3699-18-1Relevant articles and documents
One-electron reduction of N-chlorinated and N-brominated species is a source of radicals and bromine atom formation
Pattison, David I.,O'Reilly, Robert J.,Skaff, Ojia,Radom, Leo,Anderson, Robert F.,Davies, Michael J.
, p. 371 - 382 (2011)
Hypochlorous (HOCl) and hypobromous (HOBr) acids are strong bactericidal oxidants that are generated by the human immune system but are implicated in the development of many human inflammatory diseases (e.g., atherosclerosis, asthma). These oxidants react readily with sulfur- and nitrogen-containing nucleophiles, with the latter generating N-halogenated species (e.g., chloramines/bromamines (RR′NX; X = Cl, Br)) as initial products. Redox-active metal ions and superoxide radicals (O2 ?-) can reduce N-halogenated species to nitrogen- and carbon-centered radicals. N-Halogenated species and O2 ?- are generated simultaneously at sites of inflammation, but the significance of their interactions remains unclear. In the present study, rate constants for the reduction of N-halogenated amines, amides, and imides to model potential biological substrates have been determined. Hydrated electrons reduce these species with k2 > 109 M-1 s-1, whereas O2?- reduced only N-halogenated imides with complex kinetics indicative of chain reactions. For N-bromoimides, heterolytic cleavage of the N-Br bond yielded bromine atoms (Br?), whereas for other substrates, N-centered radicals and Cl-/Br- were produced. High-level quantum chemical procedures have been used to calculate gas-phase electron affinities and aqueous solution reduction potentials. The effects of substituents on the electron affinities of aminyl, amidyl, and imidyl radicals are rationalized on the basis of differential effects on the stabilities of the radicals and anions. The calculated reduction potentials are consistent with the experimental observations, with Br? production predicted for N-bromosuccinimide, while halide ion formation is predicted in all other cases. These data suggest that interaction of N-halogenated species with O 2?- may produce deleterious N-centered radicals and Br?.
Glutarimidyl Chemistry: Substitution Reactions. Mechanism of "Ziegler Brominations"
Luening, U.,Seshadri, S.,Skell, P. S.
, p. 2071 - 2077 (2007/10/02)
Glutarimidyl (G-radical) radicals are generated in liquid-phase chain reactions by halogen atom abstractions from N-haloglutarimides by alkyl radicals.These reactions are carried out in the presence of small amounts of alkenes which act as halogen scavengers to eliminate halogen atom chains.The distinguishing characteristics of glutarimidyl radicals are (1) a constant hydrogen abstraction ratio (kneo-C5H12/kCH2Cl2)H = 5.3 at 15 deg C, over a wide range of reaction conditions, (2) no ring opening with glutarimidyls lacking 2-substituents, and (3) ring opening to make 4-bromoalkanoyl isocyanates with N-bromoglutarimides substituted by methyl(s) in the 2-position.Glutarimidyl radical hydrogen abstraction selectivities are characterized by early transition states for a variety of substrates, with behavior similar to that shown by chlorine atoms and by succinimidyl radicals.With adequate scavenging of bromine, using 1,3-butadiene or norbornene, brominations of benzylic hydrogen take place with the G-radical carrier, with selectivities similar to those obtained with Cl-radical, thus providing definitive proof that "Ziegler brominations" are not attributable to G-radical hydrogen abstractions.
