Lecture 10 - Explosions 10

Question 1

why is there a need for next generation explosives

Answer 1

current explosives are not very environmentally clean

a lot of detonations produce side products to what is expected on paper

Question 2

how can we reduce the production of CO and C from explosives

Answer 2

use explosives with a higher nitrogen content - these are more likely to release N2 which is already in the air

Question 3

how can explosives be tunes to have the properties we want

Answer 3

make small tweaks to the chemical structure to change the:

crystal packing
detonation products
tagging

Question 4

why is tagging important

Answer 4

to stop explosives being used in an illicit manner

Question 5

what are the two groups of chemical structures explosives are made of

Answer 5

energetic groups - these give us the power

stabilising groups - these are use to make explosives less shock sensitive as most energetic groups are not very stable

Question 6

what are 6 examples of energetic groups seen in explosives

Answer 6

nitro groups = NO2
azide groups = N3
alkyne = carbon triple bond
O-O = in peroxides
high ring strain = cubes
tetrazoles =a 5 membered ring with 4 nitrogen’s and 1 carbon

Question 7

what are two examples of stabilising groups seen in explosives

Answer 7

aromatic rings (benzene)
and amine groups (NH2)

Question 8

when testing new explosives what PPE is required

Answer 8

helmet
face shield
leather coat
Kevlar gloves
Kevlar suit
blast shield

Kevlar = shock resistant

Question 9

what is the maximum amount of a new explosive that is tested

Answer 9

500mg - usually a lot less is used

Question 10

what class of molecules are an interest for being used as the new primary explosives and why

Answer 10

azidotetrazoles

these exhibit multiple spontaneous explosions = sensitive

they have a large number of nitrogen atoms per molecule = entropically favourable detonation

clean N2 gas product

Question 11

how can the stability of azidotetrazoles be increased

Answer 11

use a base in the formation e.g LiOH or MgOH or NaOH or FeOH so a metallic salt is formed

Question 12

how are azidotetrazoles formed

Answer 12

combine bromocyanide with azide salt

then treat with the base to create a metal salt of the azidotetrazole

Question 13

what class of molecule are of interest to becoming the new secondary explosives and why

Answer 13

nitroiminotetrazoles

has comparable properties to RDX
more energetic than azidotetrazoles but stability comes from the aromatic ring

Question 14

when can explosive salts be produced

Answer 14

when nitroiminotetrazoles are paired with guanidiniums

Question 15

what are the conditions needed for a nitration

Answer 15

nitric acid and the presence of another strong acid e.g H2SO4

Question 16

which analytical technique would be best to determine if oxygen balance predicted products are correct and why

Answer 16

FTIR - can look at small molecules and how they differ by vibrational bonds

NMR = not good for mixtures
GC = cant separate water easily
LC = we form gases so not good

Question 17

what can a small change to the structure of an explosive have a big impact on

Answer 17

the detonation products

this is why we need to test before using explosives as the expected results aren’t always seen practically

Question 18

what is a cleaner decomposition of explosives correlated with

Answer 18

a less negative oxygen balance

Question 19

what factors affect the stability of an explosive

Answer 19

oxygen balance

crystal packing

presence of double and single bonds

Question 20

what is the relationship between density and impact sensitivity of explosives

Answer 20

increase in density sees increase in sensitivity

Question 21

what can be used to control the crystal packing of explosives but what is the issue with this

Answer 21

explosive salts

the behaviour can be hard to predict

Question 22

why do the presence of more double and triple nitrogen bonds in an explosive not always work

Answer 22

it can be synthetically challenging

but the presence of these can be enthalpically favourable for the explosion

Question 23

will adding a stabilizing group always make an explosive stable

Answer 23

No

Question 24

what is another type of new secondary explosive developed by the US military and national labs

Answer 24

hexanitrohexaazowurzitane or Cl20

this has lots of ring strain

Question 25

what are the desired properties to consider when making new explosives (6)

Answer 25

explosive power
melting point
sensitivity
tunability
safety
time and energy needed for synthesis - is this practical to scale up for larger amount

Question 26

how can stereochemistry affect properties of explosives

Answer 26

stereoisomers need different types of synthesis

they will have different sensitivities

testing is needed to see their state at room temp - liquid or solid

melting points will be different - impacting if they can be easily casted or not

Question 27

what are the effects of incorporating more nitrogen double and triple bonds into explosives

Answer 27

increased stability
high energy release
higher sensitivity
non toxic by products (N2 gas)
can tune molecules more easily by reacting with these bonds

hard to store safely due to increased sensitivity

Question 28

how can IR spectroscopy be used to assess oxygen balance of modern explosives

Answer 28

can look at the ratio of the oxidiser to the fuel

analyses functional groups and identify the fuel and oxidiser