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Formatik
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Quote: Originally posted by blogfast25  | | Edit: and in any case DCM's good for separting the floating K from the slag, at room temperature. I've just done it on a large collection of fines,
afterwards rinse with kerosene... |
Dichloromethane and potassium mixture has a shock sensitivity of 0.06 mkg and yields a "relatively strong explosion" when exposed to the shock.
Mercury fulminate in the same instance had a shock sensitivity of 0.04 mkg. Alkali metals and halogenated organic solvents are typically shock
sensitive systems. Lithium, sodium, potassium, then Na-K alloy with the solvents are most sensitive, sensitivity increasing respectively from left to
right. Some mixtures are so sensitive, that one just has to slightly bump them and they detonate strongly.
Source for this: Über Explosionen mit Alkalimetallen. Zeitschrift für Elektrochemie und angewandte physikalische Chemie, 31: 549–551. H.
Staudinger.
Btw. I admire everyone's work here and contribution to this new method of potassium manufacture. Keep up the good work.
[Edited on 12-1-2011 by Formatik]
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blogfast25
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Thanks Formatik for the well wishes and for the information on DCM/K. I wonder what is meant by ‘mkg’… ‘milli kilogram’? That makes no
sense. ‘mass kilogram’? That would be Newton.
Here’s what I did. A few small k balls (total < 0.1 g) were mixed with about 1 ml of DCM, the K floated. Shaking the tube nothing happened. I
then carefully heated the tube on steam bath and the DCM started to boil and I got reaction with the K. Nothing spectacular: they didn’t dissolve,
explode or burst into flames; they just darkened to the point of blackness (C?) But remember that the K balls had previously been stored under
kerosene, so the DCM had been diluted somewhat.
Next I made a mixture of about 50/50 v/v DCM/kerosene (they are miscible) and added a mixture of K-balls (< 0.5 g) and MgO reaction slag, the
K-balls floated and the MgO sank to the bottom. The K-balls were then skimmed off and dropped into Shellsol D70 and rinsed a few times with small
amounts of that solvent to eliminate any DCM. The separation is neat and quick. And uneventful, all at RT.
The then clean K balls were then subjected again to coalescence experiments involving heating and cooling them to above and to below K’s MP to try
and get them to merge. I also (re)tried garage chemist’s trick with the IPA. All in all it’s very slow and frustating process which at times had
me wishing those glistening balls were Hg and not K!
So while mixing DCM with K in larger amounts is probably really silly, for the purpose for instance of yield determination, using a mixture of DCM and
kerosene as a floatation liquid is probably a relatively safe option. C2Cl4 may be even safer because it has a higher density and less of it can be
used in the floatation mix to reach d ≥ 0.9 and get K to float comfortably.
Of course organic inert solvents with d > 0.9 due to hetero atoms are to be preferred but tend to be much more expensive (see dioxane or THF).
Next attempt at coalescing will be using octane (well, 99 octane unleaded car juice), hoping that the lower viscosity of that solvent will make a
difference to the rate of coalescence. The BP of n-octane is about 125C.
************
Unfortunately, probably due to additives, the 99 % octane petrol reacts slightly but persistently with the potassium, with gas evolution. The light
yellow green colour of the petrol gives way to a darker brownish tone. So as a coalescing solvent it can’t be used, at least not without prior
distillation.
[Edited on 12-1-2011 by blogfast25]
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MagicJigPipe
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Normally I would expect that unit to be "meters*kilograms". Does it have another name? I don't know. I've never heard of it.
Something to look up though.
EDIT:
From Wikipedia:
| Quote: |
Impact Sensitivity is expressed in terms of the distance through which a standard weight must be dropped to cause the material to explode.
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Mass of standard weight times the distance?
[Edited on 1-13-2011 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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Eclectic
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Maybe useful solvents in this application:
http://www.novolyte.com/documents/brochures/glymes-and-grign...
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Formatik
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Concerning test values
Staudinger was using a fallhammer method to get those values. The kilogram-meter (kgm): for every meter, 1kg of mass equivalent.
0.06 m was needed. Then 0.06m*100cm/m = 6cm for 1kg. The usual older tests used about 2kg weights. So, equivalently here, 3cm falling distance for
2kg.
Additional notes:
The increasing size of halogen substitution of the solvent generally increases sensitivity of the aforementioned mixtures also, which is why carbon
tetrachloride mixtures are among the most sensitive. Pentachloroethane and tetrachloroethane are even much more sensitive as noted in the next paper,
so much so, that after some time of mixing (with Na-K alloy) that without any external shock, explosions have occurred. Staudinger also noted in this
other paper, Erfahrungen über einige Explosionen. Angewandte Chemie, 35: 657–659: some neutral sulfur products like carbon disulfide, and
some oxygen containing compounds like CO2 when mixed with alkali metals and when exposed to shock, detonate also (no values given).
@blogfast25:
Staudinger reported (first paper above) potassium with pentachloroethane or bromoform at first showed little shock sensitivity, but these reacted
chemically forming a grey mass, whereby the shock sensitivity of the system enormously increased, so that spontaneous explosion can occur. The shock
sensitivity not being due to heat generated, since even after cooling, it remains, but the sensitivity has to do do with the formation of an unstable
intermediate. In some cases, spontaneous explosion occurs, but the intermediate can also decompose quietly into KCl and carbon. Likely, a similar less
sensitive intermediate formed in your experiment. A visible change usually must not occur, Staudinger also noted sodium or potassium with CHCl3 or
CCl4, etc. showed no reaction or explosion, and that it appeared the metal remained unreacted under the liquid (heterogeneous system). I am also not
sure if these mixtures respond to warmth, like they do to shock. Also, mercury fulminate is very shock sensitive, but in an open vessel I would think
it might take some good agitation before it would come explosion. Similar to mixtures which are similar in sensitivity. In all cases, I would entierly
avoid all chlorinated solvents solely out of the hazard of dangerous intermediates.
[Edited on 13-1-2011 by Formatik]
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watson.fawkes
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| Quote: Originally posted by Formatik | | Staudinger was using a fallhammer method to get those values. The kilogram-meter (kgm): for every meter, 1kg of mass equivalent.
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Did these devices have standard contact area? If not, I don't see how this measure represents a physical
standard, as opposed to a device-bound practical one. The invariant of mass*height is a representative of gravitational potential energy, so you
multiply by the earth's gravitational acceleration 'g' to get a physical energy. But if you spread that energy out too far, it's fairly clear that the
number become meaningless.
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blogfast25
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@watson and Formatik:
I believe the test procedure is described in the *.pdf on chloroform explosions linked to here:
http://www.sciencemadness.org/talk/viewthread.php?tid=5112#p...
I quote:
“About 0.3 g. of sodium or of potassium or of the liquid
alloy was sealed up in a small glass bulb, 6 to 8 mm. in
diameter, which had a capillary stem 15 to 20 mm. in
length. This was placed in the bottom of a narrow testtube
and held in place by a collar of glass (a section of
glass tubing) which was sintered to the inner wall of the
test-tube. The latter was then drawn down, chloroform
(1 to 2 cc.) was introduced, and the explosive capsule was
sealed. These capsules could be prepared in advance and
could be kept safely as long as desired.
For studying the products of the explosion a […]”
The bit about ‘could be kept safely as long as desired’ really caught my attention.
I’m also a little surprised that so relatively little mention is made about the potential dangers of alkali metals in contact with haloalka(e)nes
(or even aryl halides?) in the wider literature.
Since as the value of 0.06 kgm is indeed not a strict scientific unit, it’s quite relative. If a guest at a dinner table accidentally drops a 1 l
bottle filled with water from 6 cm above the table, does that constitute quite a shock or not?
I appreciate that higher chorine content of the solvent aggravates the problem but in the case of C2Cl4, mixing 1 litre of a 0.8 density hydrocarbon
solvent with only 0.14 litre of the 1.622 density C2Cl4 yields a mixture of d ≈ 0.9. Solid K would already float in such mix, containing only
0.14/1.14 x 100 = 12.2 v% C2Cl4. At 24 v% the density becomes about 1, at 18 v% about 0.95.
It would be interesting to strap an ampoule of potassium in DCM, TCE or C2Cl4 to a heavy object and drop it from a small height (while keeping a safe
distance!) to see if Stausinger’s results can be reproduced and explosion occurs.
@Ecclectic:
Butyl diglyme is an interesting thought, it’s just borderline in density (0.88). I expect it to be very expensive. But it did jog my grey matter
towards other hetero atom containing compounds like light ethylene glycol esters or oxalic (or malonic) acid esters: diethyl oxalate has a density of
about 1.08, should be rather easy to synthesise but it’s relatively viscous…
But by and large there are other possibilities that don’t involve coalescing the globules that are too small to recover: provided they can be
separated more or less completely from slag, there seems no impediment dictated by the proposed mechanism to add these ‘fines’ to the next
reaction. Either this initial K will react with the KOH.H2O (forming more KOH) or it will dissolve as KOR, any left overs may even promote coalescence
of newly formed K.
[Edited on 13-1-2011 by blogfast25]
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Formatik
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| Quote: Originally posted by watson.fawkes | | Did these devices have standard contact area? If not, I don't see how this measure represents a physical standard, as opposed to a device-bound
practical one. The invariant of mass*height is a representative of gravitational potential energy, so you multiply by the earth's gravitational
acceleration 'g' to get a physical energy. But if you spread that energy out too far, it's fairly clear that the number become meaningless.
|
The fallhammer test used a rigid device, you can see an example of one picture of it here.
As long as they aren't touching each other, yeah, they are safe. Not something I would be carrying around in my pockets. Tenny Davis also shows the
schematic in his COPAE book (in the forum library), on pg. 403.
| Quote: | | I’m also a little surprised that so relatively little mention is made about the potential dangers of alkali metals in contact with haloalka(e)nes
(or even aryl halides?) in the wider literature. |
Gmelin's Handbuch mentions it under all entries of the alkali metals concerning organic solvents. Bretherick's Handbook also mentions it a bit.
| Quote: | | I appreciate that higher chorine content of the solvent aggravates the problem but in the case of C2Cl4, mixing 1 litre of a 0.8 density hydrocarbon
solvent with only 0.14 litre of the 1.622 density C2Cl4 yields a mixture of d ≈ 0.9. Solid K would already float in such mix, containing only
0.14/1.14 x 100 = 12.2 v% C2Cl4. At 24 v% the density becomes about 1, at 18 v% about 0.95. |
If C2Cl4 were to form the similar type of highly unstable intermediates as penta- and tetrachloroethane, then it's possible it could pose a
spontaneous explosion or decomposition risk, depending on the nature of a reaction in a diluent. Bretherick's at the least states potassium and
tetrachloroethylene explode when heated together (to ~ 97 C), except when the metal was free of any oxide film.
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blogfast25
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@Formatik:
Well, for:
CCl4 + 4 Na === > C + 4 NaCl
The theoretical heat of reaction would be + 366 [CCl4] + 4 x (- 411) [NaCl] = - 1,278 kJ/mol, a very high value, thus a very high negative ΔG and
a very strong drive for the reaction to proceed. That would be similar for most halocarbons, with the highest values for those with highest degree of
halogenation. Like all reactions you have to surpass the kinetic barrier to get them started (concept of ‘activation energy’) but this kinetic
barrier could quite literally be overcome with a kinetic shock, if the barrier is quite low. The 97C in the case of C2Cl4 suggests very low activation
energy. A shock wave running through the mixture could greatly increase collision speeds between the halocarbons and the metal, equivalent to heating,
with initiation as a (n explosive) result.
Formatik, you can now relax  , I won’t be pursuing this anymore, except for with
a sense of mischief to try and get a plastic ampoule with some C2Cl4 and a very small amount of K to explode on impact. Thanks for your input.
[Edited on 14-1-2011 by blogfast25]
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Formatik
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| Quote: Originally posted by blogfast25 | | A shock wave running through the mixture could greatly increase collision speeds between the halocarbons and the metal, equivalent to heating, with
initiation as a (n explosive) result. |
Well, yes. Gmelin states mixtures of even lesser sensitive lithium mixtures with halogenated hydrocarbons can be initiated with blasting caps.
| Quote: | | Formatik, you can now relax , I won’t be pursuing this anymore, except for with
a sense of mischief to try and get a plastic ampoule with some C2Cl4 and a very small amount of K to explode on impact. Thanks for your input.
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Sounds like good harmless family fun. Take care, since it looks like significant
amounts of phosgene could also form.
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condennnsa
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I post this to let everyone know that in case of lack of magnesium for this synthesis, I have bought it from Likurg in Poland. 750 g for 11 euro. The
owner , Tomasz, is very reliable , he even talks in realtime via googletalk, and my package arrived in only 4 days.
I tested this magnesium for trace aluminum , by reaction with NaOH solution, there was no sign of reaction.
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blogfast25
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Not wanting to rain on your parade but a test for traces of Al in Mg by dunking it in NaOH is likely to be very insensitive (poor resolution).
Unfortunately there are no quick, cheap and colourful tests available to detect Al, at least not AFAIK. Pyro Mg is unlikely to be uncontaminated
by Al though: Mg and Al simply aren’t very likely bed fellows because Mg is produced by electrolysis of MgCl2. At those temperatures, AlCl3 (a
largely non-ionic compound) is seriously volatile.
You’ll only find Al in Mg metal if someone deliberately put it there for alloying purposes, not as a ‘natural’ contamination…
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blogfast25
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’One pot’ with Kerosene
6.12 g KOH flakes, 3.11 g Mg (reagent), 1.32 g 2-methyl-butan-2-ol (t-amyl alcohol) were all mixed together with 40 ml of medium kerosene (deodorised
lamp oil, flash point min. 61 C, £2.70/l, supplier Caldo Oils via local hardware store). Note the slightly lower amount of solvent and higher amount
of alcohol (0.015 mol).
Temperature was rapidly taken up to 200C which was reached at t = 10 min and refluxing was very strong. I lost a little bit of material through the
refluxer (glass tube with iced water kitchen roll wrapped around it) but that subsided shortly after. Strong hydrogen evolution and then the solvent
started clouding over, as per usual.
Potassium fines started to appear at about t = 1 h. After about 1 ½ h, hydrogen evolution had largely subsided. I measured hydrogen evolution using a
test tube gazometer over 15 mins and found it to correspond to a reaction rate of about 8 mmol/h of K (four millimol per hour of H2), according to 2
KOH + 2 Mg === > 2 K + 2 MgO + H2. To put this into perspective, at a rate of 8 mmol/h of K, reducing about 0.1 mol of KOH would take about 12.5
hours! It’s therefore safe to state that at t = 1.5 h the reduction reaction must have been 90 % or more completed. If I had any dioxane I would
stop reaction at about t = 2 h and recover the formed K with that solvent. Alas that wasn’t case and I had to continue for another 2 h until (after
cooling it looked like this; mostly 3-4 mm globules, no larger ones this time:
During this test coalescence was very visible, mainly because most of the MgO had formed in clumps, not fine sand (which tends t obscure the view a
lot).
Conclusions:
1. box standard kerosene works about as well as Shellsol D70
2. ‘One pot’ method confirmed to work as in previous experiment
3. increased level of catalyst didn’t seem to have a dramatic effect on reaction rate
Tomorrow: yield determination.
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Picric-A
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Has anybody tested this method using diesel fuel?
Diesel is composed of 75% saturated hdyrocarbons (primarily parrafins) and 25% aromatics. After reading the whole thread it looks like aromatics are a
no no however has anybody actually tested this?
Diesel has almost ideal b.p. and to say it is incredibly cheap and readily available would be an understatement...
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blogfast25
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| Quote: Originally posted by Picric-A | Has anybody tested this method using diesel fuel?
Diesel is composed of 75% saturated hdyrocarbons (primarily parrafins) and 25% aromatics. After reading the whole thread it looks like aromatics are a
no no however has anybody actually tested this?
Diesel has almost ideal b.p. and to say it is incredibly cheap and readily available would be an understatement... |
Nurdrage much above used Tetralin ®, that’s highly aromatic. AFAIK no one has tried diesel yet. With a (Wiki stated) density of 0.832 liquid
potassium might float in it, which seems to offer an advantage for coalescing the metal.
&&&&&&&&&
My crop for the latest experiment was about 50 %, lower than with Shellsol D70 and definitely due to poorer coalescing: I lost quite a bit of fine
metal. Also the MgO was very crusty (almost no ‘sand’) and some potassium got stuck in it.
The crop: 2 g of potassium in a round flask under Shellsol D70; the poor focus doesn’t do it justice, the metal is very clean skinned:
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Picric-A
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Re. storing alkali metals in aromatics, Acros Organics (part of Fisher) supply powdered sodium metal in a toluene suspension... surely they would not
supply a highly reactive form of a metal in something it reacts with?!
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blogfast25
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Toluene is one I want to try and achieve separation of the K metal and the MgO slag by floatation: toluene has a density of 0.8669 (@ RT) (K, d =
0.862 at RT, d = 0.828 at MP). It may even be possible to achieve coalescence by heating the floating K to just above its melting point. Toluene (or
xylene) are of course far too low boiling to consider as a reaction medium.
I bought a heavier kerosene (‘outdoor lamp oil’) with a measured density of d = 0.85 at about 10C. I’ll be trying it as a reaction medium
tomorrow, hoping to get the produced K to float and possibly coalesce more, like in Nurdrage’s experiments with ‘IR Grade Paraffin oil’ and
Tetralin.
[Edited on 22-1-2011 by blogfast25]
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mr.crow
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Great work on the experiments with lamp oil! I need to find some in the dead of Canadian winter.
Xylenes are also available as label remover at home depot, but may have surfactants in it.
Couldn't you just mash your balls together (hehe) in a test tube with mineral oil? Or will this just make it split up even more?
Double, double toil and trouble; Fire burn, and caldron bubble
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blogfast25
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| Quote: Originally posted by mr.crow | | Couldn't you just mash your balls together (hehe) in a test tube with mineral oil? Or will this just make it split up even more?
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The latter, mr crow. Dispersing K is a lot easier than making it coalesce. But you gave me an idea: mechanically pressing cold, solid K balls into
each other may be a possibility, followed by melting. A bit like pressing oil from olives - LOL.
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Satan
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In those
conditions (K + MgO + toluene) potassium will metalate toluene, giving benzyl potassium.
Ref: http://pubs.acs.org/doi/abs/10.1021/jo01122a005
[Edited on 23-1-2011 by Satan]
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blogfast25
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Satan: you wrote: “those conditions”. Which conditions exactly are you referring to? I can’t access that article. Floatating K
at RT using toluene or xylene is probably possible provided the metal is sufficiently clean (solid impurities would increase its density).
I seem to remember that ‘sodium powder’ is produced by rapidly stirring molten Na in toluene, followed by quenching, but don’t quote me on that
w/o references.
Edit: Perhaps more relevant to the metalation of aryl and alkyl compounds with organometallic Li/Na/K compounds is this Google book reference here. Methinks that we’re far off the conditions described if toluene, xylene or possible diphenylmethane (higher
density) were to be used as K floatating agents (rather than as reaction media or coalescing media).
And here's a Wiki reference to ‘sodium sand’:
In former times, the sodium was provided in the form of "sodium wire" or "sodium sand", a fine dispersion of sodium prepared by melting sodium in
refluxing xylene and rapidly stirring, was common.
Again no reference to sodium metalating the xylene.
%$£$%$£$%$£
I didn’t have time to run a complete test with the heavier kerosene, so I did a couple of other things.
The density of the ‘Caldo Oils’ medium kerosene used above was measured and clocked in at 0.81, much lower than the ‘outdoor grade’ (0.85),
which will be tested tomorrow.
Then I did another coalescence experiment, this time putting all my K-balls (large, medium, small) in one basket (pardon the pun) under Shellsol D70
and heated them in the usual apparatus to BP of the solvent (somewhat above 200C). Here coalescence was very visible and very swift: in about 30 mins
most of the K had fused into a few larger balls. You can see (the solvent is clean) the balls merge, each instance of balls merging being almost
instantaneous.
So basically my hunch that coalescing at just above the MP (where the potassium’s viscosity is highest) is plain wrong, it appears the opposite:
lowest solvent viscosity and lowest metal viscosity together lead to fastest coalescence. Here’s the bottom of the 100 ml Erlenmeyer during cooling:
5 g of fairly large potassium reguli under light kerosene:
[Edited on 23-1-2011 by blogfast25]
[Edited on 23-1-2011 by blogfast25]
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DJF90
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| Quote: | Sodium oxide, calcium oxide, or magnesium oxide with potassium metal is a
new and unique metalating agent which has made possible the metalation of
toluene in a yield as high as 90 %. Sodium is not effective under these conditions.
In the absence of these oxides, metalation by either potassium or sodium occurs
to a small extent only. |
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blogfast25
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Well, that more or less clears it up then, although it remains strange that Nurdrage’s best result was obtained with Tetralin.
What are you quoting from, DJF?
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DJF90
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The article you said you couldn't get. Thats the summary.
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blogfast25
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For some reason in the case of ACS publications my browser (IE) doesn’t show this first page they now offer instead of an abstract, it’s quite
frustrating: I can only read the title, authors and biblio references…
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