Reactivity of amines toward tert‐butoxy radicals: Effect of solvent and amine structure

Abstract

In the above paper, there was an error in the ordinate of Figure 1 (p. 122). The numbers that were shown should have been 7.0 and 6.0 rather than 2.0 and 1.0.

Switch-Over in Photochemical Reaction Mechanism from Hydrogen Abstraction to Exciplex-Induced Quenching: Interaction of Triplet-Excited versus Singlet-Excited Acetone versus Cumyloxyl Radicals with Amines

“…Apart from the structurally or stereoelectronically distinct amines 2 and 10 − 13 , the reactivity of cumyloxyl radicals reveals a correlation with the IP values of the amines (log k r = 13.6−0.73IP, r = 0.939, n = 8). This supports the notion previously expressed for tert -butoxyl radicals in high-temperature gas-phase experiments, namely, that H abstraction from amines depends on the donor ability, i.e., involves some degree of charge transfer. Note also that the reactivity difference between 10 and 11 , both toward cumyloxyl (Table ) and tert -butoxyl radicals, is larger than expected on purely statistical grounds (factor 2), which provides another indication for CT contributions to this radical reaction, since the IP of 10 lies above that of 11 (Figure ).…”

“…Quenching of Triplet Acetone. The observed phosphorescence quenching rate constants are close to those for the interaction of alkoxyl radicals with aliphatic amines, a reaction for which a direct H abstraction operates. , In fact, the reactivity of acetone in the excited triplet state can be nicely correlated for all amines with the reaction rate constants of cumyloxyl radicals (Figure , log k q = 1.95 + 0.807 log k r , r = 0.920, n = 13). The comparable absolute reactivity of the radical and the excited state leads us to the interesting 3,6-8 but for amines uncommon conclusion that the same mechanism, i.e., direct H abstraction by the oxygens, is operative.…”

Development of Oxygen Scavenger Additives for Future Jet Fuels. A Role for Electron-Transfer-Initiated Oxygenation (ETIO) of 1,2,5-Trimethylpyrrole?

“…It is known that such a mechanistic sequence would result in an increase in reaction rate with an increase in solvent polarity owing to the existence of a dipolar contribution to the transition state for radical additions to TMP. 17 In the previous study 5 of the autoxidation of TMP in chlorobenzene at 131 °C our data suggests that two pathways are operative: oxygen-promoted TMP radicalcation chemistry and TMP peroxyl-radical chemistry. If, reactions D and E are occurring in dodecane at 120 °C, then a similar process at a more rapid rate should occur in chlorobenzene at 131 °C.…”

“…Subsequent addition into TMP followed by addition of oxygen to form a peroxyl radical would complete the chain sequence (reaction E). It is known that such a mechanistic sequence would result in an increase in reaction rate with an increase in solvent polarity owing to the existence of a dipolar contribution to the transition state for radical additions to TMP …”

Quenching of n,π*-Excited States in the Gas Phase: Variations in Absolute Reactivity and Selectivity

“…The importance of the electron donor strength of the substrate in hydrogen atom transfer reactions has just recently been emphasized for amines with cumyloxyl radicals and triplet acetone as abstracting species . It was tentatively suggested, akin to previous suggestions for radical reactions, , that a polar transition state effect is operative in the hydrogen abstraction from amines, and this argument may apply for ethers as well. An abstracting electron-deficient alkoxyl radical or n,π*-excited state (ketone or azoalkane) may polarize the transition state (e.g., as explicitly shown for ethers in Scheme ).…”