Ozonation of Amines

Abstract

A review of the literature concerning reactions of ozone with amines has given rise to the working hypothesis that these reactions all involve initially the electrophilic attack of ozone to give an adduct for which at least three different reaction routes are available: loss of molecular oxygen to give an amine oxide or further reaction products thereof, an intramolecular oxidation of a side chain, and dissociation to nitrogen cation radicals and the ozonate anion radical, followed by further reactions of these. Results from ozonations of tert-butylamine and tri-n-butylamine, which furnish additional evidence for the above competitions, are described.>Tphe literature suggests several ways in which ozone reacts with amines.

Nonaromatic aminium radicals

“…An electronegative substituent or constrained ring system forces s character into the orbital of the unpaired electron. The effect of substituents has been explained both on the basis of electronegativity con-cepts152 and conjugative destabilization;153 the latter interpretation appears correct.15313 The carbon-centered radicals [11][12][13][14] are classical examples of alkyl radicals on the basis of large isotopic 13C hyperfine couplings to the centeral carbon atoms; many other nonplanar alkyl radicals have also been identified. 159 The formal positive charge on the central nitrogen atom in an aminium radical should result in a more rigidly planar, less easily deformed species as compared to the isoelectronic alkyl radical.…”

Ozone Promotes Chloropicrin Formation by Oxidizing Amines to Nitro Compounds

“…18 Ozonation and chlorination of free amino acids generally produced chloropicrin at <0.2% yields, but yields were up to 8.5% and 1% for glycine and lysine, respectively. 19,20 In the synthetic chemistry literature, ozonation of amines in organic solvents produced nitrated products 21,22 at up to 92% yield, 23 but yields were <20% in water. 24,25 The purpose of this study was to characterize the formation pathways and precursors of halonitromethanes (e.g., chloropicrin) during ozonation followed by chlorination.…”

Ozone-Mediated Amine Oxidation and Beyond: A Solvent-Free, Flow-Chemistry Approach

“…One particularly interesting application of ozone is in the reaction with amines. While it was previously thought that ozone degrades primary amines, , later evidence demonstrated that carefully chosen conditions could give detectable quantities of nitroalkane products . These substrates can act as versatile intermediates for further derivatization and can be readily converted into most other functional groups in a handful of steps .…”

“…Initial reports on ozone-mediated amine oxidation in organic solvents note moderate yields and formation of a wide range of byproducts resulting from side chain oxidation or decomposition via radical or carbocation intermediates (Scheme A). ,− Furthermore, the authors found that solvent selection played a key role in byproduct distribution and selectivity of the reaction. Halogenated solvents such as chloroform gave the best yields and product selectivity; however, they also formed toxic phosgene gas when degraded by ozone.…”

“…While it was previously thought that ozone degrades primary amines, 5,6 later evidence demonstrated that carefully chosen conditions could give detectable quantities of nitroalkane products. 7 These substrates can act as versatile intermediates for further derivatization and can be readily converted into most other functional groups in a handful of steps. 8 Existing means of performing this amine oxidation most commonly involve hazardous reagents such as hypofluorous acid 9 or Caro's acid, 10 both of which present a serious threat of explosion and injury if mishandled in a lab setting.…”