Organic Chemistry of Explosives

Nitrodesilylation 103

as the sole product (62 %), whereas longer reaction times with 4.0 equivalents of dinitrogen

pentoxide yields the high explosive, metriol trinitrate (4) as the sole product (88 %).

The use of oxetanes for the synthesis of polynitrate esters is generally of less value than the

use of epoxides, which are readily available from the epoxidation of alkenes.^87 The analogous

reaction of azetidines with dinitrogen pentoxide is a route to 1,3-nitramine-nitrates and these

reactions are discussed in Section 5.8.2.^88

3.4.3 Other oxygen heterocycles

Saturated cyclic ethers with ring sizes greater than four exhibit much less internal strain and so

the driving force for ring cleavage is much lower; tetrahydropyran and oxepane react slowly

with dinitrogen pentoxide in chlorinated solvent to yield complex mixtures resulting from

oxidation and oligomerization.^89

O 2 NO O

ONO 2 O 2 NO

O

CHO

44 45

46

OO

Figure 3.26

Cyclic formals react with dinitrogen pentoxide in chlorinated solvent to yield unstable but

interesting ring-opened products, including hemiformal nitrates; 1,3-dioxolane (44) reacts to

yield a mixture of hemiformal nitrate (45) and formal ether (46) products.^89 Similar products

are formed from acyclic formals and dinitrogen pentoxide.^89

3.5 Nitrodesilylation

R^2

R^2

R^2

R^1

N 2 O 5 , CH 2 Cl 2

OSi R^1 ONO 2 + (Eq. 3.10)

R^2

R^2

R^2

O 2 NOSi

Figure 3.27

Millar and co-workers^90 treated a number of silyl ethers with a solution of dinitrogen pentox-

ide in methylene chloride at subambient temperature and obtained the corresponding nitrate

esters through silicon–oxygen heteroatom cleavage (Equation 3.10). These reactions, known

as nitrodesilyations, are an important route to nitrate esters and very amenable to the synthesis

of polynitrate-based high energy materials for explosives and propellants. The same reactions

with silylamines yield nitramines (Section 5.7).

O

47

Me 3 SiOCH 2 CH 2 OSiMe 3

O

48

O 2 NOCH 2 CH 2 ONO 2

2.2 eq N 2 O 5

CH 2 Cl 2 , -5 °C, 35 %

Figure 3.28