Organic Chemistry of Explosives

96 Synthetic Routes to Nitrate Esters

3.2.6 OtherO-nitrating agents

3.2.6.1 Boron trifluoride hydrate–potassium nitrate

Olah and co-workers^55 reported using a nitrating agent composed of boron trifluoride hydrate

and potassium nitrate for theO-nitration of alcohols. The method provides a route to nitrate

esters of high purity and essentially free from nitrite esters. This reagent is also nonoxidizing.

Olah found that a range of primary and secondary alcohols could be converted to their nitrate

esters with this reagent: 2-methyl-1-propyl nitrate (62 %),n-pentyl nitrate (75 %), cyclopentyl

nitrate (60 %),n-butyl nitrate (48 %) and 1-methylheptyl nitrate (79 %) are a few of the nitrate

esters prepared from the parent alcohols. The reagent is not of general application for tertiary

alcoholO-nitration; although 1-adamantanol nitrate is obtained in 86 % from the correspond-

ing alcohol,tert-butyl alcohol undergoes dehydration and polymerization. The acidity of the

reagent varies considerably depending on the degree of hydration of the boron trifluoride. It

has been used for theC-nitration of some deactivated aromatic substrates.^56

3.2.6.2 Lithium nitrate–trifluoroacetic anhydride

A mixture of anhydrous lithium nitrate and trifluoroacetic anhydride in acetonitrile in the

presence of sodium carbonate has been used to convert alcohols to nitrate esters for a range

of peptide, carbohydrate and steroid substrates.^57 Yields are good to high but products need

purification to remove trifluoroacetate ester impurities, which can be significant in the absence

of the carbonate. A similar system used for the nitration of electron-rich aromatic heterocycles

employs trifluoroacetic anhydride with ammonium or potassium nitrate.^58

3.2.6.3 Thionyl nitrate and thionyl chloride nitrate

Thionyl chloride nitrate and thionyl nitrate are preparedin situfrom the reaction of a solution

of thionyl chloride in THF with one and two equivalents of silver nitrate respectively, during

which time silver chloride precipitates from solution.^59

HO OH

OH

26

HO ONO 2

ONO 2

ONO 2

ONO 2

1

OH

27

O 2 NO

O 2 NO

OH

28

1 eq SOCl(NO 3 ),

2 eq SOCl(NO 3 ),

3 eq SO(NO 3 ) 2 ,

THF, 65 %

THF, 70 %

THF, 100 %

Figure 3.16

Both reagents are efficient for theO-nitration of primary and secondary hydroxy groups.^59

Thionyl chloride nitrate can be used for the selective nitration of primary hydroxy groups in the