid then warmed with a small flame. Then a paraffin covered glass plate with the writing
"fluorine, Moissan" exposed on the glass, was placed over the dish.
There was no mention of using a hood, or the toxicity of HF! Apparently God was the unseen partner in high school chemistry labs in those days.
The single most important condition for a successful synthesis is good mixing - Nicodem
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ScienceSquirrel
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There was the friendly Kipps apparatus sitting in the corner leaking hydrogen sulphide and experiments with troughs filled with mercury as well ...
Happy days
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entropy51
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Quote: Originally posted by ScienceSquirrel  | There was the friendly Kipps apparatus sitting in the corner leaking hydrogen sulphide and experiments with troughs filled with mercury as well ...
Happy days |
Small potatoes indeed
compared to a kilo of APAN. And we all survived, apparently none the worse for it.
In high school we etched glass as Magpie described, in the hood. There were two wax bottles of HF in the stockroom as well. They were slowly emptied
by those of us who needed it for home use. IIRC we carried it home in little plastic bottles, most likely in our pocket.
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Regolith
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Entropy I assume you meant the aqueous acid of HF. Or you live in Siberia and the classroom never went above 19C.
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peach
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| Quote: Originally posted by Magpie | | I like the idea of casting metal retorts using the lost wax process (or similar). I still want to cast an RBF out of silver. This is a craft that I
hope we can develop on this forum someday. |
There's a group on yahoo called Hobbicast (or hobbycast) which I joined when I was about 13 or something like that. There are a lot of guys on there
building furnaces and casting things at home. You will enjoy the discussion. I have seen people lost casting with styrofoam, with the styrofoam in
place as the metal goes in!  The results are not winning any beauty
competitions, but it works.
To make the internal hollow for an RBF, you'd need to use a core (as they do when casting engine blocks); which will leave a surface finish that is a
serious bitch to clean. I can't think of any easy way to spin or roto cast it either. The core finish is machined down and then honed if it's going
through something like a chamber, but doing that with an RBF would be mighty difficult given the lack of access to the insides.
It may be easier with a sphere to form it from sheet and silver solder it together. Another possibility would be plating the silver (or gold) onto a
form or base metal instead; if you're getting ambitious, platinum plating.
Casting a small retort for things like this HF idea from lead I would imagine to be far simpler. Particularly if the internal surface finish doesn't
much matter. I mean, if it doesn't have to be polished to a glass finish.
[Edited on 15-2-2011 by peach]
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Magpie
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Thanks for the info peach. Someday when I get serious about metal casting I look those boys up.
Do you have a reference for this?
The single most important condition for a successful synthesis is good mixing - Nicodem
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madscientist
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garage_chemist, here's an excerpt from the Sixth Edition of Cotton's Advanced Inorganic Chemistry (p. 74):
| Quote: | Fluorosulfuric Acid
Fluorosulfuric acid is made by the reaction:
SO<sub>3</sub> + HF = FSO<sub>3</sub>H
or by treating KHF<sub>2</sub> or CaF<sub>2</sub> with oleum at ~250C. When freed from HF by sweeping with an inert gas, it
can be distilled in glass apparatus. Unlike ClSO<sub>3</sub>H, which is explosively hydrolyzed by water, FSO<sub>3</sub>H is
relatively slowly hydrolyzed. The acid is one of the strongest pure liquid acids and, as noted in Sect. 2-11, is used in superacid systems. An
advantage over other acids is its ease of removal by distillation in vacuum. The extent of self-ionization
2FSO<sub>3</sub>H <--/--> FSO<sub>3</sub>H<sub>2</sub><sup>+</sup> +
FSO<sub>3</sub><sup>-</sup>
is much lower than for H<sub>2</sub>SO<sub>4</sub> and consequently interpretation of cryoscopic and conductometric
measurements is fairly straightforward.
In addition to its solvent properties, FSO<sub>3</sub>H is a convenient laboratory fluorinating agent. It reacts readily with oxides and
salts of oxo acids at room temperature. For example, K<sub>2</sub>CrO<sub>4</sub> and KClO<sub>4</sub> give
CrO<sub>2</sub>F<sub>2</sub> and ClO<sub>3</sub>F, respectively. |
I weep at the sight of flaming acetic anhydride.
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Fleaker
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| Quote: Originally posted by Magpie | Thanks for the info peach. Someday when I get serious about metal casting I look those boys up.
Do you have a reference for this? |
@Magpie--I should have said was in both cases as regrettably they are both now dead. Wilkinson is far before my time, but my mentor knew
Cotton quite well being an inorganic chemist--very smart guy, but very obstinate and intractable. I heard many a story about Professor Cotton and how
helpful he was to his group members (I mean that in earnest). I'm sure most here know about the incident with the ACS chairmanship...
Also, check out backyardmetalcasting.com. Casting a silver RBF would be VERY difficult if one is to do it economically, even by lost wax. It can be
done (the journeyman's test of skill was to cast a teacup, saucer, and spoon through clever fileting and core use). Regardless, you'd have to pour
very hot and the silver would be very gassy. I've melted many kilograms of silver--the hotter you get it, the more porosity. In a thin wall flask (say
3 mm thick) you may get away with it if the sand or investment is fairly coarse. You'd be better of to use silver sheet and braze it or somehow weld
it (not easy given its thermal conductivity).
Even though the layer is thin, you might just try silvering the flask interior.
@Madscientist--this [6th] is the edition I have so I couldn't have helped him with the exact reference he wanted. Thank you.
@everyone--given the experiments garage chemist conducts...I fear little for his safety. He's arguably one of the most competent people doing amateur
science as far as I can tell.
[Edited on 16-2-2011 by Fleaker]
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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watson.fawkes
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| Quote: Originally posted by Fleaker | | Casting a silver RBF would be VERY difficult if one is to do it economically, even by lost wax. It can be done (the journeyman's test of skill was to
cast a teacup, saucer, and spoon through clever fileting and core use). Regardless, you'd have to pour very hot and the silver would be very gassy.
I've melted many kilograms of silver--the hotter you get it, the more porosity. |
Is the dissolved gas only
hydrogen, or are there other constituents? For example, hydrogen is the predominant gas in gassy aluminum. It's the only one with appreciable
solubility. It's picked up from moisture adhering to the charge and from atmospheric water. I've seen the solubility data for aluminum, but not for
silver.
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