PowerLabs NitroStarch Synthesis |
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Yet another POWERLABS exclusive!
Nitro starch Laboratory synthesis:
Nitro starch, is actually a mixture of several nitrate
esters of starch with the formula [C6H7(OH)x(ONO2)y]n
where x+y=3 and n is any whole number from one on up. The exact composition
depends on the reaction conditions during the nitration. Nitrostarch found a use
as a filler in hand grenades back in WWII, and also in mining explosives It was
first made when H. Barconnot nitrated cellulose and starch back in 1833. At that
time nitrocellulose and nitrostarch were thought to be one and the same. Then A.
B�champ applied various methods of separating them in 1862. The US first began
to produce nitrostarch in 1888 under the name Volney Powder. Various companies
produced nitrostarch throughout both world wars, but the US emerged as its sole
manufacturer.
It was after being enquired by a British Chemist as to the manufacture of
this compound that I realized that the Internet did not yet have a source of
information as to how its synthesis may be performed. Knowing the similarities
between it and nitrocellulose, and having performed the synthesis of nitrocellulose
numerous times before, it was realized
that nitro starch could be made in a similar way, and so experiments were
performed to find out
exactly how. The first batches suffered from nitration runaway, excess
un-nitrated starch,
and decomposition during acid neutralization. After 5 failed attempts which
included anything from dumping the reaction halfway to having to evacuate the
room to flee a cloud of billowing nitrogen dioxide vapor, a somewhat effective
procedure was devised, which is shown below for informational
purposes.
As with any other nitration, this procedure is
hazardous and involves the use of highly corrosive acids. The final product is
toxic and dangerous. This should only be attempted by experienced chemists!
Reactants: |
Glassware: |
150mL Glass beaker. |
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Pipette |
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Stirring Rod |
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Funnel/filter paper |
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Ice bath |
Here all the
chemicals used in the synthesis are seen, from left to right, back to front: Sulphuric Acid (98%), Nitric Acid (68%), Distilled
water, corn starch, 150mL pyrex beaker, thermometer, spatula.
A
solution of 65mL Sulphuric Acid (98%) and 35mL Nitric Acid (68%) are mixed in a
150mL beaker and allowed to cool (the dehydration of the nitric acid produces
enough heat to warm the solution by as much as 60C, so it is very important to
start off with the acids at no more than room temperature, and to cool the
mixture down to 10C or so prior to the addition of starch.
Starch is than added slowly whilst the mixture is stirred vigorously until all
of the 18cc have dissolved. During the addition the temperature rises and it is
important that it does not go above 35C. Once all of the starch has dissolved
the mixture is placed on a hot plate and heated to 40C for one and a half hours,
with occasional stirring. It forms into a white precipitate with a consistency
similar to honey.
Once the heating period is complete the
nitro starch and
acids mixture are added to 400mL of cold distilled water and stirred. Once
stirring stops the nitro starch can be seen precipitating in the bottom of the
beaker. As with nitrocellulose, the nitrated version of starch looks no
different from what was started out with. Filtering this acid solution presents a
special problem, however: It will weaken the filter paper and cause it to rip.
Attempting to neutralize it with a carbonate will require very large amounts of
it and cause everything to foam out of the beaker. Neutralizing it with ammonium
hydroxide causes it to boil over and decomposes the nitrate. My solution was to
use a micropore nylon filter which was not attacked by the acid, and filter the
solution through it, with considerable loss of the final product. Decantation
might prove worthwhile if one is willing to wait the long time required for all
of the nitro starch to precipitate at the bottom.
The final product of any nitration will always contain some residual acid and
oxides of nitrogen which can make it extremely unstable and prone to self
decomposition when stored over time. It is thus necessary to neutralize this
acidity. The industrial method calls for washing with Ammonium Hydroxide
solution, however I found that my nitro starch decomposed when treated that way.
I decided to boil it in sodium bicarbonate solution instead, and add some Urea
to the final product so as to take up any nitrogen oxides produced (this is
essentially what is done to nitrocellulose).
Here you see the final product, after 5 failed attempts. It consists in a fine powder that is mostly
white but due to some decomposition during the acid neutralization phase (it
seems as though nitro starch is highly temperature sensitive) acquired a
brownish tint. It dissolves in acetone much in the same way nitrocellulose does.
The product deflagrates with a very hot flame in exactly the same way as
nitrocellulose, as can be seen on the picture to the left. Clicking on the
picture will show a video of this particular burn test (146kb). It was concluded
that nitrocellulose is a much more worthwhile starting product for nitrations.
Questions? Comments? Suggestions? E-mail me!
Hits since 23/05/01.
Last updated 11/02/10
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