agent_entropy - 4-9-2006 at 19:04
HMTD was prepared according to COPAE from the sciencemadness library. After the step where the filtered HMTD is rinsed with alcohol (methanol was
used) the filtrate solution was left alone for about 20 hours. After that period needle-like crystals large enough to be seen with the naked eye were
found in the bottom of and encrusting the sides of the beaker containing the filtrate. These were assumed to be a second crop of HMTD and were
filtered and rinsed with more methanol, the rinse methanol solution running into the same solution of filtrate. However, upon standing only a few
minutes the new filtate solution precipitated white powder (too fine to see an individual crystal with the naked eye). This crop of precipitate was
also filtered and rinsed with methanol. Again, the same fine white precipitate developed within a few minutes. This was repeated several times and
the same result was observed each time. Finally, the last crop of precipitate was filtered but the methanol rinse was omitted. This time no more
precipitate formed. Upon addition of fresh methanol, still no precipitate formed.
The initial batch of HMTD had dried by this time (yield approx. 46% of theoretical, after some slippage due to residue left on containers and filter)
and its identity was confirmed by applying flame to a small portion, its deflagration was consistent with that of HMTD.
The second crop of crystals that formed on standing for 20 hours, were tested by applying flame to a small portion while still damp with methanol,
alongside a portion of known HMTD dampened with methanol. The deflagration/combustion of the test and the control were practically indistinguishable.
Each burned while making the same sound as a gas flame does in a moderate wind, with frequent small flashes of greater brightness in the flame.
Edit: After drying, this second crop of crystals was also tested by deflagration. A significant portion of the precipitate is indeed HMTD however
after its deflagration small bits of white material are left, indicating that the precipitate is a mixture of at least two compounds.
The third and subsequent crops of precipitate were tested in a similar manner but did not behave like the first two. These crops let the methanol
burn away without greatly affecting the mass of white powder. When the methanol was nearly depleted the flame almost went out, but kept burning with
a much less intense flame.
Edit: The dried unknown product, when heated to decomposition (fairly quickly by a torch) in a steel crucible melts and turns brown/black while
yielding visible fumes which are mostly white with a yellow/tan tinge then turning a much darker tannish yellow. The fumes smell slightly stinging
like ammonia with another smell perhaps similar to that of burning hair, but much more mild. Upon continued heating the material stops emitting fumes
and some black ashes are left which resemble wood charcoal. Note: The white material left after deflagration of the second crop of precipitate behaves
in the same way when heated strongly.
The unknown product is soluble in water and insoluble in toluene, heptane and methanol. It is also insoluble in both conc. HCl and conc. H2SO4 with
no directly observable reaction in either. However, in the conc. H2SO4 the unknown formed white sticky globs which despite the stickyness maintained
a grainy texture.
It seems possible that the third and subsequent crops of precipitate could be some form of the original hexamine that was left unreacted, although it
seems like there was more precipitate than there would be hexamine left, it also behaves much differently from hexamine when tested by burning
(hexamine merely burns, it does not melt, nor does it turn brown/black).
Any ideas on what this second product is?
[Edited on 5-9-2006 by agent_entropy]
quicksilver - 6-9-2006 at 06:36
Are all avenues of contamination eliminated? Has there been any varience from the COPAE formula such as % of peroxide? Contaminants & associated
issues is where I would first look. Perhaps the hexamine has a binder ?
?
Rosco Bodine - 6-9-2006 at 11:04
If citric acid was used then the impurity is likely ammonium citrate byproduct . Acetic acid would
likely be a better choice if an organic acid is wished
to be used .
A good experiment would be to simply dissolve
HDN in cold 27% H2O2 with the peroxide in about
15-20% excess of theory . Providing for overpressure relief in a lightly sealed bottle having a threaded cap ,
let the mixture sit in a freezer for about 60-72 hours
to get the HMTD . I haven't tried this but expect the
yield should be something like 90% of theory based
upon HDN and it should be very pure , requiring
no neutralization , just a distilled water rinse .
The HDN already contains as bound acid the precise
ammonia byproduct neutralization equivalent of nitric acid which will be required for the formation of HMTD .
So this should eliminate any acid measurement errors
concerning what is a pH sensitive reaction .
It has been a source of some speculation that a possible double salt of HMTD and AN could form from such a mixture of cold peroxide and HDN , if to
the initial mixture
is added AN to its saturation point in the cold mixture ,
( perhaps to a point of even some excess AN present as solid ) , creating a reaction system which favors a
coprecipitation of a double salt HMTD/AN . There is a
patent by Callery related to this .
agent_entropy - 6-9-2006 at 12:16
It just finally ocurred to me that citric acid is not very soluble in methanol, and now I see that citrates were already suggested (good call). I
tried heating some citric acid to decomposition but it behaved differently from the unknown so I suspect that it is some sort of citrate.
There may have been some sources of contamination; unrecrystallized hexamine (though there does not appear to be anything but hexamine in my tablets),
baquacil brand 27% H2O2 (stabilizers?) [adjusted for 3% difference in conc. from COPAE], citric acid from foodstore (at least claims to be pure),
technical grade methanol... However, there was WAY too much of this stuff for it to have been any of those minor contaminants.
I'll have to try again using acetic acid (5% white distilled vinegar ok?) and see what that does.
Rosco Bodine - 6-9-2006 at 15:29
Glacial acetic is probably needed to avoid dilution
of the peroxide .