The Laser-Induced Nitrations of Several Hydrocarbons

Abstract

The Army uses nitrated compounds as explosives and propellants. The ability to selectively nitrate materials is a much-needed process. Laser-induced chemistry possesses the potential to drive some reactions in an efficient and selective manner. Laser-induced chemistry may be useful in driving nitration reactions toward specific products. Reported herein are the results of several successful attempts to laser-induce the reaction of nitrogen dioxide with hydrocarbons of 3, 4, and 5 carbons. Specifically, the tunable continuous wave (cw) infrared laser was used to drive the reaction between nitrogen dioxide, NO₂, and propane, n-butane, isobutane, and n-pentane. The major products of the reactions were secondary (tertiary in the isobutane reaction) nitrohydrocarbons, of the same chain length as the reacting hydrocarbon. Some short-chain nitrated compounds were also identified. The yield of 2-nitrobutane observed in the nitration of butane is ∼20% on the basis of the depletion of NO₂. The propane reacted with NO₂ to produce mostly 2-nitropropane with a smaller yield of 5–9%. The analogous reaction of pentane produced ∼9% of the major product, which is believed to be 2-nitropentane. The isobutane nitration resulted in approximately a 10% yield of 2-methyl-2-nitropropane. The results of these laser-induced reactions are contrasted to the corresponding thermal reactions. The reaction mechanism is also discussed for these two processes.