The Chemistry of Powder and Explosives - Sciencemadness Dot Org

PENTAERYTHRITE TETRANITRATE 279
erythrite crystallizes from water in white tetragonal crystals,
m.p. 253°. One part requires 18 parts of water at 15° for its
solution.
PETN may be prepared, according to Naoum, 109 by adding
100 grams of finely powdered pentaerythrite to 400 cc. of nitric
acid (1.52) while the temperature is maintained between 25° and
30° by efficient cooling. Toward the end of the nitration a certain
amount of the tetranitrate crystallizes out. The separation of the
product is completed by the gradual addition of 400 cc. of concentrated
sulfuric acid (1.84) while the stirring and cooling are
continued. The mixture is not drowned, but the crude PETN
(85-90% of the theory) is filtered off directly, and washed first
with 50% sulfuric acid and then with water. It still contains
some occluded acid and is purified, according to Naoum, by dissolving
in hot acetone to which a little ammonium carbonate is
added, and filtering the hot solution into twice its volume of 90%
alcohol by which the PETN is precipitated in fine needles.
Pentaerythrite may also be nitrated satisfactorily, and probably
in better yield, without the use of sulfuric acid and with the
use of nitric acid from which the nitrous acid has been removed.
Preparation of Pentaerythrite Tetranitrate. Four hundred cc. of
strong white nitric acid—prepared by adding a little urea to fuming
nitric acid, wanning, and blowing dry air through it until it is completely
decolorized—is cooled in a 600-cc. beaker in a freezing mixture
of ice and salt. One hundred grams of pentaerythrite, ground to pass
a 50-mesh sieve, is added to the acid a little at a time with efficient
stirring while the temperature is kept below 5°. After all has been
added, the stirring and the cooling are continued for 15 minutes longer.
The mixture is then drowned in about 3 liters of cracked ice and water.
The crude - product, amounting to about 221 grams or 95% of the
theory, is filtered off, washed free from acid, digested for an hour with
a liter of hot 0.5% sodium carbonate solution, again filtered off and
washed, dried, and finally recrystallized from acetone. A good commercial
sample of PETN melts at 138.0-138.5°. The pure material
melts at 140.5-141.0°, short prismatic needles, insoluble in water, difficultly
soluble in alcohol and ether.
Pentaerythrite tetranitrate is the most stable and the least
reactive of the explosive nitric esters. It shows no trace of decomposition
if stored for a very long time at 100°. While nitrocellulose
109 Op. dt., p. 244.